WO2016145539A1 - Cellule d'écoulement électrochimique et ultramicroélectrode - Google Patents

Cellule d'écoulement électrochimique et ultramicroélectrode Download PDF

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WO2016145539A1
WO2016145539A1 PCT/CA2016/050314 CA2016050314W WO2016145539A1 WO 2016145539 A1 WO2016145539 A1 WO 2016145539A1 CA 2016050314 W CA2016050314 W CA 2016050314W WO 2016145539 A1 WO2016145539 A1 WO 2016145539A1
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Prior art keywords
flow
capillary
electrochemical
wire
cell
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PCT/CA2016/050314
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English (en)
Inventor
Janine MAUZEROLL
Laurence DANIS
Tomer Aharon NOYHOUZER
Michael Edward SNOWDEN
Ushula Mengesha TEFASHE
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The Royal Institution For The Advancement Of Learning/Mcgill University
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Publication of WO2016145539A1 publication Critical patent/WO2016145539A1/fr

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/66—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light electrically excited, e.g. electroluminescence
    • 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
    • G01N27/416—Systems

Definitions

  • the present disclosure relates generally to systems for electroanalysis, and more particularly to electrochemical flow cells, ultramicroelectrodes, and methods for manufacturing each.
  • an electrochemical flow cell comprises several electrodes, such as a working electrode, and auxiliary electrode and a reference electrode, which work together with an electrochemical detector to apply a controlled electrical potential for a sample fluid to flow across.
  • Electrochemical flow cells which employ electrochemical flow cells are well known and may offer a number of advantages in comparison to static liquid processes, such as the automation of continual and batch measurements, and permit stages of liquid replacements and automated mixing.
  • the use of such electrochemical flow cells may thus permit the precision and accuracy of the measurements in electroanalysis to be improved, as better control and optimization of the process is possible.
  • Electrochemical flow systems also permit the control of mass transport for analytical studies and a number of other applications. For example, a high rate of mass transport can be used to study reaction kinetics for homogeneous and heterogeneous reactions.
  • the majority of commercially available electrochemical flow systems rely on flow injection analysis (FIA) combined with either "jet-flow” (sometimes called “wall-jet”) or "flow-by" methodologies in the electrochemical flow cells. Improved electrochemical flow cells are therefore sought.
  • FIA flow injection analysis
  • electrochemical flow cells include a number of electrodes.
  • the flow cells are microscopic in size, correspondingly micro-scale electrodes, or ultramicroelectrodes (UMEs) may therefore be employed. Improved UMEs may also be sought, whether to be used in electrochemical flow cells or in other electrochemical applications.
  • UMEs are defined as electrodes with at least one dimension smaller than 25 m . Apart from their small dimensions they may offer several advantages including, for example, high sensitivity, fast steady state response, low double-layer charging currents, high scan rates and small ohmic losses. Furthermore, their small current requirements enable electrochemical measurements in low conductive media, e.g. organic solvents, where the voltage drop associated with high solution resistance makes these experiments difficult for convention electrodes.
  • low conductive media e.g. organic solvents
  • UMEs Common geometries of such UMEs include disk, hemispherical, inlaid ring, ring-disk, and finite conical.
  • the most frequently used geometry for UMEs is disk, whereby an electroactive material is embedded within an outer insulating layer.
  • UMEs have been used in a variety of applications including biological systems, charge transport at liquid/liquid interfaces, and corrosion studies.
  • RG is defined as the ratio between the radius of the insulating sheath ( r T ) and the radius of electroactive surface ( a ).
  • UMEs with small RG are essential in scanning electrochemical microscopy (SECM) in order to reduce tip-to-substrate distance ( d ), allowing for a higher sensitivity.
  • SECM scanning electrochemical microscopy
  • the RG also has a significant effect on the current recorded during SECM approach curve measurements.
  • a smaller RG will result in a larger current at short tip-to-substrate distances ( ⁇ 5) because of enhanced contributions from back diffusion of the mediator. They also decrease the probability of contact between the insulating sheath of the UME and the sample, which experimentally occurs upon axial misalignment of the UME.
  • the fabrication of known disk UMEs has focused on gold or platinum disk UMEs, which required labour intensive processes and limited ability to batch process and/or automate their manufacture.
  • UME manufacturing methodology it would be beneficial to provide a fabrication methodology for UMEs that reduces the fabrication time, provides highly reproducible UME geometries, and allows for a wide range of electroactive materials including platinum and gold but also silver, mercury, and carbon fiber. It would be further beneficial for the UME manufacturing methodology to be applicable to microreference electrodes, such as but not limited to, Ag I AgCl microreference electrodes, and to electrodes which may be used in electrochemical flow cells.
  • an electrochemical flow cell comprising: a cell body having an inlet, an outlet, and a flow passage extending between the inlet and outlet to define a flow path for fluid flowing through the cell body; a number of flow- through electrodes disposed within the cell body and in said flow passage, the flow path extending through said flow-through electrodes, which each have an electrode surface disposed transverse to a flow direction along the flow path through the flow passage, said flow-through electrodes arranged in serial flow succession within the flow passage and including at least an upstream working electrode, a downstream reference electrode, and a counter electrode disposed between the working electrode and the reference electrode, the flow-through electrodes having a plurality of apertures therein through which the fluid passes; and wherein the working electrode is positioned within the flow passage at a predetermined distance downstream of the inlet of the cell body, said predetermined distance corresponding to a streamwise location at which substantially fully developed laminar flow of the fluid flowing along the flow path through the cell body.
