The Surface Modification And Photoelectrocatalysis Property Research Of Hematite

As a new energy source with great potential,hydrogen has high calorific value,no pollution,easy storage and wide sources.Photochemical cells can store solar energy in the form of hydrogen,and the preparation of cheap and stable catalysts is the focus.?-Fe₂O₃ has a suitable bandgap?².1 eV?,high theoretical photoelectric conversion efficiency,excellent chemical stability and low cost.It is a very promising photoelectric material.However,its shortcomings are obvious:poor conductivity,short photogenerated electron-hole diffusion length,resulting in easy recombination of photogenerated carriers and high oxygen evolution potential,which seriously hinder its application and development.Ion doping and surface modified OER catalyst are mainly used to overcome these shortcomings and improve the PEC performance.In this paper,?-Fe₂O₃ was prepared by hydrothermal method,and then surface modification was carried out by loading cocatalyst on?-Fe₂O₃.Physical characterization was carried out by means of Raman,SEM,TEM,UV,XPS,etc.LSV,IPCE,EIS and Mott-Schottky plots were used to study its photocatalytic properties,and the structure-activity relationship and mechanism of the catalysts were explained.It is divided into the following four parts:?1?Ti-doped hematite photoanode nanoarrays decorated with cobalt-iron phosphate?CoFePi?ultrathin nanolayers greatly enhanced bulk and surface charge separation efficiency,as well as passivate surface states for promoting the PEC water oxidation activity.The synergistic interactions of CoFePi nanolayers with the Ti-Fe₂O₃ photoanode yield current densities of 1.75 mA/cm² in 0.1 M KOH at 1.23 V_RHEHE under AM1.5 G illumination,which is 3 fold higher than bare hematite photoanode.Collectively,theresultsdemonstratedthatthesynergistic Ti-Fe₂O₃/CoFePi photoanode is promising for PEC water oxidation for hydrogen production.?2?By constructing appropriate chemical reaction on Ti-Fe₂O₃ nanoarrays,cobalt-iron borate?CoFeBi?nanolayers were formed on Ti-Fe₂O₃ surface and a large number of oxygen vacancies were formed at the same time.The PEC properties of photocathodes after chemical reduction were studied.The results show that the generation of oxygen vacancies greatly reduces surface recombination and open voltage,improves charge transfer efficiency.The loading of CoFeBi enhances the kinetics of water oxidation at the interface,so that the photocurrent density of 1.82 mA/cm² can be obtained in 0.1 M KOH at 1.23 V_RHE.?3?Ultrathin phosphate ion?Pi?nanolayers were modified on Ti-Fe₂O₃nanoarrays.In 0.1M KOH solution,the photocurrent density of Ti-Fe₂O₃/Pi photocathode reaches 1.56 mA/cm² at 1.23 V_RHE,which is significantly higher than that of Ti-Fe₂O₃?0.92 mA/cm²?and pure?-Fe₂O₃?0.5 mA/cm²?.The photoelectrochemical analysis shows that the ultrathin Pi nanolayers can passivate the surface of Ti-Fe₂O₃,inhibit charge recombination,increase the photovoltaic voltage and reduce the initial potential.Moreover,by improving the injection efficiency of surface charge,the kinetics of surface water oxidation is improved,and the photocurrent is enhanced.?4?Fe_2-xB_xO₃ nanolayer was formed on the surface of the?-Fe₂O₃nanoarrays by a dipping-annealing method.Photoelectrochemical studies show that Fe_2-xB_xO₃ accelerates surface water oxidation kinetics,reduces surface recombination,improves charge interfacial injection efficiency,and greatly enhances PEC water oxidation performance of?-Fe₂O₃photoanode.The photocurrent density at 1.23 V_RHE can reach 1.25mA/cm² in 1 M KOH solution.In addition,the phase charge separation efficiency and conductivity of?-Fe₂O₃ were improved by doping B element,and the photocurrent density reached 1.0 mA/cm² under the same test conditions.