Photoelectrochemical Water Splitting Of BiFeO₃ Photocathodes For Hydrogen Evolution Reaction

With the growth of the global population and the expansion of the total economic volume,the consumption of fossil fuels has become an indispensable part of daily life.However,the excessive consumption of traditional fossil fuels leads to various environmental problems.Therefore,it is imperative to develop a clean,low-cost,renewable green energy.Photoelectrochemical（PEC）water splitting technology can directly convert solar energy into hydrogen energy for use,which is an effective way to solve energy and environmental problems.Among many photoelectrode materials,bismuth ferrite（BiFeO₃）has attracted considerable attention due to its stable chemical properties and narrow band gap.However,the photoelectrocatalytic properties of BiFeO₃are not impressive because of the low carrier mobility and the limitation of the solar energy conversion efficiency.To overcome the mentioned drawbacks,we improve the photoelectrochemical performance of BiFeO₃by ion doping and constructing composite materials with other semiconductors in this work.The composite material which is favorable for photogenrated carrier separation was prepared in one step by flame method.Bi and Fe precursor films were obtained on FTO by spin coating,and BiFeO₃/Bi₂O₃photocathode was successfully fabricated on the basis of the precursor films by flame annealing.Compared to the BiFeO₃photoelectrode,the BiFeO₃/Bi₂O₃composite shows a positive shift in the onset potential,reaching a photocurrent density of-0.21 m A/cm²at the potential of 0.38 V_RHEand the photon-to-current efficiency is significantly improved.The formation of composites effectively reduces the recombination of photogenerated carriers,promotes interfacial charge transfer,provides more active sites for surface reactions,and thus improves the photoelectrocatalytic activity of the photocathode.The location of BiFeO₃band is regulated by Sm³⁺doping to promote photoelectrocatalytic water reduction.Precursor thin films were prepared on FTO by spin coating,and Sm³⁺doped BiFeO₃thin films with different concentrations were successfully synthesized by flame annealing.Among them,Bi_0.95Sm_0.05Fe O₃photocathode exhibits the most excellent photoelectrochemical performance,and the photocurrent density can reach-0.1061 m A/cm²at 0 V_RHEpotential,which is 5.6 times higher than that of BiFeO₃photocathode at the same potential.From the microstructure,optical and photoelectrochemical properties,we concluded that the higher photoelectrocatalytic activity of Sm³⁺doped BiFeO₃thin films comes from the stronger absorption ability of visible light;the higher carrier concentration and the more activity sites.Meanwhile,oxygen vacancies were introduced in semiconductor photoelectrocatalysts by Sm³⁺doping,which facilitates the effective separation and migration of photoinduced electron-hole pairs as well as hinders the recombination of photogenerated carriers.