Novel Iron-based Semiconductor Photoanodes For Photoelectrochemical Water Splitting

Global warming,energy shortage and environmental pollution has been a potential global crisis.Harvesting sunlight to produce clean hydrogen fuel remains one of the main challenges to solve the energy shortage and to overcome global warming.In this regard,photoelectrochemical cells(PEC)H2 is a promising method for providing clean energy with the use of soalr energy to water splitting.In general,the anodic reaction involves the oxidation of water in both cases.A high overpotential is necessary for water oxidation,because of the slow kinetics involves multi-electron and multi-proton transfer.Considerable attention has focused on development of high performance and commercial photoelectrochemical cells with an efficient and practical photoanode which can be used to oxidize water to O2 in a stable manner.It is widely studied on n-type semiconductors that can act as efficient photoanodes for solar water oxidation.A suitable photoanode materials should have a small band gap to make full use of visible light as well as a sufficiently positive valence band edge to provide sufficiently overpotential for the water oxidation.Over the past few decades,?-Fe2O3 has been intensively studied for PEC water oxidation because of its cheap price,non-toxicity,photochemical stability for long-term operation and small band gap etc.However,it would be confronted with the bottleneck due to the poor conductivity,short hole diffusion length and slow water oxidation kinetics.Since then,it is one of the key factors to find novel iron-based semiconductor photoanodes for applying this technology to PEC water splitting.In this dissertation,the PEC performances and their potential application value of h-YFeO3 and ZnFe2O4 are discussed.The main research contents are as follows1)Developing a novel rare earth iron-based perovskite photoanode,hexagonal YFeO3(h-YFeO3),for PEC water splitting.Rare earth elements are low-cost due to its abundant reserves.As well as iron-based oxides,they have good physical and chemical stability.h-YFeO3 with wide-spectrum response acts as a photoanode material for solar water splitting due to its ideal band gap(approximately 1.88 eV).h-YFeO3 and o-YFeO3 nanoparticles were synthetized vis a facile sol-gel method.Nanoparticle-assembled YFeO3 films,as photoanodes,were fabricated by electrophoretic deposition for PEC water splitting for the first time.As-prepared h-YFeO3 nanoparticle-assembled films have a saturation water-splitting photocurrent of approximately 0.08 mA cm-2 and a noticeable onset potential of 0.95 V vs.RHE under AM 1.5 G simulated sunlight(100mW cm-2).2)A facile spray pyrolysis method to prepare Ti-doped ZnFe2O4 for boosting photoelectrochemical water splitting.ZnFe2O4 is known as a good magnetic material,while there are also some reports on their photocatalytic performances for degradation or water splitting.However,ZnFe2O4 alone as a kind of photoelectrode material is rarely reported.There are various shortages for preparing ZnFe2O4 photoanodes and the PEC performances.As a result,a facile spray pyrolysis method was used to prepare pure and Ti-doped ZnFe2O4.The carrier concentration and the capability of charge carrier transport were obviously enhanced by introducing Ti4+ to substitute Fe3+in the ZnFe2O4 lattice.Thus,we can get a satisfactory results of photoelectrochemical performances.Under illumination of AM 1.5 G simulated sunlight,the photocurrent reaches 0.35 mA cm-2 and the onset potential is 0.95 V vs.RHE.