Interface Engineering Of Hematite Photoanodes For Highly Efficient Photoelectrochemical Water Splitting

Photoelectrochemical（PEC）water splitting as an ideal way to solve the energy crisis and environmental pollution has gained lots of interests in recent years.Among various semiconductors,hematite（α-Fe₂O₃）has been considered as a promising material for PEC water splitting due to its favorable optical band gap,excellent chemical stability in alkaline environment,abundance,and low cost.However,some drawbacks,such as poor electrical conductivity,short life and diffusion length of photogenerated holes,as well as slow oxygen evolution reaction kinetic,seriously restrict its PEC performance.In this thesis,different strategies have been developed to promote the PEC performance of hematite by improving the surface/interface properties,including the introduction of two-dimensional titanium carbide underlayer,the surface co-modification of Pt and P,the construction of BP（Black Phosphorus）/Fe₂O₃heterostructure have been developed.The main research contents are as follows:（1）A Ti₃C₂ MXene underlayer modified hematite（Ti-Fe₂O₃）photoanode was prepared via a simple drop-casting followed by hydrothermal and annealing processes.Owing to the bifunctional role of Ti₃C₂ MXene underlayer in improving the interfacial properties of FTO（fluorine-doped tin oxide,F:SnO₂）/hematite and providing Ti source for the construction of Fe₂TiO₅/Fe₂O₃ heterostructure in hematite nanostructure,the bulk and interfacial charge transfer dynamics of hematite are significantly enhanced,and consequently resulting in an improved PEC performance.Compared with the pristine hematite,the as-prepared Ti-Fe₂O₃ photoanode shows an increased photocurrent density from 0.80 m A cm^-2 to 1.30 m A cm^-2 at 1.23 V vs.RHE.Moreover,a further promoted PEC performance including a dramatically increased photocurrent density of 2.49 m A cm^-2 at 1.23 V vs.RHE and an obviously lowered onset potential is achieved for the Ti-Fe₂O₃ sample after the subsequent surface F-treatment and the loading of Fe NiOOH cocatalyst.（2）The Pt and P co-treatment can greatly boost PEC activity of hematite photoanode.The obtained Pt P-Fe₂O₃ photoanode exhibits a remarkably increased photocurrent density of 2.61 m A cm^-2 at 1.23 V vs.RHE,over 3 times higher than that of the pristine Fe₂O₃ sample.XPS,XAS and HRTEM characterizations show that in the P-treatment process,the Pt species can impel the proceeding of the reaction between PH₃ and Fe₂O₃,and consequently result in a more visible Fe PO₄ overlayer on the hematite surface.Therefore,under working conditions,the Fe PO₄ overlayer can be surface reconstructed to an efficient Fe OOH cocatalyst to provide more sites for the OH^-group capture and thus greatly accelerate the OER kinetics of hematite.Simultaneously,the Pt-incorporation significantly promotes the charge transport and separation in the Pt P-Fe₂O₃ photoanode by largely increasing the donor density.Hence the OER occurred at neighboring Fe OOH active sites is further facilitated.（3）A heterostructure photoanode by integrating BP nanoflakes and hematite was fabricated,in which the functional phosphate by the partially oxidation of BP could tightly bridge hematite and BP and improve the interfacial charge transfer.The well-matched band structures of BP and hematite,as well as the highly-efficient oxygenOER activity of BP can significantly facilitate the charge separation and transfer for enhanced water oxidation performance.As a result,the as-prepared heterostructure exhibits a high photocurrent density of 3.02 m A cm^-2 at 1.23 V vs.RHE,much better than that of the sample without BP modification.Furthermore,a remarkable photocurrent density of 3.81 m A cm^-2 at 1.23 V vs.RHE with good photostability can be achieved after the loading of Fe NiOOH cocatalyst.