  • the electrochemical flow cell as defined above may have a flow passage that is free of flow disturbances to generate substantially fully developed laminar flow throughout the flow passage of the flow cell, from at least the upstream working electrode and the outlet of the flow passage.
  • the flow passage of the electrochemical flow cell as defined above may be substantially circular in cross-sectional shape and defines a diameter.
  • the flow-through electrodes of the electrochemical flow cell as defined above may have flow-facing electrode surfaces that are symmetrical about two perpendicular planes of symmetry.
  • At least the working electrode and the counter electrode may have honeycomb configurations, and may be honeycomb screen-printed electrodes.
  • honeycomb configurations of the working electrode and the counter electrode may define a plurality of individual passages that extend in a direction of the flow path between the flow-facing electrode surfaces on an upstream side and a downstream surface on an opposite side of the flow-through electrodes, the individual passages providing substantially uninterrupted fluid flow therethrough.
  • the electrode surfaces of said electrodes in the electrochemical flow cell as defined above may be disposed perpendicularly to the flow direction through the flow passage.
  • the electrochemical flow cell may be modular, permitting a number of said electrochemical flow cells to be interconnected with each other.
  • the electrochemical flow cell may be operable to simultaneously acquire absorbance and electrochemiluminescence (ECL) measurements.
  • ECL electrochemiluminescence
  • a hydrodynamic electrochemiluminescence (ECL) device comprising the electrochemical flow cell as defined above may also be provided, wherein the electrochemical flow cell generates an electrochemiluminescence (ECL) signal.
  • a method of obtaining at least one of electrochemical and spectroscopic measurements from respective sensor may also be provided, which includes connecting the electrochemical flow cell as defined above to the respective sensor in electrical flow communication and generating a fluid flow through the electrochemical flow cell.
  • a flow system in connection with the electrochemical flow cell as defined above may further comprise a spectroscopic sensing module having a spectroscopic detector in communication with at least the working electrode.
  • a flow system in connection with the electrochemical flow cell as defined above may further comprise an electrochemical sensing module in communication with at least the working electrode, the electrochemical sensing module being configured to perform at least one of potentiometric, galvanostatic, and impedance based electrochemical measurements.
  • an ultramicroelectrode comprising: pulling a capillary according to a predetermined pulling profile, the predetermined pulling profile applying substantially equal tensile forces to each of the opposed ends of the capillary in opposite directions to form a narrowed neck in the capillary, the narrowed neck defining a capillary wall that is symmetrical relative to a longitudinal axis extending centrally through the capillary at the narrowed neck thereof; severing the narrowed neck of the capillary to form two separate micropipette tips, each having an opening symmetrically defined within the capillary walls; inserting an electroactive wire into the opening defined within the capillary wall of at least one of the tip ends formed from the pulled capillary; and sealing the tip end having the electroactive wire inserted therein by applying heat to fuse the electroactive wire within the surrounding capillary walls.
  • the step of severing the narrowed neck of the capillary may include at least one of applying the tensile forces until the capillary breaks at the narrowed neck and breaking the narrowed neck of the pulled capillary at predetermined position.
  • breaking the narrowed neck may further comprise applying local heat to the predetermined position heat using a laser.
  • the method as defined above may further comprise forming the ultramicroelectrode to have a ratio of a radius of the capillary wall to a radius of the electroactive wire at the tip end of less than 10. This ratio may more particularly be from 2.5 to 3.6, and more particularly still may be about 3.
  • the step of sealing may include using a fusion process wherein a temperature based fusion of the capillary to the electroactive wire occurs.
  • the method as defined above may further comprise selecting the electroactive wire to be one of a metal wire or a fiber wire.
  • the method as defined above may further comprise severing the narrowed neck of the capillary at a substantial midpoint thereof.
  • a method of forming a multicore ultramicroelectrode using the method of as defined above is also provided, wherein the capillary is a soft glass capillary, and the method further comprises inserting multiple electroactive wires into the soft glass capillary after the steps of pulling and severing.
  • the method as defined above may further comprise using electrodeposition on an exposed surface of the electroactive wire to form a hemispherical tip of the ultramicroelectrode.
  • the method as defined above may further comprise providing the capillary with a plurality of bores extending therethrough.
  • a method of manufacturing a multicore ultramicroelectrode comprising: pulling a double-barrel soft glass capillary of predetermined inner and outer diameters according to a predetermined pulling profile; pulling until the capillary breaks at the reduced neck producing two pulled pipette with a sealed extremity with two separate compartment; at least one of pulling until the capillary breaks at the reduced neck producing two pulled pipettes and breaking the pulled capillary at the reduced neck at predetermined position; inserting a predetermined length of wire or fiber into one of the two compartment of the reduced neck of the pulled capillary and a predetermined length of a silver wire in the second one; sealing the pulled capillary to the wire or the fiber and the silver wire via a predetermined fusion process; exposing the electroactive surface of the UME; and depositing silver chloride on the exposed silver disk
  • a method of manufacturing a multicore ultramicroelectrode comprising: at least one of pulling and molding a glass preform having a predetermined outer geometry and a plurality of bores of predetermined inner diameters according to either a predetermined profile or a predetermined event occurs; inserting a predetermined length of at least one of the wire and the fiber into at least one reduced bore of the plurality of bores; and sealing the at least one reduced bore to the at least one of the wire and the fiber via a predetermined fusion process.
