A nanoporous Ir / Ta2O5 composite material for oxygen evolution in acidic electrolyzed water

Abstract

The present invention belongs to the field of electrochemical technology, and provides a nanoporous Ir / Ta2O5 composite material, a preparation method thereof, and an application as an acidic oxygen evolution reaction catalyst. Through the combination of melt spinning and surface dealloying, the large-scale preparation of the nanoporous Ir / Ta2O5 catalyst is realized. The obtained catalyst is a self-supporting material and can be directly used as an electrode. The nanoporous structure increases the specific surface area of the catalyst, exposing more active sites. The synergistic effect between Ir and Ta2O5 not only improves the catalytic activity but also greatly increases the stability of the catalyst in the acidic oxygen evolution reaction. This catalyst has higher electrocatalytic oxygen evolution reaction activity and stability than commercial Ir / C catalysts in acidic electrolytes. The proton exchange membrane water electrolysis device assembled with this catalyst and commercial Pt / C catalyst has excellent hydrogen production performance by water electrolysis and can maintain stability for 260 h at a current density of 100 mA cm ‑2 .

Description

Technical Field

[0001] The invention belongs to the technical field of electrochemistry, and specifically relates to a nanoporous Ir / Ta2O5 composite material, a preparation method and application of an acidic water electrolysis oxygen evolution reaction. Background Art

[0002] Hydrogen production by water electrolysis consists of two parts: the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode. It is an efficient and clean way to produce hydrogen. Among them, the oxygen evolution reaction at the anode involves a four-electron transfer process, and the reaction kinetics are very slow, which is the main reason limiting the energy conversion efficiency of the water electrolysis device. Therefore, efficient OER electrocatalysts are indispensable components in the electrocatalytic water splitting system. Among the many water electrolysis hydrogen production technologies, acidic proton exchange membrane (PEM) water electrolysis devices have attracted widespread attention due to their advantages such as high energy efficiency, few hydrogen impurities, low ohmic loss and fast response speed. However, under acidic conditions, many electrocatalytic materials cannot withstand the high voltage of OER, resulting in oxidation and dissolution, which cannot meet the requirements of long-term use. Finding efficient, stable and low-cost acidic OER catalysts is of great significance to promote the industrial development of PEM water electrolysis hydrogen production.

[0003] According to previous research, iridium dioxide (IrO2) catalyst is recognized as an OER catalyst with high catalytic activity and good stability, but it is still difficult to meet the growing demand for industrial applications. In addition, the production of precious metal Ir is scarce and expensive, which greatly increases the application cost of PEM water splitters. Modifying Ir-based catalysts to increase stability as much as possible while improving catalytic activity has become a practical way to reduce the cost of industrial applications. Summary of the invention

[0004] Considering the shortcomings of the current research, the technical problem to be solved by the present invention is to provide a nanoporous Ir / Ta2O5 composite material, a preparation method and its application. The catalyst prepared by the method has good catalytic activity and stability in acidic OER. The PEM water splitter assembled by the catalyst and the commercial Pt / C catalyst can efficiently and stably electrolyze water to produce hydrogen.

[0005] The present invention provides a method for preparing a nanoporous Ir / Ta2O5 composite material, and the technical scheme is as follows:

[0006] S1) preparing IrTaCoB amorphous alloy strips by arc melting and melt spinning;

[0007] S2) Perform surface dealloying treatment on the IrTaCoB amorphous alloy strip to obtain a nanoporous Ir / Ta2O5 composite material. Preferably, in S1, the arc melting is carried out using elemental Ir, elemental Ta, elemental Co, and elemental B as raw materials to obtain an IrTaCoB alloy ingot.

[0008] In S1, the IrTaCoB alloy ingot is subjected to melt spinning to obtain an IrTaCoB amorphous alloy strip. Preferably, the rotation speed of the melt spinning is 3000 rpm.

[0009] Preferably, the atomic ratio of the IrTaCoB amorphous alloy strip is Ir:Ta:Co:B = 15:15:42:28.

