EP2744751A2 - Procédés et appareil pour la fabrication et l'utilisation de structures en nanofeuille de pétale de graphène - Google Patents

Procédés et appareil pour la fabrication et l'utilisation de structures en nanofeuille de pétale de graphène

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Publication number
EP2744751A2
EP2744751A2 EP12845269.5A EP12845269A EP2744751A2 EP 2744751 A2 EP2744751 A2 EP 2744751A2 EP 12845269 A EP12845269 A EP 12845269A EP 2744751 A2 EP2744751 A2 EP 2744751A2
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EP
European Patent Office
Prior art keywords
approximately
substrate
graphitic
carbon
gps
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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EP12845269.5A
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German (de)
English (en)
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EP2744751A4 (fr
Inventor
Jonathan Clay Claussen
David Benjamin Jaroch
Timothy S. Fisher
David Marshall PORTERFIELD
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Purdue Research Foundation
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Purdue Research Foundation
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Publication of EP2744751A2 publication Critical patent/EP2744751A2/fr
Publication of EP2744751A4 publication Critical patent/EP2744751A4/fr
Withdrawn legal-status Critical Current

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82B—NANOSTRUCTURES FORMED BY MANIPULATION OF INDIVIDUAL ATOMS, MOLECULES, OR LIMITED COLLECTIONS OF ATOMS OR MOLECULES AS DISCRETE UNITS; MANUFACTURE OR TREATMENT THEREOF
    • B82B3/00—Manufacture or treatment of nanostructures by manipulation of individual atoms or molecules, or limited collections of atoms or molecules as discrete units
    • B82B3/0009—Forming specific nanostructures
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82B—NANOSTRUCTURES FORMED BY MANIPULATION OF INDIVIDUAL ATOMS, MOLECULES, OR LIMITED COLLECTIONS OF ATOMS OR MOLECULES AS DISCRETE UNITS; MANUFACTURE OR TREATMENT THEREOF
    • B82B1/00—Nanostructures formed by manipulation of individual atoms or molecules, or limited collections of atoms or molecules as discrete units
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y40/00—Manufacture or treatment of nanostructures
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/182—Graphene
    • C01B32/184—Preparation
    • C01B32/186—Preparation by chemical vapour deposition [CVD]
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/28—Electrolytic cell components
    • G01N27/30—Electrodes, e.g. test electrodes; Half-cells
    • G01N27/308—Electrodes, e.g. test electrodes; Half-cells at least partially made of carbon
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/28—Electrolytic cell components
    • G01N27/30—Electrodes, e.g. test electrodes; Half-cells
    • G01N27/327—Biochemical electrodes, e.g. electrical or mechanical details for in vitro measurements
    • G01N27/3271—Amperometric enzyme electrodes for analytes in body fluids, e.g. glucose in blood
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/28—Electrolytic cell components
    • G01N27/30—Electrodes, e.g. test electrodes; Half-cells
    • G01N27/327—Biochemical electrodes, e.g. electrical or mechanical details for in vitro measurements
    • G01N27/3275—Sensing specific biomolecules, e.g. nucleic acid strands, based on an electrode surface reaction
    • G01N27/3278—Sensing specific biomolecules, e.g. nucleic acid strands, based on an electrode surface reaction involving nanosized elements, e.g. nanogaps or nanoparticles

Definitions

  • Nanostructures have recently been utilized in a variety of biosensing applications due to their enhanced surface area, precise biomolecule-electrode connections, and enhanced delivery of application agents.
  • conductive nanostructures immobilized on electrodes enhance electrocatalytic behavior due to quantum confinement and may exhibit properties including more favorable Farad ic-to-capacitive current ratios, higher current densities, and faster mass transport by convergent diffusion than their larger micro/macro electrode counterparts.
  • large arrays of nanostructures i.e., nanoelectrode arrays [NEAs]
  • These NEA biosensors, fabricated with various nanostructures ⁇ e.g., nanowires, nanotubes, and nanocrystals) have shown promising results, displaying high
  • biofunctionalization techniques have been developed to immobilize biorecognition agents onto electrode surfaces including covalent binding through self- assembled monolayers (SAMs), non-covalent membranes, and electrodeposition with conductive polymers.
  • SAMs self- assembled monolayers
  • Non-covalent membranes can be rapidly assembled on electrode surfaces.
  • PEDOT poly(3,4-ethylenedioxythiophene)
  • PEDT is an electrically conductive polymeric material that can be utilized in biosensor interfaces due to its biocompatibility, stability, and high conductivity.
  • PEDOT Water soluble molecules can also be incorporated into the PEDOT matrix during electro-polymerization.
  • PEDOT has been used as an enzyme immobilization matrix for use in glucose and cholesterol amperometric biosensing applications.
  • Carbon nanomaterials e.g., carbon nanotubes, nanospheres, nanohorns, nanoplates, nanoparticles
  • Transition metals such as Fe and Ni have been traditionally viewed as important catalysts for sp2 carbon growth since they enable rapid dissociation of carbon-rich molecules to form metal-carbon alloys that precipitate carbon through a vapor-liquid-solid mechanism.
  • Two dimensional graphene in the form of single-layer graphene (SLG) or few layer graphene (FLG) has been the particular focus of much recent research because of its unique electronic properties.
  • GPs perpendicular to a substrate and dramatically increase the surface area from which they grow.
  • the GPs are thin, containing only a few graphitic layers, and can be catalyst free, suggesting they might be a source of free-standing graphitic material.
  • MPCVD microwave plasma- enhanced chemical vapor deposition
  • GPs can be used for field emission enhancement, hydrogen storage, sensors, nano-composites and as a growth template for nanostructures of different materials.
  • Electrochemical capacitors also known as supercapacitors or ultracapacitors, with the merits of high power density, fast power delivery or uptake and excellent cycle stability, have become some of the most promising candidates for next-generation high-performance power devices.
  • ECPs electrically conducting polymers
  • PANI polyaniline
  • Py polypyrrole
  • PDP polythiophene
  • PANI gains particular interests in the past 30 years because of its high theoretical specific capacitance (2000 F/g), high degree of processability and chemical stability in air, as well as its fairly high conductivity and favorable electrochemical cycling characteristics.
  • PANI can also be synthesized in different morphologies (e.g., films, nanofibers, arrays) on different substrates.
  • ref. indicates that the current experimental value is far less than the theoretical one, because of the limited mass transport rates of anions and relatively low PANI conductivities. Therefore, it is essential to coat PANI on templates with a high specific surface area to fully exploit its electrochemical capacitive properties.
  • Various porous carbon materials e.g., carbon cloth, activated carbon, mesoporous carbon, and carbon nanotubes were used as conductive templates.
  • Graphene a new member of carbon nanomaterials with unique properties, was also combined with PANI to fabricate composites by in situ chemical or electrochemical polymerization, and self-assembly.
  • reduced graphene oxide was used as templates or supports for PANI nanostructures.
  • Free-standing chemically converted graphene/ PANI nanofiber paper-like composite was synthesized through vacuum filtration of suspensions of the two components. The composite shows a specific capacitance of 210 F/g and 160 F/cm 3 but with a poor cycling life (21 % loss at 3 A/g after 800 cycles).
  • Reduced graphene nanosheets/PANI composite was
  • Graphene nanosheets (nanowalls), or graphitic petals (GPs), containing a few layers of graphene and growing roughly perpendicularly to a substrate over a large surface area, are the ideal candidates for electrochemcial energy storage applications, due to high specific area and high electrical conductivity. They were previously synthesized on different substrates, such as Ni foil and carbon cloth, for electrochemical energy storage application.
  • the unique sharp edges of GPs greatly increase charge storage as compared with that of designs that rely on basal plane surfaces. Density functional theory analysis shows the presence of these edges affects not only the reactivity of the carbon material toward the adsorption of Li atoms but also their diffusion properties.
  • One aspect of the present invention pertains to an apparatus including a substrate having a surface.
  • Other embodiments include a plurality of carbon mounds located on the surface.
  • Still other embodiments pertain to a plurality of graphitic petals, each petal growing from a corresponding one of said mounds.
  • Another aspect of the present invention pertains to a method for depositing carbon on a surface. Some embodiments include providing a substrate having an outer surface. Yet other embodiments include depositing carbon on a roughened outer surface. Still other embodiments include growing a graphitic petal from the carbon on the roughened surface.
  • Yet another aspect of the present embodiment pertains to a method for depositing carbon on a surface. Some embodiments include providing a substrate having a first layer of a first material on top of a second layer of a second material, the first layer having an outer surface. Other embodiments include diffusing a third gaseous material through the first layer. Yet other embodiments exposing the substrate during said diffusing to an electrical field. Still other embodiments include depositing a fourth material containing carbon on the outer surface.
  • Another aspect of the present embodiment pertains to a biosensor.
  • embodiments include an electrode. Yet other embodiments include a silica based wafer, multilayered petal nanosheets supported by the wafer, and platinum
  • nanoparticles supported by the nanosheets include an
  • Still another aspect of the present invention pertains to a method of producing a biosensor. Some embodiments include providing an electrode comprising a silica based wafer, petal nanosheets supported by the wafer, and electrodepositing platinum nanoparticles on the nanosheets. Still other embodiments include electrodepositing an enzyme and poly(3,4-ethylenedioxythiophene) on the electrode.
  • Yet another aspect of the present invention pertains to a supercapacitor.
  • Some embodiments include a carbon nanotube substrate.
  • Yet other embodiments include graphitic petal structure supported by the substrate, and manganese dioxide supported by the graphitic petal structure.
  • FIGs. 1 -1 a through 1 -1 c illustrate characterization of the graphene petal nanosheets (GPN) electrodes before and after exposure to an oxygen plasma etch.
  • FIG. 1 -1 a illustrates field emission scanning electron microscopy (FESEM) micrographs of a GPN electrode grown by microwave plasma chemical vapor deposition (MPCVD) on a Titanium (Ti) coated silicon substrate. Inset shows a magnified view.
  • FESEM field emission scanning electron microscopy
  • FIG. 1 -1 b discloses raman spectra of the GPNs displaying an intensity increase in the D peak after O 2 plasma etch.
  • FIG. 1 -1 c shows cyclic voltammograms created by scanning the potential between -0.2 V and 0.6 V at a scan rate of 100 mV/s versus a Ag/AgCI reference electrode in 4 mM Fe(CN) 6 3" and 1 M KNO 3 .
  • FIG. 1 -1d displays a hydrogen peroxide (H2O2) calibration plot displaying amperometric sensing of H 2 O20xidation in 20 ml_ of phosphate buffered saline (PBS) (pH 7.4) via a 3-electrode electrochemical set-up with a working potential of 500 mV.
  • H2O2 concentration increases of 10 ⁇ are injected into the test vial while a working potential of 500 mV is applied between the GPN and Pt auxiliary electrodes.
  • Inset portrays a bar graph of H2O2 sensitivity of the GPN electrode before and after the oxygen plasma etch.
  • FIGs. 1 -2a through 1 -2f illustrate characterization of the platinum nanoparticle modified graphene petal nanosheet (PtNP-GPN) electrodes before enzyme
  • FIGS. 1 -2a through 1 -2e illustrate field emission scanning electron microscopy (FESEM) micrographs of PtNPs electrodeposited on GPNs.
  • FIG. 1 -2a illustrates FESEM micrographs of PtNPs electrodeposited on GPNs with current pulses (500 ms) of 312 ⁇ ) used to electrodeposit Pt nanoparticles of distinct size and density onto the GPNs.
  • FIG. 1 -2b illustrates FESEM micrographs of PtNPs electrodeposited on GPNs with current pulses (500 ms) of 625 ⁇ ) used to electrodeposit Pt nanoparticles of distinct size and density onto the GPNs.
  • FIG. 1 -2c illustrates FESEM micrographs of PtNPs electrodeposited on GPNs with current pulses (500 ms) of 1 .25 mA) used to electrodeposit Pt nanoparticles of distinct size and density onto the GPNs.
  • FIG. 1 -2d illustrates FESEM micrographs of PtNPs electrodeposited on GPNs with current pulses (500 ms) of 2.5 mA used to electrodeposit Pt nanoparticles of distinct size and density onto the GPNs.
  • FIG. 1 -2e illustrates FESEM micrographs of PtNPs electrodeposited on GPNs with current pulses (500 ms) of 5.0 mA used to electrodeposit Pt nanoparticles of distinct size and density onto the GPNs.
  • FIG. 1 -2f shows a bar graph displaying the H2O2 sensitivity of the GPN electrode before and after oxygen plasma etch and the PtNP-GPN electrodes. Errors bars show standard deviation for 3 different experiments.
  • FIG. 1 -3a illustrates a tilted cross-sectional schematic illustrating the GOx/PEDOT biofunctionalized PtNP-GPN glucose biosensor with adjacent magnified view portrayal of GOx immobilized on a single PtNP. Glucose binds within the GOx enzymatic pocket producing H 2 O 2 while consuming O 2 .
  • FIG. 1 -3b displays glucose calibration plots of the Pt-GPN biosensors.
  • Pt electrodeposition current pulses of 312 ⁇ , 625 ⁇ , 1 .25 mA, 2.5 mA, and 5.0 mA portray the dynamic current response for a glucose concentration range of 5 - 60 mM by 5mM aliquots.
  • FIG. 1 -3c shows linear glucose sensing range with linear regression analysis and coefficient of determination (R 2 ) corresponding to FIG. 3b.
  • FIG. 1 -3d discloses glucose calibration plots for a glucose concentration range of approximately 0.01 mM to approximately 26.65 mM: (1 ) by incremental glucose concentration steps of 10 ⁇ within the glucose concentration range of 10-50 ⁇ , (2) by incremental glucose concentration steps of 100 ⁇ within the glucose concentration range of 100-500 ⁇ , (3) by incremental glucose concentration steps of 1 mM within the glucose concentration range of 1 -5 mM, (4) by an incremental glucose concentration step of 2.5 mM within the glucose concentration range of 5-7.5 mM, (5) by an
  • FIG. 1 -3e shows linear glucose sensing range and coefficient of determination (R 2 ) corresponding to FIG. 3d.
  • FIG. 1 -4a illustrates glucose sensing ranges of the Pt-GPN glucose biosensors. Pt electrodeposition current pulses of 312 ⁇ , 625 ⁇ , 1 .25 mA, 2.5 mA, and 5.0 mA are compared to glucose levels found in urine, blood, tears, and saliva.
  • FIG. 1 -4b displays biosensor lifetime measurements where the glucose sensitivity for each distinct Pt-GPN glucose biosensor was monitored over a period of 5 weeks.