  • a modular device for controlling fluid flow to electrochemical and spectroscopic sensors may also be provided which comprises: an inlet system, where laminar pipe flow is established; and a flow through electrochemical sensing module with well-defined hydrodynamics; and a spectroscopic sensing module for measuring at the electrode surface; and an outlet system for the removal of solution.
  • the device as defined above may further incorporate an electrode assembly within the electrochemical sensing module, which may be configured to perform potentiometric, galvanostatic, and/or impedance based electrochemical measurements.
  • Electrochemical sensors can be also be combined to create sensor arrays or generator-collector electrode assemblies.
  • the electrochemical module within the flow cell can be used with different electrochemical flow techniques, e.g. continual flow, fluid injection, stop-flow.
  • the device may also provide a modular component which houses a spectroscopic detector, focused upon the electrode.
  • an electrochemical device that can perform both electrochemical and spectroscopic measurements. The measurements can be performed simultaneously or individually.
  • the outlet module of the device described above may help remove waste fluid and does not allow the egress of measured sample back to the areas of detection.
  • the device as described above may be suitable for electrochemical luminescence (ECL), as well as other applications. It can also be embedded in other analytical devices for example inlet or outlet of a high performance liquid chromatography (HPLC).
  • ECL electrochemical luminescence
  • HPLC high performance liquid chromatography
  • Figure 1 is a schematic view of a complete electrochemical flow cell in accordance with one embodiment of the present disclosure
  • Figures 2A and 2B are schematic side view representations of flow-by and jet- flow type flow cell electrode configurations of the prior art;
  • Figure 2C is a schematic side view representation of a flow-through type electrode in accordance with an embodiment of the present disclosure, for use in the electrochemical flow cell of Figure 1;
  • Figure 3 A is a partial top plan view of the electrode of Figure 2C;
  • Figure 3B is a partial cross-sectional view of the electrode of Fig. 2C, showing flow velocity though the electrode and the flow cell;
  • Figure 4A-4B are voltammogram graphs showing the results of voltammetry analysis conducted in 1 mM FcMeOH (ferrocene methanol) and 0.1 M KCl at a scan rate of 100 mV s "1 for a number of different flow rates through the electrode of Fig. 2C and the flow cell of Figure 1 ;
  • Figure 5A is a voltammogram graphs showing the results of voltammetry analysis conducted for flow through the electrode of Fig. 2C and the flow cell of Figure 1, wherein current response was measured for different concentrations of K 4 Fe(II)CN 6 in solution at a constant flow rate of 6mL min "1 ;
  • Figure 5B is a graph of current (in mA) vs. concentration (in mM), showing the anodic peak versus the concentration of K 4 Fe(II)CN 6 in solution;
  • FIG. 5C depicts the electrochemiluminescence (ECL) signal measurements obtained from the flow cell of Figure 1 over time, for 1 mM Tris(bipyridine)ruthenium(II) with 0.2 M of the co-reactant tripropylamine (TPrA) dissolved in 0.1 M phosphate buffer pH 7.3;
  • ECL electrochemiluminescence
  • FIG. 6 depicts a schematic representation of a method of manufacturing ultramicroelectrodes (UMEs) in accordance with an embodiment of the disclosure
  • Figure 7 depicts optical micrographs for various disk UMEs formed with different electrode materials according to the method of Figure 6;
  • Figure 8A depicts steady-state voltammograms for UMEs of different electrode materials manufactured according to the method of Figure 6;
  • Figure 8B depicts negative and positive feedback approach curves for UMEs of different electrode materials as manufactured according to the method of Figure 6;
  • Figure 9 depicts optical micrographs of a mercury disk UME after electrodeposition and mechanical polishing manufactured according to an embodiment of the invention together with negative and positive feedback approach curves for said mercury disk UME;
  • Figure 10 depicts optical micrographs of Ag I AgCl a microreference electrode manufactured according to an Ag I AgCl embodiment of the invention together with steady-state voltammograms for 10 different microreference electrodes;
  • Figure 11 depicts a mercury deposition curve according to an embodiment of the invention together with linear sweep voltammetry results
  • Figure 12 depicts steady-state voltammograms for bare disk electroactive surface UMEs and for Hg hemisphere UMEs with a Hg hemisphere deposited on the surface exploiting Pt, Au, Ag and C with insets of optical micrographs with a scale bar of 25 ⁇ ;
  • Figure 13 depicts optical micrographs of a burst 25 ⁇ silver UME together with the same UME after a quick re-polish together with steady-state voltammograms for both the burst and the re-polished 25 ⁇ Ag disk UMEs as manufactured using processes according to embodiments of the invention.
  • Figure 14 depicts exemplary UMEs according to embodiments of the invention with multiple electrodes.
  • the electrochemical flow cell 10 (or simply "flow cell") of the present disclosure is a modular cell which enables scaling the device as may be required and also permits modulation of the cell output signal without a substantial loss in reproducibility and accuracy. This is at least partially enabled by maintaining laminar flow though in the cell 10, as will be seen. By sustaining laminar flow through the cell, the flow cell 10 may enable improved predictability of the output signal and a better match between the actual signal output and the theoretical output which can be calculated using theory.
