Application Of Bismuth Vanadate Based-photoanode For Photoelectrochemical Water Splitting System

As the energy crisis and environmental problems become more serious,it is extremely urgent to look for new green and sustainable energy solution.In recent years,one kind of artificial photosynthesis,which can utilize solar light as an energy source,hydrogen as an energy storage,and water as a raw material,is becoming more popular in energy conversion engineering and receives widespread attention.Photoelectrochemical cell?PEC?,based on the characteristics of semiconductor materials which photo-generated carriers can be motivated under illumination,can directly use solar energy to split water and convert it into hydrogen.It is one of the most promising and environment friendly hydrogen production technology.This paper will systematically introduce the synthesis and preparation of BiVO₄ semiconductor materials,as well as the modification strategy of BiVO₄-based photoanode,and its practical application in photoelectrochemical cells.Compared with wide bandgap semiconductor materials that can only absorb ultraviolet light,bismuth vanadate based-photoanode successfully split water into hydrogen by utilization of visible light and achieve higher photoelectric conversion efficiency in photoelectrochemical cell.The study achieves the following main results:1?The NiO/BiVO₄ heterojunction photoanode was successfully synthesized.With NiO loading,the photoelectrochemical performance of BiVO₄ photoanode is improved.The applied bias photoconversion efficiency of the NiO/BiVO₄ heterojunction photoanode reaches 0.72%,which is 4.8 times than that of the pure BiVO₄ photoanode.Our experiments and analysis show that the loading of NiO can simultaneously promote the separation of electron-hole pairs in the bulk phase of BiVO₄ and improve the surface oxygen evolution kinetics.At 0.6 V_RHE,the bulk charge separation efficiency of pure BiVO₄ photoanode is 51%,while that of NiO/BiVO₄ photoanode could reaches 65%.Furthermore,at 1.23 V_RHE,the surface charge transfer efficiency of pure BiVO₄ is 19%,and that of NiO/BiVO₄ photoanodes achieves 59%.Consequently,the photoelectrochemical performance of BiVO₄ photoanode is significantly improved by the synergistic effect of enhanced bulk charge separation and boosted surface charge transfer.2?We designed a BiVO₄-based dual photoanodes system,which improves the light absorption performance and shortens the charge transfer path.Two different nanostructured BiVO₄ photoanodes were successfully prepared:TBVO with high transmittance and NBVO with strong absorbance.By controlling the electrodeposition time of the film,synergy optimization between light trapping performance and charge separation efficiency of dual BiVO₄ photoanodes was obtained.At 1.23 V_RHE,the photocurrent densities of TBVO and NBVO reaches 1.98 mA cm^-2 and 2.11 mA cm^-2,respectively.In the tandem photoanode system,different optical characteristics of the two BiVO₄ photoanodes are optimized.The combined photocurrent density of the front TBVO electrode/back NBVO electrode reaches 3.03 mA cm^-2.The surface oxygen evolution kinetics of the photoanode is further improved by loading the co-catalyst.Finally,the applied bias photoconversion efficiency of tandem photoanode achieves 1.49%.