Application of a bismuth molybdate-based composite electrode material in hydrogen evolution reaction, oxygen evolution reaction and oxygen reduction reaction

Abstract

The present invention belongs to the field of electrocatalysis technology and relates to the application of a bismuth molybdate-based composite electrode material in hydrogen evolution reaction, oxygen evolution reaction and oxygen reduction reaction. The composite electrode material is: NiO / Bi2Mo x W 1‑x O6, where 0 ≤ x ≤ 1. The present invention first applies the composite electrode material to electrocatalytic hydrogen evolution reaction, oxygen evolution reaction and oxygen reduction reaction; the oxygen reduction reaction kinetics shows a four-electron transfer pathway, the hydrogen evolution reaction and oxygen evolution reaction have the lowest overpotential, and the oxygen reduction reaction has the largest half-wave potential and limiting current density; compared with the monomer, the composite material has excellent electrocatalytic performance and good application prospects, and will not cause secondary pollution to the environment during the application process; in addition, after 24 h of cyclic stability test, the oxygen reduction reaction of the composite electrode material is very stable.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalysis, and relates to the application of a bismuth molybdate tungsten-based composite electrode material in hydrogen evolution reaction, oxygen evolution reaction and oxygen reduction reaction. Background Art

[0002] The increasingly severe environmental degradation and energy consumption crisis have become two major challenges faced by human development. Therefore, developing new environmentally friendly technologies and finding alternative clean energy sources are our current urgent needs. At present, electrocatalytic water splitting technology is often used for hydrogen production because the electrocatalytic hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are safe and environmentally friendly and will not pollute the environment. The oxygen reduction reaction (ORR) is a key reaction in metal-air batteries and fuel cells, but there are problems of energy loss and slow kinetics in these three electrode reactions. Platinum (Pt)-based and their alloys have high ORR and HER kinetic activities, and RuO2 also shows high OER kinetic activity. However, the use of these noble metal materials is limited due to problems such as resource shortage, low reserves, high price and poor stability. Therefore, finding a highly efficient, low-cost and stable alternative electrode material has become a hot spot in the development of electrocatalysis.

[0003] Molybdate materials belong to non-noble metal catalysts, which are inexpensive and rich in reserves. However, the conductivity of molybdate materials is generally poor, which is the main reason restricting their development in electrocatalysis. Therefore, molybdate materials are mainly used as precursor materials in electrocatalysis to prepare alloys, sulfides, phosphides, composites, etc. with better conductivity. Using electronic regulation means to regulate their electronic structure can stimulate their catalytic potential and realize efficient catalytic reactions. Specific strategies for electronic regulation include doping, changing the material composition, forming defects or vacancies, etc. Research shows that regulating schemes such as heterojunction (see: Journal of Materials Science & Technology, 2022, 110, 152-160) and doping modification (see: Chemical Engineering Journal, 2021, 426, 131884) can improve the electrocatalytic performance of materials.

[0004] Molybdate materials are widely used in the field of photocatalysis. However, their conductivity is generally average, and their electrocatalytic properties have not been developed. Currently, photocatalysis and electrocatalysis are important ways for the chemical treatment of water splitting and pollutant degradation, and are effective means for collecting energy in the environment. However, photocatalysis and electrocatalysis are essentially different. Photocatalysis uses semiconductor photocatalysts to promote photochemical reactions, and photo-generated electron-hole pairs participate in the subsequent redox reactions. Electrocatalysis is a special form of catalysis that can accelerate the charge transfer between the electrode and the electrolyte interface. The most common electrocatalyst is a catalyst attached to the electrode surface or serving as the electrode surface. There are significant differences between electrocatalytic reactions and photocatalytic reactions in many aspects such as energy conversion forms, catalyst characteristics, chemical nature, and driving methods of redox reactions. Although some materials have high catalytic activity in the field of photocatalysis (see: Journal of Colloid and Interface Science, 2018, 509, 18 - 24; see: Journal of Nanoparticle Research, 2021, 23, 265), they have not been widely used in the field of electrocatalysis because photocatalysis requires the absorption of photon energy and often uses semiconductors with appropriate band gaps. Its light absorption ability and the ability to transfer photo-generated electrons / holes directly determine the quality of catalytic performance. One of the core indicators is the band edge positions of the valence band and the conduction band. Electrocatalysis does not involve such excitation behaviors, but requires electrons to directly participate in the reaction as reactants or products. The catalytic performance is often closely related to the conductivity of the catalyst and the chemical activity of local active sites (see: Angewandte Chemie International Edition, 2019, 12(58), 3730 - 3747; see: Advanced Materials, 2019, 31(31), 1806296).

[0005] Therefore, compared with molybdates with excellent photocatalytic performance but poor electrocatalytic performance, whether the electrocatalytic performance of the composite material prepared from this molybdate as the precursor material can be significantly improved, and whether it can further broaden the application field of molybdate materials has become a hot topic of concern for researchers. Summary of the Invention

[0006] Aiming at the problems existing in the prior art, the present invention provides an application of a bismuth molybdate tungstate-based composite electrode material in hydrogen evolution reaction, oxygen evolution reaction, and oxygen reduction reaction. The composite electrode material is: NiO / Bi2Mo x W 1-xO6, where 0 ≤ x ≤ 1. When the composite electrode material is applied to electrode catalysis, it has more excellent HER, OER, and ORR performance than the pure bismuth molybdate electrode material, improving the intrinsic activity of bismuth molybdate, enhancing the catalytic efficiency, having good cycle stability, and possessing good prospects for electrocatalytic applications.

