US20150017418A1

US20150017418A1 - Porous framework and method for its manufacture

Info

Publication number: US20150017418A1
Application number: US13/940,918
Authority: US
Inventors: Chun Kwan Tsang; Jian Lu; Yang Yang Li
Original assignee: City University of Hong Kong CityU
Current assignee: City University of Hong Kong CityU
Priority date: 2013-07-12
Filing date: 2013-07-12
Publication date: 2015-01-15
Also published as: CN105359316A

Abstract

A method for fabricating a porous framework includes contacting a substrate with a solution containing a plurality of component materials are dissolved in the solution. A solid composite made of the plurality of component materials is electrodeposited onto the substrate. A plurality of electrodepositing voltages is applied to vary a relative proportion of the component materials in the composite being electrodeposited, and at least one of the plurality of component materials is selectively etched away from the composite to form a plurality of pores.

Description

FIELD

The invention relates generally to a method for manufacturing a framework that has approximately microscopic, mesoscopic or nanoscopic pores with widths that vary predictably along their length, and a framework with such pores.

BACKGROUND

Because of their wide range of potential applications (e.g., for future automobiles), supercapacitors as a type of charge storage device have attracted tremendous attention. Challenge in the development of supercapacitors include how to achieve high power densities, cycling stability, and energy densities. Attempts to meet these challenges have included coating electroactive materials on different host structures and materials, such as inverse-opal networks, metal nanoparticles, or porous conductive frameworks, for using the electroactive materials more efficiently by providing a larger working surface area for diffusion-controlled redox reactions.
However, inverse-opal networks are complex and limited to small sample sizes, and the often loose contact between neighboring electroactive materials-coated metal nanoparticles generally leads to high internal resistances due to a lack of short pathway to the charge collector in the structure. Porous conductive frameworks coated with electroactive materials permit direct charge transfer from the usually poorly conductive electroactive materials to the charge collectors. However, their specific capacitance and cycling stability remain limited and there is no ability to rationally control their porosity (volume fraction of pores) or pore geometry (e.g., pore size) throughout the structure. Reported conductive frameworks display a fairly homogeneous single-layered porous morphology throughout the entire structure, limiting available surface area. Thus, there is a need for methods for manufacturing supercapacitor electrode frameworks with high power densities, cycling stability, and energy densities, such as by predictably modifying their architecture to increase surface area.

SUMMARY

In one embodiment, a method for fabricating a porous framework is provided. The method includes contacting a substrate with a solution containing a plurality of component materials dissolved therein. A solid composite made of the plurality of component materials is electrodeposited onto the substrate. A plurality of electrodepositing voltages is applied to vary a relative proportion of the component materials in the composite being electrodeposited. And at least one of the plurality of component materials is etching away selectively from the composite to form a plurality of pores.
In another embodiment, a framework is provided. The porous framework includes a structure with a plurality of pores, with a pore width at a distance along a length of the plurality of pores of between 1 nanometer and 10 microns, and an approximately predetermined variation in the pore width along the length of the pore.

DRAWINGS

These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings, wherein:

FIGS. 1A-H are line graphs representing hypothetical relationships between electrodepositing voltage profiles applied during an electrodepositing step and compositional profiles across a thickness of a composite structure created by the electrodepositing step, in accordance with an aspect of the invention;

FIG. 2 is a diagram illustrating a variation in pore diameter achieved in accordance with an aspect of the invention;

FIG. 3 is a diagram illustrating a method for manufacturing a porous framework, and a porous framework manufactured by such a method, in accordance with an aspect of the invention; and

FIGS. 4A-F are scanning electron microscopic images of porous frameworks in accordance with an aspect of the invention.

