CATALYST CHANNELS WITH ANISOTROPIC STRUCTURES BY 3-D PRINTING

Abstract

A three-dimensional non-noble-metal-based electrocatalysis electrode structure is provided. The electrode structure includes one or more layers of fused and approximately aligned elongated electrocatalyst nanoparticles that include a non-noble metal alloy or non-noble metal compound. Anisotropic nanochannels are positioned between the fused and approximately aligned elongated electrocatalyst nanoparticles that are configured to transfer generated gas bubbles therethrough. The elongated electrocatalyst nanoparticles may be nanorods that may have a diameter of approximately 20 to 50 nanometers and a length of approximately 80 to 300 nanometers. The anisotropic nanochannels may have a channel width of approximately 50-150 nanometers. The non-noble metal may be one or more of iron, cobalt, nickel, copper, molybdenum, or tungsten. The one or more layers of fused and approximately aligned elongated electrocatalyst nanoparticles may be 3-D printed elongated electrocatalyst nanoparticles, and each layer has a thickness of approximately 50 to 200 microns.

Description

FIELD OF THE INVENTION

The present invention generally relates to nanoengineered catalyst materials; more particularly, nanoengineered anisotropic catalyst materials with anisotropic porous channels that facilitate gas bubble transfer during electrolysis.

BACKGROUND OF THE INVENTION

Electrochemical water splitting powered by renewable energy sources is capable of producing high purity hydrogen on a large scale with zero carbon emissions; this is considered a promising approach to reduce environmental pollution associated with fossil fuels. However, the scarcity, high cost and unsatisfactory stability of noble metal catalysts have significantly restricted the development of commercial water electrolysis systems. Consequently, it is important to develop highly-efficient and robust electrocatalysts based on non-noble metals for deployment in industry.

In general, there are two typical strategies employed to improve the activity of electrocatalysts: (i) enhancing the intrinsic activity of single active site and (ii) increasing the exposed number of active sites. Regarding strategy (i), various modification methods have been explored to alter the surface electronic structures of catalysts to maximize the activity of a single active site, including cation/anion doping, defect manipulation, surface strain modification, and facet and crystal phase engineering. Regarding strategy (ii), electrocatalysts are typically prepared in-situ on three-dimensional (3D) conductive substrates, such as metal foams, carbon cloths, etc. This fabrication technique effectively improves the contact between catalysts and current collectors, which is able to reduce the concentration of electrically insulating junction points among catalyst particles, ultimately leading to higher electrochemical active surface area (ECSA) and charge carrier transfer efficiency.

Nevertheless, even though there are catalysts developed based on the above two strategies, their electrochemical performance is still far from satisfactory. One main limitation may be attributed to the slow detachment process of gas bubbles produced on the catalyst surface. Gas bubble release from electrodes dictates the efficiency of electrochemical water splitting. In particular, when operating at high current density, extensive amounts of gas bubbles are generated on the electrodes; these gas bubbles block large portions of the catalytically active surface area. This blockage increases the bubble ohmic overpotential and limits the hydrogen production rate.

Therefore, taking the above factors into account, candidates for commercially feasible electrocatalysts should simultaneously provide (i) the ability to be manufactured by large-scale and low-cost processes; (ii) a maximum exposed ECSA in electrolytes; (iii) a proper electronic structure of active sites; (iv) quick conversion between gas bubbles and electrolytes on the electrode surface.

Recently, for electrochemical applications, 3D printing technologies have been employed to design and fabricate hierarchical electrodes with periodic micro-size pores, exhibiting unique physical and mechanical properties. Particularly, once the gas bubbles nucleate and grow on the electrode surface during electrochemical reactions, the bubbles will rise under the influence of buoyancy in the electrolyte. Compared with irregular pores randomly scattered in the internal space of commercial 3D substrates, ordered micron-sized pores in a 3D-printed periodic structure may effectively reduce the frequency of bubble collisions and deformations, thus resulting in a quick bubble release. Prior studies of gas bubble dynamics has been primarily focused on pores on the order of several hundred microns. However, gas bubble transfer behaviors within the interspace of material structures on the order of tens to hundreds of nanometers has not been adequately addressed.