  • FIG. 1 -4c discloses selectivity test demonstrating minimal interference from 100 ⁇ aliquots of uric acid (UA), acetaminophen (AP), and ascorbic acid (AA) and successful detection of glucose (5 mM) within the backdrop of said electroactive, interfering species for the Pt-MGPN glucose biosensor (Pt electrodeposition of 2.5 mA).
  • FIG. 2-1 Schematic diagram of the MPCVD chamber illustrating the approximate location of the oxidized silicon substrate with respect to the plasma.
  • FIG. 2-2 Surface morphologies of etched SiO 2 /Si after the hydrogen plasma etching before GP growth, (a) SiO 2 Si boundary showing an advancing etch front (arrow indicated), (b) A magnified image of the etch front.
  • FIG. 2-3 AFM images of a micrometer-size EOS feature on the etched SiO 2 Si substrate, (a) Top-view (b) 3-dimensional, perspective view. Trenches or fissures in the EOS feature are apparent.
  • FIG. 2-7 Top-view FESEM images of GPs grown for 15min in a plasma power of 700 W.
  • FIG. 2-8 Raman spectra of GPs prepared for 1 min, 5 min and 15 min.
  • FIG. 2-9 (a) A TEM image of an as-grown GP. (b) A high-resolution TEM image of the GP.
  • FIG. 2-10 GP growth for different durations (a) 1 min of growth, when carbon deposits form nanoislands across the surface of the substrate, (b) 7 min of growth, when large GPs emerge from nanoscale cones, (c) 10 min of growth, when the coexistence of the smaller and larger GPs appears and (d) 20 min of growth, when a full coverage of GPs fills the surface of the substrate.
  • FIG. 2-1 1 Top-view FESEM images of GPs prepared on the oxidized silicon substrates at (a) 700 W, (b) 300W both for 7 min.
  • FIG. 2-12 Controlled formation of nanocones and GPs by a simple scratch on a silicon substrate with a 500-nm-thick oxide layer, (a) A low magnification image illustrating three scratched lines, (b) A top-view high magnification image of the boxed region of (a). The confined growth of GP is evident, (c) Evidence for nanocone growth. (d) A cross-sectional SEM image of a substrate cleaved perpendicular to a scratched line. The image shows a reduced oxide layer thickness, the presence of nanocones, and the growth of GPs.
  • FIG. 3-1 Schematic illustration of CC/GPs/PANI nanostructures as high- performance EC electrodes.
  • the synthesis process involves two steps: (I) uniform and large-area coverage of GPs on highly conductive CC substrate by MPCVD method; (II) Controlled and conformal PANI nanoscale thin layer coating on CC/GP substrates by electropolymerization method.
  • FIG. 3-2 Structural characterization of CC/GPs/PANI hybrid composite.
  • A SEM images of pure carbon cloth (inset, lower magnification);
  • B SEM images of a fully GP covered CC substrate, (inset, a high magnification of GPs)
  • C A high magnification of conformal PAN I coating on GP surfaces.
  • D Raman characterization of pure CC, CC/GPs and CC/GPs/PANI.
  • FIG. 3-3 Electrochemical performances of the CC/GPs/PANI electrodes.
  • A Both the mass specific capacitance and area-normalized specific capacitance as a function of electrochemical polymerization time at 2 mV/s for CC/GPs/PANI electrode.
  • B CV curves of the hybrid CC/GPs/PANI composite electrode (5 min of PANI electropolymerization) at different scan rates of 2, 5, 10, 20, 50 and 100 mV/s with potential windows ranging from 0 to 0.8 V vs. Ag/ AgCI in 1 M H 2 SO aqueous electrolyte.
  • FIG. 3-4 Galvanostatic constant-current charge/discharge performance of
  • CC/GPs/PANI hybrid composite electrode (A) Galvanostatic constant-current charge/discharge performances are evaluated for the CC/GPs/PANI hybrid electrode at different constant-current densities. (B) Specific capacitances of the CC/GPs/PANI hybrid electrode at different constant-current densities. (C) Ragone plot of the estimated specific energy and specific power at various charge/discharge rates (current densities). The dashed line region for electrochemical capacitors was cited from previous references. (D) Charge/discharge cycling test at the current density of 10 mA/cm 2 , showing -7% loss in capacitance after 2000 cycles. FIG. 3-5. Electrochemcial performances of the two-terminal highly flexible supercapacitors.
  • A Schematic illustration of all-solid state highly flexible CC/GPs/PANI supercapacitors based on PVA-H 2 SO polymer gel electrolyte.
  • B Galvanostatic charge/discharge performances of as-prepared all-solid-state supercapacitors.
  • C Comparison of the specific energy and power density (per cm 3 of stack) of typical electrolytic capacitors, batteries, commercial supercapacitors and as-prepared devices in a Ragone plot.
  • D Charge/discharge cycling test at the current density of 5 mA/cm 2 , showing -10% loss after 1000 cycles.
  • E CV curves at 5 mV/s for the supercapacitor group from 0 V to 2.5 V in both normal and bent conditions.
  • FIG. 4-1 SEM images of (a) graphitic petals, (b) A magnified image of graphitic petals showing smooth surfaces, (c) MnO2 coated on graphitic petals, (d) A magnified image of uniform MnO2 coating on graphitic petals.
  • FIG. 4-2. (a) Cyclic voltammetry curves of the MnO2/GP/BP composites at different scan rates in 1 M Na2SO 4 aqueous electrolyte, (b) Cyclic voltammetry curves of BP, GP/BP, MnO 2 /BP, and MnO 2 /GP/BP at 10 mV/s.
  • FIG. 5-2 A uniform and large-area coverage of GPs on flexible CC substrates.
  • FIG. 5-3 SEM morphology of PANI coated on CC/GPs for different
  • electropolymerization time (a) 5 min, (b) 10 min, and (c) 20 min.
  • FIG. 5-4 Current vs. time during PANI electropolymerization process for both pure CC and CC/GP substrate.
  • FIG. 5-5 (A) Galvanostatic constant-current charge/discharge curves of the CC/GPs/PANI electrode at higher current densities. (B) IR drop of the CC/GPs/PANI electrode in 1 M H 2 SO 4 electrolyte.
  • FIG. 5-6 (A) CV curves at 5 mV/s of a single flexible supercapacitor device base on CC/GPs/PANI electrode with polymer gel as electrolyte; (B) normal (C) bent and (D) twisted conditions.
  • FIG. 6-3.1 FESEM images of nanoscale cones observed in the middle regions of the substrate after a growth time of 15 min for a plasma power of 700 W. (a) Side-view; (b) top-view
  • FIG. 6-3.2 High resolution TEM and EELS characterization of a thin slice cut from a nanocone.
  • (e) HRTEM image of the SiO 2 /C interface of the nanocone indicates the graphitic nature of the C layers with an interlayer distance of 0.35 nm. The dark spots in the image correspond to a Pt protection layer deposited during sample preparation.
  • FIG. 6-3.6 SEM images of (a) graphitic petals, (b) A magnified image of graphitic petals showing smooth surfaces, (c) MnO 2 coated on graphitic petals, (d) A magnified image of uniform MnO 2 coating on graphitic petals.
  • FIG. 6-3.7 (a) Cyclic voltammetry curves of the MnO 2 /GP/BP composites at different scan rates in 1 M Na 2 SO 4 aqueous electrolyte, (b) Charge/discharge curve of MnO 2 /GP/BP at different current densities, (c) Specific capacitances of MnO 2 /GP/BP (black), MnO 2 /BP (red), GP/BP (dark cyan) and BP (blue) at different scan rates, (d) Ragone plot of the estimated specific energy and specific power at various current densities, (f) Capacity retention of MnO 2 /GP/BP as a function of cycle number.
  • FIG. 6-3.9 (A) SEM images of pure carbon cloth (inset, lower magnification); (B)
  • FIG. 6-4.1 (A) SEM image of etched GP electrode patterns; (B) A higher magnification of the GP electrodes coated with Ti/Au; (C) A low-magnification SEM image (side view) and a higher magnification of the GP patterned electrodes, indicating that the electrode has a uniform thickness of 4 micro-meter. (D) The boundaries of GP layers nesting on each other are marked (see red dots), demonstrating the 3D structures and sharp edges.
  • FIG. 6-4.3 Electrochemical characterization of GP-based micro-supercapacitors.
  • A Specific capacitances vs. scan rates before electrochemical oxidation.
  • B Specific capacitances vs. scan rates after electrochemical oxidation for 30 min.
  • C Ragone plots of Ragone plot energy density vs. power density for as-prepared micro-supercapacitors in aqueous electrolytes and the up-to-date reported values of different electrode materials in organic electrolytes.
  • D Cyclic stability of as-prepared GP-based micro- supercapacitors.
  • FIG. 6-4.4 Schematic of growth process of CNT/GP patterns for micro- supercapacitor application.
  • FIG. 6-4.5 SEM characterization of CNT/GP structures on Si/SiO 2 substrates.
  • A SEM characterization of interdigitated CNT/GP patterned electrodes for micro- supercapacitors at a low magnification.
  • B A tilted SEM image of a CNT/GP electrode.
  • C A top view of CNT/GP electrode.
  • D A side view of CNT/GP electrode.
  • FIG. 6-4.6 Electrochemical Characterization of CNT/GP micro-supercapacitors.
  • (A) shows the cyclic voltammetry curves of patterned CNT/GP electrodes at different scan rates.
  • FIG. 6-4.7 Free-standing GP foam after removing Ni foam, (a)-(c) optical image of free-standing GP foam, (d) and (e) SEM images of GP foam at a low and high magnification.
  • FIG. 6-4.8 (a) CC micro-conduits on carbon cloth at a lower magnification, (b) A
  • FIG. 6-4.9 (a) CNT/GP micro-conduit on CC at a low magnification, (b) A CNT/GP micro-conduit with a heart shape, (c) A CNT/GP micro-conduit at higher magnification, (d) CNT/GP at a high magnification.
  • One embodiment of the present invention pertains to a nanostructured biosensor that addresses some of the limitations that nanoelectrode array biosensors currently face.
  • one embodiment includes the growth of multilayered graphene petal nanosheets (GPNs) on a silicon wafer through a chemical vapor deposition technique.
  • GPNs act as a conductive template for subsequent Pt nanoparticle electrodeposition.
  • An electrodeposition process is used to grow platinum nanoparticles (PtNPs) along the graphene petal edges and planes to enhance electrochemical performance.
  • PtNPs platinum nanoparticles
  • the size and density of the PtNPs are manipulated to improve the biosensor sensitivity and dynamic sensing range.
  • biofunctionalization protocol is used to electrodeposit an enzyme with the electrically conductive polymer Poly(3,4-ethylenedioxythiophene) (PEDOT) onto the electrode surface.
  • PEDOT electrically conductive polymer Poly(3,4-ethylenedioxythiophene)
  • the enzyme glucose oxidase (GOx) is encapsulated within the PEDOT matrix for subsequent amperometric glucose sensing.
  • GOx glucose oxidase
  • the optimized PtNP- GPN glucose biosensor performance proves to be exemplary with strong glucose sensitivity even after 5 weeks of use, minimal interference from endogenous
  • electroactive species i.e., ascorbic acid, uric acid, and acetaminophen
  • electroactive species typically found in human serum samples, and a low detection limit and wide linear sensing range that improves upon the performance of glucose biosensors previously reported in the literature.
  • a monolithic layer of GPNs were grown across a Ti coated silicon substrate through a microwave plasma chemical vapor deposition technique.
  • the petals grow across the surface of the electrode— protruding a distance of approximately 500 nm from the surface (FIG. 1 -1 ).
  • the 1 - 10 nm thickness of the petals is consistent with previous reported morphologies corresponding to 5 - 25 graphene layers.
  • the GPN electrodes were exposed to a 30 second oxygen plasma etch.
  • the Raman spectra of the GPNs before and after the oxygen plasma etch is shown in FIG. 1 -1 b.
  • the Raman spectra display a D band near 1350 cm “1 , a G band near 1580 cm “1 , and a 2D band near 2700 cm “1 .
  • the D peak which is a disorder induced peak, arises only in the presence of defects.
  • the peak intensity ratio both l D /l G and I2D IG
  • FWHM full width at half maximum
  • the oxygen plasma etch results in an increase in the I D /IG ratio, (from 0.17 to 0.48), thus indicating increased defects in the plasma treated GPN. These defects created through plasma etching assist in subsequent nanoparticle deposition by serving as nanoparticle nucleation sites.
  • the heterogeneous electron transfer (ET) rate of carbon based electrodes is highly dependent upon electrode surface structure.
  • the rate of ET is enhanced at exposed edge planes or defect sites in lieu of the basal plane surface.
  • ferricyanide cyclic voltammetry before and after the oxygen plasma etch was performed while the separation between the anodic and cathodic peak currents ( ⁇ ⁇ ) was measured (FIG. 1 -1 c). As illustrated in FIG.
  • cyclic voltammetry measurements were taken by immersing the electrodes in 4mM Fe(CN) 6 3" and 1 M KNO3 and scanning the potential between -0.2 V and +0.6 V at a scan rate of 100 mV/s versus a Ag/AgCI reference electrode.
  • the GPN electrodes exhibit an ET rate that is well suited for electrochemical sensing.
  • the peak anodic current (lp a ) more than doubles from 0.28 ⁇ 0.5 mA to 0.58 ⁇ 0.5 after the plasma O 2 etch— indicating an enhancement in the electro-reactivity of the electrode.
  • H 2 O 2 hydrogen peroxide
  • the measurable electroactive species byproduct of oxidase enzymes including GOx.
  • Amperometric H 2 O 2 testing was first performed via a 3 electrode set-up, were the GPN electrode was biased with 500 mV against a Pt wire auxiliary in 20 ml_ of phosphate buffered saline (PBS: pH 7.4) while Ag/AgCI acted as the reference electrode.
  • H 2 O 2 calibration plots are created by adding aliquots of H 2 O 2 with increasing concentration into the test vial while the solution is continuously stirred (500 rpm) (FIG. 1 -1 d). The effect of the plasma etching is clearly noticeable as the sensitivity to H 2 O 2 increases from 0.015 mA mM “1 cm “2 to 0.595 mA mM “1 cm “2 before and after etching respectively.
  • nanoparticles of varying size and density are electrodeposited onto the GPNs (FIGs. 2a- 2e).
  • Pt nanoparticles are electrodeposited through a current pulse technique with a similar 3-electrode set-up discussed below.