[0007] The preparation method of the composite electrode material of the present invention includes the following steps:

[0008] (1) Dissolve ammonium molybdate, ammonium metatungstate, bismuth nitrate, and nickel source in a mixed solution A composed of anhydrous ethanol and N,N-dimethylformamide, adjust the solution pH to 1.0 - 4.0, and then add citric acid and stir to obtain a nickel oxide / bismuth molybdate tungstate solution;

[0009] (2) Take the nickel oxide / bismuth molybdate tungstate solution prepared in step (1) and add it to a mixed solution B composed of anhydrous ethanol and N,N-dimethylformamide in which polyvinylpyrrolidone (PVP) is dissolved, and stir until the solution is evenly mixed to obtain a nickel oxide / bismuth molybdate tungstate sol;

[0010] (3) Electrospinning the nickel oxide / bismuth molybdate tungstate sol prepared in step (2) at room temperature to obtain nickel oxide / bismuth molybdate tungstate gel fibers;

[0011] (4) Put the nickel oxide / bismuth molybdate tungstate gel fibers prepared in step (3) into a drying oven for drying, and then calcine in an air atmosphere to obtain a bismuth molybdate tungstate-based composite electrode material.

[0012] Preferably, the nickel source in step (1) is nickel nitrate hexahydrate or nickel acetate tetrahydrate.

[0013] Preferably, in step (1), the molar ratio of Mo to W is 1:(0 - 1); the molar ratio of Mo to Bi is (0 - 1):2; the molar ratio of Bi to Ni is 1:1; the molar ratio of the nickel source to citric acid is 1:(2 - 6).

[0014] Preferably, in step (1), the volume ratio of anhydrous ethanol to N,N-dimethylformamide is 1:1; the molar volume ratio of the nickel source to the mixed solution A is 1:(4 - 10), unit mmol mL -1 .

[0015] Preferably, in step (1), the solution pH is adjusted with nitric acid with a mass concentration of 66 wt% or hydrochloric acid with a mass concentration of 37 wt% or acetic acid with a mass concentration of 99 wt%.

[0016] Preferably, in step (2), the volume ratio of anhydrous ethanol to N,N-dimethylformamide is 1:4; the mass volume ratio of polyvinylpyrrolidone to the mixed solution B is (0.8 - 1.0):(10 - 15), unit g mL-1 .

[0017] Preferably, in step (3), the receiving distance of the electrospinning is 15 - 20 cm, and the ejection rate is 1.0 - 1.5 mL h -1 , the voltage is 15 - 25 kV, and the relative humidity is 15 - 30%.

[0018] Preferably, in step (4), the drying temperature is 40 - 60 °C, and the drying time is 6 - 12 h; the calcination temperature is 500 - 700 °C, and the heating rate is 1 - 5 °C min -1 1, and the heat preservation time is 1 - 2 h.

[0019] To achieve the above object, the present invention provides the following technical solutions:

[0020] The present invention provides an application of a bismuth molybdate tungstate-based composite electrode material in hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). The bismuth molybdate tungstate-based composite electrode material is NiO / Bi2Mo x W 1-x O6, 0 ≤ x ≤ 1.

[0021] Preferably, the application method of the composite electrode material NiO / Bi2Mo x W 1-x O6 (0 ≤ x ≤ 1) in hydrogen evolution reaction, oxygen evolution reaction, and oxygen reduction reaction includes the following steps:

[0022] (1) Add the composite electrode material and conductive carbon black into a mixed solvent of isopropanol and naphthol, ultrasonically disperse evenly to obtain a mixed solution, drop the mixed solution on a rotating disk electrode, and dry it under vacuum conditions to obtain a working electrode;

[0023] (2) After assembling the working electrode obtained in step (1) with a counter electrode and a reference electrode, immerse it in a KOH electrolyte solution to obtain a three-electrode system for hydrogen evolution reaction, oxygen evolution reaction, or oxygen reduction reaction;

[0024] (3) Set the scanning speed and rotation speed of the working electrode prepared from the composite electrode material, and use the three-electrode system described in step (2) to perform hydrogen evolution reaction, oxygen evolution reaction, and oxygen reduction reaction respectively;

[0025] Before performing the hydrogen evolution reaction, introduce nitrogen into the KOH electrolyte solution until it is saturated; before performing the oxygen evolution reaction and the oxygen reduction reaction, introduce nitrogen and oxygen into the KOH electrolyte solution until it is saturated.

[0026] Further preferably, the concentration of the composite electrode material in the mixed solution in step (1) is 0.005 - 0.01 g L -1, the concentration of the conductive carbon black is 0.001~0.005 g L -1 .

[0027] Further preferably, in step (1), the volume ratio of isopropanol to naphthol solution in the mixed solvent is 3:1.

[0028] Further preferably, in step (1), the rotating disk electrode is a glassy carbon electrode, and the area of the glassy carbon electrode is 0.196 cm 2 ; the loading amount of the composite electrode material on the glassy carbon electrode is 200~400 μg cm -2 , and the vacuum drying time is 6~12 h.

[0029] Further preferably, in the three-electrode system for the hydrogen evolution reaction in step (3), a graphite rod is used as the counter electrode, a Hg / HgO electrode is used as the reference electrode, and the concentration of the electrolyte KOH is 1 mol L -1 .