SUMMARY OF THE INVENTION

The present invention nanoengineers catalyst materials, creating anisotropic porous channels that facilitate gas bubble transfer; the nanoengineered catalyst materials demonstrate superior electrocatalytic performance and excellent long-term operational stability. The nanoengineering technique involves additive manufacturing, such as direct ink writing, of anisotropic nanoparticles, such as nanorods, to form 3-D electrodes. In one embodiment, NiMo-based structures with anisotropic porous channels may be used as electrocatalysts for an evolution reaction (HER) in seawater. The ECSA (geometric area) and the ECSA-specific activity (mass activity per ECSA) of prepared 3D structures are unusually high, demonstrating their effectiveness for contact between electrocatalysts and electrolytes. Further, the structures are advantageous for optimizing gas bubble transfer behaviors. It was determined that capillary force is an important mechanism during gas bubble release and the electrolyte phase conversion process. Combined with the electrochemical measurement. it is evident that the 3D-printed electrodes exhibit superior electrocatalytic performance and excellent long-term operational stability with an extremely low overpotential of ˜150 mV at a current density of 500 mA/cm2 in 1 M KOH seawater. Therefore, low-cost additive manufacturing may be used to produce highly efficient electrocatalysts for high-purity hydrogen production.

In one aspect, the present invention provides a three-dimensional non-noble-metal-based electrocatalysis electrode structure. The electrode structure includes one or more layers of fused and approximately aligned elongated electrocatalyst nanoparticles that include a non-noble metal alloy or non-noble metal compound. Anisotropic nanochannels are positioned between the fused and approximately aligned elongated electrocatalyst nanoparticles that are configured to transfer generated gas bubbles therethrough.

In one aspect, the elongated electrocatalyst nanoparticles are nanorods that may have a diameter of approximately 20 to 50 nanometers and a length of approximately 80 to 300 nanometers.

In one aspect, the anisotropic nanochannels have a channel width of approximately 50-150 nanometers.

The non-noble metal may be one or more of iron, cobalt, nickel, copper, molybdenum, or tungsten.

The one or more layers of fused and approximately aligned elongated electrocatalyst nanoparticles may be 3-D printed elongated electrocatalyst nanoparticles, and each layer has a thickness of approximately 50 to 200 microns.

The one or more layers of fused and approximately aligned elongated electrocatalyst nanoparticles are deposited on a substrate.

The substrate may be a current collector selected from carbon, graphite, copper, or nickel.

In a further aspect, the present invention provides a method for making a three-dimensional non-noble-metal-based electrocatalysis electrode structure that includes 3-D printing elongated electrocatalyst nanoparticles of a non-noble metal alloy or non-noble metal compound to deposit one or more approximately aligned elongated electrocatalyst nanoparticle layers and fusing the approximately aligned elongated electrocatalyst nanoparticles at an elevated temperature to create a fused structure having anisotropic nanochannels configured to transfer generated gas bubbles therethrough.

The elongated electrocatalyst nanoparticles may be formed by hydrothermal synthesis.

The hydrothermal synthesis may include reacting non-noble metal salt precursors at an elevated temperature and pressure to precipitate the non-noble metal-based elongated electrocatalyst nanoparticles.

Precipitated elongated electrocatalyst nanoparticles may be combined with a surfactant and subjected to extrusion-based 3-D printing to align the elongated electrocatalyst nanoparticles in the deposited layer.

The fusing of the approximately aligned elongated electrocatalyst nanoparticles may be performed at an elevated temperature of 300-700° C.

A reducing treatment may follow the fusing of the elongated electrocatalyst nanoparticles at an elevated temperature.

The elongated electrocatalyst nanoparticles may be nanorods.

The elongated electrocatalyst nanoparticles may include nickel and molybdenum.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure may be readily understood from the following detailed description with reference to the accompanying figures. The illustrations may not necessarily be drawn to scale. That is, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. There may be distinctions between the artistic renditions in the present disclosure and the actual apparatus due to manufacturing processes and tolerances. Common reference numerals may be used throughout the drawings and the detailed description to indicate the same or similar elements.

FIGS. 1a-1e show (1a, 1b) TEM images and (1c) HRTEM image of the NiMoO₄ nanorods. (1d) XRD pattern and (1e) specific surface area of the NiMoO₄ nanorods.

