Preparation method and application of nickel-cobalt oxide modified molybdenum-doped bismuth vanadate composite photo-anode

Abstract

The invention discloses a preparation method and application of a nickel-cobalt oxide modified molybdenum-doped bismuth vanadate composite photo-anode, and belongs to the application field of hydrogen production through water decomposition in photoelectrochemical reaction engineering. The preparation method comprises the following steps: obtaining a Mo-BiVO4 photo-anode through an electro-deposition and calcination combined method, preparing a precursor solution containing bimetallic nickel and cobalt by using cobalt nitrate hexahydrate, nickel nitrate hexahydrate and boric acid, immersing the Mo-BiVO4 photo-anode into the precursor solution, and growing a nickel-cobalt oxide (NiCoOx) cocatalyst on the surface of Mo-BiVO4 by using a photo-assisted electro-deposition method, thereby obtaining the Mo-BiVO4 photocatalyst. According to the NiCoOx cocatalyst modified Mo-BiVO4 composite photoanode and the preparation method thereof, the photocurrent density of the optimal NiCoOx cocatalyst modified Mo-BiVO4 composite photoanode obtained by the preparation method disclosed by the invention is 5.2 times that of pure bismuth vanadate. The preparation method has the advantages of simple operation method, easily available raw materials, low economic cost and good stability.

Description

Technical Field

[0001] The invention relates to a preparation method and application of a nickel-cobalt oxide modified molybdenum-doped bismuth vanadate composite photoanode, belonging to the application field of photoelectrochemical reaction engineering water decomposition to produce hydrogen. Background Art

[0002] Bismuth vanadate (BiVO4) is considered to be a very promising photoelectrode material for photoelectrochemical (PEC) systems due to its narrow band gap, good visible light absorption ability and remarkable stability. However, the photogenerated electron-hole pair recombination rate of BiVO4 photoanode is high and the photoelectron conductivity is poor. Previous studies have also proposed that the fundamental problem of charge transfer in BiVO4 is that the conduction band is mainly composed of V3d orbitals. The VO4 tetrahedra in BiVO4 are not connected to each other, resulting in free electrons can only jump between VO4 tetrahedra, resulting in low electron mobility. In order to address these limitations, various strategies have been developed to improve the photoelectric performance of BiVO4 photoanodes, mainly through morphology control, element doping, and the formation of heterojunctions.

[0003] Among them, doping BiVO4 with high-valent metal elements is an effective means to increase carrier density and promote charge separation. Mo ions can be used as dopants to enhance carrier density and as structural guides to promote one-dimensional nanostructures to form effective charge transfer paths. Modifying the photoanode by loading co-catalysts can significantly improve the activity of surface sites, which not only retains the excellent properties of the photoanode surface, but also induces the generation of highly active sites, providing sufficient space for reactions occurring at the interface. The synergistic effect of co-catalysts and bismuth vanadate can effectively accelerate the water oxidation kinetics and promote charge separation and transport, thereby significantly promoting the PEC water oxidation process and improving the activity of water decomposition to produce hydrogen.

[0004] However, to date, there is still no report on the use of light-assisted electrodeposition of nickel (Ni) and cobalt (Co) bimetallic oxide co-catalysts on the surface of bismuth vanadate photoanode and photoelectrochemical reaction to decompose water to produce hydrogen. Summary of the invention

[0005] The purpose of the present invention is to overcome some defects in the prior art and provide a method for preparing a composite photoanode of molybdenum-doped bismuth vanadate modified with nickel-cobalt oxide and its application. x The catalyst can improve the internal photogenerated charge transfer efficiency and surface water oxidation kinetics of the Mo-BiVO4 photoelectrode, and has good application prospects in the fields of hydrogen production by photoelectrocatalytic water decomposition.

[0006] In order to achieve the above technical purpose, the technical solution adopted by the present invention is as follows:

[0007] The present invention first provides a method for preparing a nickel-cobalt oxide modified molybdenum-doped bismuth vanadate composite photoanode, the method comprising the following steps:

[0008] A molybdenum-doped bismuth vanadate (Mo-BiVO4) film is prepared by an electrodeposition combined with a calcination method, that is, a Mo-BiVO4 photoanode is obtained; a precursor solution containing bimetallic nickel (Ni) and cobalt (Co) is prepared, and the Mo-BiVO4 photoanode is immersed in the precursor solution by a three-electrode electrochemical system, and electrodeposition is performed by linear scanning under light, and after completion, the obtained material is washed and dried to obtain NiCoO x / Mo-BiVO4 composite photoanode.

[0009] The method for preparing the precursor solution containing bimetallic nickel (Ni) and cobalt (Co) is as follows: dissolving the Ni source and the Co source in a boric acid buffer solution and continuously stirring until completely dissolved; adding potassium hydroxide (KOH) to adjust the pH, and passing nitrogen for a certain period of time to prepare a precursor solution containing bimetallic nickel (Ni) and cobalt (Co).