[0030] Further preferably, in the three-electrode system for the oxygen evolution reaction in step (3), a platinum wire is used as the counter electrode, a Hg / HgO electrode is used as the reference electrode, and the concentration of the electrolyte KOH is 1 mol L -1 .

[0031] Further preferably, in the three-electrode system for the oxygen reduction reaction in step (3), a platinum wire is used as the counter electrode, a Hg / HgO electrode is used as the reference electrode, and the concentration of the electrolyte KOH is 0.1 mol L -1 .

[0032] Further preferably, in step (3), the scanning rate is 5~10 mV s -1 , and the rotation speed is 400-1600 rpm.

[0033] This technical solution applies a nickel oxide / bismuth molybdate composite electrode material to the field of electrocatalysis for the first time, and conducts HER, OER, and ORR tests on the composite electrode material. The results show that the composite electrode material has excellent electrocatalytic HER, OER, and ORR performances and is a three-functional electrode material with good application prospects.

[0034] Term description:

[0035] Room temperature: It has the meaning well-known to those skilled in the art and refers to 25±5 ℃.

[0036] All chemical reagents used in the present invention are of analytical grade and are not further treated.

[0037] The present invention has the following advantages compared with the prior art:

[0038] 1. For the first time, the present invention applies the nickel oxide / bismuth molybdate tungstate composite electrode material (NiO / Bi2Mo x W 1-x O6, 0 ≤ x ≤ 1) to the electrocatalytic hydrogen evolution reaction, oxygen evolution reaction, and oxygen reduction reaction. The oxygen reduction reaction kinetics shows a four-electron transfer pathway. The hydrogen evolution reaction and oxygen evolution reaction have the lowest overpotentials, and the oxygen reduction reaction has the largest half-wave potential and limiting current density. Compared with the monomers, the composite has excellent electrocatalytic performance and good application prospects.

[0039] 2. The electrocatalytic activity of the nickel oxide monomer and bismuth molybdate tungstate (Bi2Mo 0.75 W 0.25 O6) prepared in the present invention is extremely poor. However, for the composite electrode material, compared with the nickel oxide monomer and Bi2Mo 0.75 W 0.25 O6, the HER overpotential is as low as 372 mV, and the Tafel curve slope is as low as 100 mV dec -1 ; the OER overpotential is as low as 510 mV, and the Tafel curve slope is as low as 99 mV dec -1 ; the ORR half-wave potential is 0.63 V, and the Tafel curve slope is as low as 76 mV dec -1 , making it an excellent trifunctional composite electrode material.

[0040] 3. After 24 h of cyclic stability testing, the oxygen reduction reaction of the composite electrode material prepared in the present invention is very stable.

[0041] 4. The composite electrode material prepared in the present invention will not cause secondary pollution to the environment during application. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is the X-ray diffraction pattern of the electrode materials prepared in the examples and comparative examples of the present invention.

[0043] Figure 2 It is the scanning electron microscope photograph of the NiO / Bi2Mo 0.75 W 0.25 O6 composite electrode material in the example of the present invention;

[0044] Among them, a is the low-magnification scanning electron microscope (SEM) photograph; b is the high-magnification scanning electron microscope (SEM) photograph.

[0045] Figure 3 It is the transmission electron microscope photograph of the NiO / Bi2Mo 0.75 W 0.25 O6 composite electrode material in the example of the present invention;

[0046] Among them, c is a low-magnification transmission electron microscope (TEM) photograph; d is a high-magnification transmission electron microscope (TEM) photograph.

[0047] Figure 4 The composite electrode material prepared in Example 1 of the present invention was subjected to a scan rate of 10 mV s in a 1 M KOH solution saturated with N2. -1 LSV curve of HER.

[0048] Figure 5 This is the Tafel curve of the HER of the composite electrode material prepared in Example 1 of the present invention.

[0049] Figure 6 The composite electrode material prepared in Example 2 of the present invention was subjected to a scan rate of 10 mV s in a 1 M KOH solution saturated with N2 and O2. -1 LSV curve of OER.

[0050] Figure 7 This is a Tafel curve of the OER of the composite electrode material prepared in Example 2 of the present invention.

[0051] Figure 8 The composite electrode material prepared in Example 3 of the present invention was subjected to a scan rate of 10 mV s in a 0.1 M KOH solution saturated with N2 and O2. -1 LSV curve of ORR.

[0052] Figure 9 This is a Tafel curve of the ORR of the composite electrode material prepared in Example 3 of the present invention.

[0053] Figure 10 The electrode materials prepared in Comparative Examples 1 and 4 of the present invention were quenched in a 1 M KOH solution saturated with N2 at a scan rate of 10 mV s -1 LSV curve of HER.

[0054] Figure 11 The Tafel curves of HER of the electrode materials prepared in Comparative Examples 1 and 4 of the present invention are shown.

[0055] Figure 12 The electrode materials prepared in Comparative Examples 2 and 5 of the present invention were saturated with N2 and O2 in 1 M KOH solution at a scan rate of 10 mV s -1 LSV curve of OER.

[0056] Figure 13 This is the Tafel curve of the OER of the electrode material prepared in Comparative Example 5 of the present invention.

