Influence Of Extremely Rapid High Temperature Annealingon The Photoelectrochemical Water Splitting Performance Of ?-Fe₂O₃ Photoanode

Photoelectrochemical?PEC?water splitting is an efficient approach to convert solar energy into non-polluted chemical fuels to resolve energy supply and relatedenvironment pollution issues.Improvingcharge transportation and transfer abilities are the key issues to enhance PEC performance of photoelectrodes in the field.In the thesis,hematite??-Fe₂O₃?was used as photoanode due to its wide spectral response,an appropriate valance band position for oxygen evolution,and excellent chemical stability.We mainly study on the mechanism of extremely rapid high temperature annealing?ER-HTA?treatment to PEC performance ofhematite photoanode,and combining with interface modification to further increase photogenerated electron and hole separation efficiency,developing effective methodes to improve photoelectrochemical water splitting ofhematite photoanode.The main contents are as follows:To solve the matter of poor crystallinity and severe bulk recombination of hematite,FTO/Fe₂O₃ was used as photoanode and treated with traditional annealing method at500oCfor30 minutes and ER-HTA for 30 seconds,respectively.Our research indicated that ER-HTA could improve crystallinity and remove detrimental surface states,which contribute to enhanced charge transport ability in the bulk of hematite and charge transfer in the interface of Fe₂O₃/electrolyte,hence,substantially increase photogenerated charge separation.In addition,comparing to traditional high temperature annealing,ER-HTA can decrease theconductivity loss of FTOsubstrate and maximize the electron collection efficiency,thus,hematite photoanodesexhibiting an excellent PEC performance.To solve the strong charge recombination in the interface of ?-Fe₂O₃ and FTO substrate,introducing ultrathin underlayer of TiO₂ nanosheets?TiO₂ NS?with high crystallinity using layer by layer deposition to block the back transfer of electrons from FTO to hematite films and increase photogenerated electron and hole separation efficiency.Then,FTO/TiO₂/Fe₂O₃ photoanode were sintered by ER-HTA treatment.The studyindicated thatTiO₂ underlayer could suppress the recombination of electrons back transfer from FTOand Ti could diffuse into hematite films when sintered at high temperature.Ti4+ acting as donor dopants can elevate donor densities and enlarge band bending,which facilitate to photogenerated charge separation.Besides that,improved crystallinity,accelerated charge transportation,and increased interface charge transfer ability induced by ER-HTA treatment also contributed to the enhanced the photocurrent density of FTO/TiO₂/Fe₂O₃ photoanodes.In summary,these comparative studies have shown that ER-HTAcould decrease charge recombination in the bulk and surface of hematite photoanode.Meanwhile,the elements could diffuse easily into hematite acting as dopants.This annealing method is easy to operate and can be used to other materials or prepare doped hematite with other elements,and it is important for optimizingphotoanode materials in the development of photoelectrochemical water splitting.