[0010] Furthermore, the Ni source includes Ni(NO3)2·6H2O or NiCl2·6H2O; the Co source includes Co(NO3)2·6H2O or CoCl2·6H2O.

[0011] Furthermore, in the precursor solution containing bimetallic nickel (Ni) and cobalt (Co), the molar ratio of metallic nickel to cobalt is 1-5:10.

[0012] Furthermore, the concentration of the boric acid buffer solution is 0.5 M, the pH value is adjusted to 7-9 by KOH, and nitrogen is introduced for more than 30 minutes to ensure that other gases in the solution are exhausted.

[0013] In the three-electrode electrochemical system, the Mo-BiVO4 photoanode is used as the working electrode (WE), the Ag / AgCl electrode is used as the reference electrode (RE), and the platinum wire is used as the counter electrode (CE).

[0014] The Mo-BiVO4 photoanode is immersed in the precursor solution and is subjected to linear scanning under illumination during the electrodeposition process. The light source is a 300W xenon lamp and the light intensity reaching the electrode is 100mW / cm 2 .

[0015] Furthermore, the linear scanning rate is 50 mV / s, the sink voltage of the electrodeposition is -0.2-0.5 V, and the cycle is 2-4 times.

[0016] In the above method, the washing is washing with deionized water, and the drying condition in the oven is drying at 60° C. for 12 hours.

[0017] The present invention also provides NiCoO prepared by the method x / Mo-BiVO4 composite photoanode.

[0018] The present invention also provides the use of the photoanode prepared by the method in photoelectrocatalytic water decomposition to produce hydrogen.

[0019] Beneficial effects of the present invention:

[0020] At present, there are many studies on the modification of bismuth vanadate photoelectrodes, including ion doping, composite co-catalysts, etc. However, the preparation of NiCoO by light-assisted electrodeposition is still unsatisfactory. x There is no report on the surface of Mo-BiVO4 photoanode.

[0021] The present invention uses a light-assisted electrodeposition method to composite nickel-cobalt bimetallic oxide (NiCoO) on the surface of molybdenum-doped bismuth vanadate (Mo-BiVO4) x ) co-catalyst to prepare nickel cobalt oxide / molybdenum doped bismuth vanadate (NiCoO x / Mo-BiVO4) composite photoanode, the method of the present invention makes NiCoO x The Ni and Co in the co-catalyst work together to further enhance the surface conductivity of Mo-BiVO4. The nickel-cobalt oxide nanolayer has the functions of enhancing the surface charge separation efficiency, promoting the water oxidation ability of the photoelectrode surface, improving the photoelectrocatalytic performance, enhancing the electrode oxidation resistance, slowing down the photocorrosion of bismuth vanadate, and extending the working life of the electrode. After PEC testing, it was found that the NiCoO prepared by the method of the present invention has the following advantages: x The BiVO4 photoanode exhibited 5.3 mA / cm at 1.23 V (standard hydrogen electrode potential) under AM 1.5G illumination. 2 The photocurrent density of NiCoO is 1.8 times higher than that of the original Mo-BiVO4 photoanode and 5.2 times higher than that of pure BiVO4. x The / BiVO4 photoanode also exhibits higher charge transfer efficiency, which has obvious advantages compared with the existing BiVO4-based photoelectrodes for water decomposition and hydrogen production.

[0022] In the present invention, Ni and Co bimetallic precursor solutions are used to prepare nickel cobalt oxide (NiCoO) by adjusting the ratio of Ni and Co under light-assisted electrodeposition. x ) co-catalyst to improve the PEC performance of molybdenum-doped bismuth vanadate; the method of the present invention has the advantages of adjustable metal molar ratio and simple composite method, and the water decomposition activity of the composite photoelectrode is significantly improved compared with the simple molybdenum-doped bismuth vanadate photoelectrode.

[0023] The present invention loads NiCoO on the surface of molybdenum-doped bismuth vanadate by light-assisted electrodeposition xThe invention provides a new idea for solving the serious charge recombination problem of Mo-BiVO4, and also provides a new basis for the efficient modification of other semiconductors. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Pure BiVO4, Mo-BiVO4 and NiCoO prepared in Example 2 x XPS diffraction spectrum of / Mo-BiVO4 photoanode sample, the inset in the upper right corner is NiCoO x The enlarged part of the dashed box of the / Mo-BiVO4 photoanode sample.

[0025] Figure 2 Pure BiVO4, Mo-BiVO4 and NiCoO prepared in Example 2 x SEM images of / Mo-BiVO4 photoanode samples (Figures a and d are pure BiVO4; Figures b and e are Mo-BiVO4; Figures c and f are NiCoO x / Mo-BiVO4).

[0026] Figure 3 NiCoO prepared in Example 2 x High-resolution transmission electron microscopy (HRTEM) image (a) and mapping element distribution map (b) of the Mo-BiVO4 composite photoanode.