  • the present flow cell 10 and thus the electrodes 12 therein employ a "flow-through” type configuration as shown in Fig. 2C.
  • the fluid e.g. reactant
  • the cell 10 flows through the cell 10, from an inlet 13 to an outlet 15 thereof, by serially flowing through each of the electrodes 12 in succession.
  • the flow cell 10 includes a cell body 20 having the inlet 13, the outlet 15, and a flow passage 22 defined by and within the cell body 20 and extending between the inlet 13 and the outlet 15 to define a flow path 17 for fluid flowing through the cell body 20.
  • a number of electrodes 12 are disposed within the flow passage 22 of the cell body 20.
  • Each of these electrodes 12 is a flow-through type electrode having an electrode surface 19 disposed transverse (and in at least one embodiment, substantially perpendicularly) to a flow direction 17 through the flow passage 22.
  • the flow-through electrodes 12 have a plurality of apertures or other suitable openings or fluid flow passages or conduits therein through which the fluid can pass.
  • the electrodes 12 are arranged in serial flow succession within the flow passage 22, such flow entering the cell body 20 via its inlet 13 must first flow through an upstream working electrode 14, before flowing to an intermediate counter electrode 16 and then, in turn, to a most downstream reference electrode 18. Fluid flow exiting the reference electrode 18 then flow toward the outlet 15 of the flow body 20.
  • the flow- through electrodes 12 include an upstream working electrode 14 at which the electrochemical reaction occurs, an intermediate counter electrode 16 which is used to pass current density between the working electrode 14 and a downstream reference electrode 18 having a fixed potential. These three electrodes are disposed sequentially and in serial flow within the flow passage of the cell body.
  • the working electrode 14 is disposed closest to the inlet 13 of the cell
  • the reference electrode 18 is disposed closest to the outlet 15 of the cell
  • the counter electrode 16 is disposed between the upstream working electrode 14 and the downstream reference electrode 18.
  • the working electrode 14 and the counter electrode 16 may be honeycomb flow-through electrodes, as will be described.
  • the reference electrode 18 may be formed by a small wire and a thin film.
  • the most upstream one of the electrodes 12 within the flow cell 10, namely the working electrode 14, therefore receives substantially un-interrupted fluid flow from the inlet 13 of the cell.
  • the working electrode 14 is positioned within the flow passage 22 at a predetermined distance Le downstream of the inlet 13 of the cell body 20. This predetermined distance or length Le is selected such as to corresponding to a streamwise location within the flow passage 22 at which substantially fully developed laminar flow of the fluid flowing along the flow path 17 occurs.
  • This distance Le will vary depending on a number of factors, mainly the Reynolds Number of the fluid in question and the diameter D (or cross-sectional area for a non-circular cell flow passage) of the flow passage 22, however given these known parameters one skilled in the art will be able to accurately determine the point at which substantially fully developed laminar flow will occur given the particular conditions and parameters of the flow cell 10, the overall flow system in general and its intended use.
  • the distance Le of the working electrode 14 downstream of the inlet 13 of the flow cell 10 corresponds to the fluid dynamic "entrance effect" of flow through a pipe (or in this case, the flow passage 22 of the cell body 20).
  • Boundary layers develop along the walls of the flow passage 22 as a result of the solid surface exerting a retarding shear force on the flow which reduces the speed of the flow near the walls.
  • the effect of the passage wall is "felt" further out into the flow.
  • the flow in this region is said to be developing.
  • the boundary layers developing on the walls reach the center line of the passage, at which point the shape of the velocity profile no longer changes with any increasing distance.
  • the entrance length (Le) is therefore the length of pipe or cell flow passage 22 required for the flow to become fully developed.
  • the entrance length (Le) is a function of the diameter (D) of the passage 22 and the Reynolds Number (Re), as follows:
  • the Reynolds number (Re) is a dimensionless diameter which determines the nature of the flow regime (i.e. : laminar or turbulent) for incompressible fluid flow in a pipe/channel.
  • Reynolds numbers less that about 2300 indicate laminar flow, and Reynolds number greater than about 4000 indicate turbulent flow.
  • a Reynolds number between these values indicates that the flow is transitional. Reynolds number is calculated as follows:
  • Re pVD/ ⁇ wherein p is density, V is velocity, D is pipe diameter, and ⁇ is dynamic viscosity.
  • Re T transition Reynolds number
  • the fluid flow reaching the working electrode 14 is therefore intended to be as laminar as possible
  • the fluid flow through the entire flow length of the cell 10, that is from at least the working electrode 14 to the outlet 15 of the flow passage may also be kept as laminar as possible. This is possible given the relative lack of flow disturbances in the flow cell 10 and the flow-through nature of each of the electrodes 12, which will be described in further detail below.
  • the flow-through configuration of the electrodes 12 and the cell 10 offers several benefits over the flow by and jet-flow systems of the prior art, as seen in Figures 2A-2B.
  • the radial flow gives a change in solution velocity across the electrode which may create stagnation points in the fluid flow, which may reduce temporal resolution for injection style analytical studies.
  • the electrodes 12, and particularly the working electrode 14 are honeycomb screen-printed electrodes.