[0010] Preferably, in S2, the surface dealloying treatment is specifically as follows:

[0011] Place the IrTaCoB amorphous alloy strip in a 0.1 M hydrofluoric acid solution. The corrosion times are 4 h, 8 h, and 12 h, preferably 8 h. The present invention also provides a nanoporous Ir / Ta2O5 catalyst prepared according to the above preparation method. This catalyst has a three-layer structure. The upper and lower layers are nanoporous Ir-Ta2O5 composite materials obtained after surface dealloying, and the middle layer is an IrTaCoB amorphous alloy. Since the main catalytic action of this three-layer structure catalyst is in the upper and lower surface layers, the catalyst is labeled as a nanoporous Ir / Ta2O5 composite material.

[0012] The present invention also provides the application of the nanoporous Ir / Ta2O5 composite material in electrocatalytic acidic OER. In a 0.5 M sulfuric acid solution, the reaction overpotential when the current density reaches 10 mA cm -2 is only 217 mV, and the Tafel slope is 46.1 mV dec -1 . It can maintain a stable catalytic ability for 200 h at a current density of 100 mA cm -2 . The catalytic activity and stability are significantly better than those of commercial Ir / C catalysts.

[0013] Preferably, the specific method for the electrocatalytic acidic OER test is as follows:

[0014] Adopt a common three-electrode test system. The nanoporous Ir / Ta2O5 composite material is used as the working electrode, a carbon rod is used as the counter electrode, and a mercury-mercurous sulfate electrode is used as the reference electrode to conduct an electrocatalytic OER performance test. The electrolyte is a 0.5 M sulfuric acid solution.

[0015] The present invention also provides the application of the nanoporous Ir / Ta2O5 composite material in PEM water electrolysis for hydrogen production. The current density of this PEM water splitting cell reaches 1 A cm-2 The required voltage is 1.70 V, and it can maintain stable hydrogen production by electrolyzing water for 260 h at a current density of 100 mA cm -2 .

[0016] Preferably, the specific method for hydrogen production by electrolyzing water is as follows:

[0017] In a PEM water electrolysis cell, a 20 wt% commercial Pt / C catalyst coated on carbon paper is used as the cathode, the anode material is the above-mentioned nano-porous Ir / Ta2O5 composite material, a Nafion117 membrane is used as the proton exchange membrane between the two electrodes, and the cathode, anode, and proton exchange membrane are pressed at 90 °C for 5 h by hot pressing to obtain a membrane electrode. The electrolyte is 0.5 M sulfuric acid solution.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: A self-supporting nano-porous Ir / Ta2O5 composite material is prepared by a one-step dealloying method. This method has a simple process and can be realized for large-scale preparation. The obtained self-supporting nano-porous Ir / Ta2O5 composite material can be directly used as the anode electrode of a PEM water electrolysis cell, avoiding problems such as the coverage of catalytic active sites, low electron transfer rate, and easy shedding of the catalyst caused by the use of binders, and simplifying the manufacturing process of the PEM water electrolysis cell. The nano-porous structure increases the contact area between the electrolyte and the catalyst surface, exposes more active sites of the catalyst, increases the collision probability between the reaction products and the active sites, and improves the catalytic activity of the catalyst. The synergistic effect between Ir and Ta2O5 reduces the catalytic reaction energy barrier and improves the stability of the material. In a 0.5 M sulfuric acid solution, the catalyst exhibits excellent electrocatalytic OER activity and stability superior to commercial Ir / C catalysts. The assembled PEM water electrolysis cell thus has excellent hydrogen production ability by electrolyzing water and can maintain stability for 260 h. Description of the Drawings

[0019] Figure 1 It is the preparation flow chart of Example 1.

[0020] Figure 2 It is the X-ray diffraction (XRD) pattern, where A is the XRD pattern of the IrTaCoB strip, and B is the grazing incidence XRD pattern of Example 1.

[0021] Figure 3 It is the scanning electron microscope (SEM) image of Example 1, where A is the top view and B is the cross-sectional view.

[0022] Figure 4 It is the acidic OER polarization curves of Examples 1-3 and commercial IrO2 and Ir / C catalysts.

[0023] Figure 5Tafel slope curves of Examples 1-3 and commercial IrO2 and Ir / C catalysts.

[0024] Figure 6 Acidic OER stability curves of Example 1 and commercial Ir / C catalyst.

[0025] Figure 7 Physical diagram of PEM water electrolysis cell.

[0026] Figure 8 Comparative polarization curves of hydrogen production by electrolyzing water in PEM water electrolysis cell.

