| In the21st century, human beings are confronted with two problems: energy andenvironment problems, due to the continuous industrialization development.Compared with traditional energy resources, as the precious gift of nature, solarradiation provides a seemingly infinite and environmental source of energy. Recently,scientists and engineers have sustained a vigorous search for the way to make use ofsolar energy. The photoelectrochemical water splitting is a effective way to transformthe solar energy into chemical energy. Since the photoelectric effect on TiO2havebeen discovered, photoelectrochemical water splitting on the semiconductor materilashas made significant progress.Among examined photoanodes, hematite (-Fe2O3) stands out since it has afavorable band gap, extraordinary chemical stability and cheapness.The theoreticalmaximum STH (Solar-to-hydrogen conversion efficiency) of-Fe2O3is as high as12.9%when-Fe2O3is used as photoanode. However, the reported efficiencies ofα-Fe2O3are notoriously lower than this predicted value. In a photocatalytic reaction,the separation and transportation of photoinduced electron and hole has an importanteffect on photocatalytic performance. The photoelectrochemical(PEC) performance ofhematite electrodes are adversely affected by bulk recombination, which are inducedfrom the low electron mobility and very short diffusion length of holes, and surfacerecombination which are induced from the poor oxygen evolution reaction andsurface states. Therefore, the key factor of PEC performance improvement is how toincrease the transportion and diffusion of photoindued holes and electrons and reduce the bulk combination and surface combination. Elemental doping is one of theeffective methods that could reduce the bulk combination in conductor materials. Theelectronic dopants have been frequently introduced into hematite to attain high carrierconductivities, which promotes the separation of photoindued holes and electrons andreduces the bulk combination. Surface treatment offers an obvious approach topassivate the surface state, which could reduce the surface combination. Here, weemploye the elemental doping and surface treatment to modity the-Fe2O3nanorodarrays. With the electrochemistry, photo electrochemistry test methods, the features ofphotogenerated charges in the-Fe2O3were revealed and finally utilized to direct thedesign and synthesis of effective photoanode materials theoretically andexperimentally.The thesis of this article contains the two parts below:1. The study on the photoelectrochemical water splitting performance of Ti4+doped-Fe2O3photoanode materials: We have prepared Ti4+doped-Fe2O3nanorodarrays through the hydrothermal method on FTO. Due to the lower doping level, thenano-structure has been retained. Electrochemistry test shows that the Ti dopantincreases the donor density of Ti4+doped-Fe2O3from6.0×1018to2.4×1019cm-3,which would increase the transportion of charge. Photoelectrochemistry test showsthat the smaller charge transfer resistance reduced the bulk combination and increasedthe PEC performance.2. The study on the photoelectrochemical water splitting performance of surfacetreatment on Ti4+doped-Fe2O3photoanode with Al3+: In this study, we employ thechemical bath deposion method to treat the surface of Ti4+doped-Fe2O3photoanodewith Al(NO3)3and urea. The SEM and HRTEM shows that the treat progress has noeffect on morphology. Electrochemistry test indicates that the PEC performanceenhancement is not mainly due to accelerated OER kinetics,increased donor densityor depressed back reaction. The analysis of the SPV transient and photoelectrochemistry test suggest that the main effect of surfacetreatment with Al3+is topassivate the surface states, decrease the surface recombination of charge at thesurface and promote the photo oxidation reaction.The whole reaearches provided a basic understanding in experimental adtheoretical for designing optimized,novel,high performance-Fe2O3photoanodematerials. |
PDF Full Text Request