Light Guided Placement of Platinum Catalysts on Silicon Microwire Array Photocathodes

Abstract

Silicon microwire arrays decorated with catalyst particles are a promising design for photoelectrochemical conversion of water and sunlight to hydrogen fuel. This device geometry reduces the material quality requirements for the semiconductor due to its tolerance of short carrier diffusion lengths and allows for direct integration within flexible polymer membranes which are required for product separation. In a water splitting photocathode, electrons generated within the microwires are collected at catalyst sites to electrochemically reduce water to hydrogen gas. When highly active catalysts such as platinum are utilized, the collection efficiency of electrons at catalyst sites can become a limiting factor in device performance. Because the carrier generation rate within silicon microwires is non-uniform, determining the optimal distribution of catalyst particles is a challenge. Controlled photoelectrodeposition of metals on silicon microwires can be used to localize catalysts near regions where carrier generation is highest. To demonstrate this concept, silicon microwire arrays were decorated with platinum via controlled photoelectrodeposition. The illumination wavelength during photoelectrodeposition was varied to control the location of platinum catalysts on the microwire arrays. The influence of the distribution of catalyst on the performance of hydrogen evolving microwire array photocathodes was investigated.