A dual photoelectrode and its preparation method and application

Abstract

The present invention discloses a dual photoelectrode and its preparation method and application, wherein the dual photoelectrode includes a ZIF‑67 / g‑C3N4 photocathode and a BiVO4‑RuO2‑IrO2 / Ti photoanode. The present invention uses titanium mesh as a substrate to prepare a BiVO4‑RuO2‑IrO2 / Ti photoanode, and uses carbon felt as a substrate to prepare a ZIF‑67 / g‑C3N4 photocathode. Under illumination conditions, the photoanode can effectively reduce the oxygen overpotential and improve the efficiency of photogenerated electrons, while the photocathode provides more reducing power for autotrophic microorganisms through the enrichment of carbon dioxide and the action of photogenerated electron holes, which is used to increase the rate of organic acid production from carbon dioxide. The present invention reduces the applied voltage, improves the efficiency of electron transfer between microbial electrodes, and increases the rate of organic acid production through the effective matching of dual photoelectrodes, providing ideas for the efficient conversion and utilization of carbon dioxide.

Description

Technical Field

[0001] The present invention belongs to the technical field of microbial electrosynthesis, and in particular relates to a dual photoelectrode and a preparation method and application thereof. Background Art

[0002] Climate change caused by greenhouse gas emissions, including carbon dioxide, has become a major ecological and environmental issue worldwide. Capturing carbon dioxide and converting it into high-value-added chemicals is considered an effective approach to achieving carbon neutrality. Microbial electrosynthesis (MES) is a production process in which microorganisms utilize electrons from electrodes as an energy source, using CO₂ as the sole carbon source, to reduce CO₂ to valuable chemicals. The productivity and efficiency of MES depend largely on the rate of electron transfer. Therefore, many recent strategies have focused on improving the rate of direct electron transfer, such as increasing the electrode's specific surface area, conductivity, surface roughness, and constructing 3D electrodes. Furthermore, hydrogen evolution catalysts can be used to increase hydrogen yield, indirectly enhancing the electron transfer rate. Against this backdrop, recent literature has proposed a photoelectrode-assisted MES system combined with solar energy. Specifically, photocatalytic semiconductor materials are incorporated into the electrodes. During this process, photogenerated electron-hole pairs at the electrodes can reduce the external potential, increase the electron transfer rate, and thus enhance the performance of the MES.

[0003] The earliest reported photoelectrode-assisted MES system employed a silicon nanowire-supported TiO2 photocathode and a fluorine tin oxide (FTO)-supported TiO2 photoanode, utilizing microbial CO2 reduction to acetic acid (NanoLett. 2015, 15, 3634-3639). However, the acetic acid production rate remained low, and the photocatalytic efficiency was low. The primary issue was that the photoelectrode was constructed with TiO2, which only responds to ultraviolet light, which accounts for less than 5% of solar energy, significantly reducing its solar energy utilization efficiency. Furthermore, the anode, supported by FTO, has moderate conductivity and a smooth surface. The generation of oxygen during water electrolysis at the anode can easily cause the catalyst to dislodge over time. Furthermore, water oxidation at the anode has a high kinetic barrier, requiring significant energy consumption to initiate the OER, necessitating a suitable catalyst to reduce the OER overpotential at the anode. For the cathode, the low solubility of CO2 in the solution limits the supply of substrates and affects the bioelectrochemical conversion efficiency of CO2. In addition, the reduction of carbon dioxide requires the cathode to provide a large number of electrons. Therefore, the selection of the cathode must be suitable for the attachment of microorganisms and the mass transfer of substrates, and the cathode must have an efficient photogenerated electron-hole separation ability, so that it can better accept the photogenerated electrons from the anode and improve the efficiency of microbial electrosynthesis. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the present invention provides a dual photoelectrode and a preparation method and application thereof, which effectively solves the technical problem of low electron transfer rate.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for preparing a dual photoelectrode, the dual photoelectrode comprising a photocathode and a photoanode, the photocathode being ZIF-67 / g-C3N4 and the photoanode being BiVO4-RuO2-IrO2 / Ti;

[0007] The preparation method of the photocathode comprises the following steps:

[0008] Step A) dissolving carbon nitride in deionized water and ultrasonicating for 30 minutes, then adding Co(NO3)2·6H2O to the above solution and stirring for 30 minutes to obtain a carbon nitride-Co mixed solution;

[0009] Step B) 2-methylimidazole was slowly added dropwise to the carbon nitride-Co mixture. After the addition was complete, the mixture was stirred at room temperature for 1 hour and then allowed to stand for 24 hours. The resulting precipitate was centrifuged, washed three times with water, and dried at 60° C. for 24 hours to obtain ZIF-67 / g-C3N4.