FIGS. 2a-2e show (2a) Images of the fabricated samples in different stages. (2b and 2c) are SEM images of the top and side views of the printed sample, respectively. (2d and 2e) are SEM images of the side and top views of the final sample, respectively.

FIGS. 3a-3b show (3a) and (3b) the XRD patterns and pore size distributions of the prepared samples.

FIGS. 4a-4g show: (4a) HER polarization curves obtained with the printed NiMo with 4 layers, 6 layers and 8 layers of catalyst structures. The NiMo powders are prepared at 740° C. characterized in 1 M KOH seawater electrolyte; (4b) corresponding Tafel slopes. (4c) Comparison of he mass activity among the samples with different layers and with powders. (4d) ECSA values obtained from CV curves. (4c) HER polarization curves obtained with the NiMo foam with 6 layers of catalyst structures prepared at 680° C. 740° C. and 800° C., respectively. (4f) Plots showing the extraction of the Cdl values; (4g) chronoamperometric test of printed NiMo with 6 layers of catalyst structures prepared at 680° C. in 1 m KOH seawater with a current density of 500 mA cm⁻².

FIG. 5 schematically depicts a 3D printing technique to form a three-dimensional non-noble-metal-based electrocatalysis electrode

FIGS. 6A-6C show the microstructure of the electrode of FIG. 5.

DETAILED DESCRIPTION

In the following description, embodiments of the present invention are set forth as preferred examples. It will be apparent to those skilled in the art that modifications, including additions and/or substitutions may be made without departing from the scope and spirit of the invention. Specific details may be omitted so as not to obscure the invention; however, the disclosure is written to enable one skilled in the art to practice the teachings herein without undue experimentation.

DEFINITIONS

Nanorods: Nanorods are a type of elongated nanoparticles. Nanorods may have a circular, rectangular, triangular, or square cross section in which the major dimension of the cross section may be on the order of 1-100 nanometers. They typically have an aspect ratio (that is, the ratio of the length divided by the width) on the order of approximately 3 to 6.

Hydrothermal Synthesis: Hydrothermal synthesis refers a reaction for synthesizing elongated nanoparticles from a solution of nanoparticle precursors, typically, metal salts. The solvent may be an aqueous solvent. At elevated temperature and pressure (e.g., in an autoclave, above the boiling temperature of water to increase the pressure above atmospheric pressure), highly crystalline materials are precipitated.

Approximately Aligned: By “approximately aligned” it is meant that 60 to 90 percent of the elongated nanorods have their longitudinal axes arranged parallel to the longitudinal axis of the layer plus or minus 20 degrees From the longitudinal axis.

The present invention nanoengineers electrocatalyst materials to form an electrocatalyst structure than includes anisotropic channels that expedite gas bubble transfer of bubbles formed from an electrolysis reaction. The nanoengineered structure demonstrates superior electrocatalytic performance and excellent long-term operational stability.

In one aspect a three-dimensional non-noble-metal-based electrocatalysis electrode structure 100 is formed as seen in FIGS. 6A-6C. The electrode structure includes one or more layers 10 of fused and approximately aligned elongated electrocatalyst nanoparticles. The electrocatalyst nanoparticles, best seen in FIG. 6C, may be nanorods 20 having a diameter on the order of 20 to 50 nanometers and a length on the order of 80 to 300 nanometers. The electrocatalyst nanoparticles are made from a non-noble metal alloy or non-noble metal compound. Examples of particular non-noble metals include iron, cobalt, nickel, copper, molybdenum, or tungsten. Particular electrocatalyst alloys include those made from a nickel molybdenum alloy, nickel copper allow, nickel cobalt alloy, cobalt molybdenum alloy, or copper molybdenum alloy.

Anisotropic nanochannels 30 are positioned between the fused and approximately aligned elongated electrocatalyst nanoparticles configured to transfer generated gas bubbles therethrough. The nanochannels have a channel width of approximately 50-150 nanometers. The channels may have a tortuous path through the fused nanoparticle structure. The capillary action of the nanochannels is believed to facilitate bubble transfer, increasing the ability of the electrocatalyst material to make further contact with the electrolyte. The nanochannels may be within an individual layer of fused, elongated nanoparticles or may be between adjacent layers of fused, elongated nanoparticles. Each layer of fused, elongated nanoparticles has a thickness of approximately 50 to 200 microns; several layers may be formed, depending upon the thickness of each layer. In one embodiment, a six-layer structure is selected. A total electrode thickness is typically on the order of 300 microns to 2500 microns.