[0057] Figure 14LSV curves of the ORR of the electrode materials prepared in Comparative Examples 3 and 6 of the present invention in N2- and O2-saturated 0.1 M KOH solutions at a scan rate of 10 mV s -1 -1

[0058] Figure 15 Tafel curves of the ORR of the electrode materials prepared in Comparative Examples 3 and 6 of the present invention

[0059] Figure 16 ORR cyclic stability test of the composite electrode material NiO / Bi2Mo 0.75 W 0.25 O6 in 0.1 M KOH solution Detailed implementation manners

[0060] The present invention will be further described below in conjunction with specific embodiments, and the advantages and features of the present invention will become clearer as the description proceeds. However, the embodiments are exemplary only and do not constitute any limitation to the scope of the present invention. Those skilled in the art should understand that the details and forms of the technical solutions of the present invention can be modified or replaced without departing from the spirit and scope of the present invention, but such modifications and replacements all fall within the protection scope of the present invention.

[0061] All the equipment used in the application examples are conventional equipment and can be obtained commercially.

[0062] Example 1

[0063] Application of a bismuth molybdate-based composite electrode material NiO / Bi2Mo x W 1-x O6 (x = 0, 0.25, 0.5, 0.75, 1) in HER, including the following steps:

[0064] (1) Weigh 7 mg of the composite electrode material and 2 mg of conductive carbon black, add them to 1 mL of a mixed solvent with a volume ratio of isopropanol to naphthol solution of 3:1, ultrasonically disperse them evenly to obtain a mixed solution. Pipette 10 μL of the mixed solution and drop it on a glassy carbon electrode with a rotating disk electrode (area: 0.196 cm 2 2), and then dry it in vacuum for 12 h to obtain a working electrode. The electrode loading of the prepared composite electrode material is 357 μg cm -2 -2

[0065] (2) Adopt a three-electrode system. The working electrode is as described in step (1), use a graphite rod as the counter electrode and a Hg / HgO electrode as the reference electrode, and the concentration of the electrolyte KOH is 1 mol L -1 -1

[0066] (3) Applications of electrocatalytic HER: Before the test, nitrogen gas was introduced to saturate the electrolyte with nitrogen. The scan rate was set to 10 mV s -1 , and the rotation speed was 1600 rpm.

[0067] The X-ray diffraction pattern (XRD) of the composite electrode material NiO / Bi2Mo x W 1-x O6 (x = 0, 0.25, 0.5, 0.75, 1) in this invention is as Figure 1 shown. It can be seen from Figure 1 that the diffraction peaks of the obtained products correspond to the standard patterns of Bi2MoO6 and Bi2WO6 (JCPDS No. 21-0102 and JCPDS No. 39-0256) respectively. The diffraction peaks at 2θ = 37.24°, 43.27° and 62.87° correspond to the standard pattern of NiO (JCPDS No. 47-1049), and no other impurity peaks were found.

[0068] The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) of the NiO / Bi2Mo 0.75 W 0.25 O6 composite electrode material described in this invention are as Figure 2 , 3 shown. It can be seen from Figure 2 , 3 that the microscopic morphology of the prepared sample is hollow nanotubes, and the diameter of the hollow nanotubes is 100 - 500 nm, and the wall thickness of the nanotubes is 50 - 150 nm.

[0069] Figure 4 The linear sweep voltammetry (LSV) curve of HER for the composite electrode material NiO / Bi2Mo x W 1-x O6 (x = 0, 0.25, 0.5, 0.75, 1) in Example 1 in 1 M KOH solution with a scan rate of 10 mV s -1 is shown in Figure 5 , and Figure 4 is its Tafel curve. It can be known from Figure 5 that the overpotentials of the composite electrode material described in Example 1 at a current density of 10 mA cm -2 are 395 mV, 472 mV, 442 mV, 372 mV, 420 mV respectively, and the corresponding Tafel slopes are 114 mV dec -1 , 124 mV dec -1 , 120 mV dec -1 , 100 mV dec -1 , 119 mV dec -1。

[0070] Example 2

[0071] Application of a bismuth molybdate-based composite electrode material NiO / Bi2Mo x W 1-x O6 (x = 0, 0.25, 0.5, 0.75, 1) in OER, including the following steps:

[0072] (1) Weigh 7 mg of the composite electrode material and 2 mg of conductive carbon black, add them to 1 mL of a mixed solvent with a volume ratio of isopropanol to naphthol solution of 3:1, ultrasonically disperse evenly to obtain a mixed solution. Pipette 10 μL of the mixed solution and drop it on a glassy carbon electrode (with an area of 0.196 cm 2 ), and then vacuum dry for 12 h to obtain a working electrode. The electrode loading of the prepared composite electrode material is 357 μg cm -2 ;

[0073] (2) Adopt a three-electrode system. The working electrode is as described in step (1), use a platinum wire as the counter electrode and a Hg / HgO electrode as the reference electrode, and the concentration of the electrolyte KOH is 1 mol L -1 , to obtain a three-electrode system.

[0074] (3) Application of electrocatalytic OER: Before testing, introduce nitrogen and oxygen to saturate the nitrogen and oxygen in the electrolyte. Set the scanning rate to 10 mV s -1 , and the rotation speed to 1600 rpm.

[0075] Figure 6 For the composite electrode material NiO / Bi2Mo x W 1-x O6 (x = 0, 0.25, 0.5, 0.75, 1) in 1 M KOH solution, the LSV curve of OER with a scanning rate of 10 mV s -1 . Figure 7 is its Tafel curve. From Figure 6 and Figure 7 , it can be seen that the overpotentials of the electrode materials prepared in Example 2 at a current density of 10 mA cm -2 are 562 mV, 582 mV, 540 mV, 510 mV, 590 mV respectively, and the corresponding Tafel slopes are 133 mV dec -1 , 150 mV dec -1 , 111 mV dec -1 , 99 mV dec -1 , 148 mV dec-1 .