[0010] Step C) dissolving ZIF-67 / g-C3N4 in a solvent of 1 to 5 wt% perfluorosulfonic acid polymer and ethanol to obtain a catalyst solution; then immersing the carbon felt in the catalyst solution, stirring for 4 to 6 hours, and then taking it out and drying it to obtain a ZIF-67 / g-C3N4 photocathode;

[0011] The preparation method of the photoanode comprises the following steps:

[0012] Step a) polishing the titanium mesh, cleaning the surface stains with 5% NaOH, then etching it in 10% oxalic acid for 6 h, and then repeatedly washing it with distilled water;

[0013] Step b) H2IrCl6 and RuCl3 are dissolved in n-butanol solution and mixed to obtain a coating solution, which is then applied to the titanium mesh with a brush, dried in a drying oven for 10 minutes, then pyrolyzed in a muffle furnace for 15 minutes, and cooled to room temperature in air;

[0014] Step c) Repeat the three steps of painting, drying and pyrolysis in step b) until the weight gain of the titanium-based surface material is 1 mg / cm 2 , thereby obtaining RuO2-IrO2 / Ti electrode;

[0015] Step d) bismuth nitrate and potassium iodide are added to deionized water, and 1,4-benzoquinone ethanol solution is added. After ultrasonication for 10 minutes, the pH is adjusted to 3.5, and then it is used as an electrolyte, RuO2-IrO2 / Ti is used as the working electrode and the counter electrode, and electrochemical deposition is performed for 400 to 800 seconds. Then, acetylacetonatovanadium in dimethyl sulfoxide is brushed onto the RuO2-IrO2 / Ti electrode, and then calcined at 420°C for 1 hour. After natural cooling, it is washed with 1 mol / L sodium hydroxide to obtain a BiVO4-RuO2-IrO2 / Ti photoanode.

[0016] Preferably, the mass ratio of ZIF-67 to g-C3N4 in the photocathode is 10 to 20:1; the mass ratio of BiVO4 to RuO2-IrO2 in the photoanode is 3 to 8:1.

[0017] Preferably, in step C), the loading amount of ZIF-67 / g-C3N4 on the carbon felt is 5 to 20 mg / cm 2 .

[0018] Preferably, the molar ratio of H2IrCl6 and RuCl3 in step b) is 1:1-5.

[0019] Preferably, the electrochemical deposition in step d) uses Ag / AgCl as a reference electrode at a voltage of 0.4-0.8V.

[0020] The dual photoelectrode prepared by the above preparation method.

[0021] The application of the above-mentioned dual photoelectrode in promoting the electrosynthesis of organic acids by microorganisms.

[0022] Preferably, reducing carbon dioxide to produce acetic acid in a microbial electrosynthesis system comprises the following steps:

[0023] In the microbial electrosynthesis system, the photocathode and the photoanode are placed in the cathode chamber and the anode chamber respectively, and the two chambers are separated by a proton exchange membrane. Autotrophic microorganisms are inoculated into the cathode chamber, and a potential of -0.6 to -1.0 V vsAg / AgCl is applied. The cathode chamber and the anode chamber are illuminated at the same time, and the visible light intensity is set to 20 to 50 mW / m -2 , carbon dioxide gas is introduced, and microorganisms photoelectrocatalytically reduce carbon dioxide to produce acetic acid.

[0024] The beneficial effects of the present invention are as follows:

[0025] (1) Both the photoanode and cathode of the present invention utilize visible light, breaking through the limitation of using ultraviolet light.

[0026] (2) The photoanode of the present invention uses a titanium mesh modified with ruthenium and iridium as a carrier. This mesh has excellent electrical conductivity and resistance to oxidative corrosion, and its bond with the photocatalyst bismuth vanadate is more secure, thus extending its service life. Furthermore, the presence of ruthenium and iridium increases the oxygen evolution potential of bismuth vanadate, enhancing the efficiency of photogenerated electron generation.

[0027] (3) The photocathode of the present invention uses carbon felt as a carrier, which has good biocompatibility. The heterogeneous structure formed by ZIF-67 / g-C3N4 can effectively improve the separation of photogenerated electrons and holes. In addition, the unique MOF structure of ZIF-67 is conducive to the adsorption of carbon dioxide in the air and improves the mass transfer of the substrate.

