Construction, Modification And Photoelectrochemical Water Splitting Properties Of Fe₂O₃ Thin Films

Hydrogen generation via photoelectrochemical water splitting（PEC）is regarded as one of the most effective way to utilize solar energy,alleviating energy crises and environmental problems.α-Fe₂O₃ is supposed to be one of the most promising photoanodes for solar water splitting due to its suitable band gap,absorption of 40%sunlight,abundance,stability in aqueous solution,non-toxicity and low cost etc.However,the efficiency of solar energy conversion is still far below the theoretical value due to its poor photogenerated charge carriers lifetime,short hole-diffusion length,extremely high electron-hole recombination rate,poor conductivity and slow surface reaction kinetics etc.Therefore,recent studies mainly focus on the modification of the photoanode material to improve the PEC performance.Aiming at the problems of α-Fe₂O₃,grain goundaries decorating and element gradient doping have been successfully carried out,and the corresponding PEC properties of those materials were tested and analyzed.The specific works are as follows:1.Boosting hematite photoelectrochemical water splitting by decoration of TiO₂ at the grain boundariesTo boost the charge transfer of hematite photoanode,Fe₂O₃ with TiO₂ decoration in the grain boundaries has been constructured based on a simple chemical bath deposition.Such strategy resulted in dramatically improved photocurrent density up to 2.90 mA cm2 at 1.23 V vs.RHE.Further investigations reveal that the enhanced PEC performance can be attributed to the improved charge separation efficiency,increased charge carrier density,as well as the enlarged contact area between electrolyte and photoanode.Moreover,modification of the Fe₂O₃/TiO₂ nanoporous film with FeOOH co-catalyst could achieve a photocurrent of 3.15 mA cm^-2 at 1.23 V vs.RHE.2.Gradient Ti-doping in hematite photoanodes for enhanced photoelectrochemical performanceTwo types gradient Ti-doped Fe₂O₃ photoanodes（Fe₂O₃-Ti and Ti-Fe₂O₃）were prepared to enhance charge transport and separation efficiency.Interestingly,Fe₂O₃-Ti and Ti-Fe₂O₃ photoanodes exhibit almost identical PEC performance with photocurrent of 1.50 mA cm^-2 at 1.23 V vs.RHE.However,the onset potential of Ti-Fe₂O₃ photoanode displays a cathodic shift of 80 mV comparing with that of Fe₂O₃-Ti photoanode.Moreover,the charge separation efficiencies on the surface（ηsurface）for Fe₂O₃-Ti and Ti-Fe₂O₃ can both reach up to 96%at the higher potential range from 1.30 to 1.50 V vs.RHE,which are among the top values in the record of hematite-based photoanodes without co-catalyst.Further investigation demonstrates the forming of gradient Ti doping is not dependent on the location of the TiO₂ layer,but mainly affected by the high annealing temperature.