Modification And Photoelectrochemical Properties Of ?-Fe₂O₃ Nanorod Photoanodes

Hydrogen,as an attractive clean secondary energy,is in line with people's pursuit of pollution-free and sustainable energy.An important way to obtain hydrogen energy is photoelectrochemical water splitting by utilizing the solar energy.Metal oxide semiconductors have become promising photocatalysts for photoelectrochemical water splitting.Among them,hematite has become one of the commonly used materials for photoanodes due to its low preparation cost,abundant resources,suitable forbidden band width,excellent visible light absorption capacity and stable photoelectrochemical properties.However,due to the high charge recombinations and the short diffusion length of holes,the actual photocurrent density of hematite is much lower than the theoretical value.Various modification methods have been tried to improve the performance.In this paper,two modification methods were used to improve the photoelectrochemical properties,including the surface modification of?-Fe₂O₃ with KCl flux and the method of electrochemical reduction treatment.The details are described as follows:Exploring the effect of adding KCl as a sintering aid on the photoelectrochemical properties of?-Fe₂O₃.It was found that the photocurrent density of KCl-hematite increases from 0.34 m A cm^-2for pristine hematite to 0.54 m A cm^-2 at 1.23 V_RHE,and further to 0.90 m A cm^-2 after Co-Pi deposition.The photocurrent onset potential of KCl-hematite also shows a cathodic shift of 120 m V compared to that of the pristine hematite.The photocurrent density in water and hydrogen peroxide demonstrates the KCl-hematite can suppress the recombinations of surface charges.The analysis of Mott-Schottky curves demonatrate the improved carrier density for KCl-hematite.the results of XRD and SEM characterizations confirm that KCl flux can enhance the crystallinity and orderliness of hematite on the surface.Exploring the effect of electrochemical reduction(protonation)on the photoelectrochemical properties of?-Fe₂O₃.Protons are injected into?-Fe₂O₃ to improve its photoelectrochemical performance by applying a negative potential on the hematite photoanodes.The effects of electrochemical reduction treatment were systematically compared on hematite photocurrent with low,medium and high carrier densities.For the low-doped hematite,the photocurrent density can be increased after polarization under a more negative voltage.For hematite with the medium and high carrier density,it is found that the photocurrent density can be improved when a 0.2-0V_RHE voltage is applied.The results show that the electrons can increase the donor density in the bulk of hematite,which is reflected by the improved charge separation efficiency and conductivity in bulk for protonated hematite.