Solar Water Splitting Photoelectrodes Structured By Laser Interference Lithography

Abstract

One of the most environmentally friendly ways to produce hydrogen is by electrochemical splitting of water, using only sunlight as an energy source. In a photoelectrochemical cell with a semiconductor photoanode, water oxidation takes place on the surface of the electrode, at the interface between semiconductor and electrolyte. While photoelectrodes with structured surfaces tend to outperform planar ones, an increased surface area can be accompanied by enhanced surface recombination, which is deleterious to photoelectrode performance. Furthermore, the geometry of the surface structuring can influence light absorption and transport processes, and consequently the water splitting efficiency. In order to investigate the effect of surface structuring on water splitting performance, model photoelectrodes are needed, where the geometry and aspect ratio of the surface features can be controlled. In this work, we report on the use of laser interference lithography to generate precisely defined surface patterns on n+Si substrates. The geometry and aspect ratio of the surface features is determined during a reactive ion etching step. After etching, the samples are conformally coated with TiO2 by atomic layer deposition. Photoelectrochemical characterization of the electrodes is complemented by extensive physicochemical studies in an effort to identify the structural parameters with highest impact on performance in the photodriven water oxidation reaction. Figure 1