[0076] Example 3

[0077] Application of a bismuth molybdate-based composite electrode material NiO / Bi2Mo x W 1-x O6 (x = 0, 0.25, 0.5, 0.75, 1) in ORR, including the following steps:

[0078] (1) Weigh 7 mg of the composite electrode material and 2 mg of conductive carbon black, add them to 1 mL of a mixed solvent with a volume ratio of isopropanol to naphthol solution of 3:1, ultrasonically disperse evenly to obtain a mixed solution. Pipette 10 μL of the mixed solution and drop it on a glassy carbon electrode (with an area of 0.196 cm 2 ), and then dry it in vacuum for 12 h to obtain a working electrode. The electrode loading of the prepared composite electrode material is 357 μg cm -2 ;

[0079] (2) Adopt a three-electrode system. The working electrode is as described in step (1), with a platinum wire counter electrode and a Hg / HgO reference electrode. The concentration of the electrolyte KOH is 0.1 mol L -1 , to obtain a three-electrode system.

[0080] (3) Application of electrocatalytic ORR: Before testing, introduce nitrogen and oxygen to saturate the nitrogen and oxygen in the electrolyte. Set the scanning rate to 10 mV s -1 , and the rotation speed to 1600 rpm.

[0081] Figure 8 is the LSV curve of the ORR of the NiO / Bi2Mo x W 1-x O6 (x = 0, 0.25, 0.5, 0.75, 1) composite electrode material in a N2 and O2 saturated 0.1 M KOH solution with a scanning rate of 10 mV s -1 . Figure 9 is its Tafel curve. From Figure 8 and Figure 9 , it can be seen that the half-wave potentials of the electrode materials prepared in Example 3 are 0.51 V, 0.54 V, 0.55 V, 0.63 V, 0.52 V respectively, and the corresponding Tafel slopes are 99 mV dec -1 , 98 mV dec -1 , 96 mV dec -1 , 76 mV dec -1 , 109 mV dec -1, the limiting current densities are 3.5 mA cm -2 , 3.8 mA cm -2 , 4.1 mA cm -2 , 5.3 mA cm -2 , 3.2 mA cm -2 .

[0082] Comparative Example 1

[0083] The application of a Bi2Mo 0.75 W 0.25 O6 electrode material in HER includes the following steps:

[0084] (1) Preparation method of Bi2Mo 0.75 W 0.25 O6 electrode material: Dissolve 0.971 g of bismuth nitrate pentahydrate, 0.1312 g of ammonium molybdate, 0.0615 g of ammonium metatungstate and 1 g of citric acid in 5 mL of absolute ethanol and 5 mL of DMF, then add 1 mL of hydrochloric acid with a mass concentration of 37 wt%, and stir for 180 min to obtain a precursor solution;

[0085] (2) Weigh 1 g of polyvinylpyrrolidone (PVP) and dissolve it in 8 mL of absolute ethanol and 2 mL of DMF, and stir evenly; then add 3 mL of the precursor solution prepared in step (1) thereto to obtain a precursor sol; subject the obtained precursor sol to electrospinning at a pressure of 20 kV, a relative humidity of 30%, and room temperature, with a spinning receiving distance of 20 cm and a feeding speed of 1 mL h -1 to obtain precursor fibers.

[0086] (3) Dry the precursor fibers prepared in step (2) at 40 °C for 12 h, then place them in a muffle furnace and heat them to 600 °C at a heating rate of 1 °C min -1 , and keep them at 600 °C for 60 min to obtain Bi2Mo 0.75 W 0.25 O6 solid solution electrode material.

[0087] (4) Weigh 7 mg of the Bi2Mo 0.75 W 0.25 O6 electrode material and 2 mg of conductive carbon black, add them to 1 mL of a mixed solvent with a volume ratio of isopropanol to naphthol solution of 3:1, ultrasonically disperse them evenly to obtain a mixed solution, use a pipette to transfer 10 μL of the mixed solution, drop it on a rotating disk electrode (a glassy carbon electrode with an area of 0.196 cm 2 ), and then vacuum dry it for 12 h to obtain a working electrode, and the electrode loading of the prepared electrode material is 357 μg cm -2;

[0088] (5) A three - electrode system is adopted. The working electrode is as described in step (4). A graphite rod is used as the counter electrode and a Hg / HgO electrode is used as the reference electrode. The concentration of the electrolyte KOH is 1 mol L -1 , obtaining a three - electrode system.

[0089] (6) Application of electrocatalytic HER: Before testing, nitrogen is introduced to saturate the nitrogen in the electrolyte. The scanning rate is set to 10 mV s -1 , and the rotation speed is 1600 rpm.

[0090] The X - ray diffraction pattern (XRD) of the Bi2Mo 0.75 W 0.25 O6 electrode material prepared in this invention is as Figure 1 shown. It can be seen through Figure 1 that the diffraction peaks of the obtained product correspond to the standard pattern of Bi2WO6 (JCPDS No. 39 - 0256), and no other impurity peaks are found.