  • Five distinct currents are used to create five Pt-GPN electrodes with Pt nanoparticles of differing size and density.
  • Current pulses of 312 ⁇ initiate nanopartide growth along the GPN ridge lines with an average nanoparticle width of (46 ⁇ 5) nm.
  • the ridgeline nanoparticles grow to (86 ⁇ 5) nm at 625 ⁇ current pulses while nanoparticles ( ⁇ 20 nm) began to form on each petal face.
  • Ridgeline nanoparticles begin to coalesce at current pulses of 1250 ⁇ with average widths of (100 ⁇ 10) nm while petal face nanoparticles ( ⁇ 20 nm) begin to become more apparent.
  • the petal tips are generally coated with Pt nanoparticles ( ⁇ 10 nm in width) extending from ridgeline nanoparticles (width of (100 ⁇ 25) nm) while all visible petal faces now contain an array of nanoparticles ( ⁇ 20nm) .
  • the Pt ridgelines have now expanded in width to (300 ⁇ 50) nm while the petal face nanoparticles have grown to (35 ⁇ 10) nm.
  • the pulse deposition current the Pt nanoparticle size, density, and morphology can be altered.
  • Amperometric H2O2 calibration plots were performed in the same manner as mentioned previously with a working potential of 500 mV.
  • the H2O2 sensitivity of the GPN electrode is enhanced with the introduction of Pt as the sensitivity jumps from 0.595 mA mM “1 cm “2 (GPN electrode after oxygen plasma etch) to 9.71 mA mM “1 cm “2 , an increase of more than 16 fold, after Pt electrodeposition with 312 ⁇ current pulses.
  • the H2O2 sensitivity continues to increase for higher Pt electrodeposition current pulse until a maximum sensitivity of 13.7 mA mM "1 cm “2 is reached for the Pt-GPN biosensor with 2.50 mA current pulses.
  • Pt was electrodeposited onto planar highly ordered pyrolytic graphite (HOPG) at the same conditions (2.5 mA current pulses, 250 cycles) as the optimized Pt-MGPN electrode.
  • HOPG planar highly ordered pyrolytic graphite
  • the enzyme GOx is mixed with the conductive polymer PEDOT and subsequently electrodeposited onto the electrode surface.
  • glucose is broken down by GOx into hydrogen peroxide (H 2 O 2 ) and is subsequently oxidized at the electrode surface, producing measurable current signal (Eq. 1 & 2).
  • FIG. 3a A schematic portraying the biofunctionalized PtNP-GPN glucose biosensors as well as the enzymatic function of GOx is illustrated in FIG. 3a.
  • Amperometric glucose sensing is carried out in the same 3-electrode set-up and working potential (500 mV) as the amperometric H 2 O 2 testing.
  • Amperometric glucose calibration plots for all 5 PtNp-GPN biosensors were created by adding successive aliquots of increasing concentrations of glucose and measuring the corresponding steady-state signal response, typically achieved within 5 seconds (FIGs. 3b-3e).
  • the glucose sensitivity for the Pt-GPN biosensors and linear sensing range of the PtNp- GPN glucose biosensors follow similar trends found in the amperometric H 2 O 2 testing where values continue to increase for higher Pt electrodeposition current pulses until a maximum sensitivity (0.24 ⁇ mM "1 cm “2 ) and linear sensing range (0.01 - 50 mM) is reached for the PtNp-GPN biosensor with 2.50 mA current pulses (FIGs. 3a-3e and FIG. 4).
  • Table 1 Electrochemical biosensor performance comparison of glucose biosensors based upon, graphene/graphite, carbon nanotubes, and metallic nanoparticles.
  • the sensing range of the optimized Pt-GPN biosensor was wider respectively then other nanostructured biosensors reported in the literature. Furthermore, the linear sensing range of the Pt-GPN biosensor not only enables glucose sensing within the physiological range for blood glucose found within healthy patients with blood glucose within the range of approximately 3.6 mM and approximately 7.5 mM (65 mg/dL - 135 mg/dL) and diabetic patients with blood glucose within the range of approximately 1 .1 mM and approximately 20.8 mM (20 mg/dL - 350 mg/dL); it enables glucose sensing in saliva, tears, and urine as well— opening the door for unique glucose sensing paradigms were glucose levels from distinct human serums could be monitored simultaneously (FIG. 4a).
  • the durability of GOx/PEDOT electrodeposition technique was validated by performing glucose biosensing measurements over a 5 week period. Between weekly testing, the sensors were stored within a capped Petri dish with no refrigeration— mimicking off-the-shelf storage typical of home blood glucose monitoring systems. The sensitivity of the optimized Pt-GPN biosensor retained more than 75% of its sensitivity even after 5 weeks of testing— demonstrating the robust nature of the enzyme immobilization protocol with cyclic testing and storage (FIG. 4b).
  • the glucose selectivity of the PtNP-GPN glucose biosensors was tested by sensing glucose within three known electroactive species (uric acid (UA), acetaminophen (AP), and ascorbic acid (AA)), commonly found in human serum samples.
  • uric acid (UA), acetaminophen (AP), and ascorbic acid (AA) commonly found in human serum samples.
  • a glucose concentration of 5 mM (which corresponds to a typical human blood glucose level) electrochemically monitored after the addition of 100 ⁇ aliquots of AP, UA, and AA exhibits minimal interference from endogenous electroactive species as illustrated by FIG. 4c.
  • a glucose concentration of 5mM was electrochemically monitored for all 5 sensors after physiological relevant concentrations (1 ⁇ ) of UA, AP, and AA were added to the test vial according to previous inference testing protocols.
  • the percent ratio of current response for interfering substance to glucose is presented in Table 2.
  • the Pt-GPN glucose biosensors that were created with respective Pt current pulses of 625 ⁇ , 1 .25 mA, and 2.5 mA maintain a minimal current response of UA, AP, and AA . Furthermore, the biosensor retains more than 75% of its sensitivity even after 5 weeks of use and storage at room temperature ( ⁇ 25°C)
  • GPNs graphene petal nanosheets
  • the emergence of GPN is in its infancy within the research literature, but initial research has begun to uncover favorable electrochemical properties stemming from the exposed petal tips that exhibit the fast ET rates typically found in graphitic edge planes.
  • Various embodiments include the concept of using the GPNs as templates for Pt nanoparticle growth to enhance the electro-reactivity of the petals and in effect present a nanoelectrode array fabrication protocol that eliminates the complexity of traditional NEA design that typically includes anodic alumina or polycarbonate templates and/or multi-step lithography steps.
  • Pt nanoparticle GPNs outperform conventional planar Pt nanoparticle/ HOPG in terms of H2O2 sensitivity ( -5:1 respectively), thus demonstrating the impact nanostructured, three dimensionally arrayed MGPNs fused with Pt nanoparticles can exhibit in electrochemical sensing.
  • the electrodeposition of GOx with PEDOT onto the PtNP modified GPNs enables robust glucose sensing with minimal interference for over one month from endogenous electroactive species commonly found in human serum samples.
  • the results of the selectivity experiments can be explained in part by the electrodeposited PEDOT layer.
  • electrodeposited PEDOT tends to repel negatively-charged electrochemical interferents (e.g. , ascorbic and uric acid) due to electrostatic repulsion during electrochemical biosensing.
  • electrochemical interferents e.g. , ascorbic and uric acid
  • the bottom-up growth of GPNs on a silicon wafer, electrodeposition of Pt nanoparticles, and electrodeposition of enzyme encapsulated within the conductive polymer PEDOT are all scalable fabrication techniques that can be potentially integrated into a wide array of electronic devices.
  • This highly sensitivity biosensing platform should be quite versatile as the GOx can be interchanged with other enzymes such as glutamate oxidase, lactate oxidase, and alcohol oxidase for the advancement of basic research and in-field biosensing associated with neurological disorders, patient trauma, food quality, and next generation bio-ethanol fuel technologies.
  • various inventive embodiments incorporate these fabrication protocols into lab-on-a-chip platforms where the GPNs, PtNPs, and respective enzymes can all be electrodeposited onto distinct microelectrodes for multi-plexed biosensing purposes.
  • immobilized glutamate oxidase allows the testing of glutamate levels for the diagnosis and treatment of Alzheimer's disease, Parkinson's disease, and epilepsy.
  • the technology can also be employed in a wide range of non-medical fields. Examples include incorporation of acetylcholinesterase enzyme to detect organophosphorus pesticides in agricultural applications, polyphenol oxidase to detect the presence of phenolic pollutants in environmental applications, and organophosphorus hydrolase to detect nerve-agents for national defense.
  • the platform represents an enabling technology for the detection of miniscule quantities of a wide variety of analytes.
  • a thin film of Ti (100 nm) is e-beam evaporated onto an oxidized silicon wafer [P ⁇ 100> Si (5 ⁇ ), SiO 2 (500 nm)] at a base pressure of 5.0 10-7 Torr.
  • the metalized wafer is diced with a diamond-blade dicing saw (Disco DAD-2H/6) into equally-sized electrodes (0.35cm 2 ) after a thin film of AZ1518 photoresist is spun and hard baked (10 min at 120°C) unto the wafer to protect the surface during cutting operation.
  • the electrodes are solvent cleaned with acetone, methanol, and isopropyl alcohol and subsequently dried under a gentle stream of N 2 gas to remove the photoresist and debris before GPN Synthesis.
  • the growth of the GPNs is carried out by microwave plasma chemical vapor deposition (MPCVD) with a SEKI AX5200S MPCVD reactor.
  • the Ti coated silicon electrodes are elevated 6 mm above a 5.1 cm diameter molybdenum puck, placed inside the MPCVD reactor chamber and heated to 700 ° C in a hydrogen ambient by a 3.5 kW radio-frequency power supply at a pressure of 30 Torr.
  • a hydrogen plasma is generated over the sample via a 5 kW ASTeX AX2100 microwave generator, while methane (CH 4 ) gas, the acting precursor for GPN growth, is pumped into the chamber for 10 minutes at a flow rate of 10 SCCM.
  • the hydrogen plasma decomposes the methane gas to permit monolithic GPN growth across the entire surface of the electrode (FIG. 1 -1 a).
  • the GPN electrode was exposed to an O 2 plasma etch within a Plasma Tech Reactive Ion Etch (RIE).
  • RIE Plasma Tech Reactive Ion Etch
  • the GPN electrode was placed inside the vacuum chamber of the reactor and pumped down to a base pressure of 0.1 mTorr to eliminate/minimize contaminating species that may have been introduced into the chamber during loading.
  • O2 was introduced into the chamber at a flow rate of 50 SCCM and the chamber pressure was adjusted to 60 mTorr.
  • a O2 plasma was generated over the GPN electrode for 30 seconds by setting the RF generator to the 100 W power setting.
  • a 3 electrode electrochemical set-up (BASi Epsilon Three-Electrode Cell Stand - potentiostat) where the GPNs acted as the working electrode, Pt gauze as the auxiliary electrode, and Ag/AgCI as the reference electrode were dipped within a plating bath consisting of 4 mM H 2 PtCI 6 -6H 2 O (Sigma Aldrich 206083) and 0.5 M Na 2 SO 4 (Fluka 71960) to electrodeposit Pt nanoparticles onto the GPN electrodes.
  • a plating bath consisting of 4 mM H 2 PtCI 6 -6H 2 O (Sigma Aldrich 206083) and 0.5 M Na 2 SO 4 (Fluka 71960)
  • Glucose oxidase is first mixed with Poly(3,4-ethylenedioxythiophene) (PEDOT) before it is electrodeposited onto the PtNP-GPN electrodes.
  • PEDOT Poly(3,4-ethylenedioxythiophene)
  • the GOx/PEDOT solution is created by first mixing 0.1 M poly(styrenesulfonate) in H 2 O. Next, 0.03 M 3,4- ethylenedioxythiophene (Sigma Aldrich 483028) is added to the mixture while the solution is agitated.
  • the enzyme glucose oxidase (GOx) (Sigma Aldrich G7141 ) is next added to the mixture in a concentration of 2 mg/ml.
  • the subsequent PEDOT/GOx solution is electrodeposited onto each Pt-GPN electrode via constant current pulses of 1 mA that are applied between the working electrode (Pt-GPN) and auxiliary electrode (Pt gauze) for 500 cycles.
  • any conductive polymers or, intrinsically conducting polymers including any organic polymers that conduct electricity.
  • Such compounds typically have metallic conductivity or can be semiconductors, and are organic materials. They can offer high electrical conductivity and preferably do not show similar mechanical properties to other commercially available polymers. The electrical properties can be fine-tuned using the methods of organic synthesis and by dispersion techniques.
  • this enzyme could be glucose oxidase and the conductive polymer could be PEDOT which is produced by mixing poly(styrenesulfonate) in H 2 O and then adding M 3,4- ethylenedioxythiophene to the mixture while the solution is agitated. Then enzyme is added to this mixture before electrodeposition.
  • Raman spectroscopy was performed using T64000 system by Horiba Scientific. All the spectra were collected at room temperature using a laser excitation at 488 nm wavelength. The laser power was 2 mW and a 50X objective lens was used.
  • a S-4800 Hitachi microscope was utilized at a power setting of 5.0 kV to obtain all field emission scanning electron microscopy (FESEM) micrographs. No additional processing steps were required before image analysis.
  • FESEM field emission scanning electron microscopy
  • Complex patterns can be generated at the nanoscale using a diamond tip mounted to a microcantilever rastered across a substrate by a controller operating a contact mode AFM.
  • a simple patterning technique will allow the controlled growth of GPs on oxidized silicon substrates for many promising practical applications.
  • the plasma source consists of a 2.45 GHz frequency microwave power supply with variable power.
  • Oxidized silicon wafers p-type ⁇ 1 1 1 >
  • the substrate dimension in these experiments is 1 x1 cm 2 .
  • the GP growth time varied from 30 s to 30 min to produce samples at different stages of growth.
  • the substrates were initially exposed to hydrogen plasma for approximately 6 min, during which the plasma power gradually increased from 300 W to 700 W.
  • a plasma power of 300 W visible plumes appeared at each corner of the substrate because of the high localized electric field.
  • plasma power increased to 700 W the size of plumes increased, and eventually they coalesced to cover the entire substrate.
  • This plasma is sufficient to heat the samples from room temperature up to ⁇ 1 100 °C, as measured by a dual-wavelength pyrometer (Williamson PRO 92). After introducing CH 4 , the measured temperature decreases slightly to -1000 °C.
  • a lower plasma power 300 W was used during GP growth for some experiments.