DETAILED DESCRIPTION

In the following description and the claims that follow, whenever a particular aspect or feature of an embodiment of the invention is said to include, comprise, or consist of at least one element of a group and combinations thereof, it is understood that the aspect or feature may include, comprise, or consist of any of the elements of the group, either individually or in combination with any of the other elements of that group. Similarly, the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise.
Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about” may not be limited to the precise value specified, and may include values that differ from the specified value. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. In the present discussions it is to be understood that, unless explicitly stated otherwise, any range of numbers stated during a discussion of any region within, or physical characteristic of, is inclusive of the stated end points of the range.
As used herein, the term “submicroscopic” generally refers to features that are between approximately one nanometer and approximately one micron in size. The term “submicroscopic” is used herein generally synonymously with the phrase “nanoscopic or mesoscopic.” The phrase “submicroscopic porous framework” and similar phrases are used herein generally to mean a porous framework having pores with a width of between approximately one nanometer and approximately one micron. However, the term “submicroscopic” is used herein generally to refer only to approximate dimensions, and is not intended to categorically exclude all features with dimensions that are only slightly outside of the range of one nanometer to one micron. In some embodiments of the invention, a feature of a dimension of several microns or more is achieved. It should be understood that descriptions herein of a submicroscopic dimension or feature or method of attaining a submicroscopic dimension or feature may be modified to attain a feature on the order of several microns or more in accordance with the invention.
The present invention includes a method for manufacturing a porous framework with submicroscopic pores whose architecture may be predetermined, or approximately predetermined, dynamically, such as by creating predictable variations in pore size along a length of pores and increasing an inner surface area of pores, and porous frameworks manufactured with such method.
The invention includes a first electrodepositing step, by which a structure made of a composite of a plurality of materials is created. The materials are simultaneously electrodeposited out of solution and onto a substrate, using electrodepositing voltages such that the materials' rates of electrodepositing relative to each other are dynamically and predictably controlled over the course of the electrodepositing step.
In a second step, material is selectively etched away from the structure, creating pores in the portions of the structure that had previously been occupied by etched-away material. Because of a heterogeneous rate of electrode position, during an electrodepositing step, of material that is subsequently etched away, during a selective etching step, pores that are created have widths that vary along their lengths in regions where more of the etched away material had been electrodeposited than where less had been, or from where more material had been etched-away etched away from were less had been.
Regarding an electrodepositing step, a solid composite structure is created on a substrate by electrodeposition. Materials the composite structure is made of are determined according to solutes present in an electrodepositing solution. As a non-limiting example, a structure made of a metallic bialloy may be created by dissolving salts of the two constituent metals in an electrodepositing solution and electrodepositing the materials simultaneously.
A voltage used to simultaneously electrodeposit a plurality of materials during an electrodepositing step may be varied over time such that a ratio of materials being simultaneously electrodeposited changes over the course of an electrodepositing step. As a non-limiting example, for one period of time, t₁, one electrodepositing voltage, V₁, may be applied that causes more of one of a simultaneously plated out materials, M₁, to be plated out than another simultaneously plated-out material, M₂. Under these conditions, during t₁, more M₁will be plated out than M₂, causing a portion of the composite structure to contain more M₁than M₂. The longer the duration of t₁, the thicker that portion of the composite structure will be. Similarly, for another period of time, t₂, another electrodepositing voltage, V₂, may be applied that causes more of the other simultaneously plated out material, M₂, to be plated out than the first, M₁. Under these conditions, during t₂, more M₂will be plated out than M₁, causing a portion of the composite structure to contain more M₂than M₁. The longer the duration of t₂, the thicker that portion of the composite structure will be. Furthermore, by successively alternating between V₁and V₂, alternate portions of the composite structure that contain alternately higher proportions of M₁to M₂and vice versa may be formed. A thickness of each such created portion of the composite structure may be increased or decreased by increasing or decreasing t₁and/or t₂, respectively. Relative amounts of M₁and M₂per portion may also be specifically controlled by applying electrodepositing voltages that result in specific relative proportions of materials to simultaneously plate out.