  • the honeycomb configuration of the electrodes 12 define an electrode surface 19 that is symmetrical about a six planes of planes of symmetry extending through corners of the hexagonal shaped honeycomb electrode surface and through the central point of each edge of the hexagon.
  • Fig. 3A see the insert
  • two exemplary planes of symmetry are shown. It is however to be understood that fewer or more planes of symmetry may alternately be provided. For example, two planes of symmetry that are perpendicular to each other are possible, both with the hexagonal shape of the honeycomb configuration and/or with alternate electrode shapes.
  • a substantially uniform electrode surface 19 extends across the entire flow passage 22 of the cell.
  • the honeycomb electrodes 19 define a plurality of individual passages 24 which extend between the upstream electrode surface 19 and a downstream surface of the electrode 12. These passages 24 which extend in the flow- wise direction through the electrode therefore permit the fluid to flow through the electrodes 12.
  • the modular flow-through cell 10 of the present disclosure is capable of performing both qualitative and quantitative measurements, and is further able to perform ECL measurements.
  • the flow cell 10 may therefore be able to be used in a variety of different research fields, ranging from fundamental studies, such as those relating to reaction mechanisms for example, to applied analysis, such as for sensing biological, organic and inorganic compounds for example.
  • the flow cell 10 may also be scaled up and used in different industrial process or for online environmental monitoring, for example only.
  • the flow cell 10 may therefore offer several improvements over the existing commercially available systems, and may be used for a number of different applications.
  • the flow cell 10 uses a flow-through methodology to obtain a reliable hydrodynamic profile, which may also dramatically increases the mass transport and increases the sensitivity of the detection while at the same time improving the signal to noise (S/N) ratio.
  • the flow cell 10 can incorporate electrodes composed of different materials (such as: Au; Pt; and glassy carbon), and allow collection efficiency measurements for the study of homogenous kinetics, or the measurement of a generated species stability.
  • the design of flow cell 10 can be adjusted for different purposes, thereby making it possible to increase the range of applications from a scientific and commercial point of view.
  • the design of the flow cell 10 of the present disclosure can also be further miniaturized, in order to make it usable for applications such as in-field measurements such as environmental monitors and remote sensors. Additionally, as noted above, the flow cell 10 is able to perform ECL measurements, which provides significant possibilities.
  • the electrochemical flow cell 10 as described above includes a number of electrodes 12. Because of the very small size of such flow cells 10, and therefore of the electrodes used therein, in order to provide predictable and accurate results, reproducibility and manufacturability considerations of the electrodes 12 become important. Because of their microscopic size, it has been found that improvement may also be sought with respect to the ability to consistently and accurately produce the electrodes 12 in general, and the working electrodes 14 in particular given that this is where the electrochemical reaction occurs.
  • UME ultramicroelectrode
  • SECM scanning electrochemical microscopy
  • the UMEs as produced in accordance with the present disclose may also be used for conducting electrochemical measurements in low conductive media (such as organic solvents, etc.), where the voltage drop associated with high solution resistance makes such experiments difficult for conventional electrodes.
  • UMEs may be defined as electrodes with at least one dimension smaller than 25 ⁇ .
  • UMEs permit a very small voltage drop, which leads to a very small voltage distortion at the electrode-solution interface. This may permit, for example, using a two-electrode setup in voltammetric experiments, instead of a more conventional three-electrode setup. Apart from their small dimensions they may offer several advantages including, for example, high sensitivity, fast steady state response, low double-layer charging currents, high scan rates and small ohmic losses. Furthermore, their small current requirements enable electrochemical measurements in low conductive media, e.g. organic solvents, where the voltage drop associated with high solution resistance makes these experiments difficult for convention electrodes.
  • UMEs with small RG are also used in scanning electrochemical microscopy (SECM), in order to reduce tip-to-substrate distance ( d ) and thus allowing for a higher sensitivity.
  • SECM scanning electrochemical microscopy
  • the RG of a UME is defined as the ratio between the radius of the insulating sheath ( f T ) and the radius of electroactive surface ( a ).
  • the RG also has a significant effect on the current recorded during SECM approach curve measurements. A smaller RG will result in a larger current at short tip-to-substrate distances ( ⁇ 5) because of enhanced contributions from back diffusion of the mediator. They also decrease the probability of contact between the insulating sheath of the UME and the sample, which experimentally occurs upon axial misalignment of the UME.
  • UMEs Common geometries of such UMEs include disk, hemispherical, inlaid ring, ring-disk, and finite conical.
  • the most frequently used geometry for UMEs is disk, whereby an electroactive material is embedded within an outer insulating layer.
  • UMEs have been used in a variety of applications including biological systems, charge transport at liquid/liquid interfaces, and corrosion studies.
  • the inventors have developed an improved method of manufacturing such UMEs, in order to address at least some of these reproducibility and fabrication issues known to exist with existing UMEs.
  • the UMEs are produced in accordance with the method of fabrication(s) as will be described below have been found to be precisely reproducible with accurate geometries. This therefore enables exact quantitative analysis given the highly reproducible geometries of the electroactive area and the surrounding glass. Better control of the diffusion field around the electrode may thus be possible, enabling the quantification of very low levels of analytes.
  • the UMEs were fabricated using a P-2000 laser-based micropipette puller system (Sutter Instruments), a PC-10-CA vertical pipette puller (Narishige) and a vacuum pump.