[0027] Figure 4 Pure BiVO4, NiCoO prepared in Examples 1-3 x JV test diagram of / Mo-BiVO4 composite photoanode.

[0028] Figure 5 Pure BiVO4, Mo-BiVO4 and NiCoO prepared in Example 2 x JV test diagram of / Mo-BiVO4 composite photoanode.

[0029] Figure 6 Pure BiVO4, Mo-BiVO4 and NiCoO prepared in Example 2 x Photoelectric impedance spectroscopy (PEIS) diagram of / Mo-BiVO4 composite photoanode. DETAILED DESCRIPTION

[0030] The present invention is described in detail below in conjunction with the embodiments so that those skilled in the art can better understand the present invention, but the present invention is not limited to the following embodiments.

[0031] Unless otherwise defined, the terms (including technical terms) used herein should be interpreted as having the same meaning as commonly understood by those skilled in the art to which the present invention belongs. It will also be understood that the terms used herein should be interpreted as having the meaning consistent with their meanings in the content of this specification and related technologies, and should not be interpreted in an idealized or excessive form unless specifically defined as such herein.

[0032] The preparation of BiOI and BiVO4 photoanodes in the embodiment is based on the method published by Professor Tae Woo Kim and Kyoung-Shin Choi in Science in 2014 to synthesize BiOI and BiVO4 photoanodes (Nanoporous BiVO4 Photoanodes with Dual-Layer Oxygen Evolution Catalysts for Solar WaterSplitting). That is, the first step is to prepare the BiOI photoanode by electrodeposition, and the second step is to add 1% mass fraction of Mo source (acetylacetonato molybdenum) to the V source (acetylacetonato vanadium) when preparing the molybdenum-doped bismuth vanadate (Mo-BiVO4) photoanode, and finally obtain the molybdenum-doped bismuth vanadate (Mo-BiVO4) photoanode. Without adding the molybdenum source, the V source is directly added to the surface of the BiOI photoelectrode for calcination to obtain the pure bismuth vanadate (BiVO4) photoanode.

[0033] The specific method is as follows: first, BiOI is electrodeposited on FTO. At the same time, the DMF solution of molybdenum acetylacetonate is added to the N,N-dimethylformamide (DMF) solution of vanadium acetylacetonate so that the concentration of the mixed DMF solution is 1% (mass fraction). Then, the mixed DMF solution is added to the surface of BiOI and calcined at 450°C for 2 hours to obtain a molybdenum-doped bismuth vanadate (Mo-BiVO4) photoanode.

[0034] In the present invention, NiCoO x Stands for nickel cobalt oxide.

[0035] Example 1: NiCoO x Preparation of / Mo-BiVO4 composite photoanode

[0036] Step (1): depositing a bismuth oxide iodide (BiOI) film on FTO conductive glass to obtain a BiOI photoanode.

[0037] Step (2): Add the DMF solution of molybdenum acetylacetonate to the N,N-dimethylformamide (DMF) solution of vanadium acetylacetonate so that the concentration of the mixed DMF solution is 1% (mass fraction), then deposit the mixed DMF solution on the surface of BiOI, calcine at 450°C for 2 hours, and finally obtain a molybdenum-doped bismuth vanadate (Mo-BiVO4) photoanode.

[0038] Step (3): Dissolve 0.01 mol Ni(NO3)2·6H2O and 0.1 mol Co(NO3)2·6H2O in 80 mL 0.5 M boric acid buffer solution. After fully dissolved, add KOH to adjust the pH value to 8.4, and introduce N2 bubbling for 30 min to remove dissolved oxygen in the solution to obtain a precursor solution. Then immerse the Mo-BiVO4 photoanode obtained in step (2) in the obtained precursor solution and stir. Use a three-electrode electrochemical system, with the Mo-BiVO4 photoanode as the working electrode (WE), the Ag / AgCl electrode as the reference electrode (RE), and the platinum wire as the counter electrode (CE). Irradiate at an intensity of 100 mV / cm under a 300 W xenon lamp. 2 , electroplating is performed, the linear scanning rate is 50mV / s, the deposition voltage is -0.2-0.5V for one cycle, and the cycle in this embodiment is 2 times.

[0039] After the deposition, the photoelectrode was washed with deionized water and dried in an oven at 60 °C for 12 h to obtain a nickel-cobalt oxide-modified molybdenum-doped bismuth vanadate composite photoanode (denoted as NiCoO x / Mo-BiVO4 composite photoanode).

[0040] The NiCoO obtained by the present invention x / Mo-BiVO4 composite photoanode is used for photoelectrocatalytic reaction to decompose water to produce hydrogen.

[0041] Example 2: NiCoO x Preparation of / Mo-BiVO4 composite photoanode

[0042] Step (1): depositing a bismuth oxide iodide (BiOI) film on FTO conductive glass to obtain a BiOI photoanode.

