Design And Fabrication Of Bismuth Vanadate Based Nanoheterostructures And Their Photoelectrochemical Performance

The rapid development of modern industry has changed people’s lives tremendously.However,the ensuing global energy shortage and environmental deterioration are becoming more and more serious,which have also become an important reason for hindering the development of many countries.Therefore,the development of new renewable energy is imperative.Solar energy has the advantages of cleanness,security,cheapness and abundant reserves.It is the most abundant renewable energy resource and can fully meet the global energy demand.However,due to some disadvantages of solar energy such as intermittent and severe weather dependence,it is a challenge to capture,exploit,store and distribute solar energy.Hydrogen is expected to replace fossil energy for large-scale applications thanks to its high calorific value,cleanliness and non-pollution,which is considered to be an ideal form of energy storage.Photoelectrochemical hydrogen production technology is a very promising energy technology because it combines the advantages of solar energy and hydrogen energy,realizing the conversion of solar energy into hydrogen for storage.Since the first discovery of TiO2 for photoelectrochemical(PEC)water splitting in 1972,researchers have developed a range of semiconductor materials photoanodes including WO3,Fe2O3,BiVO4,TaON,CuWO4,and so on.Among these materials,bismuth vanadate(BiVO4)has attracted extensive attention due to its suitable band gap(～2.4 eV),abundant element reserves,low cost,and favorable conduction band edge location for water splitting.However,BiVO4 suffers from severe bulk photogenerated carrier recombination,slow surface oxygen evolution kinetics,a large number of surface states,and serious corrosion of the material under illumination,greatly limiting its photoelectrochemical water splitting efficiency.In order to solve these problems,BiVO4-based heterojunction photoanodes were constructed to realize the regulation of the light absorption,charge transport and surface oxygen evolution reaction kinetics of the electrode for obtaining an efficient and stable water splitting photoanode finally.The specific research contents are as follows:1.Cu2S/BiVO4 heterostructure and its surface cocatalyst modification.The threedimensional nanoporous BiVO4 based electrode material was prepared by electrodeposition and subsequent heat treatment.The Cu2S/BiVO4 nanoheterojunction was constructed by loading Cu2S nanoparticles on BiVO4 by a simple continuous ionic layer adsorption and reaction method.In order to protect the heterojunction from being oxidized and accelerate surface oxygen evolution reaction kinetics,a thin CoFe-OH amorphous layer was uniformly deposited on the surface by electrodeposition.The research results show that the loading of Cu2S can effectively broaden the light absorption range of BiVO4 and the CoFe-OH can greatly improves the surface oxygen evolution kinetics process,which significantly improves the photoelectrochemical performance and stability of water splitting.The photocurrent density of CoFe-OH/Cu2S/BiVO4 increased from 2.03 mA/cm2 to 3.07 mA/cm2,and it can maintain stably photocurrent density for 60 min without obvious decrease at 1.23V vs.RHE.This work demonstrates the possibility of sulfides as efficient and stable catalysts for solar-driven water oxidation reactions.2.Ni@NiO/BiVO4 heterostructure and its photoelectrochemical water splitting performance.The nanoporous BiVO4 photoanode was prepared by a similar method mentioned above firstly,and then the Ni nanoparticles prepared by a solution method were spin-coated on BiVO4-Subsequently,the obtained samples were annealed at 400℃ in air,and the surface Ni was oxidized to NiO partly to form a Ni@NiO core-shell structure.The results show that the Ni@NiO core-shell structure not only acts as an excellent cocatalyst for oxygen evolution,but also can passivate the surface states and improve the hole transfer capability of the photoanode,thereby greatly improving the photoelectrochemical performance of the composite photoanode.The Ni@NiO/BiVO4 photoelectrode can approach a photocurrent density of 2.6 mA/cm2 at 1.23 V vs.RHE,and a surface charge separation efficiency of nearly 80%,which is much better than those of unmodified BiVO4(1.8 mA/cm2,64%).In addition,Ni@NiO/BiVO4 also exhibits good photoelectrochemical stability,and the final photocurrent density maintained by Ni@NiO/BiVO4 is 2.2 times that of BiVO4 after long-term PEC testing.