[0027] Figure 9 Stability curves of hydrogen production by electrolyzing water in PEM water electrolysis cell. Detailed implementation mode

[0028] In order to better understand the technical content of the present invention, detailed explanations will be given below in combination with examples. It is particularly pointed out that the present invention is not limited to the following examples, and all other examples based on the present invention without innovative changes belong to the protection scope of the present invention.

[0029] Example 1

[0030] Preparation of nano-porous Ir / Ta2O5 composite material:

[0031] Weigh elemental Ir, elemental Ta, elemental Co and elemental B according to the atomic ratio Ir:Ta:Co:B = 15:15:42:28. Use a vacuum melting furnace to repeatedly arc-melt the weighed precursors to obtain a homogeneous IrTaCoB alloy ingot. Subsequently, put the IrTaCoB alloy ingot into a strip casting machine, and use a rapidly rotating copper roller to quickly cool the molten IrTaCoB alloy ingot to obtain an IrTaCoB amorphous alloy strip. The rotation speed of the copper roller is 3000 rpm. Place the obtained IrTaCoB amorphous alloy strip in a 0.1 M hydrofluoric acid solution for chemical etching. After 8 hours, take out the strip, repeatedly wash it with deionized water to remove the remaining etching solution, and dry it to obtain the nano-porous Ir / Ta2O5 composite material.

[0032] See Figure 1 , Figure 1 Schematic diagram of the preparation process of the catalyst material of the present invention.

[0033] Figure 2 XRD pattern. Among them, A is the XRD pattern of the IrTaCoB strip, and B is the grazing incidence XRD pattern of Example 1. It can be seen from the figure that the IrTaCoB strip is an amorphous structure. After surface dealloying, atomic rearrangement occurs on the strip surface to form an Ir / Ta2O5 composite material.

[0034] Figure 3 It is a SEM image. Among them, A is the top view of the nano-porous Ir / Ta2O5 composite material, and B is the cross-sectional view. It can be seen from the figure that after surface dealloying, Ir / Ta2O5 is a nano-porous structure with a pore size of about 5 nm, and the depth of surface dealloying for 8 h is about 280 nm.

[0035] Example 2

[0036] According to the preparation process of Example 1, the only difference is that the surface dealloying treatment time is 12 h.

[0037] Example 3

[0038] According to the preparation process of Example 1, the only difference is that the surface dealloying treatment time is 4 h.

[0039] The acidic OER performance of the catalysts prepared in Examples 1 to 3 was tested. The specific method is as follows:

[0040] The three-electrode system was used for testing. The working electrode was the nano-porous Ir / Ta2O5 composite material, which is a self-supporting material and can be directly used as an electrode. The reference electrode was a mercury-mercurous sulfate electrode, the counter electrode was a carbon rod, and the electrolyte was a 0.5 M sulfuric acid solution. An electrochemical workstation was used to collect data. Before the test, nitrogen was introduced into the electrolyte for 30 minutes to saturate it. The working electrode was activated by cyclic voltammetry (CV), and the activation voltage range was 1.2 - 2.2 V vs. RHE, and the scanning rate was 50 mV s -1 , and the number of cycles was 20 to make the working electrode reach a stable state.

[0041] Electrocatalytic activity test: Linear sweep voltammetry (LSV) was used to evaluate the electrocatalytic activity of the working electrode. The test voltage range was 1.2 - 2.2 V vs. RHE, and the scanning rate was 5 mV s -1 , and the number of scanning cycles was more than 3. The electrochemical workstation recorded the current situation on the working electrode with the change of voltage, and the data after stabilization was taken for analysis.

[0042] Electrocatalytic stability test: Chronopotentiometry (CP) was used to evaluate the electrocatalytic stability of the working electrode. A constant current density of 100 mA cm -2 was applied to the working electrode, and the electrochemical workstation recorded the change of voltage under a constant current density for 200 h. The electrocatalytic activity tests of commercial IrO2 and Ir / C catalysts were carried out under the same conditions. Specifically, commercial IrO2 and Ir / C catalysts were loaded on a glassy carbon electrode, and the loading amounts were 0.25 mg Ir cm -2 and 0.1 mg Ir cm-2 。

[0043] Figure 4 LSV curves after impedance correction for Examples 1 - 3 and commercial IrO2 and Ir / C catalysts. It can be seen from the figure that the acidic OER activity of Example 1 is the best, reaching 10 mA cm -2 and only requiring an overpotential of 217 mV.