FIGS. 1A-H are line graphs illustrating non-limiting examples of a relationship between an electrodepositing profile applied during an electrodepositing step and a proportion of materials constituting a composite structure at given distances across its thickness. An electrodepositing voltage profile may be a sequence of a plurality of voltages that are applied in a temporal sequence during an electrodepositing step. FIGS. 1A, 1C, 1E, and 1G illustrate different electrodepositing voltages applied across an electrodepositing step. The X-axis of these line graphs represents time elapsed during the electrodepositing step (t), and the Y-axis represents the electrodepositing voltage (V) applied at a given time, t. In FIGS. 1A, 1C, 1E, and 1G, a voltage gradient varies across an electrodepositing step according to a square wave, a sinusoidal wave, a triangular wave, and a non-linear curve, respectively. FIGS. 1B, 1D, 1F, and 1H illustrate different compositional profiles across a thickness of the composite structure resulting from application of the electrodepositing voltage profiles illustrated in FIGS. 1A, 1C, 1E, and 1G, respectively. A compositional profile may be a proportion of a composite structure, at a distance across a height of the composite structure that is composed of a given material in relation to how much of the composite structure is composed of another material or other materials at that height. The X-axis of the graphs in FIGS. 1B, 1D, 1F, and 1H represents a distance across a thickness of the composite structure (d), and the Y-axis represents a ratio of one material to another (R) constituting the composite structure at a given distance, d.
In FIGS. 1B, 1D, 1F, and 1H, a ratio R varies across a distance d according to a square wave, a sinusoidal wave, a triangular wave, and a non-linear curve, respectively, in accordance with a corresponding electrodepositing voltage profile illustrated in FIG. 1A, 1C, 1E, or 1G, respectively. Thus, an electrodepositing profile applied during an electrodepositing step corresponds to a compositional profile of the composite structure across its thickness. It should be understood that the representative profiles in FIGS. 1A-H are illustrative only and non-limiting, and a wide variety of profiles that are not shown in FIGS. 1A-H may be attained in accordance with the invention.
With regard to a selective etching step, one of the materials that constitutes the composite structure synthesized by the electrodepositing step is selectively etched away, leaving behind a framework made of non-etched material. Selective etching may be accomplished according to known methods appropriate to selectively etch away the desired material. Non-limiting examples include contacting the composite structure with an etching substance and electrochemical etching. Non-limiting examples of an etching substance include hydrochloric acid, ammonia, nitric acid, and hydrofluoric acid, and any etching substance appropriate to selectively etch away a desired material may be used. Other known methods of etching appropriate to selectively etch a desired material away from the composite structure may also be employed. Selective etching may be relatively selective or partially selective, rather than absolutely selective. An etching step may etch away a plurality of materials, but more of one material than another, or may incompletely etch away one material.
Selective etching causes pores to form in portions of the structure that were previously occupied by etched-away material, yielding a porous framework. Pores may also be formed by rearrangement during a selective etching step of the structural relationship between atoms of material that is not etched away. A pore volume of the framework at a distance across a thickness of the framework approximately reflects a proportion of the framework at that distance that had previously been occupied by etched-away material. A pore volume is how much of a framework at a given distance across its thickness consists of pores compared to non-etched-away material. Thus, a pore volume profile across the thickness of a framework reflects a previous compositional profile of the composite structure across its thickness, before selective etching. Because a compositional profile of a composite structure was caused by a voltage profile applied during an electrodepositing step, a pore volume profile of the porous framework that is formed also results from a voltage profile that was applied before selective etching, during are electrodepositing step. For example, where a voltage was applied according to a periodic profile during an electrodepositing step, a pore volume profile across a thickness of a framework may approximately correspond to the same periodic profile.
A pore volume profile across the thickness of a framework may result from a variation in the width of a pore across its length. An axis extending through a length dimension of a pore may extend from the base of a framework to its top. An axis of a pore's length dimension may be approximately orthogonal to the thickness of a framework. Thus, a location across a length of a pore may correspond to a distance across a thickness of a framework. In such cases, a height of a pore corresponds approximately to a height of the framework, and a distance along a length of a pore may be considered a distance along a height of a pore. A width of such a pore at a given height depends on a proportion of etched-away material that constituted a composite structure at that distance across its thickness before the etching step. Thus, for such a pore, where a composite structure at a given distance A across its thickness contained more of a substance that was subsequently etched away during selective etching than did another distance B across the composite's thickness, a width of a pore at its height corresponding to distance A is higher than its width at another height corresponding to distance B. Because of stochastic variability in an electrodepositing step or rearrangement during a selective etching step of the structural relationship between atoms of material that is not etched away, it should be understood that a pore volume profile across a thickness of a framework may approximately correspond to a voltage profile applied during the electrodepositing step in accordance with an aspect of the invention.