[0091] Figure 10 For the Bi2Mo 0.75 W 0.25 O6 electrode material prepared in Comparative Example 1 in 1 M KOH solution, the LSV curve of HER at a scanning rate of 10 mV s -1 is shown in Figure 11 , and its Tafel curve is shown in Figure 10 and Figure 11 . It can be seen from -2 that the over - potential of the electrode material prepared in Comparative Example 1 at a current density of 10 mA cm -1 is 542 mV, and the slope of its corresponding Tafel is 197 mV dec 0.75 W 0.25 O6 electrode material in Example 1 (HER over - potential as low as 372 mV, Tafel curve slope as low as 100 mV dec -1 ) is compared, and its electrocatalytic activity for HER is poor.

[0092] Comparative Example 2

[0093] An application of a Bi2Mo 0.75 W 0.25 O6 electrode material in OER includes the following steps:

[0094] (1) The preparation method of the Bi2Mo 0.75 W 0.25 O6 electrode material is as described in Comparative Example 1;

[0095] (2) Weigh 7 mg of the Bi2Mo 0.75 W 0.25 O6 electrode material and 2 mg of conductive carbon black, add them to 1 mL of a mixed solvent with a volume ratio of isopropanol to naphthol of 3:1, ultrasonically disperse them evenly to obtain a mixed solution. Pipette 10 μL of the mixed solution and drop it on a rotating disk electrode (a glassy carbon electrode with an area of 0.196 cm 2 ), and then dry it under vacuum for 12 h to obtain a working electrode. The electrode loading of the prepared electrode material is 357 μg cm -2 ;

[0096] (3) Adopt a three-electrode system. The working electrode is as described in step (2), use a platinum wire as the counter electrode and a Hg / HgO electrode as the reference electrode, and the concentration of the electrolyte KOH is 1 mol L -1 .

[0097] (4) Application of electrocatalytic OER: Before testing, introduce nitrogen and oxygen respectively to saturate the nitrogen and oxygen in the electrolyte. Set the scanning rate to 10 mV s -1 , and the rotation speed to 1600 rpm.

[0098] Figure 12 For the Bi2Mo 0.75 W 0.25 O6 electrode material in 1 M KOH solution, the LSV curve of OER at a scanning rate of 10 mV s -1 . As can be seen from Figure 12 , it is difficult to obtain the overpotential required for the prepared electrode material to reach a current density of 10 mA cm -2 . The overpotential is very large and there is no electrocatalytic activity.

[0099] Comparative Example 3

[0100] An application of a Bi2Mo 0.75 W 0.25 O6 electrode material in ORR, including the following steps:

[0101] (1) The preparation method of the Bi2Mo 0.75 W 0.25 O6 electrode material is as described in Comparative Example 1;

[0102] (2) Weigh 7 mg of the Bi2Mo 0.75 W 0.25The O6 electrode material and 2 mg of conductive carbon black were added to 1 mL of a mixed solvent with a volume ratio of isopropanol to naphthol solution of 3:1, and ultrasonically dispersed evenly to obtain a mixed solution. 10 μL of the mixed solution was pipetted and dropped on a glassy carbon electrode (with an area of 0.196 cm 2 ), and then vacuum dried for 12 h to obtain a working electrode. The electrode loading of the prepared electrode material was 357 μg cm -2 ;

[0103] (3) A three-electrode system was adopted. The working electrode was as described in step (2), a platinum wire was used as the counter electrode, and a Hg / HgO electrode was used as the reference electrode. The concentration of the electrolyte KOH was 0.1 mol L -1 .

[0104] (4) Application of electrocatalytic ORR: Before testing, nitrogen and oxygen were introduced to saturate the nitrogen and oxygen in the electrolyte. The scanning rate was set to 10 mV s -1 , and the rotation speed was 1600 rpm.

[0105] Figure 14 For the Bi2Mo 0.75 W 0.25 O6 electrode material prepared in Comparative Example 3 in N2 and O2 saturated 0.1 M KOH solution, the LSV curve of ORR at a scanning rate of 10 mV s -1 , Figure 15 and its Tafel curve. From Figure 14 and Figure 15 , it can be seen that the half-wave potential of the electrode material prepared in Comparative Example 3 is 0.39 V, and the corresponding Tafel slope is 249 mV dec -1 , and the limiting current density is very small (2 mA cm -2 ), compared with the ORR performance of the NiO / Bi2Mo x W 1-x O6 (x = 0, 0.25, 0.5, 0.75, 1) composite electrode material described in Example 3 (half-wave potential is 0.63 V, Tafel curve slope is as low as 76 mV dec -1 , and the limiting current density can reach 5.3 mA cm -2 ), the electrocatalytic ORR activity is extremely poor.

[0106] Comparative Example 4

[0107] An application of a nickel oxide electrode material in HER, including the following steps:

[0108] (1) Preparation method of nickel oxide electrode material: Dissolve 0.249 g of nickel nitrate hexahydrate in 8 mL of absolute ethanol and 2 mL of DMF, stir for 180 min to obtain a precursor solution;

[0109] (2) Weigh 1 g of polyvinylpyrrolidone (PVP) and dissolve it in the precursor solution obtained in step (1), stir evenly to obtain a precursor sol; Electrospinning is carried out on the obtained precursor sol under the conditions of a pressure of 20 kV, a relative humidity of 30%, and room temperature, the spinning receiving distance is 20 cm, and the feeding speed is 1 mL h -1 , to obtain precursor fibers.

[0110] (3) Dry the precursor fibers prepared in step (2) at 40 °C for 12 h, then place them in a muffle furnace, and heat them to 600 °C at a heating rate of 1 °C min -1 , and keep them at 600 °C for 60 min to obtain the nickel oxide electrode material.