The layers may be deposited on a substrate which may act as a current collector. Examples of current collectors include carbon, graphite, copper, nickel, and other known current collector materials.

In a further aspect, the present invention provides a method for making a three-dimensional non-noble-metal-based electrocatalysis electrode structure using a three-dimensional (3-D) printing technique. Elongated electrocatalyst nanoparticles of a non-noble metal alloy or non-noble metal compound are 3-D printed to deposit one or more approximately aligned elongated electrocatalyst nanoparticle layers. In particular, extrusion-based 3-D printing aligns the elongated nanoparticles during the deposition, especially when the elongated nanoparticles are mixed with a polymer-based surfactant.

In particular, the elongated particles may be mixed with a polymer-based surfactant such as a poloxamer which includes a hydrophobic chain of polyoxypropylene with two hydrophilic chains of polyoxyethylene. An exemplary poloxamer is polyoxamer 407 with a molecular mass of 4000 g/mol and a 70% polyoxyethylene content. This polyoxamer is commercially available as PLURONIC F127. When polyoxamer 407 is mixed with water, a hydrogel is formed that is useful for nanoparticle alignment.

The 3-D printing involves extrusion through a small orifice such as a nozzle, syringe, or other aperture. Typical aperture diameters are on the order of 500-1000 microns. FIG. 5 depicts a nozzle that is depositing the electrode structure shown in FIGS. 6A-6C. A variety of 3-D printing apparatus may be used that print in various arrays to form the 3-D structure. FIG. 5 depicts a common printing pattern of successive layers deposited with their primary axes disposed at 90 degrees with respect to adjacent layers, but other patterns may also be used. Following 3-D printing the approximately aligned elongated electrocatalyst nanoparticles are

fused at an elevated temperature to create a bonded structure having anisotropic nanochannels configured to transfer generated gas bubbles therethrough.

The elongated electrocatalyst nanoparticles may be formed using hydrothermal synthesis. During hydrothermal synthesis, non-noble metal precursors, for example, metal salt precursors are reacted at an elevated temperature and pressure to precipitate the non-noble metal-based elongated electrocatalyst nanoparticles. The selected temperature for fusing approximately aligned elongated electrocatalyst nanoparticles at an elevated temperature is performed at a temperature of 300-700° C.

A reducing treatment may be performed following the fusing of the elongated electrocatalyst nanoparticles. In particular, a hydrogen-containing reducing treatment at elevated temperature may be performed.

EXAMPLE

Formation of Nickel-Molybdenum Nanorods:

2.4 g of NiCl₂.6H₂O and 2.4 g of Na₂MoO₄.2H₂O were dissolved in 20 mL of distilled water, respectively. Then, the NiCl₂.6H₂O solution was added into the Na₂MoO₄.2H₂O solution slowly to form a clear and transparent mixture solution under stirring condition. The mixture solution was next sealed into a 50 mL size of Teflon-lined stainless steel autoclave reactor, which was heated at 140° C. for 12 h in an electric oven. After cooling the system to room temperature naturally, the precipitated nanorods were gathered and washed several times with ethanol and deionized water by centrifugation, eventually vacuum dried at 60° C. overnight.

In general, where the hydrothermal treatment temperature may range from 120˜180° C. or a period of time from approximately 1˜48 h.

Formation of 3-D Printing Ink:

PLURONIC F127 powder (25 wt %) was mixed with deionized water using a planetary mixer operated at 2000 rpm for 4 min to form a precursor ink base, where the ink was then placed at 4° C. overnight to have a complete dissolution. Next, the prepared Ni—Mo nanorods were mixed with the F127 precursor ink base at a weight ratio of 1:2 by the mixer operated at 2000 rpm for 2 min.

3-D Printing:

The Ni—Mo ink was loaded in a syringe and centrifuged at 4000 rpm for 2 minutes to remove all the air bubbles. The 3D electrode structure was deposited at room temperature using an extrusion-based 3-D printer with a 600 μm nozzle at a printing speed of 8 mm/s, a printing pressure of 120-200 KPa, and a spacing distance of 1 mm. After molding, the obtained 3-D printed electrodes were left to dry in ambient for 24 h to solidify the printed structure by removing the excess aqueous solvent.