[0043] Step (2): Add the DMF solution of molybdenum acetylacetonate to the N,N-dimethylformamide (DMF) solution of vanadium acetylacetonate so that the concentration of the mixed DMF solution is 1% (mass fraction), then deposit the mixed DMF solution on the surface of BiOI, calcine at 450°C for 2 hours, and finally obtain a molybdenum-doped bismuth vanadate (Mo-BiVO4) photoanode.

[0044] Step (3): Dissolve 0.01 mol mg Ni(NO3)2·6H2O and 0.1 mol Co(NO3)2·6H2O in 80 mL 0.5 M boric acid buffer solution. After fully dissolved, add KOH to adjust the pH value to 8.4, and introduce N2 bubbling for 30 min to remove dissolved oxygen in the solution to obtain a precursor mixture. Then immerse the Mo-BiVO4 photoanode obtained in step (2) in the obtained precursor solution and stir. Use a three-electrode electrochemical system with the Mo-BiVO4 photoanode as the working electrode (WE), the Ag / AgCl electrode as the reference electrode (RE), and the platinum wire as the counter electrode (CE). Irradiate at an intensity of 100 mV / cm under a 300 W xenon lamp. 2 , electroplating is performed, the linear scanning rate is 50mV / s, the deposition voltage is -0.2-0.5V for one cycle, and the cycle in this embodiment is 3 times.

[0045] After the deposition, the photoelectrode was washed with deionized water and dried in an oven at 60 °C for 12 h to obtain a nickel-cobalt oxide-modified molybdenum-doped bismuth vanadate composite photoanode (denoted as NiCoO x / Mo-BiVO4 composite photoanode).

[0046] The NiCoO obtained by the present invention x / Mo-BiVO4 composite photoanode is used for photoelectrocatalytic reaction to decompose water to produce hydrogen.

[0047] Example 3: NiCoO x Preparation of / Mo-BiVO4 composite photoanode

[0048] Step (1): depositing a bismuth oxide iodide (BiOI) film on FTO conductive glass to obtain a BiOI photoanode.

[0049] Step (2): Add the DMF solution of molybdenum acetylacetonate to the N,N-dimethylformamide (DMF) solution of vanadium acetylacetonate so that the concentration of the mixed DMF solution is 1% (mass fraction), then deposit the mixed DMF solution on the surface of BiOI, calcine at 450°C for 2 hours, and finally obtain a molybdenum-doped bismuth vanadate (Mo-BiVO4) photoanode.

[0050] Step (3): Dissolve 0.01 mol Ni(NO3)2·6H2O and 0.1 mol Co(NO3)2·6H2O in 80 mL 0.5 M boric acid buffer solution. After fully dissolved, add KOH to adjust the pH value to 8.4, and introduce N2 bubbling for 30 min to remove dissolved oxygen in the solution to obtain a precursor mixture. Then immerse the Mo-BiVO4 photoanode obtained in step (2) in the obtained precursor solution and stir. Use a three-electrode electrochemical system with the Mo-BiVO4 photoanode as the working electrode (WE), the Ag / AgCl electrode as the reference electrode (RE), and the platinum wire as the counter electrode (CE). Irradiate at an intensity of 100 mV / cm under a 300 W xenon lamp. 2 , electroplating is performed, the linear scanning rate is 50mV / s, the deposition voltage is -0.2-0.5V for one cycle, and the cycle in this embodiment is 4 times.

[0051] After the deposition, the photoelectrode was washed with deionized water and dried in an oven at 60 °C for 12 h to obtain a nickel-cobalt oxide-modified molybdenum-doped bismuth vanadate composite photoanode (denoted as NiCoO x / Mo-BiVO4 composite photoanode).

[0052] The NiCoO obtained by the present invention x / Mo-BiVO4 composite photoanode is used for photoelectrocatalytic reaction to decompose water to produce hydrogen.

[0053] Example 4: NiCoO x Preparation of / Mo-BiVO4 composite photoanode

[0054] Step (1): depositing a bismuth oxide iodide (BiOI) film on FTO conductive glass to obtain a BiOI photoanode.

[0055] Step (2): Add the DMF solution of molybdenum acetylacetonate to the N,N-dimethylformamide (DMF) solution of vanadium acetylacetonate so that the concentration of the mixed DMF solution is 1% (mass fraction), then deposit the mixed DMF solution on the surface of BiOI, calcine at 450°C for 2 hours, and finally obtain a molybdenum-doped bismuth vanadate (Mo-BiVO4) photoanode.

[0056] Step (3): Dissolve 0.01 mol Ni(NO3)2·6H2O and 0.1 mol Co(NO3)2·6H2O in 80 mL 0.5 M boric acid buffer solution. After fully dissolved, add KOH to adjust the pH value to 7, and introduce N2 bubbling for 30 min to remove dissolved oxygen in the solution to obtain a precursor mixture. Then immerse the Mo-BiVO4 photoanode obtained in step (2) in the obtained precursor solution and stir. Use a three-electrode electrochemical system with the Mo-BiVO4 photoanode as the working electrode (WE), the Ag / AgCl electrode as the reference electrode (RE), and the platinum wire as the counter electrode (CE). Irradiate at an intensity of 100 mV / cm under a 300 W xenon lamp. 2 , electroplating is performed, the linear scanning rate is 50mV / s, the deposition voltage is -0.2-0.5V for one cycle, and the cycle in this embodiment is 3 times.