[0111] (4) Weigh 7 mg of the nickel oxide electrode material and 2 mg of conductive carbon black, add them to 1 mL of a mixed solvent with a volume ratio of isopropanol to naphthol solution of 3:1, disperse them evenly by ultrasonic treatment to obtain a mixed solution, use a pipette to transfer 10 μL of the mixed solution, and drop it on a rotating disk electrode (a glassy carbon electrode with an area of 0.196 cm 2 ), and then dry it in vacuum for 12 h to obtain a working electrode, and the electrode loading of the prepared composite electrode material is 357 μg cm -2 ;

[0112] (3) Adopt a three-electrode system, the working electrode is as described in step (4), use a graphite rod as the counter electrode and a Hg / HgO electrode as the reference electrode, and the concentration of the electrolyte KOH is 1 mol L -1 , to obtain a three-electrode system.

[0113] (4) Application of electrocatalytic HER: Before testing, introduce nitrogen to saturate the nitrogen in the electrolyte. Set the scanning rate to 10 mV s -1 , and the rotation speed to 1600 rpm.

[0114] The X-ray diffraction pattern (XRD) of the nickel oxide electrode material prepared in this comparative example is as Figure 1 shown. It can be seen from Figure 1 that the diffraction peaks of the obtained product correspond to the standard spectrum of nickel oxide (JCPDS No. 47-1049), and no other impurity peaks are found.

[0115] Figure 10 For the nickel oxide electrode material prepared in Comparative Example 4 in a 1 M KOH solution, the scanning rate is 10 mV s-1 LSV curve of HER Figure 11 is its Tafel curve. From Figure 10 and Figure 11 it can be seen that the overpotential of the electrode material prepared in Comparative Example 4 at a current density of 10 mA cm -2 is 478 mV, and the slope of its corresponding Tafel is 149 mV dec -1 , compared with the NiO / Bi2Mo 0.75 W 0.25 O6 electrode material in Example 1 (HER overpotential as low as 372 mV, Tafel curve slope as low as 100 mV dec -1 ), the electrocatalytic HER activity is average.

[0116] Comparative Example 5

[0117] Application of a nickel oxide electrode material in OER, including the following steps:

[0118] (1) The preparation method of the nickel oxide electrode material is as described in Comparative Example 4;

[0119] (2) Weigh 7 mg of the nickel oxide electrode material prepared in Comparative Example 4 and 2 mg of conductive carbon black, add them to 1 mL of a mixed solvent with a volume ratio of isopropanol to naphthol solution of 3:1, ultrasonically disperse evenly to obtain a mixed solution. Pipette 10 μL of the mixed solution and drop it on a glassy carbon electrode with a rotating disk electrode (area of 0.196 cm 2 ), and then vacuum dry for 12 h to obtain a working electrode. The electrode loading of the prepared electrode material is 357 μg cm -2 ;

[0120] (3) Adopt a three-electrode system. The working electrode is as described in step (2), use a platinum wire as the counter electrode and a Hg / HgO electrode as the reference electrode, and the concentration of the electrolyte KOH is 1 mol L -1 to obtain a three-electrode system.

[0121] (4) Application of electrocatalytic OER: Before testing, introduce nitrogen and oxygen to saturate the nitrogen and oxygen in the electrolyte. Set the scanning rate to 10 mV s[[ID=4,2]] -1 and the rotation speed to 1600 rpm.

[0122] Figure 12 is the LSV curve of OER of the nickel oxide electrode material prepared in Comparative Example 5 in a 1 M KOH solution with a scanning rate of 10 mV s -1 , Figure 13 is its Tafel curve. From Figure 12 and Figure 13It can be seen that the overpotential of the electrode material prepared in Comparative Example 5 is 710 mV at a current density of 10 mA cm -2 , and the slope of its corresponding Tafel is 219 mV dec -1 . Compared with the OER performance of the composite electrode material NiO / Bi2Mo x W 1-x O6(x = 0, 0.25, 0.5, 0.75, 1) described in Example 2 (the OER overpotential is as low as 510 mV and the slope of the Tafel curve is as low as 99 mV dec -1 ), the electrocatalytic OER activity is extremely poor and basically does not have electrocatalytic activity.

[0123] Comparative Example 6

[0124] An application of a nickel oxide electrode material in ORR includes the following steps:

[0125] (1) The preparation method of the nickel oxide electrode material is as described in Comparative Example 4;

[0126] (2) Weigh 7 mg of the nickel oxide electrode material prepared in Comparative Example 4 and 2 mg of conductive carbon black, add them to 1 mL of a mixed solvent with a volume ratio of isopropanol to naphthol solution of 3:1, ultrasonically disperse evenly to obtain a mixed solution. Use a pipette to transfer 10 μL of the mixed solution and drop it on a glassy carbon electrode with a rotating disk electrode (area of 0.196 cm 2 ), and then vacuum dry for 12 h to obtain a working electrode. The electrode loading of the prepared electrode material is 357 μg cm -2 ;

[0127] (3) Adopt a three-electrode system. The working electrode is as described in step (2), use a platinum wire counter electrode and a Hg / HgO electrode as the reference electrode, and the concentration of the electrolyte KOH is 0.1 mol L -1 to obtain a three-electrode system.

[0128] (4) Application of electrocatalytic ORR: Before testing, introduce nitrogen and oxygen to saturate the nitrogen and oxygen in the electrolyte. Set the scanning rate to 10 mV s -1 , and the rotation speed to 1600 rpm.

