Rational design and preparation of composite nanostructures for solar water splitting

Artificial photosynthesis, i.e. solar water splitting, has been recognized as a green and promising way to produce clean energy fuel, hydrogen, and solve the fossil fuel shortage problem. My PhD study explores the strategies of improving the efficiency of artificial photosynthesis, and my work mainly focuses on using cheap and abundant materials to design efficient composite photoelectrode and nano-photocatalyst via enhancing light absorption and charge separation. In my first strategy, a novel design consisting of a sandwich structure of Fe2O3/Au/Fe2O3 was implemented and expected to work as an efficient photoanode for solar water splitting. Fe2O3 is a well-known cheap semiconductor which can utilize visible light energy. However, the efficiency is highly limited due to the poor charge separation. In the new design, the charge separation and photo-response are expected to be significantly improved by inserting one thin intermediate layer of Au within layers of Fe2O3 to form a tandem composite configuration. The SPR absorption from the intermediate Au layer and the resulted Plasmon-excitation induced electron transfer may enable wider light harvesting range and more efficient charge separation. All these may contribute to improve photocurrent response compared to Fe2O3 alone. The tandem layers were constructed by spin-coating of pre-synthesized Fe2O3 nanoparticles and sputtering of the gold intermediate layer. Tests on photo-current response proved that this sandwich structure exhibited much higher photo-activity efficiency as compared to the Fe2O3 photoanode. Mechanism studies on functions of Au intermediate layer well explained this enhancement. The results indicated that the Au intermediate layer was able to contribute in electron transfer as well as visible-light harvesting due to its plasmonic excitation. Such sandwich structure may be applied to other semiconductors to improve their performance in solar water splitting. DOCTOR OF PHILOSOPHY (MSE)