FIG. 2 shows a non-limiting illustrative example of a relationship between an electrodepositing voltage profile applied during an electrodepositing step and a width profile across a height of a pore created by subsequent selective etching. In this example, the axis along the pore's length is orthogonal to the thickness of the framework. Also in this example, a cross-section of the pore orthogonal to its length axis is approximately circular. Therefore, the pore's width can be, and is, generally expressed as a diameter across such cross-section. On the left of FIG. 2, a line graph shows a voltage profile that was applied during electrodepositing. On the X-axis is voltage, and on the Y-axis is progression of time during the electrodepositing step. On the right, a longitudinal cross-section-view of a pore through a framework resulting from an electrodepositing voltage profile shown on the left followed by selective etching is shown. Two materials were simultaneously plated out during an electrodepositing step. On the left, two voltages that were applied during electrodepositing are shown, V₁and V₂. During V₁, more of material 1 was deposited than of material 2, and during V₂, more of material 2 was deposited than of material 1. Voltages V₁and V₂were applied alternately, with V₁being applied for time period t₁and V₂being applied during t₂, creating a composite structure with proportional compositions of materials 1 and 2 that varied across its thickness. Following the electrodepositing step, material 2 was selectively etched away from the composite material, creating a pore illustrated on the right. The diameter of the pore is represented at different heights, with d₁across height h₁being smaller than diameter d₂across height h₂. The longer a time t₁during which a voltage profile V₁that preferentially electrodeposits a material 1 was applied during electrodepositing, the greater the height h₁of a portion of a pore with diameter d₁following selective etching, and vice versa.
The non-limiting example of a relationship between an electrodepositing voltage profile and a diameter profile of a pore illustrated in FIG. 2 is only one representation of how pore diameter and, therefore, framework architecture, may be dynamically shaped in accordance with an aspect of the invention. It should be understood that many voltage profiles could be applied during an electrodepositing step to cause correspondingly many pore diameter, or other width, profiles and porous framework architectures following selective etching. It should also be understood that a pore branch may form off of a pore's longitudinal axis, or that a pore may be straight, only approximately straight, or curved or bent, or morphology of a porous framework may be spongiform.
A particular advantage of an aspect of the invention is the creation of porous frameworks, whose pore widths vary from between 1 nanometer and 1 micron, several microns, or more. A further advantage of an aspect of the invention is an increase in surface area available on an inner surface of the pores of the porous metallic framework.
In another aspect of the invention, an inner surface of pores in a porous framework created by electrodepositing and selective etching steps are treated to, as non-limiting examples, alter a surface chemical composition, a structural feature of a surface, or to coat a surface. Inner pore surfaces may be heated, oxidized, or attached to various chemical species, as non-limiting examples. Non-limiting examples of chemical species that may be attached to an inner surface of pores are organic molecules, inorganic molecules, biomolecules, electroactive materials, and polymers. An inner surface of pores in a porous framework may be modified to create a structure that is adapted to particular uses, such as to increase the surface area available for particular chemical reactions, enhance plasmonic behavior of inner pore surfaces, and influence electron transport along an inner pore surface, as non-limiting examples. Materials may also be placed within pores without being chemically attached to an inner pore surface to adapt the characteristics of a porous framework to a particular function. A submicroscopic porous metal framework may be electroplated with an electroactive material, resulting in a high-performance supercapacitor electrode.
As a non-limiting example of creating a high-performance supercapacitor electrode, a composite structure may be created by simultaneously electrodepositing nickel and copper. A square-wave electrodepositing voltage profile may be applied during electrodepositing, with one voltage causing more copper to be electrodeposited than nickel, and another voltage causing more nickel to be deposited than copper. After the electrodepositing step, copper may be selectively etched away from the composite structure, leaving a submicroscopic porous framework made mainly of nickel. In accordance with examples described above, in this example, pores whose longitudinal axis is orthogonal to the thickness of the framework will have widths that vary periodically along their height. The resulting framework is referred to as a wavy-channel nickel framework, because of the waviness of the widths of the pores. An electroactive material such as, as a nor-limiting example, a transition metal oxide may be electroplated onto the inner surfaces of the submicroscopic pores. Non-limiting examples of transition metal oxides include nickel oxide-based materials, such as Ni^IIIO(OH). A resulting supercapacitor electrode has wide uses, such as charge storage devices, and may have a specific capacitance of more than 2300 F/g (measured at 1 A/g), and high cycling stability of over 90% capacitance retention at 50 A/g after 1000 cycles. In this and the descriptions that follow, specific capacitance was measured by dividing capacitance by the mass of the electroactive material coating on the framework, i.e., nickel oxide, not the total weight of the coated framework.
