BiVO4 / CoMOF+MWCNT photoanode and preparation method thereof

Abstract

The application belongs to the technical field of photoelectrochemistry, and particularly relates to a BiVO4 / CoMOF+MWCNT photoanode and a preparation method thereof. The BiVO4 photoanode is prepared; the Co MOF+MWCNT catalyst is prepared: Co(NO3)3.6H2O is dissolved in DMF, poured into DMF containing terephthalic acid, MWCNT is added to the solution, stirred at room temperature, and reacted in a high-pressure reaction kettle; centrifugation, washing, drying and grinding are performed; the BiVO4 / Co MOF+MWCNT photoanode is prepared: firstly, a Co MOF+MWCNT aqueous solution is prepared and placed in a sample bottle; the prepared BiVO4 photoanode is placed in the solution; after being placed at room temperature for 12 hours, the BiVO4 / Co MOF+MWCNT photoanode is taken out, washed with deionized water, dried by nitrogen blowing, and obtained.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photoelectrochemistry, and particularly relates to a BiVO4 / CoMOF+MWCNT photoanode and a preparation method thereof. BACKGROUND

[0002] With the continuous consumption of fossil fuels, energy shortage and environmental pollution problems are increasingly concerned by human society, so finding a renewable and environment-friendly fuel to replace fossil fuels has always been a research hotspot for scientists. Hydrogen energy is one of the good choices to replace fossil fuels due to its advantages of low cost, high energy density and no environmental pollution. Industrial production of hydrogen consumes a large amount of fossil fuels and produces harmful gases. It is a good solution to directly convert abundant solar energy into hydrogen energy in a sustainable way through photoelectrochemical (PEC) water splitting. BiVO4 is widely studied for PEC water splitting due to its non-toxicity, low price, suitable band gap and good photoelectrochemical stability. However, the photocurrent density of the original BiVO4 is far lower than the theoretical maximum photocurrent density 7.5 mA / cm 2 (100 mW / cm 2 ), which is due to its short hole diffusion span, slow water oxidation kinetics, poor carrier mobility and surface recombination at the photoanode / electrolyte interface. Therefore, we modify the BiVO4 surface by immersing Co MOF+MWCNT at room temperature to form a BiVO4 / Co MOF+MWCNT composite photoanode, so as to improve the photoelectric PEC water splitting performance. SUMMARY

[0003] To achieve the above purpose, the application provides a BiVO4 / CoMOF+MWCNT photoanode, and a preparation method thereof, which comprises the following steps:

[0004] 1) preparing a BiVO4 photoanode;

[0005] 2) preparing a Co MOF+MWCNT catalyst: dissolving Co(NO3)3·6H2O in DMF, pouring into DMF containing terephthalic acid, adding MWCNT to the solution, stirring at room temperature, and performing reaction in a high-pressure reaction kettle, centrifuging, washing, drying and grinding;

[0006] 3) preparing a BiVO4 / Co MOF+MWCNT photoanode: first, preparing a Co MOF+MWCNT aqueous solution, putting it into a sample bottle, putting the prepared BiVO4 photoanode into the solution, placing it at room temperature for 12 hours, then taking it out, washing it with deionized water, and blowing it dry with nitrogen to obtain the BiVO4 / Co MOF+MWCNT photoanode.

[0007] The BiVO4 / CoMOF+MWCNT photoanode, the preparation method of the BiVO4 photoanode comprises the following steps:

[0008] 1) Pretreatment of FTO conductive glass: the FTO glass is sequentially cleaned with detergent, acetone, anhydrous ethanol and deionized water;

[0009] 2) Preparation of electrodeposition solution: Bi(NO3)3.5H2O and KI are sequentially added to a nitric acid solution, and the solution is stirred vigorously until it turns orange red, and then the solution is added to an ethanol solution of benzoquinone, and the solution is ultrasonically treated until it turns deep red and there are no dense bubbles on the liquid surface;

[0010] 3) A part of the FTO glass sheet is immersed in the electrodeposition solution as a working electrode, a Pt wire is used as a counter electrode, and Ag / AgCl is used as a reference electrode; a three-electrode system is adopted, and a uniform BiOI film is prepared by electrodeposition at an input voltage of-0.1 V vs.Ag / AgCl for 300 s;

[0011] 4) Vanadyl acetylacetonate is dissolved in DMSO, and then dropped and coated on the surface of the BiOI; the reaction is carried out at high temperature, V2O5 on the surface of the BiVO4 is removed, and after the black impurities on the surface of the BiVO4 plate are completely dissolved and turn into golden yellow, the BiVO4 plate is cleaned and dried.