Thermal Treatment:

The printed electrode was subsequently annealed at 500° C. for 2 hours with a heating rate of 1° C. min-1 under an air atmosphere. This was followed by a reduction treatment under an Ar/H₂ (200 sccm/50 sccm) environment for 2 hours with a heating rate of 5° C. min-1 at 680° C., respectively. Once the structure is cooled to room temperature, the H₂ feeding was stopped and 10 sccm O₂/Ar (1:9) gas mixture was introduced for 30 min to passivate the surface.

Electrode Characterization

Firstly, the morphology of the prepared electrode structure was characterized via TEM and HRTEM. As shown in FIGS. 1a and b, the nanomaterials exhibited nanorod-like morphology with a diameter with around 40 nm. In the HRTEM image, the lattice fringes with the interplanar spacings is 0.29 nm. In addition, the X-ray diffraction (XRD) pattern (FIG. 1d) confirmed the prepared material is NiMoO4.xH₂O (PDF 13-0128). The specific surface area is 22.7 m₂/g (FIG. 1e).

The anisotropic structure was realized by the shear force inside of the nozzle during the extrusion process with NiMoO₄.xH₂O nanorod/F127 as the printing ink. FIG. 2a shows the digital photos of the printed samples in different processing stages. The framework of the material remains intact, but the volume shrinks a bit under the effect of high temperature. FIGS. 2b and 2c are the SEM image of top and side view of the fresh printed sample. Since the NiMoO4.xH₂O nanorods undergo shear-induced alignment during the printing process, the orientation of nanorods is long-range ordered with the assistance of F127 fluid (FIGS. 2d and 2e). The final product kept the long-range ordered structure under well-controlled processing parameters, where the width of nanorods is around 37 nm, being consistent with the TEM results. Especially, the nanorods are connected with each other under high temperature to form a conductive network, which can significantly reduce the number of electrically insulating junction points. Moreover, this unique structure allows nearly all electrocatalysts in the internal space to participate in the reaction, being superior to conventional 3D substrates employed to maximize the energy conversion area.

The XRD results revealed that the crystal composition of electrodes composed of Mo (JCPDS No.42-1120), Ni₃Mo (JCPDS No.17-0572) and MoNi₄ (JCPDS No.65-5480) (FIG. 3a). This finding indicates that the only difference between these two electrodes is the transfer channel orientation. FIG. 3b exhibited the cumulative pore-volume and pore-size distribution curves of the catalyst obtained from mercury-intrusion porosimeter method. Obvious sharp peaks are observed in the logarithmic differential pore-volume distribution versus pore size distribution plots, designating the uniform pore size distribution. The pore size of product was close to 95.4 nm. The porosity analysis showed the porosity and tortuosity of electrode as 83.8% and 3.2, respectively. Moreover, the total pore volume is 842.2 mm3 g⁻¹ for electrode, demonstrating a larger exposed electrochemical surface area in the electrolyte.

Electrolysis Using 3-D Printed Electrodes

A large-area multilayer NiMo-based electrocatalyst electrode NiMoAS (3DPM NiMoAS) was 3-D printed, and corresponding electrochemical measurements were tested in a three-electrode configuration with 1 M KOH seawater (pH=13.98). In order to optimize the 3-D multiscale structure, the electrochemical properties of 3DPM NiMoAS electrocatalysts with different numbers of layers (including 4 layers, 6 layers and 8 layers) prepared at 740° C. were first evaluated, as shown in FIG. 4a. Surprisingly, the NiMo-based powder exhibits the highest overpotential at the current density of 100 mA cm-2, while the performance of 3DPM NiMoAS electrodes is substantially enhanced. The 3DPM NiMoAS-8L shows the most outstanding performance among these samples. At only 282 mV.

it provides a geometric current density of ˜500 mA/cm². The Tafel slopes of the samples were then obtained, which elucidate the electron transfer kinetics. As depicted in FIG. 4b, the fitted Tafel slope of 3DPM NiMoAS-8L is 92.7 mV dec-1 when the overpotential is less than 120 mV. This overpotential is smaller than those of 3DPM NiMoAS-4L (160.8 mV dec-1), 3DPM NiMoAS-6L (117.7 mV dec-1) and NiMo powder (190.2 mV dec-1), respectively. While the overpotential is larger than 120 mV, the Tafel slope of 3DPM NiMoAS-8L approaches 208.4 mV dec-1, indicating a low electron transfer process at large current densities, which is attributed to the limited gas bubble movement within the 3D framework as discussed above.