  • the electroactive surfaces were exposed and polished using a Tegrapol 23 variable speed grinder / polisher. All electrochemical measurements were performed using an Electrochemical Probe Scanner 3 (HEKA Elektronik) in a three- electrode setup with a platinum wire counter electrode. All potentials were recorded relative to a chloridized silver wire quasi-reference electrode, unless specified otherwise, which had been manufactured at McGill University.
  • Optical micrographs were obtained using a customized Axio Vert.Al inverted microscope.
  • FIG. 6 a complete schematic of the disk UME fabrication technique according to an embodiment of the present disclosure is presented.
  • the soda-lime glass capillary were cleaned using 10% v/v nitric acid for 1-2 hours, rinsed with nanopure water, and dried in an oven ( 100°C ) for 12 hours, first stage 110.
  • a capillary was pulled using a single line heating and pulling program (Heat: 240; Fil: 5; Vel: 60; Del: 140; Pul: 70), at the second stage 120.
  • Equal tensile force was applied at each end of the capillary along with simultaneous heat from a C0 2 laser, resulting in the severing of the narrowed neck and thus production of two symmetric micropipette tips, as shown at the third stage 130.
  • a 10 mm long section of electroactive material in wire or fiber form for example silver (Ag), gold (Au), carbon (C), or platinum (Pt) was inserted into the pulled micropipette tip.
  • electroactive material in wire or fiber form for example silver (Ag), gold (Au), carbon (C), or platinum (Pt)
  • the wire/fiber traveled downward until trapped in the sealed extremity.
  • the assembly was then inserted into a PC-I0-CA vertical pipette puller, fourth stage 140, and a vacuum pump was attached to the open end of the micropipette, and the pressure was reduced for approximately 5 minutes to minimize bubble formation.
  • the wire was sealed by centering the assembly inside a Kanthal heating coil and applying heat for - 10 - 205 after maximum temperature was reached (bright orange coil), fifth stage 150.
  • the sealed wire was connected to a copper (Cu) wire using conductive silver epoxy, which was subsequently cured at 120°C f or 1 5 minutes.
  • the assembly was inserted into a larger borosilicate capillary to provide additional reinforcement, and the overlapping edges were sealed using epoxy.
  • a gold connector pin was then soldered to the copper wire, completing the assembly, sixth stage 160.
  • the electroactive surface of the UME was exposed using a grinder/polisher (400 rpm, 4000 grit) followed by an alumina powder polishing.
  • a pre-thinning step 120 of the outer glass capillary is performed, prior to severing the thinned neck region. Because of the equal forces applied to the capillary in opposite directions, the thinned neck region is formed having at least a very symmetric geometry, if not perfect symmetry. This has to be done to the glass capillary without the wire in place therewithin. Consequently, a high concentricity between the electroactive wire (whether formed of metal or fiber), once it is subsequently inserted into the capillary after this pre-thinning step, is achieved. This enables a very precise ratio of the amount of exposed electroactive wire tip to the surrounding glass sheath of the capillary.
  • a very precise RG value of the UME so produced which is the ratio between the radius of the insulating glass sheath ( r T ) and the radius of electroactive wire tip (a ).
  • this ratio RG is less than 10, and in a further particular embodiment the ratio RG obtained is about 3.
  • the resulting ultramicroelectrode so formed does not require any additional side polishing, after the sealing of the electroactive wire within the narrowed neck of the pulled capillary.
  • Hg UMEs offer an extended solvent window in the negative potential region and an increase of sensitivity compared to Pt.
  • a post fabrication sequence was performed upon Au disk UMEs with an Au disk diameter of 25 ⁇ . These were initially chemically etched by immersion in aqua regia (nitro- hydrochloric acid) solution for 10 - 20 min . The Au UME was then rinsed with acetone and nanopure water to halt etching. Hg was then electrodeposited onto the recessed electroactive surface of the UME using the same procedure as for Hg hemispherical UMEs described below in Section A6.
  • Disk UMEs were stored in a degassed, 0.5% acidified 0.1 M KN0 3 solution.
  • Equation (1) The microreference electrodes were stored in 0.1 M KCl w en not in use.
  • Hg hemispherical UMEs with Ag, Au, C, or Pt, were fabricated by electrodeposition according to the reaction given in Equation (2). Briefly, an Hg hemisphere was electrodeposited onto the electroactive surface of a disk UME using 10 mM Hg 2 ⁇ N0 3 ⁇ in 0.1 M KN0 3 acidified to 0.5% with HN0 3 solution. The electrochemically-controlled deposition was performed by applying a potential of -0.5 V vs. Hgl HgSO until the current reached ⁇ /2 (-1.57) times the initial current from the 25 ⁇ disk UME.
  • the Hg deposition curve is shown Figure 6 A wherein a potential of OF was held for 0.35 seconds before a potential step of -0.5 V vs. Hgl HgSO (saturated K 2 S0 4 ) was applied for a duration of 300 seconds.
  • the full coverage of the electroactive surface has been investigated for both Hg disk and hemispherical UMEs. Similar to the Hg disk UME, see Figure 6B, the hemispherical UMEs display the expected shift in proton reduction to more negative potentials compared to the bare disk UMEs.
  • the Hg hemispherical UMEs were stored in degassed, 0.5% acidified 0.1 M ⁇ 3 solution.