[0012] In step 4) of the BiVO4 / CoMOF+MWCNT photoanode, the reaction at high temperature is carried out at a temperature increasing rate of 2 ℃ per minute to 450 ℃ for 2 h.

[0013] In step 2) of the BiVO4 / CoMOF+MWCNT photoanode, the pH of the nitric acid solution is 1.7.

[0014] In step 2) of the BiVO4 / CoMOF+MWCNT photoanode, the mass ratio of Co(NO3)3.6H2O to MWCNT is 20:1.

[0015] In step 2) of the BiVO4 / CoMOF+MWCNT photoanode, the reaction is carried out at 120 ℃ for 12 h.

[0016] The BiVO4 / CoMOF+MWCNT photoanode has the following advantages:

[0017] 1) The preparation method is simple and easy to operate.

[0018] 2) The catalyst prepared by the method has a photocurrent density of 4.15 mA / cm 2 at 1.23 V vs.RHE. Figure 4 BRIEF DESCRIPTION OF DRAWINGS

[0019] ​Figure 1 SEM image of BiVO4 photoanode.

[0020] Figure 2 SEM image of BiVO4 / Co MOF+MWCNT photoanode.

[0021] Figure 3 XRD image of the prepared catalyst.

[0022] Figure 4 Linear sweep voltammetry curves of BiVO4, BiVO4 / MWCNT, BiVO4 / Co MOF and BiVO4 / Co MOF+MWCNT.

[0023] Figure 5 Chronoamperometry curves (i-t) of BiVO4, BiVO4 / Co MOF and BiVO4 / Co MOF+MWCNT electrodes at 0.7 V vs. RHE. DETAILED DESCRIPTION

[0024] Example 1 Preparation of BiVO4 / Co MOF+MWCNT photoanode

[0025] Pre-treatment of FTO conductive glass: Firstly, the purchased 1 cm x 2.5 cm FTO glass plate was placed in a 500 mL beaker containing detergent, and about 150 mL of deionized water was added and ultrasonic for 30 min; then the washing liquid was poured out and the glass plate was washed with deionized water for several times until no obvious foam existed, and then about 150 mL of acetone was added and ultrasonic for 30 min; then about 150 mL of anhydrous ethanol was added into the beaker and ultrasonic for more than 30 min; finally, the FTO was washed with deionized water and dried with N2 for standby.

[0026] Preparation of electrodeposition solution: 150 mL of deionized water was measured in a 500 mL beaker with a burette, and 0.30 mL of concentrated nitric acid was drawn into a 1.0 mL syringe and slowly dropped into the beaker to adjust the pH, and the addition of concentrated nitric acid was stopped until the pH was adjusted to 1.70. 2.91 g of Bi(NO3)3·5H2O and 9.96 g of KI were weighed with an analytical balance, and Bi(NO3)3·5H2O and KI were added into the pH = 1.7 nitric acid solution in turn, and stirred vigorously with a stirrer until completely dissolved and the solution gradually turned orange red; 1.49 g of p-benzoquinone was dissolved in 60 mL of anhydrous ethanol, and ultrasonic was applied until no solid particles remained, and the two were mixed in a 500 mL beaker, and continued to ultrasonic until the solution turned deep red and the liquid surface was free of dense bubbles.

[0027] Preparation of BiVO4 photoanode: After the preparation of the electroplating solution, connect the electrochemical CHI660, open the constant potential time current test interface, take 15 mL of the prepared electroplating solution in a 25 mL beaker, control the FTO glass sheet with a length of only 1 cm to be immersed in the electroplating solution as the working electrode, use Pt wire as the counter electrode, and Ag / AgCl as the reference electrode; use a three-electrode system to electroplate at -0.1 V vs. Ag / AgCl for 300 s to form a uniform BiOI with a thin thickness. Take 0.106 g of vanadyl acetylacetonate and dissolve it in 1.0 mL of DMSO, mix uniformly, and then use a pipette to take 26 μL of the above solution and evenly drop it on the surface of the BiOI. Then place the BiOI plate after dropping on the spot plate in the muffle furnace, heat to 450°C at a heating rate of 2°C per minute, and continue heating for 2 h before taking it out. Move the BiVO4 plate to a large surface dish, prepare 100 mL of 1M NaOH solution, slowly pour it into the surface dish, and stir with a stirrer to remove V2O5 on the surface of BiVO4. After the black impurities on the surface of the BiVO4 plate are completely dissolved and turned into golden yellow, use a pair of tweezers to take them out in turn, rinse them with deionized water, and dry them with N2 for standby.

