Photoelectrochemical Water Splitting Property Research Of BiVO₄/Cobalt-based Co-catalyst Ternary Composite Electrodes

With fossil fuel supply constraints,increasing energy demand and environmental pollution,it has become urgent to explore clean energy alternatives to traditional fossil fuels.Hydrogen energy stands out among low-carbon energy sources due to its abundant reserves,non-polluting combustion products and no attenuation of energy,which can effectively reduce the share of fossil fuels and increase the level of clean energy development.Photoelectrochemical（PEC）water splitting for hydrogen production is considered one of the ideal ways to solve the energy crisis,because it can rationally utilize solar energy while producing clean and storable hydrogen through the coupling of semiconductors and catalysts.Among various semiconductor for water splitting,monoclinic bismuth vanadate（BiVO₄）photoanode has narrow bandgap（2.4 e V）and favorable band edge position,which allows visible light capture and water oxidation.However,the performance of photoelectrochemical water splitting is not very satisfactory due to its own electron-hole recombination and poor water oxidation kinetics.To address the above issues,constructing heterojunction,designing hole transport layer（HTL）and loading oxygen evolution catalyst（OEC）was used to enhance the light absorption capacity while improving the BiVO₄ photoanode PEC performance.The following are the specific contents:1.BiVO₄/PANI/Co（OH）₂ photoanode was prepared via photo-assisted electrodeposition and impregnation method.The results showed that the photoelectric performance of the BiVO₄/PANI/Co（OH）₂ electrode was significantly enhanced at 1.23V vs RHE,with photocurrent density and charge separation efficiency of 4.9 m A/cm² and84%,respectively.PANI as a hole transport layer accelerated the hole transfer to the co-catalyst surface and improved the water oxidation kinetics.Simultaneously,the formation of p-n heterojunction between BiVO₄ and PANI effectively promoted the separation of electron-hole pairs and facilitated charge transfer rate of the BiVO₄ semiconductor,thus enabling excellent PEC performance.2.BiVO₄/CQDs/CoF₂ composite photoanode was synthesized on BiVO₄ by simple impregnation method.The results showed that BiVO₄/CQDs/CoF₂ photoanode acquired photocurrent density of 4.5 m A/cm² at 1.23 V_RHE under simulated sunlight irradiation（AM 1.5G,100 m W/cm²）.The outstanding PEC performance is due to the interaction between CQDs and CoF₂,which increased the light absorption of BiVO₄ photoanode and enhanced the water oxidation kinetics of BiVO₄ surface,thus improving the charge separation efficiency.3.BiVO₄/BNQDs/CoBi photoanode was constructed by impregnation and photo-assisted electrodeposition.It was found that BNQDs could significantly improve the light capture performance of BiVO₄ nanoarrays.Meanwhile,BNQDs as the hole transport layer can quickly transfer holes to the co-catalyst interface,which promoted the carrier transport of BiVO₄ photoanode.BiVO₄/BNQDs nanocomposite structure remarkably improved the photogenerated charge separation performance by forming type Ⅱ heterojunctions.CoBi as a co-catalyst further facilitated the kinetic performance of water oxidation at the intrinsic BiVO₄ interface.By optimizing the loading of CoBi on the BiVO₄/BNQDs electrode,the final composite electrode achieved a photocurrent density of 5.1 m A/cm² and the separation efficiency of up to 92%,which were 3.5 and 1.1 times higher than those of the pure BiVO₄ photoanode,respectively.