[0044] Figure 5 Tafel slope curves for Examples 1 - 3 and commercial IrO2 and Ir / C catalysts. It can be seen from the figure that the Tafel slope of Example 1 is the smallest, being 46.1 mV dec -1 , indicating that the catalytic reaction kinetics of Example 1 is the fastest.

[0045] Figure 6 Electrocatalytic OER stability curve for Example 1. At a constant current density of 100 mA cm -2 , Example 1 can maintain stable catalysis for 200 h, indicating that the nanometer porous Ir / Ta2O5 composite material has very excellent catalytic stability in acidic OER.

[0046] The catalyst prepared in Example 1 was tested for hydrogen production by electrolyzing water. The specific method is as follows:

[0047] The cathode is a commercial Pt / C catalyst coated on carbon paper, and the anode is the catalyst prepared in Example 1. A Nafion117 membrane is used as the proton exchange membrane between the two electrodes. The cathode, anode and proton exchange membrane are hot - pressed at 90 °C for 5 h to form a tight membrane electrode. The electrolyte used is 0.5 M sulfuric acid solution. The electrocatalytic hydrogen production activity was tested in the voltage range of 1.0 - 2.8 V vs. RHE, and its electrocatalytic hydrogen production stability was tested at a constant current density of 100 mA cm -2 .

[0048] See Figure 7 , Figure 7 which is a schematic diagram of a PEM water electrolysis cell.

[0049] Under the same conditions, a commercial Pt / C catalyst coated on carbon paper was used as the cathode, and a commercial Ir / C catalyst coated on titanium fiber paper was used as the anode to assemble a PEM water electrolysis cell. Its catalytic activity was tested under the same conditions for comparison.

[0050] Figure 8 LSV comparison curves for PEM water electrolysis hydrogen production. It can be seen from the figure that the PEM water electrolysis cell with the catalyst prepared in Example 1 has excellent hydrogen production ability by electrolyzing water. To reach a current density of 1 A cm -2 , only a voltage of 1.70 V is required, which is better than the water electrolysis cell assembled with commercial catalysts.

[0051] Figure 9 It is the stability curve of PEM electrolytic water hydrogen production. As can be seen from the figure, at a constant current density of 100 mA cm -2 , the PEM water electrolysis cell can stably produce hydrogen for up to 260 h, showing very excellent stability performance.

Claims

1. A method for preparing a nano-porous Ir / Ta2O5 composite material, characterized in that, It includes the following steps: S1) Arc melting and melt spinning of elemental Ir, Ta, Co, and B with an atomic ratio of 15:15:42:28 to obtain an IrTaCoB amorphous alloy ribbon; S2) Chemically dealloying the IrTaCoB amorphous alloy ribbon in a 0.1 M hydrofluoric acid solution for 8 h to obtain a nanoporous Ir / Ta2O5 composite material. This composite material has a three-layer structure, with the upper and lower layers being nanoporous Ir / Ta2O5 obtained after surface dealloying, and the middle layer being the undedalloyed IrTaCoB amorphous alloy.

2. A catalyst prepared by the preparation method according to claim 1, characterized in that, The catalyst has a three-layer structure, with the upper and lower layers being nanoporous Ir / Ta2O5 obtained after surface dealloying, having a pore size of 5 nm and a layer thickness of 280 nm, and the middle layer being the undedalloyed IrTaCoB amorphous alloy.

3. Application of the catalyst according to claim 2 in the electrocatalytic acidic oxygen evolution reaction.

4. The application according to claim 3, characterized in that, Using a three-electrode test system, the nanoporous Ir / Ta2O5 composite material is used as the working electrode, a carbon rod is used as the counter electrode, a mercury-mercurous sulfate electrode is used as the reference electrode, and the electrolyte is a 0.5 M sulfuric acid solution.

5. Application of the catalyst according to claim 2 in hydrogen production by electrolyzing water.

6. The application according to claim 5, wherein Assembling a proton exchange membrane water electrolyzer, using a commercial Pt / C catalyst coated on carbon paper as the hydrogen evolution reaction catalyst at the cathode, using the nanoporous Ir / Ta2O5 composite material as the oxygen evolution reaction catalyst at the anode, using a Nafion117 membrane as the proton exchange membrane between the two electrodes, and using a 0.5 M sulfuric acid solution as the electrolyte.

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