[0028] Preparation of Co MOF+MWCNT catalyst: 1 mmol of Co(NO3)3·6H2O was dissolved in 10 mL of DMF, which was poured into 10 mL of DMF containing 1 mmol of terephthalic acid, then 0.0145 of multi-walled carbon nanotubes (MWCNT) was added to the solution, the mass ratio of Co(NO3)3·6H2O to MWCNT was 20:1, the mixed solution was stirred at room temperature for 3 h, the solution was poured into a 50 mL high-pressure reaction kettle, and placed in a 120°C oven for reaction for 12 h, the solution was centrifuged at 10000 r for 10 min after taking out, and then washed with DMF and anhydrous ethanol for 3 times, the obtained precipitate was placed in a 70°C vacuum drying box for drying for 12 h, and then ground after taking out for standby.

[0029] Preparation of BiVO4 / Co MOF+MWCNT photoanode: First, prepare a 1 mg / mL Co MOF+MWCNT aqueous solution, take 10 mL and put it into a sample bottle, put the prepared BiVO4 photoanode into the solution, and place it at room temperature for 12 h, then take it out, rinse it with deionized water, and dry it with nitrogen. The preparation of BiVO4 / Co MOF+MWCNT photoanode is completed

[0030] Example 2 Preparation of BiVO4 / MWCNT

[0031] Take 1 mg MWCNT dissolved in 20 mL deionized water, ultrasonic for 30 min to make it more uniform, take 10 mL into the sample bottle, put the prepared BiVO4 photoanode into the solution, place at room temperature for 12 h, then take out, wash with deionized water, dry with nitrogen, the preparation of BiVO4 / MWCNT photoanode is completed.

[0032] Example 3 Preparation of BiVO4 / Co MOF

[0033] Dissolve 1 mmol Co(NO3)3·6H2O in 10 mL DMF, pour it into 10 mL DMF containing 1 mmol terephthalic acid, stir the mixed solution at room temperature for 3 h, pour the solution into a 50 mL high-pressure reactor, put it into a 120℃ oven for reaction for 12 h, centrifuge the solution at 10000 r for 10 min after taking it out, and wash it with DMF and anhydrous ethanol for 3 times, put the obtained precipitate into a 70℃ vacuum drying box for drying for 12 h, take it out and grind, and then prepare a 1 mg / mL Co MOF aqueous solution, take 10 mL into the sample bottle, put the prepared BiVO4 photoanode into the solution, place at room temperature for 12 h, then take out, wash with deionized water, dry with nitrogen, and the preparation of BiVO4 / Co MOF photoanode is completed.

[0034] Example 4 Electrochemical performance test

[0035] Electrochemical performance test: The electrochemical workstation used in this experiment is CHI760E, and the three-electrode system is used for electrochemical performance research, in which the platinum wire is used as the counter electrode, Ag / AgCl (3.5MKCl) is used as the reference electrode, the prepared composite photoanode is clamped on the stainless steel electrode clamp as the working electrode, and the electrolyte solution used in the test process is 1.0M boric acid buffer solution with pH=9.5, and the xenon lamp light intensity is 100mW / cm 2 . The scan rate is 50mV·s -1 . According to the Nernst equation, all the potentials measured by all the reference and Ag / AgCl electrodes need to be converted into the potential relative to the reversible hydrogen electrode (RHE): E RHE = E Ag / AgCl +0.059×pH+0.197V

[0036] Figure 1 The SEM image of the BiVO4 photoanode. It can be seen that the image is a 200-300nm worm-like structure, which is uniformly distributed, proving that the BiVO4 photoanode is successfully prepared.