  • a Hitachi S-4800 field emission scanning electron microscope (FESEM) operated at 5 kV was used to study sample surface morphology.
  • a FEI Titan 80-300 operated at 300 kV was utilized for a high-resolution transmission electron microscopy (HRTEM) to characterize structure of the as-grown GPs, as well as substrate/oxide and oxide/GP interfaces.
  • HRTEM transmission electron microscopy
  • the same instrument was equipped with Gatan imaging filter (GIF Tridiem, model 863), which allows acquisition of elemental mapping images via electron energy loss spectroscopy (EELS).
  • TEM samples for GP structure analysis were prepared by scratching a sample surface with a razor blade to remove deposited material into a vial with acetone followed by ultrasonic bath treatment for several minutes, after which a drop of obtained suspension was put onto a lacey carbon 300 mesh copper TEM grid.
  • cross-sectional TEM samples were prepared by a focused ion beam (FIB) lift-out technique in a FEI Nova 200 dual beam SEM/FIB system equipped with a KlockeTM nanomanipulator.
  • FIB focused ion beam
  • Raman characterization was performed with an Xplora spectrometer (Horiba Jobin Yvon Inc.) with a fixed laser excitation wavelength of 532 nm, power of 2.5 mW, spot size of 600 nm, and
  • FIG. 2-2 shows FESEM images of the etched substrates. A gray-scale contrast boundary is evident in FIG. 2-2(a) located at the corner edge of the substrate and demarcates a region that has been significantly etched (darker region) as compared to the substrate's center (lighter region), where substrate etching occurs at a slower rate.
  • FIG. 2-2(a) shows FESEM images of the etched substrates. A gray-scale contrast boundary is evident in FIG. 2-2(a) located at the corner edge of the substrate and demarcates a region that has been significantly etched (darker region) as compared to the substrate's center (lighter region), where substrate etching occurs at a slower rate.
  • FIG. 2-3 shows the results of parallel AFM studies which reveal a local roughening of the substrate with identifiable nanoscale trenches or fissures emanating in a roughly radial direction from a central point.
  • AFM images of several EOS features indicate that the overall height can be a few hundred nanometers above the surrounding substrate.
  • the formation of these localized EOS features is directly attributed to exposure to the hydrogen plasma.
  • the edge of the substrate couples to the plasma, producing a region with an enhanced electric field, causing the formation of a plasma sheath.
  • the nature of the sheath depends on various parameters including the geometry of the substrate, its position inside the chamber, ionizing species in the plasma, the
  • the substrate is electrically isolated from ground, and hence acts as an electrically floating object immersed in the plasma.
  • the first is an erosion of material from the SiO 2 /plasma interface, causing a gradual reduction of the SiO 2 thickness.
  • the second process is the diffusion of hydrogen atoms from the plasma through the oxide layer, causing an aggregation of H at the Si/SiO2 interface.
  • the localized trench-like surface morphologies observed in FIGS. 2-2 and 2-3 are assumed to result from reactions such as which describes a process in which hot SiO and H 2 O vapor escape from the S1O2 substrate, causing a localized swelling across the surface.
  • This reaction accelerates in regions where the electric field is relatively high (e.g., the edge of an oxidized silicon substrate) and gradually consumes the substrate as the etch front moves away from the substrate edges. Because of the release of SiO and H 2 O vapor, radial-like trenches or fissures dominate the surface of EOS features. Because of the local electric field gradient from the edge to the center of the substrate, hydrogen plasma etching will be less prevalent in the middle regions of the substrate. As a result, EOS features of nanometer size with lower densities may predominate for short etch times. Upon introduction of a carbon source (methane) to the plasma, carbonaceous material will deposit on the substrate and undergo subsequent surface diffusion.
  • a carbon source methane
  • the nanoscale trenches in the EOS features will efficiently trap diffusing carbon atoms, thus forming preferential sites for carbon aggregation. Carbon aggregation, along with direct carbon deposition onto the EOS regions, becomes one process for nucleation of fast growing GPs.
  • FIG. 3-1 shows tilted side-view and top-view SEM images from the middle region of the substrate subjected to these conditions. The emergence of nanoscale cone-like features with diameters ranging from 50 nm to a few 100 nm is evident.
  • FIG. 3-2(a)-(d) contains a bright field TEM image, silicon map, oxygen map and carbon map, respectively, of a thin slice cut from a representative nanocone.
  • the silicon map in FIG. 3-2(b) shows the extent of the silicon substrate used in these experiments.
  • the oxygen map in FIG. 3- 2(c) shows the extent of the S1O2 layer, indicating that the core of the nanocone is S1O2.
  • the original SiO 2 layer thickness was 500 nm. After hydrogen plasma etching and roughening, the SiO 2 layer is reduced to roughly 150 nm in thickness.
  • FIG. 3-2(d) shows a thin (-20 nm) carbon film conformally covering the surface of the sample.
  • a bright region observed on the nanocone indicates a locally enhanced concentration of carbon atoms. This bright region indicates where the rapid growth of a GP is likely to occur.
  • Further HRTEM characterization of the SiO 2 /C interface layer confirms that the carbon film covering the surface of the nanocone is graphitic with interlayer spacing of 0.35 nm.
  • the black smudges seen in FIG. 3-2(e) are Pt nanoparticles used to attach the sample during sample
  • the chemical composition of nanocones caused by the plasma etching may be based on the starting chemical composition of the substrate. Furthermore, a -20 nm thick C layer conformally coats the SiO 2 nanocone and shows evidence for the formation of graphitic layers. All these findings are consistent with the conclusion that nanocones form preferential sites for C aggregation and lead to the rapid growth of GP at later stages.
  • FIG. 3-3 shows side-view FESEM images of GPs emerging from nanoscale cones. The growth is non-uniform across the substrate since the GPs are found to emerge from select regions of a few nanoscale cones. Contributing factors to this highly inhomogeneous growth environment are local electric fields, varying carbon deposition rates, and microscopic cone geometry. It seems clear that once conditions are favorable for GP growth, rapid emergence of a localized GP can result.
  • FIG. 3-3(a) shows nanoscale cones and GPs at a relatively large scale.
  • FIG. 3- 3(b)-(d) shows FESEM images of individual nanoscale cones from which GPs emerge.
  • a GP grows along a radial direction from the cone axis.
  • FIG. 3-3(c) shows a GP in the shape of a horn growing from a nanoscale cone decorated with visible trenches or fissures.
  • the conical horn GP has a subtended interior cone angle of approximately 60°.
  • the outer edge of the horn is not smooth, but faceted.
  • FIG. 3-3(d) shows that a GP can be thin enough (less than 1 nm) to be semi-transparent in an FESEM.
  • FIG. 2-7 shows top-view FESEM images of rapidly growing GPs emerging from individual nanoscale cones. These images demonstrate that the rapidly growing GPs are confined to the cones. Slower growing GPs appear primarily in the flat areas between the nanocones. Some cones are decorated with a few large GPs, while others show a distribution of GP sizes.
  • Raman spectroscopy is often used to characterize the graphitic nature of the GPs. Within this context, three particular Raman peaks are useful.
  • the D band at 1350 cm -1 is known to result from various types of defects and anomalies of transverse optical vibrations near the K-point.
  • the G peak at 1580 cm -1 arises because of the doubly degenerate zone center E2g mode.
  • the 2D band at 2700 cm -1 is due to intervalley zone-boundary transverse optical phonon scattering. This peak consists of multiple sub-peaks and is difficult to analyze quantitatively if there are more than 5 graphitic layers.
  • FIG. 2-8 shows the Raman data from GPs for different growth times of 1 min, 5 min and 15 min.
  • the l D /l G and I2 D / IG ratios calculated from FIG. 2-10 for 5 min of growth are 0.38 and 0.65, respectively; those for 15 min of growth are 0.25 and 0.56, respectively.
  • the decreasing presence of defects with growth time suggests that increasingly graphitic GPs are produced over time.
  • FIG. 2- 9(a) shows a representative TEM image of as-grown GPs. The left-most edge of this micrograph provides evidence for thin nanosheets.
  • FIG. 2-9(b) shows a HRTEM image of a cross-section through a thin GP. The micrograph indicates that the petal is comprised of between 4 and 7 layers of graphene with a planar lattice spacing of approximately 0.35 nm.
  • FIG. 2-10 shows the substrate after 1 min of growth, when carbon deposits form
  • FIG. 2- 10(b) shows the emergence of GPs after 7 min of growth. Large GPs emerge from individual nanoscale cones.
  • FIG. 2-10(c) shows the substrate after 10 min of growth. The co-existence of the smaller and larger GPs is now evident.
  • FIG. 2-10(d) shows the substrate after 20 min of growth, when coverage of GPs fills the entire surface of the substrate.
  • FIG. 2-1 1 shows top-view FESEM images of the GPs observed with two different plasma powers (300 W, 700 W) but the same growth time (7 min).
  • GPs decorage the nanoscale cones (see the marked boundaries of a nanocones in FIG. 2-1 1 (a)) for a plasma power of 700 W.
  • no nanoscale cones are observed on the substrates (even at the edge of the substrates) when the plasma power is reduced to 300 W (see FIG. 2-1 1 (b)).
  • the fact that no nanoscale cones were observed for low plasma power suggests that plasma power intensity is an important factor in the formation of the nanoscale cones.
  • the plasma power directly influences two growth parameters: i) the final temperature of the substrate and ii) the intensity of electric field above the substrate.
  • a low plasma power results in a lower temperature on the surface, which reduces the diffusion rate of the carbon atoms and thus reduces the growth rate of GPs.
  • the lower power also reduces the possibility of forming nanoscale cones.
  • a low electric field leads reduces hydrogen plasma etching, which in turn hinders EOS formation and thus the formation of well-defined nanoscale cones.
  • GPs grow from the irregular and roughened SiO 2 surface due to the partial etching produced by the low- power hydrogen plasma, as shown in FIG. 2-1 1 (b).
  • Carbon species that are directly adsorbed onto the outermost edge of GPs are helpful for rapid GP growth. This process uses an enhanced electric field in the plasma, due in part to the high aspect ratio of the GPs. Direct deposition of carbon material onto a petal edge and incorporation into an emerging petal allows for rapid GP vertical growth.
  • Carbon can also fall directly onto the substrate due to decomposition of CH in the plasma. While the rate of carbon deposition may be uneven due to a variety of factors (e.g., a shadowing effect produced by larger growing petals (see FIG. 2-7(b)), the deposited carbon will randomly diffuse until a GP nucleation site is encountered.
  • Carbon may be continually etched by the plasma, either from the uppermost edge of a GP or from the substrate itself. This point emphasizes the diversity of phenomena caused by the presence of hydrogen: i) as an etchant to remove amorphous carbon, ii) as a promoter of crystalline graphite by removing secondary nuclei that might interfere with GP growth, and iii) by eliminating cross-linking of carbon at free edges of growing GPs, thus preventing excessive edge thickening.
  • the local environment encountered by unreacted C is capable (under the proper set of conditions) of transforming amorphous carbon to ordered, graphitic-like carbon sheets that take the form of GPs.
  • GPs grow rapidly from nanoscale cones.
  • FIG. 2-12 displays top-view and side-view FESEM images of a scratched substrate in an attempt to produce the controlled growth of nanocones and GPs.
  • FIG. 2- 12(a) shows three lightly scribed scratches in a Si substrate at low magnification after 6 min of growth at 700 W plasma power.
  • FIG. 2-12(b) shows a magnified top-view image of one scratched area in FIG. 2-12(a) (indicated by the rectangular box) where preferential GP growth is evident.
  • FIG. 2-12(c) is a magnified image of FIG. 2-12(b) showing that the GPs are seeded by the formation of nanocones (see arrow).
  • FIG. 2- 12(a) shows three lightly scribed scratches in a Si substrate at low magnification after 6 min of growth at 700 W plasma power.
  • FIG. 2-12(b) shows a magnified top-view image of one scratched area in FIG. 2-12(a) (indicated by the rectangular box) where preferential
  • 2- 12(d) is a typical cross-sectional FESEM image of a wafer edge that was produced by cleaving the substrate perpendicular to a scratched line.
  • FIG. 2-12(d) indicates a reduced oxide layer thickness in the scratched area of -250 nm after the hydrogen plasma etching during the growth process.
  • Cross-sectional SEM images of other scratched lines reveal reduced oxide layer thicknesses in the range of 150 to 300 nm.
  • the roughened surfaces in these cross-sectional images further corroborate the contention that GPs grow from nanocones, in agreement with the top-view SEM characterization in FIG. 2-12(c). Further experiments show that preferential GP growth is confined to all scratched lines we have tested to date.
  • FIGs. 3.2a-d disclose a bright field TEM image, silicon map, oxygen map and carbon map, respectively, of a thin slice cut from a
  • the silicon map in FIG. 3.2b shows the extent of the silicon substrate used in these experiments.
  • the oxygen map in FIG. 3.2c shows the extent of the SiO 2 layer, indicating that the core of the nanocone is SiO 2 .
  • the original SiO 2 layer thickness was 500 nm. After hydrogen plasma etching and roughening, the SiO 2 layer is reduced to roughly 150 nm in thickness.
  • the carbon map in FIG. 3.2d shows a thin (approximately 20 nm) carbon film conformally covering the surface of the sample.
  • a bright region observed on the nanocone indicates a locally enhanced concentration of carbon atoms. This bright region indicates where the rapid growth of a GP is likely to occur.
  • FIG.. 3.2e Further HRTEM characterization of the SiO 2 /C interface layer (FIG.. 3.2e) confirms that the carbon film covering the surface of the nanocone is graphitic with interlayer spacing of 0.35 nm.
  • the black smudges seen in FIG. 3.2e are Pt nanoparticles used to attach the sample during sample preparation.
  • FIG. 3.3 shows side-view FESEM images of GPs emerging from nanoscale cones after 15 min of growth under a plasma power of 700 W.
  • FIG. 3.3a shows nanoscale cones and GPs at a relatively large scale.
  • FIGs. 3.3b - d show FESEM images of individual nanoscale cones from which GPs emerge.
  • a GP grows along a radial direction from the cone axis.
  • FIG. 3.3c shows a GP in the shape of a horn growing from a nanoscale cone decorated with visible trenches or fissures.
  • the conical horn GP has a subtended interior cone angle of approximately 60°.
  • the outer edge of the horn is not smooth, but clearly faceted.
  • FIG. 3.3d shows that a GP can be thin enough (less than 1 nm) to be semi-transparent in an FESEM.