[0057] After the deposition, the photoelectrode was washed with deionized water and dried in an oven at 60 °C for 12 h to obtain a nickel-cobalt oxide-modified molybdenum-doped bismuth vanadate composite photoanode (denoted as NiCoO x / Mo-BiVO4 composite photoanode).

[0058] The NiCoO obtained by the present invention x / Mo-BiVO4 composite photoanode is used for photoelectrocatalytic reaction to decompose water to produce hydrogen.

[0059] Example 5: NiCoO x Preparation of / Mo-BiVO4 composite photoanode

[0060] Step (1): depositing a bismuth oxide iodide (BiOI) film on FTO conductive glass to obtain a BiOI photoanode.

[0061] Step (2): Add the DMF solution of molybdenum acetylacetonate to the N,N-dimethylformamide (DMF) solution of vanadium acetylacetonate so that the concentration of the mixed DMF solution is 1% (mass fraction), then deposit the mixed DMF solution on the surface of BiOI, calcine at 450°C for 2 hours, and finally obtain a molybdenum-doped bismuth vanadate (Mo-BiVO4) photoanode.

[0062] Step (3): Dissolve 0.01 mol Ni(NO3)2·6H2O and 0.1 mol Co(NO3)2·6H2O in 80 mL 0.5 M boric acid buffer solution. After fully dissolved, add KOH to adjust the pH value to 9, and introduce N2 bubbling for 30 min to remove dissolved oxygen in the solution to obtain a precursor mixture. Then immerse the Mo-BiVO4 photoanode obtained in step (2) in the obtained precursor solution and stir. Use a three-electrode electrochemical system with the Mo-BiVO4 photoanode as the working electrode (WE), the Ag / AgCl electrode as the reference electrode (RE), and the platinum wire as the counter electrode (CE) under a 300 W xenon lamp with an irradiation intensity of 100 mV / cm 2 , electroplating is performed, the linear scanning rate is 50mV / s, the deposition voltage is -0.2-0.5V for one cycle, and the cycle in this embodiment is 3 times.

[0063] After the deposition, the photoelectrode was washed with deionized water and dried in an oven at 60 °C for 12 h to obtain a nickel-cobalt oxide-modified molybdenum-doped bismuth vanadate composite photoanode (denoted as NiCoO x / Mo-BiVO4 composite photoanode).

[0064] The NiCoO obtained by the present invention x / Mo-BiVO4 composite photoanode is used for photoelectrocatalytic reaction to decompose water to produce hydrogen.

[0065] Example 6: NiCoO x Preparation of / Mo-BiVO4 composite photoanode

[0066] Step (1): depositing a bismuth oxide iodide (BiOI) film on FTO conductive glass to obtain a BiOI photoanode.

[0067] Step (2): Add the DMF solution of molybdenum acetylacetonate to the N,N-dimethylformamide (DMF) solution of vanadium acetylacetonate so that the concentration of the mixed DMF solution is 1% (mass fraction), then deposit the mixed DMF solution on the surface of BiOI, calcine at 450°C for 2 hours, and finally obtain a molybdenum-doped bismuth vanadate (Mo-BiVO4) photoanode.

[0068] Step (3): Dissolve 0.02 mol Ni(NO3)2·6H2O and 0.1 mol Co(NO3)2·6H2O in 80 mL 0.5 M boric acid buffer solution. After fully dissolved, add KOH to adjust the pH value to 8.4, and introduce N2 bubbling for 30 min to remove dissolved oxygen in the solution to obtain a precursor mixture. Then immerse the Mo-BiVO4 photoanode obtained in step (2) in the obtained precursor solution and stir. Use a three-electrode electrochemical system with the Mo-BiVO4 photoanode as the working electrode (WE), the Ag / AgCl electrode as the reference electrode (RE), and the platinum wire as the counter electrode (CE) under a 300 W xenon lamp with an irradiation intensity of 100 mV / cm 2 , electroplating is performed, the linear scanning rate is 50mV / s, the deposition voltage is -0.2-0.5V for one cycle, and the cycle in this embodiment is 3 times.

[0069] After the deposition, the photoelectrode was washed with deionized water and dried in an oven at 60 °C for 12 h to obtain a nickel-cobalt oxide-modified molybdenum-doped bismuth vanadate composite photoanode (denoted as NiCoO x / Mo-BiVO4 composite photoanode).

[0070] The NiCoO obtained by the present invention x / Mo-BiVO4 composite photoanode is used for photoelectrocatalytic reaction to decompose water to produce hydrogen.