  • Electrochemical behavior was characterized by cyclic voltammetry and
  • First to seventh image sets 200A to 200G in Figure 7 for UMEs confirm the absence of air bubbles and a proper concentric seal of the wire/fiber within the insulating glass sheath.
  • First to seventh image sets representing:
  • First image set 200A depicts a lO/wt Pt UME;
  • Second image set 200B depicts a 25 ⁇ Pt UME;
  • Third image set 200C depicts a ⁇ Au UME
  • Fourth image set 200D depicts a Au UME
  • Sixth image set 200F depicts a ⁇ ⁇ C UME
  • Seventh image set 200G depicts a 1 ⁇ C UME.
  • the scale bar in each instance being 25 ⁇ .
  • the sealed length was generally 3 - 5mm .
  • concentric alignment of the UME within the heating coil and coil temperature ( ⁇ 720°C ) were rigorously controlled. Bending effects were more prevalent when using smaller diameter wires.
  • End views of the UMEs in the right hand images of each of first to fourth image sets 200A to 200D respectively confirms ideal disk geometry with a well-centered electroactive core surrounded by an insulating sheath, requiring no further sharpening step as employed in prior art manufacturing techniques.
  • First graph 300A depicts 25 ⁇ and ⁇ Pt UMEs
  • Second graph 300B depicts 25 ⁇ and ⁇ Au UMEs
  • Third graph 300C depicts a 25 ⁇ Ag UME
  • Fourth graph 300D depicts ⁇ ⁇ and 1 ⁇ C UME.
  • First graph 300E depicts 25 ⁇ and ⁇ Pt UMEs
  • Second graph 300F depicts 25 ⁇ and ⁇ Au UMEs
  • Third graph 300G depicts a 25 ⁇ Ag UME.
  • Fourth graph 300H depicts 7 ⁇ and 1 C UME.
  • the steady state current (i ss ) is governed by the flux of redox species in solution toward the electrode surface as described by Equation (3)
  • F is the Faraday constant (96,485C e _1 )
  • a the radius of the electroactive surface
  • D * 8.7 ⁇ 0 ⁇ 6 cm 2 s ⁇ l ),
  • C * is the concentration of dissolved redox species
  • ⁇ is a tabulated factor dependent on the RG of the UME.
  • Table 1 then the diameters of the electroactive surface of the UMEs were calculated, as reported above the corresponding CVs are depicted in first to fourth graphs 300A to 300D in Figure 8B.
  • the calculated diameters are consistent with those observed in optical micrographs (first to seventh image sets 200A to 200G respectively in Figure 7) and reported by the manufacturer of the respective wire/fiber, confirming a high quality seal devoid of leaks and cracks, which would have manifested as an increased steady state current. This seal quality is further confirmed by the presence of a long current plateau over hundreds of millivolts.
  • the lack of significant hysteresis in the CVs is also qualitatively indicative of a good polishing.
  • Hg disk UMEs were fabricated using a combination of chemical etching, electrodeposition, and mechanical polishing. Optical micro- graphs were obtained at different stages of the fabrication process.
  • the side view image, first image 400A in Figure 4 highlights a chemically recessed Au UME. Etching depth can be adjusted by controlling the immersion time in aqua regia. Since the bare disk UMEs used during this fabrication process were previously characterized, it was determined that the diameter of the produced gap was equal to the diameter of the electroactive core (i.e., using a 25 ⁇ Au disk UME, the diameter of the gap was also 25 ⁇ ).
  • the side image (second image 400B in Figure 9) and top (third image 400C in Figure 9) views of the optical micrographs confirm the disk geometry of the Hg UME.
  • the top view depicted in third image 400C in Figure 9 also demonstrates that the Hg electroactive area is well-centered within the glass sheath.
  • Hg disk UMEs allow for an extended solvent window in the negative potential region, which is not possible with conventional cores such as Au or Pt, and also offers an increase of sensitivity compared to other metals for the electroanalysis of trace metal.
  • the disk geometry allows fitting to established theoretical expressions.
  • the method can also produce Hg hemispherical UMEs as description supra in respect of Section A6.
  • FIG. 10 Top and side view optical micrographs are presented in first and second images 500A and 500B in Figure 10 wherein an AgCl layer has successfully been electrodeposited onto the bare Ag disk UME.
  • cyclic voltammetry in FcMeOH was employed.
  • graph 500C in Figure 10 there are depicted cyclic voltammograms obtained with 10 different microreference electrodes and the same working electrode (25 jUm Pt disk UME).
  • the exhibited electrochemical behavior is consistent with the response obtained from a commercial (and much larger) reference electrodes. Even after 100 cycles, electrochemical response remained stable.
  • the small size of these microreference electrodes make them suitable for use in microelectrochemistry.
  • First graph 700A depicts 25 /m Pt disk UME and Hg/Pt UMEs with insert side view optical micrograph;
  • Second graph 700B depicts ⁇ Au disk UME and Hg/Au UMEs with insert side view optical micrograph
  • Third graph 700C depicts 25jUm Ag disk UME and Hg/Ag UMEs with insert side view optical micrograph
  • Fourth graph 700D depicts 1 ⁇ C disk UME and Hg/C UMEs with insert side view optical micrograph.