  • Yet another embodiment pertains to a hybrid manganese dioxide/graphitic petal structure on carbon nanotube substrates to achieve high specific capacitance, energy density, power density, and long cycle life for flexible supercapacitor application.
  • the graphitic petal/carbon nanotube architecture without any binder provides an efficient scaffold for maximizing the electrochemical performance of MnO 2 .
  • a specific capacitance (based on the mass of MnO 2 ) of 579 F/g is obtained at a scan rate of 2 mV/s in 1 M Na 2 SO 4 aqueous electrolyte.
  • the energy density and power density at 50 A g are 28.2 Wh/kg and 24.5 kW/kg (with a maximum value of 1 14 kW/kg), respectively.
  • the composite electrode shows long-term cyclic stability (less than 10% decrease of specific capacitance after 1000 cycles). Such behavior indicates that the MnO 2 /graphitic petal/carbon nanotube composite is a promising electrode material for high-performance supercapacitors. Density functional theory indicates that coating of MnO 2 on the surface of GPs enhances the conduction path of the electron transport during the charge/discharge process.
  • FIG. 3.6a SEM images of GPs synthesized by MPCVD are shown in FIG. 3.6a.
  • the petals extend approximately 500 nm out from the BP surface, and the typical span width of a single unwrinkled 2-D grain ranges from 100 nm to 500 nm.
  • the thickness of a GP layer can reach several nanometers, corresponding to less than 50 graphene layers.
  • FIG. 3.6b A magnified image of one petal marked by the rectangular box in FIG. 3.6a is shown in FIG. 3.6b, revealing the smooth surfaces of the GPs. These surfaces provide accessible sites for MnO 2 coating.
  • the crumpled structures of the vertical graphene sheets with both sides exposed to MnO 2 precursor solution can provide large specific area for coating.
  • FIG. 3.6c shows the morphology of MnO 2 coated on GPs.
  • FIG. 3.6d contains a magnified image of the area marked by the rectangular box in FIG. 3.6c, showing a thin uniform layer of MnO 2 on the smooth GP surfaces, even on the smaller petals.
  • FIG 3.7a shows the cyclic voltammetry (CV) curves of the MnO 2 /GP/BP composites at scan rates of 2, 5, 10, 20, 50, 100 mV/s in 1 M Na 2 SO 4 aqueous solution with potential windows ranging from 0 to 0.8 V.
  • the constant-current charge/discharge curves of the as-prepared MnO 2 /GP/BP hybrid structure at different current densities are shown in FIG. 3.7b.
  • the charge/discharge curves display a symmetric shape, indicating that the structure has a good electrochemical capacitive characteristic.
  • FIG. 3.7c shows comparative specific capacitances of BP, GP/BP, MnO 2 /BP and
  • MnO 2 /GP/BP calculated from CV curves at voltage scan rates from 2 to 100 mV/s.
  • the specific capacitance of the MnO 2 /GP/BP hybrid composite reaches 579 F/g (based on the mass of pristine MnO 2 ).
  • the specific capacitance of MnO 2 /GP/BP still remains close to 320 F/g, which is comparable to the rate performance reported elsewhere.
  • the specific capacitance of MnO 2 /BP is only about 266 F/g (based on pristine MnO 2 ) at 2 mV/s (see FIG. 3.7c).
  • FIG. 3.7d shows the Ragone plot for the MnO 2 /GP/BP structured electrode at different current densities. At a high current density of 50 A/g, the calculated energy density is 28.2 Wh/kg, and the average power density is 24.5 kW/kg.
  • the maximum power density, calculated from V 2 /4RM, is found to be 1 14 kW/kg. These values are higher than the reported energy density (14.8 Wh/kg) and power density (2.5 kW/kg) of electrodeposited MnO 2 films on BP substrates, suggesting that as-prepared composite is a promising electrode material for supercapacitors.
  • the hybrid CC/GPs/PANI electrodes yield greatly improved capacitive performance with a high specific capacitance of approximately 2000 F/g (based on PANI mass), close to the theoretical capacitance, and a large area-normalized specific capacitance of approximately 2.5 F/cm 2 (equivalent to a volumetric capacitance of approximately 230 F/cm 3 ) at 1 A/g.
  • the hybrid electrodes also exhibit an rate capability with an energy density of 109.9 Wh/kg and a maximum power density of 265.1 kW/kg at a high current density of 100 A/g, respectively, and long-term cycling stability (approximately 7% loss of its initial capacitance after 2000 cycles), with a coulombic efficiency of approximately 99.8%.
  • FIG. 3.9A shows the morphology and microstructure of pure carbon cloth at low (FIG. 3.9A inset) and high magnifications.
  • the diameter of a carbon fibre in the carbon cloth is approximately 9 microns.
  • the surface of a carbon fibre is relatively smooth.
  • FIG. 3.9B displays the morphology and microstructure of GPs fully covering carbon fibres at low and high (FIG. 3.9B inset) magnifications.
  • GPs are grown approximately 500 nm out from the carbon fibre surface and the typical span width of a single unwrinkled two- dimensional (2-D) plane ranges from 100 nm to 500 nm.
  • the thickness of the 2-D GP plane can reach several nanometers, corresponding to less than 50 graphene layers.
  • TEM characterizations of such GPs on carbon fibers indicates that the fiber-petal transition is continuous which facilitates electron transport at the interface between carbon fibers and GPs.
  • the diameter of a carbon fibre decorated with GPs does not change noticeably.
  • FIGs. 3.9B (inset) and 3.9C are comparative SEM images of GPs before and after electrochemical polymerization. Apparently, before the electrochemical
  • FIG. 3.9D shows comparative Raman spectroscopy of CC, CC/GPs and CC/GPs/PANI.
  • FIG. 3.1 OA displays the comparison of area-normalized specific capacitance of Pure CC, CC/GPs, CC/PANI and CC/GPs/PANI at different scan rates. Electrochemical polymerization time for both CC/PANI and CC/GPs/PANI electrodes are 5 min.
  • Pure CC contributes negligible area-normalized specific capacitance to the electrodes (0.01 F/cm 2 at a scan rate of 2 mV/s). After decorating GPs on CC by PECVD method, the area-normalized specific capacitance of the composite electrode reaches 0.7 F/cm 2 at a scan rate of 2 mV/s and decreases slightly with increasing scan rate.
  • a pure CC is electrochemically coated with PANI for comparison with the hybrid composite electrode of CC/GPs/PANI with the same PANI electropolymerization time (5 min).
  • the area-normalized specific capacitance of CC/GPs/PANI reaches 1 .84 F/cm 2 , approximately one order of magnitude higher than that of CC/PANI (0.19 F/cm 2 ).
  • the area-normalized capacitance remains 71 %, higher than the reported value in reduced graphene oxide/PANI electrodes containing binder (approximately 50 % retention at 100 mV/s), indicating beneficial rate capabilities of the hybrid CC/GPs/PANI electrode.
  • FIG. 3.10B shows the comparison of mass specific capacitance based only on PANI for both pure CC and CC/GP substrates. Apparently, PANI coated on CC/GP substrates has much higher mass specific capacitance than that on pure CC substrates. At a scan rate of 2 mV/s, the mass specific capacitance of PANI is approximately 3 times as high as that on pure CC, indicating that the unique GP structures play a synergetic role utilizing PANI in electrochemical reactions.
  • FIG. 3.10C shows the Ragone plot for the CC/GPs/PAN I composite electrode at the potential window of 0.8 V in 1 M H 2 SO aqueous electrolyte.
  • FIG. 3.10D shows the specific capacitance retention of the CC/GPs/PANI hybrid electrode as a function of charge/discharge cycling numbers.
  • the composite electrode showed approximately 7% loss in the capacitance after 2000 charge-discharge cycles, indicating excellent long-term stability.
  • Coulombic efficiency of the hybrid electrode is approximately 99.8%, indicating high efficiency of the rapid electron-transfer for charge storage and delivery.
  • FIG. 3-5A shows the schematic illustration of all-solid state highly flexible
  • CC/GPs/PANI supercapacitors based on PVA-H 2 SO 4 polymer gel electrolyte CC/GPs/PANI supercapacitors based on PVA-H 2 SO 4 polymer gel electrolyte.
  • FIG. 3-5B shows that charge/discharge curves of a CC/GPs/PANI paper-like supercapacitor at different constant current densities ranging from 1 A/g to 50 A/g.
  • FIG. 3-5C Comparison of the specific energy and power density (per cm 3 of stack) of typical electrolytic capacitors, supercapacitors and batteries in a Ragone plot is shown in FIG. 3-5C. It compares the performance of our all-solid-state flexible device with the current various kinds of state-of-the-art commercial energy storage devices.
  • the CC/CPs/PANI based supercapacitor exhibit energy densities of up to 3.38 mWh/cm 3 , a value that reaches the upper range of the lithium thin-film battery and almost approximately 10 times as high as that of the commercial 3.5V/25-mF supercapacitor.
  • the cycling life tests over 1000 cycles for the CC/GPs/PANI hybrid electrode at a current density of 5 mA/cm 2 were carried out using constant current galvanostatic charge/discharge cycling techniques in the potential windows from 0 to 0.8 V, as shown in FIG. 3-5D.
  • FIG. 3-5F demonstrated that three highly flexible devices in series, wrapped around a glass rod (inset), were used to light a green LED well. After being charged at 2.5 V for 15 min, the highly flexible device could light the LED very well for more than 30 min.
  • Symmetric micro-supercapacitors can include several-micrometer-thick layer graphitic petals, synthesized by micro-wave plasma enhanced chemical vapor deposition and patterned by conventional optical lithography and reactive ion etching techniques on oxidized silicon substrate. High charge/discharge rates up to 100,000 mV/s, three orders of magnitude higher than conventional supercapacitors, have been measured for the microdevices in 1 M H 2 SO 4 aqueous electrolyte.
  • the micro-meter sized device exhibited an energy density of 4 mWh/cm 3 (approximately 1 .6 Wh/cm 2 ) and a power density of 48 W/cm 3 (approximately 192 mW/cm 2 ) at a current of 100 ⁇ and excellent cyclic stability (1 % capacitance loss after 1 ,500 cycles).
  • FIG. 4.1 A shows SEM images of the GP micropatterns with Ti/Au coated on the top of the surfaces. The SEM images show that the width of the electrodes and the gap between are 30 ⁇ and 35 ⁇ , respectively.
  • FIG. 4.1 B displays a magnified SEM image of micro-patterns, showing that Ti/Au metal films are coated on the surface of the GPs.
  • FIG. 4.1 C shows side-view SEM images of GP micropatterns at a low
  • the thickness of the GP micro-electrodes is approximately 4 ⁇ .
  • the inset image shows the morphology of the GP structures with sharp edges.
  • the thickness of the first layer of CNWs is typically limited to several micrometers generally ⁇ 3 ⁇ because of the restricted intrinsic electric field strength across the sheath region.
  • 3D GP networks can be easily synthesized by a one-step method because of the unique setup during the growth process (elevated substrates).
  • the thickness of the GP electrode can be controlled by the growth time and plasma power.
  • 3D GP networks comprise many GP layers nesting on each other, demonstrated by the boundaries of the GP layers outlined in FIG. 4.1 D.
  • FIG. 4.3A shows specific capacitances vs. scan rates (as high as 100,000 mV/s) of GP-based micro-supercapacitors before electrochemical oxidation.
  • the volumetric capacitances calculated for GP electrodes in 1 M H 2 SO electrolyte is higher than the reported values (1 .3 F/cm 3 ) for OLCs in 1 M Et 4 NBF 4 /anhydrous propylene carbonate.
  • a high volumetric capacitance of approximately 270 F/cm 3 (equivalent to an area-normalized capacitance of 108 mF/cm 2 ) was calculated at a scan rate of 20 mV/s (see FIG. 4.3B), two orders of magnitudes higher than before the electrochemcial oxidation, while still maintaining high
  • FIG. 4.3C shows the Ragone plot energy density versus power density for as-prepared micro-supercapacitors and the up-to-date reported values for different materials- rGO in both sandwich (rGO-S) and planar (rGO-P) structures, ACs, OLCs and carbon micro-beads (CMBs) in organic electrolytes.
  • FIG. 4.3D shows the micro- supercapacitors exhibits good cyclic stability (1 % capacitance loss after 1 ,500 cycles).
  • CNTs particularly vertical aligned CNT arrays (VCNTs)
  • VCNTs vertical aligned CNT arrays
  • new fabrication techniques are still needed to achieve high ordered CNT array electrodes with excellent horizontal electronic properties and mechanical robustness.
  • GPs were selectively grown on CNT patterns for micro-supercapacitor electrode application.
  • the uniqueness of the GP strengthening CNT vertical arrays overcomes the problems: (1 ) GPs intercalate CNTs arrays, further reduces the contact resistance between CNTs and also improves contacts between CNTs and bottom metal layers.
  • GPs enhance the mechanical robustness of the VCNT arrays and the orientation of VCNT arrays maintains when wetted by electrolytes, which facilitates ion diffusion during charge and discharge process.
  • GPs further increase surface area of the electrodes and thus increases specific capacitances.
  • the schematic of fabrication process of GP/CNTs are showing in FIG. 4.4.
  • Ti/AI/Fe tri-layer catalysts (30/10/5 nm) were deposited on Si/SiO 2 wafer by Vecco thermal evaporator at a base pressure of 1 .0 10 "7 Torr. Then the substrates are loaded on a 55-mm-diameter Mo puck in the MPCVD chamber.
  • H 2 (50 seem) and CH (10 seem) were introduced as gas sources, with a pressure of 10 Torr total pressure.
  • the plasma power during the growth was 300 W and the substrates were heated to 800 °C.
  • the CNT growth time in this work was 30 min.
  • FIG. 4.5A shows SEM characterization of interdigitated CNT/GP patterned electrodes for micro-supercapacitors at a low magnification. The spaces between two adjacent electrodes are 100 ⁇ and GP-free zones.
  • FIG. 4.5B shows a tilted SEM image of a CNT/GP electrode.
  • FIG. 4.5C and 4.5D are a top-view and side-view SEM images of CNT/GP electrodes, respectively.
  • FIG. 4.6 shows the electrochemical characterization of CNT/GP patterned electrodes for micro-supercapacitors.
  • FIG. 4.6A shows the cyclic voltammetry curves of patterned CNT/GP electrodes at different scan rates in 1 M H 2 SO aqueous electrolyte.
  • FIG. 4.6B shows the charge/discharge curves of CNT/GP-CNT/GP electrodes at different current densities.
  • FIG. 4.6C displays comparative CV curves of micro- supercapacitors based on CNT-CNT and CNT/GP-CNT/GP electrodes at a scan rate of 20 mV/s.