In FIG. 3, three structures are shown representing such an example. The first structure, shown on the left, is a composite structure composed of a nickel-copper bialloy. This structure was created by simultaneously electrodepositing nickel and copper onto a substrate. During the electrodepositing step, a wave-form electrodepositing voltage profile was applied, oscillating between a voltage that preferentially electrodeposited nickel and another voltage that preferentially electrodeposited copper. The resulting composite structure possesses alternating layers of a bimetallic alloy, referred to as composition modulated-multilayers, whose proportional composition of nickel relative to copper depends on the voltage that was applied during electrodeposition of each layer. In this non-limiting example, layers of a bialloy consisting of 37% nickel and 63% copper alternate with layers of a bialloy consisting of 62% nickel and 38% copper.
Continuing to refer to FIG. 3, after the electrodeposition step, in this non-limiting example copper is selectively etched away from the composite structure, leaving a submicroscopically porous framework made predominantly of nickel, as shown in the middle of FIG. 3. Because the concentration of copper differed from layer to layer of the composite structure, the width of pores formed upon selectively etching away copper differs along the length of the pores. Where a level of the composite material was predominantly made of copper, the width of the resulting pores is relatively larger than at a level that was predominantly made of nickel. The resulting submicroscopically porous framework is referred to as a wavy-channel nickel framework. Pores formed like a tunnel running perpendicularly between the surfaces of the framework.
Continuing to refer to FIG. 3, after the etching step, in this non-limiting example a nickel-oxide is electrodeposited onto the inner surfaces of the pores, forming what is referred to as a wavy-channel nickel-oxide/nickel film. As shown in this non-limiting example, the nickel-oxide-plated inner surfaces of the submicroscopic pores through the nickel framework have easy accessibility to hydroxide ions in a solution in which electrochemical measurements of the framework may be made, such as an aqueous potassium hydroxide solution in which cyclic voltammography may be performed. Fast electron transport is also enabled, the enlarged surface area of the pores dramatically increases electrode specific capacitance, and electrode cycling stability is greatly enhanced.
FIGS. 4A-F are scanning electron micrographic images of a submicroscopically porous framework manufactured in accordance with the non-limiting example of the invented method just described. FIGS. 4A and 4B show an elevation view of the framework, whereas FIGS. 4C through 4F show side views. Insets in FIGS. 4A and 4B show higher magnification than the balance of FIGS. 4A and 4B, and FIGS. 4E and 4F show higher magnification images of the images shown in FIGS. 4C and 4D. FIGS. 4B, 4D, and 4F show a wavy-channel nickel-oxide/nickel film, in which the nickel-oxide is Ni^IIIO(OH), and FIGS. 4A, 4C, and 4E show the same structure as it existed as a wavy-channel nickel framework, before it was electroplated with nickel-oxide.
To create the structure depicted in FIGS. 4A, 4C, and 4E, a 10-layered dense nickel-copper bialloy composition-modulated multilayer was first electrodeposited with a voltage square wave modulated between −0.84 and −0.81 V to generate a corresponding composition square-wave varying between 62% nickel/38% copper and 37% nickel/63% copper. Copper was then selectively etched away, resulting in a square-wave pore volume profile across the submicroscopically porous nickel framework that varied between 56% and 27%. The pores measured from between 50 nanometers and 150 nanometers in diameter. To create the structure pictured in FIGS. 4B, 4D, and 4F, the wavy-channel nickel framework was electrochemically coated with nickel oxide. The deposited nickel oxide was Ni^IIIO(OH). Variation in pore width across pore height and pore volume profiles across framework thickness that are approximately square-wave, in accordance with the square-wave electrodepositing voltage profile applied during the electrodepositing step, may be seen in FIGS. 4C-F.
Electrochemical measurements of electrode materials fabricated in accordance with the examples illustrated in FIGS. 3 and 4B, D, and F were carried out in a 1 M potassium hydroxide aqueous solution at room temperature. At a charge/discharge current of 1 A/g, the measured overall specific capacitance of the wavy-channel nickel-oxide/nickel film was 2760 F/g, representing one of the highest values among nickel oxide-based supercapacitors. The dramatically high specific capacitance of the wavy-channel nickel-oxide/Ni electrode material may be mainly attributed to the enlarged specific surface area of the ultra-thin Ni^IIIO(OH) layer coated on the inner surfaces of the submicroscopic pores. Considering that charge is generally stored through electrochemical reactions within a very shallow skin depth (usually several nm) of electro-active materials in a supercapacitor, this specific wavy-channel submicroscopic architecture is particularly useful for maximizing the usage of the electro-active materials and increasing their specific capacitances.