Since the 3DPM NiMoAS electrode has a larger surface area, the comparison of current density obtained from geometric area would provide limited information regarding the superiority of the 3-D printing technology. Therefore, it is necessary to evaluate the HER performance in terms of the mass activity, where the linear sweeping curves is normalized by metal loading amount. As illustrated in FIG. 4c, the highest mass activity among the 3DPM NiMoAS samples was obtained for 3DPM NiMoAS-6L with the values of 4.7 mA mg-1@-0.3 V, which corresponds to 9.1 times of the mass activity of NiMo powder (0.5 mA mg-1@-0.30 V). Moreover, to investigate the ECSA of prepared samples, the electrochemical double layer capacitance was obtained from the CV curves characterized in the non-Faradaic region. The summarized results of ECSA-specific geometric area and ECSA-specific mass activity values are presented in FIG. 4d, suggesting that all the 3D PRM NiMoAS samples show the better performance than the powder-based NiMo electrocatalysts. Notably. the ECSA can be affected not only by the mass transport of products formed within the nanostructure but also by their conductivity.

After confirming the 6-layer structure for the maximization of catalytic performance, the HER performance of the 3DPM NiMoAS-6L prepared with different temperatures was also evaluated in the 1 M KOH seawater (FIG. 4c). Particularly, the overpotential of 3DPM NiMoAS-6L-680° C. is found to be 128 mV when the current density is 500 mA cm⁻². This overpotential is 179 mV and 327 mV lower than those of the 3DPM NiMoAS-6L-740° C. and 3DPM NiMoAS-6L-800° C., respectively. The ECSA-specific geometric area in FIG. 4f indicates that the electronic structure of active sites in the electrocatalysts prepared at the lower temperature is more beneficial for the HER process. However, the electrocatalyst treated at a lower temperature (<680°° C.) has poor mechanical properties, being unable to solidify into a stable 3D structure.

The stability of 3DPM NiMoAS-6L-680° C. under electrocatalytic operation was further investigated, where a long-term CV test is performed at 500 mV/s. There is no obvious degradation observed for electrolysis even after a long period of 100 h, suggesting the technological potential of employing these robust catalysts over a long time for electrochemical applications (FIG. 4g).

INDUSTRIAL APPLICABILITY

In this invention, we employ the shear force alignment in additive manufacturing to design NiMo-based structures with anisotropic porous channels as electrocatalysts for hydrogen evolution reaction (HER) in seawater. Based on the complementary experimental and theoretical investigation, the unique anisotropic structure not only fully exposes the active sites in the electrolyte, but also facilitates the rapid electrolyte-hydrogen phase conversion during electrochemical reactions. Importantly, the gas bubble generation and release mechanisms have been thoroughly characterized and uncovered. For anisotropic structures, when the gas bubbles leave the catalyst surface, they are subjected to the upward buoyancy force in the electrolyte, electrolyte penetration pressure parallel to the channel, and penetration pressure perpendicular to the channel. Under such combined action, hydrogen is more effectively pushed out of the structure along the channels. In this case, the obtained 3D electrode exhibits superior electrocatalytic performance and excellent long-term operational stability with an extremely low overpotential of ˜150 mV at a current density of 500 mA/cm² in 1 M KOH seawater. This work will provide a practical scenario for designing highly-efficient HER electrocatalysts through advanced additive manufacturing to further develop hydrogen energy in the future.

The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention for various embodiments and with various modifications that are suited to the particular use contemplated. While the methods disclosed herein have been described with reference to particular operations performed in a particular order, it will be understood that these operations may be combined, sub-divided, or re-ordered to form an equivalent method without departing from the teachings of the present disclosure. Accordingly, unless specifically indicated herein, the order and grouping of the operations are not limitations. While the apparatuses disclosed herein have been described with reference to particular structures, shapes, materials, composition of matter and relationships . . . etc., these descriptions and illustrations are not limiting. Modifications may be made to adapt a particular situation to the objective, spirit, and scope of the present disclosure. All such modifications are intended to be within the scope of the claims appended hereto.