  • FIG. 4.6A shows the cyclic voltammetry curves of patterned CNT/GP electrodes at different scan rates in 1 M H 2 SO aqueous electrolyte.
  • FIG. 4.6B shows the charge/discharge curves of CNT/GP-CNT/GP electrodes at different current densities.
  • FIG. 4.6C displays comparative CV curve
  • 4.6D displays comparative CV curves of CNT and CNT/GP electrodes at a scan rate of 20 mV/s in a three-electrode system (Ag/AgCI as a reference electrode). Both FIGs. 4.6C and 4.6D show that decorations of GP on arrays significantly reduces the internal resistances, making the CV curves more rectangular.
  • Ni foam (MTI Corp., thickness: 1 .6 mm, purity> 99.99%, surface density: 350 ⁇ 30g/m A 2 and porosity: >95%) was used as a 3-D template to grow GPs in a MPCVD system. Before the growth, the Ni foam was compressed (700 LBs press force, Fairweather, model: HIP 1 - ⁇ ) from 1 .6 mm to 1 10 m in order to couple well with hydrogen plasma. The Ni foam substrate, with a diameter of 12 mm, was elevated 17 mm above a Mo puck by ceramic spacers. The sample was subjected to MPCVD conditions of H 2 (50 seem) and CH 4 (10 seem) as the primary feed gases at 20 Torr total pressure. The plasma power was 500W.
  • the growth time was 30 min.
  • the Ni foams covered with graphite petals were immersed in a PMMA solution (4 wt% in ethyl lactate), and then baked at 180 C for 30 min.
  • the samples were then put into a 3M HCI solution at 80°C for 5 h to completely dissolve the nickel to obtain GP foam-PMMA composite.
  • free-standing GP foams were obtained by dissolving the PMMA with hot acetone at 55°C.
  • SEM images of free-standing GP foams (see FIGs. 4.7a-c) after removing Ni templates can be seen as in FIGs. 4.7d and 4.7e.
  • GP ligaments can be as thin as 1 ⁇ with a hollow channel inside (See FIGs. 4.7e).
  • Ti/AI/Fe tri-layer catalysts (30/10/5 nm) were deposited on carbon cloth substrates by Vecco thermal evaporator at a base pressure of 1 .0 10 "7 Torr. Then the substrates are loaded on a 55-mm-diameter Mo puck in the MPCVD chamber.
  • H 2 (50 seem) and CH 4 (10 seem) were introduced as gas sources, with a pressure of 10 Torr total pressure.
  • the plasma power during the growth was 300 W and the substrates were heated to 800 °C.
  • CNTs are growing on the surface of carbon micro-fibers in the shape of conduits, with an outer diameter of 30 - 40 ⁇ , as shown in FIGs. 4.8a and 4.8b.
  • FIG. 4.9 displays the SEM images of GPs grown on surfaces of CNTs.
  • CNT/GP micro-conduit shows CNT/GP micro-conduits on CC substrates at a lower magnification.
  • the shape of CNT/GP micro-conduit is similar to CNT conduit on CC.
  • FIG. 4.9b displays a CNT/GP micro-conduit in a heart shape.
  • FIGs. 4.9c and 4.9d show GPs decorating CNT structures at a higher magnification.
  • the typical span width of a single unwrinkled 2-D plane ranges from 100 nm to 200 nm.
  • the thickness of the 2-D GP planes can reach several nanometers, corresponding to less than 50 graphene layers.
  • CNT/GP micro-conduit consists of a lot of tree-branch structures, in which CNTs serves as a branchlet and GPs as leaves as illustrated in FIG. 4.9d.
  • GPs increase the specific areas of the CNT structure.
  • (2) GPs improve the mechanical properties of CNT micro-conduits by intercalating CNT tightly together.
  • (3) GPs further improve the electron conductivity of the conduit and reduce contact resistance between CNTs.
  • Cyclic voltammetry characterization of CNT/GP micro-conduit electrodes with different scan rates in a three-electrolyte system is shown in FIG. 4.10.
  • a specific capacitance of as high as 0.8 F/cm 2 at 2 mV/s was achieved, indicating that the hybrid electrodes are ideal candidates as electrodes for electrochemcial supercapacitors and lithium ion batteries.
  • Hybrid manganese dioxide/graphitic petal structures grown on carbon nanotube substrates are shown to achieve high specific capacitance, energy density, power density, and long cycle life for flexible supercapacitor applications.
  • Vertical nanoscale graphitic petals were prepared by microwave plasma chemical vapour deposition on commercial carbon nanotube substrates and subsequently coated with a thin layer of MnO 2 .
  • the graphitic petal/carbon nanotube architecture without any binder provides an efficient scaffold for maximizing the electrochemical performance of MnO 2 .
  • a specific capacitance (based on the mass of MnO 2 ) of 580 F/g is obtained at a scan rate of 2 mV/s in 1 M Na 2 SO aqueous electrolyte.
  • the energy density and power density at 50 A g are 28 Wh/kg and 25 kW/kg, respectively.
  • the composite electrode shows long-term cyclic stability (less than 10% decrease in specific capacitance after 1000 cycles) while maintaining a small internal resistance. Parallel density functional studies were performed to investigate the stability and electronic structure of the MnO 2 /graphene interface.
  • Electrochemical capacitors known as supercapacitors or ultracapacitors, with high power density, fast power delivery and long cycle life, promise to complement or even replace batteries in energy storage applications such as uninterruptible back-up power supplies, load-leveling, portable electronics, hybrid electronic vehicles and renewable energy systems.
  • suitable electrode materials should undergo fast reversible redox reactions.
  • Metal oxides ⁇ e.g., MnO 2 , RuO 2 , VO, Fe 2 Os
  • Carbon materials ⁇ e.g., carbon nanotubes, carbon fibres, activated carbon, graphene are useful as supercapacitor electrodes due to high specific area, high conductivity and low mass density.
  • vertical graphene nanosheets or graphitic petals (GPs) are useful as active electrode materials in ECs.
  • this highly conductive and two-dimensional (2-D) carbon nanosheet structure as a nanotemplate has not yet been systematically studied and optimized to exploit the electrochemical properties of the pseudocapacitive materials ⁇ e.g., metal oxide).
  • Various embodiments of the present invention pertain to the EC performance of vertical GPs grown by microwave plasma chemical vapor deposition (MPCVD) on flexible commercial buckypaper (BP).
  • MPCVD microwave plasma chemical vapor deposition
  • BP flexible commercial buckypaper
  • MnO2/GP/BP composite electrode This substrate, when coated with a thin MnO2 layer, forms an architecture referred to as a MnO2/GP/BP composite electrode.
  • the GP/BP architecture offers an effective scaffold for exploiting the electrochemical behavior of MnO2, realizing high energy and power density characteristics for
  • the formation of petals in one embodiment uses a plasma environment.
  • the plasma source consists of a 2.45 GHz frequency microwave power supply with variable power.
  • Commercial buckypaper (Nanocomp Technologies, Inc., USA), washed in 6 M HNO 3 for 15 min to eliminate the residuals and surfactant before GP growth, was used as substrates to grow GPs.
  • the substrates elevated 9 mm above a Mo puck by ceramic spacers, were subjected to MPCVD conditions of H 2 (50 seem) and CH 4 (10 seem) as the primary feed gases at 30 Torr total pressure.
  • the substrates were initially exposed to hydrogen plasma for approximately 2 min, during which the plasma power gradually increased from 300 W to 600 W.
  • the GP growth duration was 20 min.
  • the typical dimensions of the samples were 15 mm ⁇ 5 mm.
  • a neutral precursor solution (pH 7) for the MnO 2 coating process was prepared by mixing 0.1 M Na 2 SO 4 (Alfa Aesar) and 0.1 M KMnO 4 (Alfa Aesar) solutions.
  • the GPs grown on BP were immersed into the solution, which was kept at 80°C in an oven for 40 min. The loading amount was controlled by adjusting the immersion time.
  • the sample was then rinsed with deionized water and subsequently annealed at 200°C for 3 hours using a hotplate in air.
  • the mass of coated MnO 2 was calculated from the weight difference before and after the coating process.
  • the loading amount of MnO 2 in this study is approximately 1 10 g, measured using a microbalance with an accuracy of 1 g.
  • the electrochemical performance of the MnO 2 /GP/BP hybrid structure was evaluated using a BASi Epsilon electrochemical system (Bioanalytical Systems Inc., Indiana, USA).
  • the standard three-electrode cell consisted of Ag/AgCI as the reference electrode, Pt mesh as the counter electrode and the synthesized composite sample as the working electrode.
  • a 1 M Na 2 SO solution served as the electrolyte at room temperature.
  • Scan rates of 2, 5, 10, 20, 50, and 100 mV/s were employed for cyclic voltammetry, and charge/discharge measurements were carried out at different current densities of 5, 10, 20, 30, 40 and 50 A/g.
  • Long-term cyclic stability of the composite electrodes was evaluated repeatedly at 100 mV/s for 1000 cycles.
  • a potential window in the range from 0 to 0.8 V was used in all measurements.
  • a Hitachi S-4800 field emission scanning electron microscope (FESEM) was used to image the surface morphology of all the samples.
  • MnO 2 forms many different crystallographic structures. The different structures are
  • FIG. 4-1 a SEM images of GPs synthesized by MPCVD are shown in FIG. 4-1 a.
  • the petals extend approximately 500 nm from the BP surface, and the typical span width of a single unwrinkled 2-D petal ranges from 100 nm to 500 nm.
  • the thickness of a GP can reach several nanometers, corresponding to less than 50 graphene layers.
  • FIG. 4-1 b A magnified image of one petal marked by the rectangular box in FIG. 4-1 a is shown in FIG. 4-1 b, revealing the smooth surfaces of the GPs. These surfaces provide easily accessible sites for MnO 2 coating.
  • the crumpled structures of the vertical graphene sheets with both sides exposed to MnO 2 precursor solution offer large specific area for coating.
  • FIG. 4-1 a SEM images of GPs synthesized by MPCVD are shown in FIG. 4-1 a.
  • the petals extend approximately 500 nm from the BP surface, and the typical span width of a single
  • FIG. 4-1 c shows the morphology of MnO 2 coated on GPs.
  • FIG. 4-1 d contains a magnified image of the area marked by the rectangular box in FIG. 4-1 c, clearly showing a thin uniform layer of MnO 2 on the smooth GP surfaces, even on the smaller petals.
  • FIG. 4-2a shows cyclic voltammetry (CV) curves of the MnO 2 /GP/BP composites at scan rates of 2, 5, 10, 20, 50, 100 mV/s in 1 M Na 2 SO 4 aqueous solution with potential windows ranging from 0 to 0.8 V.
  • FIG. 4-2b shows a comparison of CV curves for BP, GP/BP, MnO 2 /BP and MnO 2 /GP/BP at a fixed scan rate of 10 mV/s.
  • the shapes of these curves are quasi-rectangular, indicating the presence of electrical double-layer capacitance and pseudocapacitance.
  • the MnO 2 - coated GP/BP architecture involves redox reactions in the cyclic voltammetry tests as Mn atoms are converted into higher/lower (IV/III) oxidation states. These conversions are induced by intercalation/extraction of H 3 O + or alkali cations (Na + ) to/from the MnO 2 outer layer.
  • the mechanism of this reaction can be expressed as the following reaction:
  • C is the specific capacitance in F/g
  • s is the scan rate in V/s
  • M is the mass of the added MnO 2 to the electrodes in g
  • V h and V/ are high and low potential limits of the CV tests in V
  • / is the instantaneous current on CV curves
  • V is the applied voltage (V).
  • the specific capacitance of BP at a scan rate of 2 mV/s calculated from the CV curves is 27 F/g, which is comparable to reported values for CNTs.
  • the specific capacitance of GP/BP (based on total mass of the two components) calculated at 2 mV/s is 47 F/g, which is approximately 70% higher than that of bare BP.
  • the specific capacitance of the MnO 2 /GP/BP composites was calculated based on the mass of pristine MnO 2 for the following reasons: (1 ) The surface of carbon was coated with MnO 2 ; consequently, the carbon materials would participate weakly in the charge storing process as charge is primarily stored at the outer layer of MnO 2 through a Faradic reaction. (2) The specific capacitances of BP and GP/BP are mainly of the electrostatic double-layer type and are far smaller than the specific capacitance of MnO 2 caused by Faradic redox reactions, making it reasonable to calculate the specific capacitance based on the mass of pristine MnO 2 .
  • FIG. 4-2c shows comparative specific capacitances of BP, GP/BP, MnO 2 /BP and MnO 2 /GP/BP calculated from CV curves at voltage scan rates from 2 to 100 mV/s.
  • the specific capacitance of the MnO 2 /GP/BP hybrid composite reaches 580 F/g (based on the mass of pristine MnO 2 ).
  • the specific capacitance of MnO 2 /GP/BP still remains close to 320 F/g, which is comparable to the rate performance reported by others.
  • the specific capacitance of MnO 2 /BP is only about 266 F/g (based on pristine MnO 2 ) at 2 mV/s (see FIG. 4-2c).
  • the superior rate capability of MnO 2 /GP/BP composites demonstrates the advantages of this new architecture of GP/BP as a highly conductive scaffold for maximizing the utilization of the practical electrochemical performance of MnO 2 . Since previous studies show that only a very thin layer of MnO 2 is involved in the charge storage process, the specific capacitance of MnO 2 coated on the supporting GP/BP can likely be further improved by optimizing the thickness of coated MnO 2 layer.
  • the energy density E (in Wh/kg) and the power density P (in kW/kg) are important parameters to characterize the electrochemical performance of
  • FIG. 3.7d shows the Ragone plot for the MnO 2 /GP/BP structured electrode at different current densities. At a high current density of 50 A g, the calculated energy density is 28 Wh/kg, and the average power density is 25 kW/kg. These values are more promising than reported energy densities (14.8 Wh/kg) and power densities (2.5 kW/kg) of electrodeposited MnO 2 films on BP substrates.
  • Various embodiments of the present invention include MnO 2 /GP/BP composites as electrode material in supercapacitor applications.
  • Cycle lifetime is a factors in supercapacitor applications.
  • Typical issues facing MnO 2 -based electrodes in aqueous electrolyte include: mechanical expansion of MnO 2 during ion insertion/desertion processes, MnO 2 film detachment from electrode surfaces, and Mn dissolution into electrolyte.
  • a cyclic stability test over 1000 cycles for the MnO 2 /GP/BP structured electrode at a scan rate of 100 mV/s was carried out in a potential window ranging from 0 to 0.8 V.