[0071] Example 7: NiCoO x Preparation of / Mo-BiVO4 composite photoanode

[0072] Step (1): depositing a bismuth oxide iodide (BiOI) film on FTO conductive glass to obtain a BiOI photoanode.

[0073] Step (2): Add the DMF solution of molybdenum acetylacetonate to the N,N-dimethylformamide (DMF) solution of vanadium acetylacetonate so that the concentration of the mixed DMF solution is 1% (mass fraction), then deposit the mixed DMF solution on the surface of BiOI, calcine at 450°C for 2 hours, and finally obtain a molybdenum-doped bismuth vanadate (Mo-BiVO4) photoanode.

[0074] Step (3): Dissolve 0.03 mol Ni(NO3)2·6H2O and 0.1 mol Co(NO3)2·6H2O in 80 mL 0.5 M boric acid buffer solution. After fully dissolved, add KOH to adjust the pH value to 8.4, and introduce N2 bubbling for 30 min to remove dissolved oxygen in the solution to obtain a precursor mixture. Then immerse the Mo-BiVO4 photoanode obtained in step (2) in the obtained precursor solution and stir. Use a three-electrode electrochemical system with the Mo-BiVO4 photoanode as the working electrode (WE), the Ag / AgCl electrode as the reference electrode (RE), and the platinum wire as the counter electrode (CE) under a 300 W xenon lamp with an irradiation intensity of 100 mV / cm 2 , electroplating is performed, the linear scanning rate is 50mV / s, the deposition voltage is -0.2-0.5V for one cycle, and the cycle in this embodiment is 3 times.

[0075] After the deposition, the photoelectrode was washed with deionized water and dried in an oven at 60 °C for 12 h to obtain a nickel-cobalt oxide-modified molybdenum-doped bismuth vanadate composite photoanode (denoted as NiCoO x / Mo-BiVO4 composite photoanode).

[0076] The NiCoO obtained by the present invention x / Mo-BiVO4 composite photoanode is used for photoelectrocatalytic reaction to decompose water to produce hydrogen.

[0077] Example 8: NiCoO x Preparation of / Mo-BiVO4 composite photoanode

[0078] Step (1): depositing a bismuth oxide iodide (BiOI) film on FTO conductive glass to obtain a BiOI photoanode.

[0079] Step (2): Add the DMF solution of molybdenum acetylacetonate to the N,N-dimethylformamide (DMF) solution of vanadium acetylacetonate so that the concentration of the mixed DMF solution is 1% (mass fraction), then deposit the mixed DMF solution on the surface of BiOI, calcine at 450°C for 2 hours, and finally obtain a molybdenum-doped bismuth vanadate (Mo-BiVO4) photoanode.

[0080] Step (3): Dissolve 0.04 mol Ni(NO3)2·6H2O and 0.1 mol Co(NO3)2·6H2O in 80 mL 0.5 M boric acid buffer solution. After fully dissolved, add KOH to adjust the pH value to 8.4, and introduce N2 bubbling for 30 min to remove dissolved oxygen in the solution to obtain a precursor mixture. Then immerse the Mo-BiVO4 photoanode obtained in step (2) in the obtained precursor solution and stir. Use a three-electrode electrochemical system with the Mo-BiVO4 photoanode as the working electrode (WE), the Ag / AgCl electrode as the reference electrode (RE), and the platinum wire as the counter electrode (CE) under a 300 W xenon lamp with an irradiation intensity of 100 mV / cm 2 , electroplating is performed, the linear scanning rate is 50mV / s, the deposition voltage is -0.2-0.5V for one cycle, and the cycle in this embodiment is 3 times.

[0081] After the deposition, the photoelectrode was washed with deionized water and dried in an oven at 60 °C for 12 h to obtain a nickel-cobalt oxide-modified molybdenum-doped bismuth vanadate composite photoanode (denoted as NiCoO x / Mo-BiVO4 composite photoanode).

[0082] The NiCoO obtained by the present invention x / Mo-BiVO4 composite photoanode is used for photoelectrocatalytic reaction to decompose water to produce hydrogen.

[0083] Example 9: NiCoO x Preparation of / Mo-BiVO4 composite photoanode

[0084] Step (1): depositing a bismuth oxide iodide (BiOI) film on FTO conductive glass to obtain a BiOI photoanode.

[0085] Step (2): Add the DMF solution of molybdenum acetylacetonate to the N,N-dimethylformamide (DMF) solution of vanadium acetylacetonate so that the concentration of the mixed DMF solution is 1% (mass fraction), then deposit the mixed DMF solution on the surface of BiOI, calcine at 450°C for 2 hours, and finally obtain a molybdenum-doped bismuth vanadate (Mo-BiVO4) photoanode.

