Low-dimensional materials for high performance photoelectrochemical water splitting electrodes

The solar water splitting is the third generation of solar energy utilizing technology for future energy problem. Through the past years, the technology has been amazingly meliorated, and theoretical basis has been enormously progressed. In recent days, much endeavor has been dedicated to enhancing solar water splitting efficiency. For further improvement, we need to deeply understand and explore charge generation and transport in photoelectrodes and charge transfer at interfaces between the electrodes and water.

One of the most appropriate strategies for this concept would be grafting plasmonics to the photoelectrodes generally based on oxide semiconductors. We present photoelectrochemical properties of TiO₂ thin films and TiO₂ nanorods with 0-dimensional (0D) plasmonic Au nanoparticles. Our results clearly reveal the substantial enhancement of photoactivity in TiO₂ by incorporating Au plasmonic nanoparticles. We show that the enhancement is strongly dependent on the shape of the 0D Au nanoparticles, suggesting that the localized surface plamonic resonances with high electromagnetic fields act as really effective hydrogen evolution catalysts on oxide-based photoanodes.

Another appropriate strategy to develop efficient and stable water splitting photoelectrodes is the utilization of a surface protection layer which prevents photocorrosion of semiconductor photoelectrodes such as Si. We show that solution-processed 1D TiO₂ nanorods can be used as protection and antireflective layer for Si photocathodes. It is also shown that 1D TiO₂ nanorods themselves have catalytic effect to split water. Using the 1D TiO₂ nanorods, we demonstrate the state-of-the-art performance of Si photocathodes.

Finally, we are going to show chemical vapor deposition method to grow wafer-scale 2D transition metal disulfides (TMDs) such as MoS₂ and WS₂. We transfer large-area thin films composed of 2D TMDs to Si substrate to prepare efficient and stable photocathodes for solar water splitting. Atomically thin TMD films play important roles in hydrogen evolution reaction. We show the catalytic effect of 2D TMDs to dramatically lower charge transfer resistances at the semiconductor (p-Si)/electrolyte (water) interfaces. Compared with a bare Si photocathode, substantially enhanced stability of TMD/p-Si photocathodes is also presented.