  • the full surface coverage of the Hg on the active material was characterized using linear sweep voltammetry (0 V to +2.5 V versus Hg/Hg 2 S0 4 ) in a 0.1 M KN0 3 as depicted in Figure 11, whereby the proton reduction over potential shifted to more negative potentials compared to a bare disk UME.
  • potentials were recorded relative to a chloride free Hg I Hg 2 SO A (sat. K 2 S0 4 ) reference electrode.
  • the response of hemispherical Hg UMEs showed, as expected, steady-state currents that were larger for hemispherical Hg UMEs compared to bare disk UMEs.
  • first and second schematics of variant methodologies wherein multiple wires or fibers can be sealed in the soft glass capillary to produce multi-core UMEs. Accordingly, within first schematic 900A a capillary has been exploited to form the UME with 5 electrical contacts. It would be evident that the metal within each contact may be different, the same, or different combinations may be employed.
  • second schematic 900B there is depicted a UME with an integrated silver/silver chloride reference electrode 910 in conjunction with a UME 920.
  • Such an electrode is produced by a similar methodology as that described in respect of Section A3 but using a double-barrel soft glass capillary and then following this procedure the methodology described in Section A5 is applied to the silver core producing an UME with an integrated reference electrode. Accordingly, a combination may be formed such as that with first schematic 900A in Figure 14 such that the central electrode is a silver/ silver chloride reference and the outer electrodes are all gold, for example, or are gold, platinum, mercury and carbon in another embodiment or two carbon and two gold in yet another.
  • the inventors have demonstrated a general technique for the fabrication of disk UMEs with different electroactive cores, including carbon, gold, mercury, platinum, and silver.
  • This technique leads to UMEs with small RG ranging from 2.5 to 3.6 although the inventors believe smaller RGs are possible.
  • the fabrication technique reduces the time required, improves the ease of fabrication, provides controlled and reproducible geometry, and the ability to expand to multiple electroactive cores.
  • the disk UMEs produced using this technique make them suitable backbones for surface modified electrodes, demonstrated here by the production of Hg disk, hemispherical UMEs, and Ag/AgCl microreference electrodes. Further, the optimal geometry of these probes makes them highly suitable for use in SECM measurements.
  • multi-core UMEs may be formed through combining multiple capillaries, exploiting a multi-bore capillary, or exploiting a machined or drilled glass block providing improved reproducibility of bore-bore tolerances.

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Abstract

La présente invention concerne une cellule d'écoulement électrochimique qui comprend un passage d'écoulement s'étendant entre l'entrée et la sortie pour définir un trajet d'écoulement pour le fluide afin qu'il s'écoule à travers le corps de cellule en tant qu'écoulement laminaire entièrement développé. Plusieurs électrodes à écoulement traversant sont disposées à l'intérieur du passage d'écoulement. Les électrodes à écoulement traversant sont agencées en une succession d'écoulements en série dans le passage d'écoulement et elles présentent une pluralité d'ouvertures en leur sein à travers lesquelles passe le fluide. L'électrode de travail est positionnée à l'intérieur du passage d'écoulement à une distance prédéfinie en aval de l'entrée du corps de cellule qui correspond à un emplacement dans le sens du courant au niveau duquel un écoulement laminaire sensiblement entièrement développé se produit. Au moins l'électrode de travail de la cellule d'écoulement peut comprendre une ultramicroélectrode qui est fabriquée conformément à la description de l'invention. Cependant, cette ultramicroélectrode, qu'elle soit à noyau unique ou multiple, peut également être utilisée pour des applications autres que la cellule d'écoulement de l'invention.
PCT/CA2016/050314 2015-03-18 2016-03-18 Cellule d'écoulement électrochimique et ultramicroélectrode WO2016145539A1 (fr)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113029931A (zh) * 2021-05-06 2021-06-25 中国船舶重工集团公司第七二五研究所 一种多工况电偶腐蚀试验装置
CN113281396A (zh) * 2021-05-11 2021-08-20 南京工业大学 一种基于改良secm探针的催化剂性能表征方法

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US5911859A (en) * 1997-07-15 1999-06-15 Exxon Research And Engineering Co. Three-dimensional electrode (Law464)
US20120006060A1 (en) * 2010-07-08 2012-01-12 Eiji Terao Method of manufacturing glass substrate and method of manufacturing electronic components
CN202542927U (zh) * 2012-02-24 2012-11-21 浙江工业大学 一种网板柱塞流电解装置

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US5911859A (en) * 1997-07-15 1999-06-15 Exxon Research And Engineering Co. Three-dimensional electrode (Law464)
US20120006060A1 (en) * 2010-07-08 2012-01-12 Eiji Terao Method of manufacturing glass substrate and method of manufacturing electronic components
CN202542927U (zh) * 2012-02-24 2012-11-21 浙江工业大学 一种网板柱塞流电解装置

Cited By (3)

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Publication number Priority date Publication date Assignee Title
CN113029931A (zh) * 2021-05-06 2021-06-25 中国船舶重工集团公司第七二五研究所 一种多工况电偶腐蚀试验装置
CN113029931B (zh) * 2021-05-06 2023-02-21 中国船舶重工集团公司第七二五研究所 一种多工况电偶腐蚀试验装置
CN113281396A (zh) * 2021-05-11 2021-08-20 南京工业大学 一种基于改良secm探针的催化剂性能表征方法

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