The cycling stability of a wavy-channel nickel-oxide/nickel submicroscopic structure fabricated in accordance with the non-limiting examples of the invention illustrated in FIGS. 3 and 4B, D, and F was tested for 1000 charge/discharge cycles at a high current density of 10 A/g. At 10 A/g, the specific capacitance performance decreased ˜30% during the first 200 cycles and remained unvaried in the subsequent 800 cycles. The retention ratio was 68% after 1000 cycles with a good specific capacitance of approximately ˜1411 F/g. High cycling stability of over 90% capacitance retention at 50 A/g after 1000 cycles was also observed.
It should be understood that framework materials, electrodepositing voltage profiles, and surface treatments other than those disclosed herein may be used in accordance with the invention. Other combinations of metals or nonmetals may be used during the electrodepositing step to manufacture frameworks, and with a wide range and variety of electrodepositing voltage profiles. More than two materials may be electrodeposited during the electrodepositing step, and multiple steps of selective etching may be performed, selective for different materials or combinations of materials. Selective etching may be only partially selective for one or more materials, or preferential for one or more materials. Multiple electrodepositing or selective etching steps may be performed, in alternation with each other or in succession. Submicroscopic pore surfaces may remain untreated after selective etching or may be treated to alter their structure, chemical reactivity, or other behavior, according to their desired application. Frameworks can be constructed on substrates of varying shapes, and may be removed from substrates after being electrodeposited. It should be clear that a variety of manufacturing processes and submicroscopically porous frameworks manufactured in accordance with these or other variations are within the scope of the invention.
An electrodeposited solid composite structure made during the electrodeposition step in accordance with the invention may be made of any combination of materials that may be simultaneously electrodeposited according to known techniques. As non-limiting examples, materials may be metals, such as nickel, copper, zinc, aluminum, gold, and silver. As further non-limiting examples, a materials may be ceramics, polymers, and non-metallic conductive materials. A variety of pore widths may also be obtained. By varying a combination of composite materials used, an electrodepositing voltage profile applied, or selective etching methodology, pore widths may be within a range of tens of nanometers or less, a hundred or hundreds of nanometers, or several microns or more, or combinations of these ranges, as is desired. Pores' widths can range from 1-50 nanometers, 1-100 nanometers, 50-150 nanometers, 1-500 nanometers, 50-500 nanometers, 500 nanometers to 1 micron, 500 nanometers to 10 microns, 100 nanometers to 5 microns, 100-1000 nanometers, or combinations of these ranges. Pore dimensions and morphologies particularly suited to given applications may thereby be designed.
Generally, a one-pot procedure may be used to generate a structurally well defined metallic electrode framework with well defined submicroscopic porosity, high structural precision, and, laterally, architectural uniformity over a large area substrate. An electrodepositing voltage applied during an electrodepositing step may be modified temporally across a gradient or in any pattern within a wide range of parameters. For example, a gradient may be step-wise, continuous, or a combination of step-wise and continuous in succession. A gradient may follow a linear or non-linear curve, or a periodic curve, or a combination of a linear curve, a non-linear curve, and a periodic curve in succession. A periodic curve may be sinusoidal, square-wave, triangular-wave, sawtooth-wave, or any other periodic curve, alone or in combination with any other gradient or pattern in succession. Thus, throughout an electrodepositing step, any electrodepositing voltage that simultaneously plates out a plurality of materials may be applied, for any duration, and dynamically altered. Consequently, the varying proportion of materials constituting the composite structure across the thickness of the composite structure may approximately reflect an electrodepositing voltage profile that was applied during an electrodepositing step.
Frameworks with structurally precise submicroscopic pores have a wide range of uses, including, as non-limiting examples, as electrode materials, photonic materials, catalysts, chemical and biological sensors, biomedical devices, lithium-ion batteries, solar cells, water-photosplitting devices, and supercapacitors. For many such uses, increased surface area of pores may be highly beneficial. In a manufacturing process in accordance with the invention, a surface area of submicroscopic pores in a framework is increased by varying pores' width along their length, without requiring sophisticated and expensive equipment or control systems. The manufacturing process is highly efficient and amenable to automatic fabrication for mass production, and submicroscopic architectural design features of the porous framework may be predetermined and adjusted to achieve optimal performance for specific applications. In another aspect of the invention, a framework may be created on substrates with diverse geometrical features. A framework may also be detached from the substrate upon which electrodeposition occurred.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention may be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.