[0129] Figure 14 is the LSV curve diagram of the ORR of the nickel oxide electrode material prepared in Comparative Example 6 in a N2 and O2 saturated 0.1 M KOH solution with a scanning rate of 10 mV s -1 , Figure 15 is its Tafel curve. From Figure 14 and Figure 15It can be seen that the half-wave potentials of the electrode materials prepared in Comparative Example 6 are 0.43 V respectively, and the corresponding Tafel slopes are 249 mV dec -1 , and the limiting current density is very small (about 2 mA cm -2 ), which is extremely poor in electrocatalytic ORR activity compared with the ORR performance of the NiO / Bi2Mo x W 1-x O6(x = 0, 0.25, 0.5, 0.75, 1) composite electrode material described in Example 3 (the half-wave potential is 0.63 V, the Tafel curve slope is as low as 76 mV dec -1 , and the limiting current density can reach 5.3 mA cm -2 ).

[0130] Figure 16 This is the stability performance test of the NiO / Bi2Mo 0.75 W 0.25 O6 composite electrode material prepared in the example after 24 h of ORR test. It can be seen from Figure 16 that after 24 h of testing, the composite electrode material NiO / Bi2Mo 0.75 W 0.25 O6 still maintains excellent electrochemical stability.

Claims

1. Application of a bismuth molybdate-based composite electrode material in hydrogen evolution reaction, oxygen evolution reaction and oxygen reduction reaction, wherein the composite electrode material is: NiO / Bi2Mo x W 1-x O6, 0 < x < 1; The preparation method of the composite electrode material comprises the following steps: (1) Dissolve ammonium molybdate, ammonium metatungstate, bismuth nitrate and nickel source in mixed solution A composed of anhydrous ethanol and N,N-dimethylformamide, adjust the pH of the solution to 1.0 - 4.0, then add citric acid and stir to obtain nickel oxide / bismuth molybdate tungstate solution; (2) Take the nickel oxide / bismuth molybdate tungstate solution prepared in step (1) and add it to mixed solution B composed of anhydrous ethanol and N,N-dimethylformamide in which polyvinylpyrrolidone (PVP) is dissolved, stir until the solution is uniformly mixed to obtain nickel oxide / bismuth molybdate tungstate sol; (3) Electrospun the nickel oxide / bismuth molybdate tungstate sol prepared in step (2) at room temperature to obtain nickel oxide / bismuth molybdate tungstate gel fibers; (4) Put the nickel oxide / bismuth molybdate tungstate gel fibers prepared in step (3) into an oven for drying, and then calcine in air atmosphere at 500 - 700 °C to obtain bismuth molybdate tungstate-based composite electrode material.

2. The application according to claim 1, characterized in that, The application method of the composite electrode material in hydrogen evolution reaction, oxygen evolution reaction and oxygen reduction reaction comprises the following steps: (1) Add the composite electrode material and conductive carbon black into a mixed solvent of isopropanol and naphthol, ultrasonically disperse evenly to obtain a mixed solution, drop the mixed solution on a rotating disk electrode and dry it under vacuum conditions to obtain a working electrode; (2) After assembling the working electrode obtained in step (1) with a counter electrode and a reference electrode, immerse it in KOH electrolyte to obtain a three-electrode system for hydrogen evolution reaction, oxygen evolution reaction or oxygen reduction reaction; (3) Set the scanning speed and rotation speed of the working electrode prepared from the composite electrode material, and use the three-electrode system described in step (2) to carry out hydrogen evolution reaction, oxygen evolution reaction and oxygen reduction reaction respectively; Before carrying out the hydrogen evolution reaction, pass nitrogen into the KOH electrolyte until it is saturated; before carrying out the oxygen evolution reaction and oxygen reduction reaction, pass nitrogen and oxygen into the KOH electrolyte until it is saturated.

3. The application according to claim 2, wherein The concentration of the composite electrode material in the mixed solution described in step (1) is 0.005 - 0.01 g L -1 .

4. The application according to claim 2, wherein The concentration of the conductive carbon black in the mixed solution described in step (1) is 0.001~0.005 g L -1 .

5. The application according to claim 2, characterized in that, In step (1), the volume ratio of isopropanol to naphthol solution in the mixed solvent is 3:

1.

6. The application according to claim 2, characterized in that, In step (1), the rotating disk electrode is a glassy carbon electrode, and the area of the glassy carbon electrode is 0.196 cm 2 ; the loading amount of the composite electrode material on the glassy carbon electrode is 200 - 400 μg cm -2 , and the vacuum drying time is 6 - 12 h.

7. The application according to claim 2, wherein In the three-electrode system for the hydrogen evolution reaction described in step (2), a graphite rod is used as the counter electrode, a Hg / HgO electrode is used as the reference electrode, and the concentration of the electrolyte KOH is 1 mol L -1 .

8. The application according to claim 2, characterized in that, In the three-electrode system for the oxygen evolution reaction described in step (2), a platinum wire is used as the counter electrode, a Hg / HgO electrode is used as the reference electrode, and the concentration of the electrolyte KOH is 1 mol L -1 .

9. The application according to claim 2, characterized in that, In the three-electrode system of the oxygen reduction reaction described in step (2), a platinum wire is used as the counter electrode, a Hg / HgO electrode is used as the reference electrode, and the concentration of the electrolyte KOH is 0.1 mol L -1 .

10. The application according to claim 2, wherein The scanning speed described in step (3) is 5 - 10 mV s -1 , and the rotation speed is 400 - 1600 rpm.

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