[0037] Figure 2 The SEM image of the BiVO4 / Co MOF+MWCNT photoanode. Compared with Figure 1In contrast, it is proved that the BiVO4 / CoMOF+MWCNT photoanode is successfully prepared

[0038] Figure 3 The XRD pattern of the prepared catalyst. By Figure 3 It can be found that loading other catalysts on the surface of bismuth vanadate does not change the structure of bismuth vanadate.

[0039] Figure 4 The linear sweep voltammetry curves of BiVO4, BiVO4 / MWCNT, BiVO4 / Co MOF and BiVO4 / Co MOF+MWCNT. By comparison, it can be found that the unmodified BiVO4 photoanode has the lowest photocurrent density. The photocurrent density of the photoanode is significantly improved to 4.35 mA / cm 2 The photocurrent density is improved, and efficient water oxidation reaction is realized. The improvement of photocurrent density may be due to the introduction of Co MOF and MWCNT, which improves the conductivity of the photoanode and promotes the electron transfer, thereby improving the water oxidation performance.

[0040] Figure 5 The chronoamperometry curves (i-t) of BiVO4, BiVO4 / Co MOF and BiVO4 / Co MOF+MWCNT electrodes at 0.7 V vs. RHE. By comparison, it can be found that the multi-walled carbon nanotubes have certain improvement on the stability of the photoelectrode. The improvement of stability may be due to the strong combination of MWCNT and CoMOF, which makes the structure of the catalyst more stable, thereby improving the stability of the photoelectrode.

Claims

1. A BiVO4 / CoMOF+MWCNT photoanode, characterized in that, The preparation method includes the following steps: 1) Preparation of BiVO4 photoanode; 2) Preparation of Co MOF+MWCNT catalyst: Co(NO3)3·6H2O was dissolved in DMF and poured into DMF containing terephthalic acid. MWCNT was added to the solution, stirred at room temperature, and the reaction was carried out in a high-pressure reactor. The reaction was then centrifuged, washed, dried, and ground. 3) Preparation of BiVO4 / Co MOF+MWCNT photoanode: First, prepare a Co MOF+MWCNT aqueous solution and put it into a sample bottle. Then, put the prepared BiVO4 photoanode into the solution and leave it at room temperature for 12 hours. After that, take it out, rinse it with deionized water, and blow it dry with nitrogen to obtain the BiVO4 / Co MOF+MWCNT photoanode.

2. The BiVO4 / CoMOF+MWCNT photoanode according to claim 1, characterized in that, The preparation method of BiVO4 photoanode includes the following steps: 1) Pretreatment of FTO conductive glass: The FTO glass is cleaned in sequence with detergent, acetone, anhydrous ethanol and deionized water; 2) Preparation of electrodeposition solution: Add Bi(NO3)3·5H2O and KI to the nitric acid solution in sequence, stir vigorously until the solution turns orange-red, add to the ethanol solution of benzoquinone, and sonicate until the solution turns dark red and there are no dense bubbles on the surface. 3) A portion of the FTO glass sheet is immersed below the surface of the electrodeposition solution as the working electrode, with Pt wire as the counter electrode and Ag / AgCl as the reference electrode; a three-electrode system is used to electroplate a uniformly thin BiOI for 300 seconds with an input voltage of -0.1V vs. Ag / AgCl. 4) Dissolve vanadium acetylacetonate in DMSO and drop it onto the surface of BiOI. React at high temperature to remove V2O5 from the surface of BiVO4. After the black impurities on the surface of BiVO4 plate are completely dissolved and turn golden yellow, clean and dry.

3. The BiVO4 / CoMOF+MWCNT photoanode according to claim 2, characterized in that, In step 4), the reaction at high temperature is carried out by heating to 450°C at a rate of 2°C per minute and continuing to heat for 2 hours.

4. The BiVO4 / CoMOF+MWCNT photoanode according to claim 2, characterized in that, In step 2), the pH of the nitric acid solution is 1.

7.

5. The BiVO4 / CoMOF+MWCNT photoanode according to claim 1, characterized in that, In step 2), the mass ratio is Co(NO3)3·6H2O:MWCNT = 20:

1.

6. The BiVO4 / CoMOF+MWCNT photoanode according to claim 1, characterized in that, In step 2), the reaction is carried out at 120°C for 12 hours.

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