[0028] (4) The present invention uses BiVO4-RuO2-IrO2 / Ti, whose valence band is more positive than the oxidation potential of O2 / H2O, as the photoanode, and H + / H2 reduction potential of ZIF-67 / g-C3N4 as a photocathode is more conducive to anode water electrolysis and cathode hydrogen evolution. More importantly, the excitation energy of the dual photoelectrode can generate more electrons and holes, driving more electrons to combine with the holes generated from the anode and cathode, reducing the oxidation barrier of anode water, reducing the applied potential value as a whole, enhancing the transfer of cathode electrons to microorganisms, and improving the efficiency of acetic acid production. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is the electrochemical performance (OER) of the photoanode in Example 1;

[0030] Figure 2 is the photocurrent response of the photoanode in Example 1;

[0031] Figure 3 is the electrochemical performance (HER) of the photocathode in Example 1;

[0032] Figure 4 is the photocurrent response of the photocathode in Example 1;

[0033] Figure 5 The photoanode MES performance in Example 2;

[0034] Figure 6 The photocathode MES performance in Example 3;

[0035] Figure 7 The performance of the dual photoelectrode MES in Example 4;

[0036] Figure 8 The MES performance of the dual photoelectrode at different potentials in Example 5;

[0037] Figure 9 This is the MES performance of the control electrode at different potentials in Example 5. DETAILED DESCRIPTION

[0038] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0039] Example 1

[0040] A method for preparing a dual photoelectrode, the specific steps are as follows:

[0041] 1. The preparation method of ZIF-67 / g-C3N4 photocathode is as follows:

[0042] (1) Carbon nitride (g-C3N4) was first dissolved in deionized water and ultrasonicated for 30 min. Then Co(NO3)2·6H2O was added to the above solution and stirred for 30 min to obtain a carbon nitride-Co mixed solution.

[0043] (2) 2-Methylimidazole was further slowly added dropwise to the above carbon nitride-Co mixture. After the addition, the mixture was stirred at room temperature for 1 hour and then allowed to stand for 24 hours. The obtained precipitate was centrifuged, washed three times with water, and dried at 60 degrees for 24 hours to finally obtain dimethylimidazole cobalt / carbon nitride (ZIF-67 / g-C3N4), with a mass ratio of 18:1 (ZIF-67:g-C3N4).

[0044] (3) ZIF-67 / g-C3N4 was further dissolved in a solvent of 1% perfluorosulfonic acid polymer and ethanol to obtain a catalyst solution. The carbon felt was then immersed in the catalyst solution, stirred for 4 to 6 hours, and then taken out and dried to obtain a catalyst with a loading of 10 mg / cm 2 ZIF-67 / g-C3N4 photocathode.

[0045] Pure ZIF-67 electrode and g-C3N4 electrode were prepared using carbon felt as the support by the same preparation process, and blank carbon felt (CF) was used as the cathode control.

[0046] 2. The preparation method of BiVO4-RuO2-IrO2 / Ti photoanode is as follows:

[0047] (1) Polish the titanium mesh to a bright finish, clean the surface stains with 5% NaOH, then etch it in 10% oxalic acid for 6 h, and then repeatedly rinse it with distilled water.

[0048] (2) H2IrCl6 and RuCl3 with a molar ratio of 1:2 were dissolved in 9 mL of n-butanol solution and mixed to obtain a coating solution. The coating solution was then applied to the titanium mesh with a brush, placed in a drying oven for drying for 10 min, and then placed in a muffle furnace for high-temperature pyrolysis for 15 min, and cooled to room temperature in air.

[0049] (3) Repeat the above three steps of painting, drying and pyrolysis until the weight of the titanium-based surface material increases to 1 mg / cm2 , thus obtaining RuO2-IrO2 / Ti electrode.

[0050] (4) Bismuth nitrate and potassium iodide in a mass ratio of 2:7 were further added to deionized water, and 1,4-benzoquinone ethanol solution was added. After ultrasonication for 10 minutes, the pH was adjusted to 3.5, and then it was used as the electrolyte, RuO2-IrO2 / Ti was used as the working electrode and the counter electrode, and a voltage of 0.5V vs Ag / AgCl was applied. Electrochemical deposition was performed for 400 seconds, and then vanadium acetylacetonate (0.2 mol / L) in dimethyl sulfoxide was brushed onto the RuO2-IrO2 / Ti electrode, and then calcined at 420℃ for 1 hour. After natural cooling, it was washed with 1 mol / L sodium hydroxide to finally obtain BiVO4-RuO2-IrO2 / Ti (where the mass ratio of BiVO4:RuO2-IrO2 is 4:1) photoanode.

[0051] Using titanium mesh as the carrier, RuO2-IrO2 / Ti electrode and BiVO4 / Ti electrode were prepared by the same preparation process, and a blank Ti electrode was used as the anode control.