[0086] Step (3): Dissolve 0.05 mol Ni(NO3)2·6H2O and 0.1 mol Co(NO3)2·6H2O in 80 mL 0.5 M boric acid buffer solution. After fully dissolved, add KOH to adjust the pH value to 8.4, and introduce N2 bubbling for 30 min to remove dissolved oxygen in the solution to obtain a precursor mixture. Then immerse the Mo-BiVO4 photoanode obtained in step (2) in the obtained precursor solution and stir. Use a three-electrode electrochemical system with the Mo-BiVO4 photoanode as the working electrode (WE), the Ag / AgCl electrode as the reference electrode (RE), and the platinum wire as the counter electrode (CE). Irradiate at an intensity of 100 mV / cm under a 300 W xenon lamp. 2 , electroplating is performed, the linear scanning rate is 50mV / s, the deposition voltage is -0.2-0.5V for one cycle, and the cycle in this embodiment is 3 times.

[0087] After the deposition, the photoelectrode was washed with deionized water and dried in an oven at 60 °C for 12 h to obtain a nickel-cobalt oxide-modified molybdenum-doped bismuth vanadate composite photoanode (denoted as NiCoO x / Mo-BiVO4 composite photoanode).

[0088] The NiCoO obtained by the present invention x / Mo-BiVO4 composite photoanode is used for photoelectrocatalytic reaction to decompose water to produce hydrogen.

[0089] Physical phase test:

[0090] Take bismuth vanadate (BiVO4), molybdenum-doped bismuth vanadate (Mo-BiVO4) and NiCoO prepared in Example 2 x The / Mo-BiVO4 composite photoanode sample was tested by X-ray energy spectrum diffractometer and obtained as follows Figure 1 The XPS diffraction pattern shown in the figure shows that all three samples have peaks of elements O, V, and Bi. x The peaks of Ni and Co appear in the magnified image of the Mo-BiVO4 photoanode sample, proving that NiCoO x The co-catalyst is on the surface of Mo-BiVO4 photoanode.

[0091] Take BiVO4, Mo-BiVO4 and NiCoO prepared in Example 2 x The / Mo-BiVO4 composite photoanode sample was tested by scanning electron microscopy and the following results were obtained: Figure 2 The SEM image shown. From the figure, we can see that NiCoO x The promoter is not obvious, so other tests are needed to verify NiCoO x The presence of a promoter.

[0092] Take the sample of Example 2, scrape the sample on the electrode surface with a blade to obtain a powder sample, and then perform a high-power transmission electron microscope (HRTEM) test. Figure 3 The results show that molybdenum-doped bismuth vanadate (Mo-BiVO4) has good crystallinity on the 011 and 110 crystal planes, with lattice fringe spacings of 0.476 and 0.466 nm, and nickel-cobalt oxide is amorphous. In addition, the element distribution diagram clearly shows that nickel-cobalt oxide (NiCoO x ) are evenly distributed on the surface of Mo-BiVO4.

[0093] The above results indicate that the method of the present invention successfully prepared a nickel-cobalt oxide modified molybdenum-doped bismuth vanadate composite photoanode, and the nickel-cobalt oxide (NiCoO x ) are evenly distributed on the surface of Mo-BiVO4.

[0094] Furthermore, the composite photoanode prepared by the method of the present invention was tested:

[0095] Photoelectric performance test:

[0096] In the present invention, NiCoOx / Mo-BiVO4 photoanode is prepared by electrodeposition without light assistance. Compared with the NiCoOx / Mo-BiVO4 photoanode prepared by light assistance using the method of the present invention, the photoelectrochemical test performance of the photoanode prepared without light assistance is lower than that of the photoanode prepared by the method of the present invention.

[0097] All photoelectrochemical test results were obtained using an electrochemical workstation (CHI 614) in a three-electrode system using the prepared sample as the working electrode (WE), Ag / AgCl electrode as the reference electrode (RE) and platinum wire as the counter electrode (CE). Unless otherwise specified, all electrolytes were 0.5 M boric acid buffer solution with a pH of 9.5. The rated power was 300 W and the light intensity was 100 mW / cm 2 The xenon lamp light source simulates sunlight.

[0098] The effect of photoelectrochemical water decomposition to produce hydrogen by the photoanode of the present invention is reflected in the photocurrent density. Under the same test conditions, with a standard hydrogen voltage of 1.23V as a reference value, the higher the photocurrent density, the better the hydrogen production effect. Figure 4 In this example, a linear voltammetric scan (LSV) was used to perform JV tests on pure bismuth vanadate (BiVO4 photoanode), molybdenum-doped bismuth vanadate (Mo-BiVO4) and samples of Examples 1 to 3, with a voltage range of -0.6-0.8 (vs. Ag / AgCl) and a scan rate of 50 mV / s. The results are shown in Figure 4 As shown in the figure, at a bias voltage of 1.23 V (vs. RHE), pure BiVO4 (denoted as BiVO4 in the figure) and Example 1 (denoted as NiCoOx / Mo-BiVO4-2), Example 2 (denoted as NiCoO x / Mo-BiVO4-3) and Example 3 (denoted as NiCoO x / Mo-BiVO4-4) samples correspond to 1.02 mA / cm 2 、3.87mA / cm 2 , 5.30mA / cm 2 and 4.22mA / cm 2 , that is, the sample in Example 2 has the highest photocurrent density.