  • FIG. 3.7f shows the specific capacitance retention as a function of cycle number.
  • the composite electrode shows less than 10% loss in specific capacitance after 1000 charge/discharge cycles, indicating good capacity retention.
  • FIG. 4-3a A schematic diagram of MnO 2 clusters and graphene (top view) is shown in FIG. 4-3a.
  • constrained relaxation was carried out (only atomic positions of the MnO 2 are allowed to relax, with initially relaxed graphene).
  • the MnO 2 /GP composite is relaxed with energy converged to less than 2 kcal/mol.
  • the formation energy of the composite is calculated to be 128 kcal/mol, suggesting covalent bonding between MnO 2 and graphene.
  • we expect the composite to undergo compressive/tensile stresses.
  • the low interfacial resistance achieved in the MnO 2 /GP/BP electrode is a matter of interest, and we use the results of DFT calculations to provide further insight into this result.
  • the iso-electronic charge contour plot drawn in FIG. 4-3(d) is a two-dimensional cut of the charge density in a vertical plane that contains the yellow line drawn parallel to the zig-zag direction as shown in FIG. 4-3(a). This vertical plane was chosen to highlight the redistribution of charge from the graphene layer toward the oxygen atoms in MnO 2 . Further iso-electronic contour plots in different planes are provided in the supplementary information.
  • the GP/BP architecture without any binder provides an efficient scaffold for maximizing the practical electrochemical performance of MnO 2 , realizing high specific capacitance, rate capability and long-term cycle life, high energy density and high power density.
  • the metallic nature of the MnO 2 /GP composite provides a facile conduction path for electron transport in the charge /discharge process.
  • MnO 2 /GP/BP architecture may be practically useful for next generation high- performance supercapacitors.
  • Another embodiment of the present invention includes a hybrid three-dimensional nanoarchitecture by electropolymerizing aniline monomers into a nanometre-thick conformal polyaniline (PANI) film on graphitic petals (GPs) that are directly grown on highly conductive carbon cloth (CC) through microwave plasma enhanced chemical vapor deposition (MPCVD) for flexible supercapacitor applications.
  • PANI nanometre-thick conformal polyaniline
  • GPs graphitic petals
  • MPCVD microwave plasma enhanced chemical vapor deposition
  • CC/GPs/PANI electrodes yield greatly improved capacitive performance with a high specific capacitance of -2000 F/g (based on PANI mass), close to the theoretical capacitance, and a large area-normalized specific capacitance of -2.5 F/cm 2 (equivalent to a volumetric capacitance of -230 F/cm 3 ) at 1 A/g.
  • the hybrid electrodes also exhibit an excellent rate capability with an energy density of 109.9 Wh/kg and a maximum power density of 265.1 kW/kg at a high current density of 100 A/g, respectively, and an outstanding long-term cycling stability (-7% loss in its initial capacitance after 2000 cycles), with a coulombic efficiency of -99.8%.
  • all-solid-state flexible supercapacitors based on the hybrid CC/GPs/PANI electrodes are also fabricated, which show beneficial electrochemical properties, outperforming the reported all-solid- state flexible supercapacitors to date.
  • Some embodiments pertain to the fabrication of a novel hybrid nanoarchitecture by electropolymerizing aniline monomers into a nanometre-thick PANI film and conformally coating it on GPs that are directly grown on highly conductive carbon cloth through MPCVD method.
  • Such unique 3D porous networks without any binder, not only allow large loading of active electrode materials but also facilitate easy access of electrolytes to the electrodes.
  • CC/GPs/PANI electrodes yield greatly improved capacitive performance with a specific capacitance of 1502 F/g (-2000 F/g at a current density of 1 A/g) at 2 mV/s (5 min of PANI
  • As-prepared GPs serve as highly graphitic and conductive templates, which PANI films were subsequently coated conformally on by electropolymerization of aniline monomers. Schematic illustrations of such novel hybrid CC/GPs/PANI nanostructures are shown in FIG. 3-1 .
  • This strategy has several advantages: (1 ) Macroscopically, 3D carbon cloth would provide a flexible and highly conductive substrate and create channels for fast and effective electrolyte ion transport. (2) Highly graphitic and conductive GPs would largely increase the specific surface of the electrodes and provide a direct path for the electrons transport. The sharp edges of GPs would not only largely increase the charge storage but also speed up the ion diffusion due to lower energy barriers. (3) A nanoscale thin layer of PANI would enable a fast, reversible farad ic reaction and provide a short ion diffusion path.
  • the novel 3D nanostructure was achieved in one embodiment by two-step methods.
  • carbon cloth substrates elevated 9 mm above a Mo puck by ceramic spacers, are subjected to MPCVD conditions of H 2 (50 seem) and CH 4 (10 seem) as the primary feed gases at 30 Torr total pressure for 25 min.
  • SEM images in FIG. 3-2A show the morphology and microstructure of pure carbon cloth at low (inset) and high magnifications.
  • the diameter of a carbon fibre in the carbon cloth is approximately 9 microns.
  • the surface of a carbon fibre is relatively smooth.
  • FIG. 3-2B display the morphology and microstructure of GPs fully covering carbon fibres at low and high (inset) magnifications.
  • GPs uniformly cover CC substrate in a large scale, providing a basis for large-scale fabrication process (see FIG. 5-2).
  • GPs are grown approximately 500 nm out from the carbon fibre surface and the typical span width of a single unwrinkled two-dimensional (2-D) grain ranges from 100 nm to 500 nm.
  • the thickness of the 2-D GP plane can reach several nanometers, corresponding to less than 50 graphene layers.
  • TEM characterizations of such GPs on carbon fibers in our previous work indicates that the fiber-petal transition is continuous which facilitates electron transport at the interface between carbon fibers and GPs.
  • the diameter of a carbon fibre decorated with GPs does not change noticeably.
  • the thickness of CC/GPs sample grown in this condition is measured to be approximately 1 10 microns.
  • electropolymerization process is carried out on a CC/GP sample impregnated with 20 mL solution containing 0.05 M aniline monomers in 0.5 M H 2 SO at 0.8 V versus Ag/AgCI reference electrode. After the polymerization, the as-prepared composite was washed in deionized water and then dried at 80 °C over 2 hours. The adsorbed aniline monomers on the both surfaces of a vertical GP will be
  • FIGs. 3-2B (inset) and 3-2C are comparative SEM images of GPs before and after electrochemical polymerization. Apparently, before the electrochemical polymerization, 2-D unwrinkled GP surfaces are thin and smooth; however, after electrochemcial polymerization for 5 min, PANI are conformally coating GP surfaces, making them rougher and relatively thicker. The PANI mass can be easily adjusted by controlling the electrochemical polymerization time. PANI will become thicker after electrochemical polymerization for longer time. The mass of PANI in the composite is estimated from the total Faradic charge consumed in the electropolymerization reaction, assuming an average of 2.5 electrons per aniline monomer in emeraldine.
  • Raman spectroscopy is often used to characterize graphene based materials.
  • FIG. 3-2D shows comparative Raman spectroscopy of CC, CC/GPs and CC/GPs/PANI. Apart from the D and G bands in the Raman spectroscopy of CC/GPs/PANI hybrid materials, another two new representative peaks (circle indicated), indexed at 1 167 cm “1 and 1468 cm “1 , are due to the presence of PANI structure, corresponding to C-H vibrations in
  • Electrochemical polymerization time ranging from 0, 30 s, 2 min, 5 min, 8 min, 10 min to 15 min is used to study the influence of PANI mass on comprehensive
  • electrochemical properties including specific capacitance based on active material and also the overall area-normalized capacitance of the nanocomposite electrode.
  • FIG. 3-3A shows both the mass specific capacitance and area-normalized specific capacitance as a function of electrochemical polymerization time at 2 mV/s for CC/GPs/PANI electrode.
  • PANI coated on mesoporous carbon monolith carbonized from mesophase pitch at 1000 °C can have a high specific capacitance of 2200 F/g (based on PANI mass), with a significant contribution coming from electric double layer capacitance [9]. This may be because of the hydrophobic properties of carbon monolith after carbonization of mesophase pitch at high temperature, giving rise to nonuniform coverage of PANI on the electrode surface. Moreover, inflexible carbon monolith substrate will limit its practical applications. PAN I mass increases and the specific capacitance based on PAN I significantly decreases as electropolymerization time prolongs.
  • the overall area- normalized specific capacitance of the composite electrode gradually increases, reaches a saturation when electropolymerization time is 5 min and eventually reaches approximately to 2 F/cm 2 at a scan rate of 2 mV/s when electropolymerization time is 15 min.
  • FIG. 3-3B shows the cyclic voltammetry (CV) curves of the hybrid CC/GPs/PANI composite electrode (5 min of PANI electropolymerization) at different scan rates of 2, 5, 10, 20, 50 and 100 mV/s with potential windows ranging from 0 to 0.8 V vs. Ag/ AgCI in 1 M H 2 SO 4 aqueous electrolyte. Redox peaks (C1/A1 , C2/A2 and C3/A3) from the CV curves indicate the presence of pseudocapacitive PANI.
  • CV cyclic voltammetry
  • Redox transitions between a semiconducting state (leucoemeraldine form) and a conducting state (polaronic emeraldine form) are responsible for peaks C1/A1 , and the Faradaic transformation of emeraldine pernigraniline initiates the redox peaks C2 A 2 .
  • Peaks C3/A3 have been attributed to the fornnation/reduction of bipolaronic pernigraniline. It is also noted that the cathodic peaks (C 2 ) shift positively and the anodic peaks (A 2 ) shift negatively with the increment of potential sweep rates, which is because of the increment of the resistance in the electrodes.
  • FIG. 3-3C displays the comparison of area-normalized specific capacitance of
  • Pure CC, CC/GPs, CC/PANI and CC/GPs/PANI at different scan rates Electrochemical polymerization time for both CC/PANI and CC/GPs/PANI electrodes are 5 min. Pure CC contributes negligible area-normalized specific capacitance to the electrodes (0.01 F/cm 2 at a scan rate of 2 mV/s). After decorating GPs on CC by PECVD method, the area-normalized specific capacitance of the composite electrode reaches 0.7 F/cm 2 at a scan rate of 2 mV/s and decreases slightly with increasing scan rate.
  • a pure CC is electrochemically coated with PAN I for comparison with the hybrid composite electrode of CC/GPs/PANI with the same PANI electropolymerization time (5 min).
  • the area-normalized specific capacitance of CC/GPs/PANI reaches 1 .84
  • FIG. 3-3D shows the comparison of mass specific capacitance based only on PANI for both pure CC and CC/GP substrates.
  • PANI coated on CC/GP substrates has much higher mass specific capacitance than that on pure CC substrates.
  • the mass specific capacitance of PAN I is approximately 3 times as high as that on pure CC, indicating that the unique GP structures play a synergetic role utilizing PANI in electrochemical reactions.
  • This synergetic role of GPs can be attributed the following advantages: 1 ) vertical graphene nanosheets allow PANI to be coated on both sides of the GP surfaces, further increasing the specific area.
  • Rate capability is one factor for evaluating the power applications of
  • Galvanostatic constant-current charge/discharge performances are evaluated for CC/GPs/PANI hybrid electrode at different constant-current densities, ranging from 1A/g up to 100 A g based on the mass of PANI.
  • the charge/discharge cycling curves have a symmetric nature, indicating that the composite has a good electrochemical capacitive characteristic and superior reversible redox reaction. This symmetric nature of the CC curves can be maintained even at a low density of 1 A/g, as shown in FIG. 3-4A.
  • Charge/discharge curve of the hybrid electrode at higher current densities can be seen from supporting information FIG. 5-5, in which the IR drop at higher current densities can be seen.
  • the mass specific capacitance and area-normalized specific capacitance derived from the discharging curves at different charge/discharge rates (current densities) are shown in FIG. 3-4B.
  • the calculated mass specific capacitance is 1998 F/g, close to the theoretical capacitance of PANI and the area- normalized specific capacitance is approximately 2.56 F/cm 2 , corresponding to a volumetric charge storage of -237 F/cm 3 , which is higher than those reported values so far.
  • the highest area-normalized capacitance for PAN l/carbon based electrodes is reported to be 1 .8 F/cm 2 .
  • Reduced graphene oxide paper coated with PAN I show a volumetric charge storage of 135 F/cm 3 and 160 F/cm 3 .
  • PANI electropolymerized on stainless steel is reported with a area-normalized capacitance of 0.9 F/cm 2 at a deposit charge of 2.35 C/cm 2 .
  • Volumetric capacitances of PANI-based electrodes are usually higher than those of carbon nanotubes ( ⁇ 16 F/cm 3 ), graphene paper (64 F/cm 3 ), carbide-derived carbon (61 -90 F/cm 3 ) and activated carbons ( ⁇ 50 F/cm 3 ).
  • both mass specific capacitance and area-normalized capacitance decrease relatively fast at low current densities and then stay stable at high current densities.
  • the mass specific capacitance can still be as high as -1200 F/g and area-normalized capacitance 1 .5 F/cm 2 , which are consistent with the values calculated using CV curves.
  • An electrochemical supercapacitor can provide high energy density or high specific capacitance at high charging-discharging rates.
  • the internal resistance which can be determined from the initial voltage drop of the discharge curves is also an important factor affecting the maximum power of the device.
  • R is approximately 0.12 V, corresponding to a low internal resistance of 2.5 ⁇ .
  • FIG. 3-4C shows the Ragone plot for the CC/GPs/PANI composite electrode at the potential window of 0.8 V in 1 M H 2 SO aqueous electrolyte.
  • the energy density decreases from 202.2 to 109.9 Wh/ kg, while the maximum power density increases from 1 18.5 to 265.1 kW/kg, as the galvanostatic charge/discharge current increased from 1 to 100 A g.
  • Another aspect for supercapacitor applications is cycling capability or cycling life.
  • FIG. 3-4D shows the specific capacitance retention of the CC/GPs/PANI hybrid electrode as a function of charge/discharge cycling numbers.
  • the composite electrode showed -7% loss in the capacitance after 2000 charge-discharge cycles, indicating long-term stability.
  • Coulombic efficiency of the hybrid electrode is -99.8%, indicating high efficiency of the rapid electron-transfer for charge storage and delivery.
  • the novel hybrid 3D nanostructure electrode shows excellent electrochemcial properties in a three-electrode testing system, according to one embodiment.
  • the flexible composites also show potential as electrodes for advanced flexible all-solid-state supercapacitors with a two-terminal configuration.