[0052] Figure 1 The linear scan diagram of various anodes prepared in this example shows that within the linear scan range, the greater the current response of the electrode, the higher the oxygen evolution (OER) catalytic activity. Figure 1 It can be seen that Ti and BiVO4 / Ti have the smallest impact on current, while modification of RuO2-IrO2 / Ti can significantly improve the oxygen evolution activity of the electrode. Furthermore, the current of BiVO4-RuO2-IrO2 / Ti is the highest, which shows that the combination of BiVO4-RuO2-IrO2 is beneficial to improving the oxygen evolution performance.

[0053] Figure 2 is the photoelectrode response diagram of various anodes prepared in this embodiment. Figure 2 As can be seen, the current density of RuO2-IrO2 / Ti remains essentially unchanged with changes in light / darkness, indicating no photoelectric response. However, after modification with BiVO4 / Ti, a photocurrent response is observed with changes in light / darkness. Furthermore, the highest photocurrent response is achieved when BiVO4-RuO2-IrO2 / Ti is combined, indicating that the combination of the three enhances the catalyst's ability to generate photogenerated electrons and holes.

[0054] Figure 3 This is a linear scan diagram of various cathodes prepared in this example. Within the linear scan range, the greater the current response of the electrode, the higher the hydrogen evolution (OER) catalytic activity. Figure 3It can be seen that the current response of ZIF-67 / g-C3N4 is the largest, which is better than that of ZIF-67 and g-C3N4 alone, indicating that the synergy between the two is beneficial to improving its hydrogen evolution performance.

[0055] Figure 4 is the photoelectrode response diagram of various cathodes prepared in this embodiment. Figure 4 It can be seen that both ZIF-67 and g-C3N4 have photoelectric responses, but the combination of ZIF-67 / g-C3N4 is more conducive to the separation of photogenerated electrons and holes, making its final photogenerated current value the highest.

[0056] Example 2

[0057] In this example, carbon felt was used as the cathode, BiVO4-RuO2-IrO2 / Ti prepared in Example 1 was used as the photoanode, and RuO2-IrO2 / Ti and BiVO4 / Ti were used as controls. Autotrophic microorganisms were inoculated in the cathode chamber (for preparation methods, see J ChemTechnol Biotechnol 2018; 93:457-466), and a potential of -0.9 V vs Ag / AgCl was applied. The photoanode was heated at 50 mW / m -2 Under light conditions, 100% carbon dioxide was introduced and reacted for 15 days.

[0058] The experimental results are as follows Figure 5 As shown in the figure, the acetic acid concentration in BiVO4 / Ti did not increase, which is due to its high electrochemical impedance, while the acetic acid concentration of RuO2-IrO2 / Ti can reach 1.54g / L. Furthermore, when BiVO4-RuO2-IrO2 / Ti is used as a photoanode, its acetic acid concentration increases to 2.71g / L. This shows that using BiVO4-RuO2-IrO2 / Ti as a photoanode is beneficial to the efficiency of microbial electrosynthesis and conversion of carbon dioxide by enhancing the catalytic activity of OER and improving the photoelectrocatalytic efficiency.

[0059] Example 3

[0060] In this example, RuO2-IrO2 / Ti was used as the anode, ZIF-67 / g-C3N4 prepared in Example 1 was used as the photocathode, and ZIF-67 and g-C3N4, as well as CF (carbon felt) alone were used as controls. Autotrophic microorganisms were inoculated in the cathode chamber (for preparation methods, see J Chem Technol Biotechnol 2018; 93: 457-466), and a potential of -0.9 V vs Ag / AgCl was applied. The photocathode was heated at 50 mW / m -2 Under light conditions, 100% carbon dioxide was introduced and reacted for 15 days.

[0061] The experimental results are as follows Figure 6 As shown in the figure, the acetic acid concentration of ZIF-67 / g-C3N4 is the highest (3.27 g / L), which is higher than that of ZIF-67 (2.2 g / L), g-C3N4 (1.9 g / L), and CF (1.5 g / L). This shows that the heterostructure formed by the combination of ZIF-67 and g-C3N4 is conducive to the separation of photogenerated electrons and holes, and the MOF structure of ZIF-67 is conducive to the substrate absorption of carbon dioxide, thereby enhancing the efficiency of microbial electrosynthesis and conversion of carbon dioxide to acetic acid.

