Surface/Interface Modification And Water Splitting Properties Of Semiconductor Oxide Photoanodes

Photoelectrochemical water splitting is an essential strategy to solve the energy problem. The oxygen evolution occurred on photoanode is the key step to split water into hydrogen and oxygen and it is a hot topic that how to improve the water splitting performance of semiconductor photoanode. In this thesis, concentrated on the semiconductor oxide photoanode, we carried out our research on the controllable synthesis of micro/nano structures of semiconductor oxides, doping and surface modification for improving the light absorption and photogenerated electron hole pair separation, exploring effective approches to improve the semiconductor oxide photoanode photoelectrochemical properties. The main researches are as follows:TiO2nanowire arrays (NWAs) were used as photoanodes, which were further treated by hydrogen/nitrogen gas (10%) to improve the conductivity of the nanowires. Anatase/rutile heterojunctions were formed after further TiCl4treatment, which improved the electron hole pairs separation. Photoelectrochemical study indicated that the water splitting performance of TiO2nanowire arrays was significantly enhanced after the sequential treatment with hydrogen and TiCl4solution. The energy band diagram was proposed for the explanation of the enhancement in photoelectrochemical property, demonstrating the synergistic effect of hydrogen and TiCl4treatment.To solve the poor visible light absorption of photoanode of TiO2NWA, the surface plasmon effect of Au nanoparticles and surface doping effect of S anion were studied to improve the visible light photoresponse of TiO2NWAs. Our research indicated that the Au surface plasmon effect could improve the water splitting performance of TiO2NWAs under visible light, however, the photoresponse is still very weak; The sulfur anion surface doping TiO2NWAs were prepared via rapid thermal annealing, and better performance was achieved.8.5times photocurrent was observed under the potential of0.23V (vs. Ag/AgCl), while suggeated S surface doping was an effective method in enhancing visible light water splitting performance of TiO2NWAs.Given the low oxidation ability and small mobility of photogenerated holes in valence band which resulted strong recombination, we constructed an ultrathin TiO2blocking layer with good crystallinity by layer by layer deposition in the interface of and FTO substrates. Photoelectrochemical studies suggested that the blocking layer significantly enhanced water splitting performance of α-Fe2O3photoanode. The photocurrents were depended on the thickness of the underlayer, and an approximatly1.4nm thick underlayer led to the largest photocurrent which presented over forty fold increase of photocurrent and0.6V shift of photocurrent onset. Photocurrent transients measurements showed that TiO2underlayer suppress the back transfer of electrons from FTO to hematite film effectively, resulting significantly enhancement of visible light water splitting performance of planar a-Fe2O3thin film photoanode.To further suppress the recombinations originated from the small hole diffusion length, we fabricated α-Fe2O3(α-Fe2O3-NW) nanowire array by hydrothermal method and studied the blocking layer effect on the photoelectrochemical water splitting performance of α-Fe2O3-NW. Like in the planar structure, the photoelectrochemical performance of α-Fe2O3-NW was also improved in the presence of TiO2blocking layer, and stronger photocurrents were observed with the addition of H2O2as hole scavenger than that for the planar structure, indicating its potential application in the visible light photoelectrochemical water splitting.