  • paper-like CC/GPs/PANI supercapacitors are fabricated with improved supercapacitor performance.
  • FIG. 3-5A shows the schematic illustration of all-solid state highly flexible CC/GPs/PANI supercapacitors based on PVA-
  • H 2 SO 4 polymer gel electrolyte Macroscopically, as-fabricated devices possess superior mechanical properties and show no cracks or any performance degradation under highly flexible conditions, even in highly bent (180° angle bending) and twisted conditions. Galvanostatic charge/discharge performances were carried out on an individual flexible device in FIG. 3-5B, which shows that charge/discharge curves of a
  • CC/GPs/PANI paper-like supercapacitor at different constant current densities ranging from 1 A g to 50 A g.
  • the charge/discharge curves maintain almost symmetric at all current densities.
  • the calculated mass specific capacitance is -1200 F/g and an area-normalized specific capacitance of -1 .5 F/cm 2 based on a single electrode.
  • the internal resistance calculated based on the IR drop (0.0158 V) is 29 ⁇ at 1 A/g, which is higher than that in aqueous electrolyte in three-electrode system due to the intrinsic lower ion conductivity of polymer electrolyte and the inhomogeneity of large area sample preparation during device fabrication process, which will be further optimized in the future.
  • FIG. 3-5C Comparison of the specific energy and power density (per cm 3 of stack) of typical electrolytic capacitors, supercapacitors and batteries in a Ragone plot is shown in FIG. 3-5C. It compares the performance of our all-solid-state flexible device with the current various other energy storage devices.
  • the CC/CPs/PANI based supercapacitor exhibit energy densities of up to 3.38 mWh/cm 3 , a value that reaches the upper range of the lithium thin-film battery and almost -10 times as high as that of the commercial 3.5V/25- mF supercapacitor.
  • the CC/CPs/PANI based supercapacitor is able to deliver a power density of 3 W/cm 3 , which is two-orders of magnitude higher than that of the Lithium thin-film battery.
  • the cycling life tests over 1000 cycles for the
  • CC/GPs/PANI hybrid electrode at a current density of 5 mA/cm 2 were carried out using constant current galvanostatic charge/discharge cycling techniques in the potential windows from 0 to 0.8 V, as shown in FIG. 3-5D.
  • -10 % loss in capacitance after 1000 cycles and coulombic efficiencies of the hybrid electrode of -99.5% were measured for the device, indicating a relatively good stability and high efficiency of the rapid electron- transfer for charge storage and delivery.
  • FIG. 3-5E Three supercapacitor units were prepared (each size -0.5 cm ⁇ -2.0 cm) in series to light a green light-emitting-diode (LED, the lowest working potential is 1 .5 V).
  • the as-prepared supercapacitor group shows no performance degradation when in highly flexible conditions, as shown in FIG. 3-5E.
  • CV curves of the supercapacitor group (scanning from 0 V to 2.5 V) in both normal and bend conditions almost overlaps, indicating the highly flexibility of the device.
  • FIG. 3-5F demonstrated that three highly flexible devices in series, wrapped around a glass rod (inset), were used to light a green LED well. After being charged at 2.5 V for 15 min, the highly flexible device could light the LED very well for more than 30 min.
  • electrochemical performances to the current commercial supercapacitor devices Many parameters such as the thickness of the polymer gel, force applied to compress two electrodes together, concentration of acid in polymer gel and good electrical contact between two individual devices, et ai, can be optimized in order to fabricate highly flexible devices with better electrochemcial properties.
  • One embodiment pertains to a novel 3D nanostructure based on CC/GPs/PANI for highly flexible supercapacitor electrode.
  • Systematic studies were carried out to optimized the amount of PAN I mass in order to utilize PAN I to the maximum extent while also maintain a high area-normalized capacitance of the electrode in a three- electrode testing system. It is found that the existence of GPs significantly improves the comprehensive electrochemcial properties of the hybrid electrode, due to the large specific surface area and unique sharp edge structures.
  • the CC/GPs/PANI hybrid electrode shows outstanding electrochemical performances, such as high specific mass capacitance as well as high area-normalized and volumetric capacitance, good cycling life and high energy and power densities.
  • All-solid-state supereapaeitor with two slightly separated CC/GPs/PANI nanocomposite electrodes and PVA-H 2 SO Afunctional polymer gel as solid-state electrolyte and separator were fabricated and tested.
  • the flexible device shows excellent electrochemical performances in specific capacitance, energy and power density and cycling life.
  • Features of one embodiment of the present invention were demonstrated to light a green LED out under highly flexible (testing) conditions to use of this lightweight, highly flexible and all-solid state polymer based supercapacitors.
  • Yet another embodiment of the present invention pertains to the use of flexible, conductive preferably carbon-based substrate.
  • Commercial carbon cloth CC, Fuel Cell Earth LLC
  • GP graphitic petal
  • MPCVD microwave plasma enhanced chemical vapor deposition
  • the schematic diagram of the chamber for the growth process is shown in FIG. 2-1 .
  • the plasma source consists of a 2.45 GHz frequency microwave power supply with variable power.
  • the GP growth time was 25 min.
  • the plasma power is 700 W during the growth process. This plasma is sufficient to heat the samples from room temperature up to ⁇ 1 100°C, as measured by a dual-wavelength pyrometer (Williamson PRO 92).
  • H 2 SO -polyvinyl alcohol (PVA) gel polymer electrolyte was prepared as follows: 6 g H 2 SO was mixed with 60 ml deionized water and then 6 g PVA powder was added. The whole mixture was heated up steadily from room temperature to ⁇ 90 °C under vigorous stirring until the solution became clear. Then the dilute polymer electrolyte solution was cooled down to room temperature.
  • PVA polyvinyl alcohol
  • a Hitachi S-4800 field emission scanning electron microscope (FESEM) was used to image the surface morphology of the samples.
  • a FEI Titan 80-300 operated at 300 kV was utilized for a high-resolution transmission electron microscopy (HRTEM) to characterize structure of the as-grown GPs.
  • Raman characterization was performed with an Xplora spectrometer (Horiba Jobin Yvon Inc.) with a fixed laser excitation wavelength of 532 nm, power of 2.5 mW, spot size of 600 nm, and magnification of 100X.
  • Cyclic voltammetry (CV) measurements of the CC/GPs/PANI hybrid structure were carried out on a BASi Epsilon electrochemical system (Bioanalytical Systems Inc., Indiana, USA) to evaluate the specific capacitance at different scan rates from 2 mV/s to 100 mV/s.
  • Galvanostatic charge/discharge measurements (Gamry Echem Testing System, Gamry Instruments, Inc., USA) were used to evaluate the specific capacitance (Cs), internal resistance (IR), energy density (Es), power density (Ps), coulombic efficiency ( ⁇ ) and cycling life of the devices.
  • FIG. 5-2 displays a uniform and large area of GP coverage on CC substrates by MPCVD method. This device is useful as an electrode.
  • MPCVD-grown GPs are graphitic and therefore highly hydrophobic. In order to conformally coat GP surfaces with a thin layer of PANI film, prior to
  • the as-prepared samples were treated with concentrated acid H 2 SO 4 /HNO3 (3/1 v/v) at room temperature for 5 h to functionalize their surfaces so that they would be hydrophilic.
  • the sample was thoroughly washed in deionized water until pH value is ⁇ 7.
  • the three-electrode system for PANI electropolymerization was constructed with a Pt mesh as a counter electrode, Ag/AgCI as a reference electrode and CC/PANI directly as a working electrode.
  • the electrolyte was 0.5 M H 2 SO and 0.05 M aniline.
  • FIG. 5-3 shows the SEM morphologies of PANI coated on GPs for 5 min and 15 min for the electropolymerization process.
  • the mass of PANI can be controlled by the electropolymerization time.
  • FIG. 5-4 displays how current changes as a function of electropolymerization time at 0.8 V vs. Ag/AgCI for both CC and CC/GP substrates. More aniline monomers will react with the CC/GPs substrate with higher specific area, leading to higher current and more change transfer than that of only CC.
  • the internal resistance can be determined from the initial voltage drop of the discharge curves.
  • FIG. 5-5 shows voltage drop (V
  • FIG. 5-6 shows the CV curves for a single flexible device from 0V to 0.8 V at different testing conditions (e.g., normal, bent and twisted). The CV curves almost overlaps, demonstrating the high flexibility of the device. The digital photos of those testing conditions are given in FIG. 5-5.
  • Specific capacitances derived from cyclic voltammetry (CV) tests can be calculated from the equation [2] [3]: where C is the specific capacitance in F/g, s is the scan rate in V/s, M is the mass of electrodes in g, V h and Vi are high and low potential limits of the CV tests in V, / is the instantaneous current on CV curves, and V is the applied voltage in V.
  • the internal resistance R (in ⁇ ) was determined from the voltage drop at the beginning of a discharge curve by [5, 6] :
  • VIR AVm / 2I d (3)
  • V is the applied voltage in volts and At is the discharge time in seconds.
  • P max is the maximum power density.
  • the coulombic efficiency ( ⁇ ) of a battery is the ratio of the number of charges that was input into the battery during charging compared to the number that can be extracted from the battery during discharging.
  • the losses that reduce coulombic efficiency are primarily due to the loss in charge due to other redox reactions in the battery. It is calculated from the following equation [5]:
  • One embodiment of the present invention pertains to an apparatus comprising a substrate having a surface, a plurality of carbon mounds located on the surface, and a plurality of graphitic nanowalls, each nanowall growing from a
  • Yet another embodiment of the present invention pertains to a method for depositing carbon on a surface, comprising providing a substrate having an outer surface, roughening the outer surface, and depositing carbon on the roughened outer surface, and growing a graphitic petal from the carbon onthe roughened surface.
  • Yet another embodiment of the present invention pertains to a method for depositing carbon on a surface, comprising providing a substrate having a first layer of a first material on top of a second layer of a second matrial, the first layer having an outer surface, diffusing a third material through the first layer, exposing the substrate during diffusing to an electrical field and depositing a fourth material containing carbon on the roughened outer surface.
  • Yet another embodiment of the present invention pertains to a biosensor comprising an electrode comprising a wafer, multilayered petal nanosheets supported by the wafer, and platinum nanoparticles supported by the nanosheets, and
  • Yet another embodiment of the present invention pertains to a method of producing a biosensor, the method comprising providing an electrode comprising a substrate, petal nanosheets supported by the substrate, and electrodepositing platinum nanoparticles on the nanosheets, and electrodepositing an enzyme on the electrode.
  • Yet another embodiment of the present invention pertains to a method of coating of a graphitic petal surface, the method comprising providing a metal mesh counter electrode, a reference electrode and a working electrode, providing an electrolyte including an acid and aniline, and electropolymerizing the aniline to graphitic petal surface.
  • Yet another embodiment of the present invention pertains to a three dimensional nanostructure comprising a carbon cloth substrate, graphitic petal structure supported by the substrate, and a film covering the graphitic petal structure.
  • any of the preceding statements X1 through X9 wherein growing is from a nanocone. Any of the preceding statements X1 through X9 wherein nanocones have a base diameter of less than about one micrometer.
  • any of the preceding statements X1 through X9 wherein after depositing the outer surface includes a plurality of carbon-covered upwardly extending shapes. Any of the preceding statements X1 through X9 wherein the shapes are substantially conical.
  • any of the preceding statements X1 through X9 wherein the electrical field comprises radio waves. Any of the preceding statements X1 through X9 wherein the radio waves have a frequency greater than about one gigahertz.
  • electrodepositing nanoparticles includes growing nanoparticles along edges and planes of the
  • nanosheets Any of the preceding statements X1 through X9 wherein the enzyme is glucose oxidase.
  • microwave plasma enhanced chemical vapor deposition conditions include primary feed gases at 30 torr total pressure, a 2.45 GHz frequency microwave power supply, and 700 W plasma power.
  • any of the preceding statements X1 through X9 wherein the microwave plasma enhanced chemical vapour deposition conditions include a 2.45 GHz frequency microwave power supply.
  • any of the preceding statements X1 through X9 wherein the microwave plasma enhanced chemical vapor deposition conditions include a 700 W plasma power rating. Any of the preceding statements X1 through X9 wherein subjecting carbon cloth substrates to microwave plasma enhanced chemical vapor deposition occurs for approximately 25 minutes.
  • any of the preceding statements X1 through X9 further comprising the step of treating the surface of the graphitic petals with a three to one by volume mixture of sulfuric acid and nitric acid for approximately five hours.
  • any of the preceding statements X1 through X9 further comprising the steps of washing the resultant composite film with deionized water and drying the composite film for approximately two hours at approximately eighty degrees Celsius.

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Abstract

Des biocapteurs électrochimiques nanostructurés comportant de nanomatières à base de carbone offrent une plateforme de haute performance unique pour la détection électrochimique de nombreux agents biomoléculaires en raison de leurs propriétés mécaniques, électriques et chimiques uniques. Divers modes de réalisation selon l'invention présentent un biodétecteur nanostructuré pouvant être mis à l'échelle où des nanofeuilles de pétale de graphène (GPN) multi-couches, des nanoparticules de Pt et l'élément de bioreconnaissance (glucose oxydase) sont tous déposés in situ à partir d'un substrat à base de silicium. La polyvalence du biodétecteur est fortement augmentée par la modulation de la performance du biodétecteur (à savoir, sensibilité, limite de détection et plage de détection linéaire) par manipulation de la dimension de nanoparticules de Pt électrodéposées sur les GPN. Ce travail permet une conception robuste de détecteur qui est capable de détection de glucose polyvalente sur plus d'un mois avec une interférence minimale par des espèces électroactives endogènes (par exemple, acide ascorbique, acide urique, acétaminophène) couramment trouvées dans des échantillons de sérum humain. Une structure hybride dioxyde de manganèse/pétale graphitique sur des substrats de nanotube de carbone permet de parvenir à une capacitance spécifique élevée, une densité d'énergie élevée, une densité de puissance élevée et une longue durée de vie pour une application de supercondensateur flexible. Des pétales graphitiques verticaux de dimension nanométrique ont été préparés par dépôt chimique en phase vapeur assisté par plasma à micro-ondes sur des substrats de nanotube de carbone du commerce et par la suite revêtus par une couche mince de MnO2. L'architecture pétale graphitique/nanotube de carbone sans un quelconque liant assure un échafaudage efficace pour rendre maximale la performance électrochimique de MnO2. Le composite MnO2/pétale graphitique/nanotube de carbone est une matière d'électrode prometteuse pour des supercondensateurs à haute performance.
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