[0062] Example 4

[0063] In this example, BiVO4-RuO2-IrO2 / Ti prepared in Example 1 was used as a photoanode, ZIF-67 / g-C3N4 was used as a photocathode, and autotrophic microorganisms were inoculated in the cathode chamber (for preparation methods, see J Chem Technol Biotechnol 2018; 93:457-466). A potential of -0.9 V vs Ag / AgCl was applied, and the reaction was carried out for 15 days under 100% carbon dioxide. The illumination of the photocathode alone, the illumination of the photoanode alone, the illumination of neither the photocathode nor the photoanode, the illumination of the photocathode and the photoanode at the same time, and the illumination of the photocathode and the photoanode at the same time without the autotrophic microorganisms were set. The illumination intensity was set to 50 mW / m -2 .

[0064] The experimental results are as follows Figure 7 As shown in the figure, the acetic acid concentrations of the photocathode and photoanode under single illumination are 2.81g / L and 2.83g / L, respectively, and their acetic acid concentrations are very close. When the photocathode and photoanode are illuminated at the same time, their acetic acid concentration reaches 6.93g / L, indicating that the use of dual photoelectrodes can significantly improve the efficiency of microbial electrosynthesis of acetic acid. Without illumination, the acetic acid is only 1.5g / L. With illumination and no electroautotrophic microorganisms, no acetic acid can be detected in the reactor. This shows that the dual photoelectrode can transfer electrons to electroautotrophic microorganisms to reduce carbon dioxide through the action of photogenerated electron holes, and due to the synergistic effect of the dual photoelectrodes, the oxidation barrier of the photoanode water is reduced, promoting more electrons to be transferred to the photocathode. More holes generated by the photocathode combine with electrons transferred from the photoanode, increasing the electron transfer of the overall reaction, thereby improving the efficiency of carbon dioxide to acetic acid.

[0065] Example 5

[0066] In this example, BiVO4-RuO2-IrO2 / Ti prepared in Example 1 was used as a photoanode, ZIF-67 / g-C3N4 was used as a photocathode, and autotrophic microorganisms were inoculated in the cathode chamber (preparation method see J Chem Technol Biotechnol 2018; 93:457-466). The photocathode and photoanode were illuminated simultaneously (50 mW / m -2 ) conditions, an external potential of -0.6 to -0.9 V vs Ag / AgCl was applied, and a microbial electrosynthesis reactor with RuO2-IrO2 / Ti as the anode and carbon felt as the cathode was used as a control, and the reaction was carried out for 15 days under 100% carbon dioxide.

[0067] The experimental results are as follows Figure 8 、 9 As shown by Figure 8 It can be seen that the acetic acid concentrations of the dual photoelectrode of this embodiment are close at -1.0V and -0.9V, which are 6.79g / L and 6.93±0.11g / L respectively. As the applied potential decreases, the acetic acid concentration gradually decreases, but at a potential of -0.6V, the acetic acid concentration can still reach 1.31g / L. Figure 9 It can be seen that not only is the acetic acid concentration in the control group lower than that in the example group, but acetic acid is no longer produced at a potential of -0.7 V. The results show that the use of dual photoelectrodes can effectively reduce the potential during the carbon dioxide reduction reaction, increase the electron transfer rate, and thus reduce the potential for microbial electrosynthetic reduction of carbon dioxide.

[0068] Finally, it should be pointed out that although the present invention has been described with reference to the current specific embodiments, ordinary technicians in this technical field should realize that the above embodiments are only used to illustrate the present invention and are not used to limit the present invention. Various equivalent changes or substitutions can be made without departing from the concept of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of the claims.

Claims

1. Application of a dual photoelectrode in promoting electrosynthesis of organic acids by microorganisms, characterized in that: The dual photoelectrode includes a photocathode and a photoanode, wherein the photocathode is ZIF-67 / g-C3N4 and the photoanode is BiVO4-RuO2-IrO2 / Ti; the mass ratio of ZIF-67 and g-C3N4 in the photocathode is 18:1; and the mass ratio of BiVO4 and RuO2-IrO2 in the photoanode is 3~8:

1.

2. The use according to claim 1, characterized in that The process of reducing carbon dioxide to produce acetic acid in a microbial electrosynthesis system comprises the following steps: In the microbial electrosynthesis system, the photocathode and the photoanode are placed in the cathode chamber and the anode chamber respectively, and the two chambers are separated by a proton exchange membrane. Autotrophic microorganisms are inoculated into the cathode chamber, and a potential of -0.6~-1.0 V vs Ag / AgCl is applied. The cathode chamber and the anode chamber are illuminated at the same time, and the visible light intensity is set to 20~50 mW / m -2 , carbon dioxide gas is introduced, and microorganisms photoelectrocatalytically reduce carbon dioxide to produce acetic acid.

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