As used herein and not otherwise defined, the terms “substantially,” “substantial,” “approximately” and “about” are used to describe and account for small variations. When used in conjunction with an event or circumstance, the terms can encompass instances in which the event or circumstance occurs precisely as well as instances in which the event or circumstance occurs to a close approximation. For example, when used in conjunction with a numerical value, the terms can encompass a range of variation of less than or equal to +10%of that numerical value, such as less than or equal to +5%, less than or equal to +4%, less than or equal to +3%, less than or equal to +2%, less than or equal to +1%, less than or equal to +0.5%, less than or equal to +0.1%, or less than or equal to +0.05%.

Claims

1. A three-dimensional non-noble-metal-based electrocatalysis electrode structure comprising:

one or more layers of fused and approximately aligned elongated electrocatalyst nanoparticles, the electrocatalyst nanoparticles comprising a non-noble metal alloy or non-noble metal compound;

anisotropic nanochannels positioned between the fused and approximately aligned elongated electrocatalyst nanoparticles configured to transfer generated gas bubbles therethrough.

2. The three-dimensional non-noble-metal-based electrocatalysis electrode structure of claim 1, wherein the elongated electrocatalyst nanoparticles are nanorods.

3. The three-dimensional non-noble-metal-based electrocatalysis electrode structure of claim 2, wherein the nanorods have a diameter of approximately 20 to 50 nanometers.

4. The three-dimensional non-noble-metal-based electrocatalysis electrode structure of claim 3, wherein the nanorods have length of approximately 80 to 300 nanometers.

5. The three-dimensional non-noble-metal-based electrocatalysis electrode structure of claim 1, wherein the anisotropic nanochannels have a channel width of approximately 50-150 nanometers.

6. The three-dimensional non-noble-metal-based electrocatalysis electrode structure of claim 1, wherein the non-noble metal is one or more of iron, cobalt, nickel, copper, molybdenum, or tungsten.

7. The three-dimensional non-noble-metal-based electrocatalysis electrode structure of claim 1, wherein the one or more layers of fused and approximately aligned elongated electrocatalyst nanoparticles are 3-D printed elongated electrocatalyst nanoparticles, and each layer has a thickness of approximately 50 to 200 microns.

8. The three-dimensional non-noble-metal-based electrocatalysis electrode structure of claim 7, wherein the one or more layers of fused and approximately aligned elongated electrocatalyst nanoparticles are deposited on a substrate.

9. The three-dimensional non-noble-metal-based electrocatalysis electrode structure of claim 8, wherein the substrate is a current collector selected from carbon, graphite, copper, or nickel.

10. A method for making the three-dimensional non-noble-metal-based electrocatalysis electrode structure of claim 1, comprising:

3-D printing elongated electrocatalyst nanoparticles of a non-noble metal alloy or non-noble metal compound to deposit one or more approximately aligned elongated electrocatalyst nanoparticle layers;

fusing the approximately aligned elongated electrocatalyst nanoparticles at an elevated temperature to create a fused structure having anisotropic nanochannels configured to transfer generated gas bubbles therethrough.

11. The method of claim 10, further comprising forming elongated electrocatalyst nanoparticles by hydrothermal synthesis.

12. The method of claim 11, wherein the hydrothermal synthesis includes reacting non-noble metal salt precursors at an elevated temperature and pressure to precipitate the non-noble metal-based elongated electrocatalyst nanoparticles.

13. The method of claim 12, wherein precipitated elongated electrocatalyst nanoparticles are combined with a surfactant and subjected to extrusion-based 3-D printing to align the elongated electrocatalyst nanoparticles in the deposited layer.

14. The method of claim 10, wherein fusing the approximately aligned elongated electrocatalyst nanoparticles at an elevated temperature is performed at a temperature of 300-700° C.

15. The method of claim 10, further comprising a reducing treatment following the fusing of the elongated electrocatalyst nanoparticles at elevated temperature.

16. The method of claim 10, wherein the elongated electrocatalyst nanoparticles are nanorods.

17. The method of claim 10, wherein elongated electrocatalyst nanoparticles include nickel and molybdenum.