[0099] Figure 5 The photocurrent density of Mo-BiVO4 is 2.91 mA / cm 2 In contrast, Mo-doped and NiCoO-loaded x Bismuth vanadate after the catalyst (the sample of Example 2, denoted as NiCoO x / Mo-BiVO4) photocurrent density is significantly improved, and it can be clearly observed that the number of electrodeposition cycles has an effect on the NiCoO x / Mo-BiVO4 composite photoanode photocurrent density has a significant impact. When the electrodeposition cycle is 3 times, the photocurrent density of the sample is the highest, which is 5.2 times that of pure bismuth vanadate and 1.8 times that of Mo-BiVO4. At present, one of the considerations for the effect of photoelectric water decomposition to produce hydrogen is the photocurrent density, which is proportional to the amount of hydrogen produced. The higher the photocurrent density, the greater the amount of hydrogen produced. The photoelectrode prepared by the method of the present invention has a significant and outstanding effect in photoelectric catalytic water decomposition to produce hydrogen.

[0100] The number of electrodeposition cycles directly determines the loading amount of nickel cobalt oxide on molybdenum-doped bismuth vanadate. When the number of electrodeposition cycles is less than 3, it may be NiCoO x The co-catalyst content is low, resulting in NiCoO x The auxiliary catalytic effect is not obvious; when the number of electrodeposition cycles is greater than 3, it may be that NiCoO x The higher content of co-catalyst leads to the reduction of active sites on Mo-BiVO4, resulting in the degradation of performance.

[0101] Figure 6 Pure BiVO4, Mo-BiVO4 and samples of Example 2 were taken for optical impedance spectroscopy (PEIS). Figure 6 As shown in the figure, the smaller the curve radius of the sample in Example 2, the faster the carrier transfer rate is than that of pure BiVO4 and Mo-BiVO4. These results show that the NiCoO xThe presence of is beneficial to carrier separation, thereby improving the overall performance of PEC and inhibiting the recombination of photogenerated electrons and holes, solving the problem of high recombination rate of photogenerated electrons and holes in the current bismuth vanadate photoanode.

[0102] The above embodiments describe the basic principles and main features of the present invention and the advantages of the present invention. The present invention is not limited to the details of the above embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. The embodiments described are exemplary and not restrictive.

Claims

1. A method for preparing a nickel-cobalt oxide modified molybdenum-doped bismuth vanadate composite photoanode, characterized in that: The method comprises: The Mo-BiVO4 photoanode is prepared by an electrodeposition combined with calcination method; a precursor solution containing bimetallic Ni and Co is prepared, and the Mo-BiVO4 photoanode is immersed in the precursor solution by a three-electrode electrochemical system, and the electrodeposition is performed by linear scanning under light, and after the completion, the obtained material is washed and dried to obtain NiCoO x / Mo-BiVO4 composite photoanode.

2. The method according to claim 1, characterized in that The preparation method of the precursor solution containing bimetallic Ni and Co is as follows: dissolving Ni source and Co source in a boric acid buffer solution, and continuously stirring until completely dissolved; adding KOH to adjust the pH, and passing nitrogen for a certain period of time to prepare a precursor solution containing bimetallic nickel (Ni) and cobalt (Co).

3. The method according to claim 2, characterized in that The Ni source includes Ni(NO3)2·6H2O or NiCl2·6H2O; the Co source includes Co(NO3)2·6H2O or CoCl2·6H2O.

4. The method according to claim 2, characterized in that The content ratio of Ni to Co in the precursor solution containing bimetallic Ni and Co is 1 to 5:10 in terms of molar ratio.

5. The method according to claim 2, characterized in that: The concentration of the boric acid buffer solution is 0.5 M, the pH value is adjusted to 7-9 by KOH, and nitrogen is introduced for more than 30 minutes to ensure that other gases in the solution are exhausted.

6. The method according to claim 1, characterized in that In the three-electrode electrochemical system, the Mo-BiVO4 photoanode is used as the working electrode (WE), the Ag / AgCl electrode is used as the reference electrode (RE), and the platinum wire is used as the counter electrode (CE); the light source is a 300W xenon lamp, and the light intensity reaching the electrodes is 100mW / cm 2 .

7. The method according to claim 1, characterized in that The linear scanning rate is 50 mV / s, the electrodeposition sink voltage is -0.2-0.5 V, and the cycle is 2-4 times.

8. The method according to claim 1, characterized in that The drying condition is 60° C. for 12 h.

9. NiCoO prepared by the method according to any one of claims 1 to 8 x / Mo-BiVO4 composite photoanode.

10. NiCoO prepared by the method according to any one of claims 1 to 8 x / Mo-BiVO4 composite photoanode, or the NiCoO according to claim 9 x Application of / Mo-BiVO4 composite photoanode in photoelectrocatalytic water decomposition to produce hydrogen.

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