Claims

What is claimed is:

1. A method for fabricating a porous framework comprising:

contacting a substrate with a solution wherein a plurality of component materials are dissolved in the solution;

electrodepositing onto the substrate a solid composite comprising the plurality of component materials, wherein the electrodepositing comprises applying a plurality of voltages to vary a relative proportion of the component materials in the electrodeposited composite; and

selectively etching away at least one of the plurality of component materials from the composite to form a plurality of pores in the substrate.

2. The method of claim 1, wherein a component material comprises at least one of a metal and a conductive non-metal.

3. The method of claim 1, wherein a component material comprises at least one of a ceramic and a polymer.

4. The method of claim 1, wherein a surface geometry feature of the substrate comprises at least one of a flat, corrugated, patterned, and arbitrary shape.

5. The method of claim 1, further comprising treating an inner surface of the plurality of pores by at least one of altering a chemical composition of the surface, altering a structural feature of the surface, and applying a coating to the surface.

6. The method of claim 5, wherein treating comprises at least one of heating, oxidizing, and attaching a chemical species.

7. The method of claim 6, wherein the chemical species comprises at least one of an organic molecule, an inorganic molecule, a biomolecule, an electroactive material, and a polymer.

8. The method of claim 6, wherein the chemical species is a nickel-oxide.

9. The method of claim 1, further comprising placing a chemical species comprising at least one of organic molecules, inorganic molecules, biomolecules, and polymers in the plurality of pores.

10. The method of claim 1, wherein the plurality of electrodepositing voltages comprises at least one of a linear curve of electrodepositing voltages, a non-linear curve of electrodepositing voltages, and a periodic curve of electrodepositing voltages.

11. The method of claim 10, wherein the periodic curve of electrodepositing voltages comprises at least one of a sine wave, a square wave, a sawtooth wave, and a triangle wave,

12. The method of claim 1, wherein the etching comprises at least one of electrochemical etching and contacting the composite with an etching substance.

13. The method of claim 12, wherein the etching substance comprises at least one of hydrochloric acid, ammonia, nitric acid, and hydrofluoric acid.

14. The method of claim 2, wherein the metal comprises at least one of nickel, copper, zinc, silver, aluminum, and gold.

15. A framework system comprising:

a structure;

a plurality of pores in the structure;

a pore width along a length of a first pore of the plurality of pores, wherein the width is between 1 nanometer and 10 microns; and

an approximately predetermined variation in the pore width across the length of the first pore.

16. The framework of claim 15, wherein a pore of the plurality of pores comprises a longitudinal axis, wherein the longitudinal axis of the pore is approximately orthogonal to a thickness of the structure.

17. The framework of claim 15, wherein the structure comprises at least one of a metal and a conductive non-metal.

18. The framework of claim 17, wherein the metal comprises at least one of nickel, copper, zinc, silver, aluminum, and gold.

19. The framework of claim 15, wherein the structure comprises at least one of a ceramic and a polymer.

20. The framework of claim 15, wherein the pore width is between 1 nanometer and 500 nanometers.

21. The framework of claim 15, wherein the pore width is between 500 nanometers and 10 microns.

22. The framework of claim 15, wherein the predetermined variation is at least one of an approximately linear-curved variation, an approximately non-linear curved variation, and an approximately periodic variation.

23. The framework of claim 22, wherein the periodic variation is at least one of approximately sinusoidal variation, approximately square-waved variation, approximately sawtooth-waved variation, and approximately triangular-waved variation.

24. The framework of claim 15, further comprising a substance attached to a surface of the plurality of pores, wherein the substance is at least one of all organic molecule, an inorganic molecule, an electroactive material, a biomolecule, and a polymer.

25. The framework of claim 24, wherein the substance is a nickel oxide.