Optimizing Catalyst Location within Nanostructured Photoelectrodes.

The influence of catalyst location within nanostructured photocathodes on conversion efficiency is reported. Highly uniform vertically aligned silicon nanowire (VA-SiNW) arrays prepared via colloidal lithography and metal-assisted chemical etching were used as a model-system photoelectrode for the hydrogen evolution reaction. Using three-dimensional electrochemical axial lithography (3DEAL), the Pt catalyst was located either at the top, center, or bottom of the SiNWs, or uniformly throughout the array. The SiNWs were spatioselectively passivated with an insulating coating to limit charge recombination at the silicon-electrolyte interface. Our results show that the most efficient catalyst position is the center of the SiNW, with an enhanced short-circuit photocurrent that is ca. 2 times and 2.9 times higher compared to top and uniform Pt distributions, respectively. This is attributed to better charge extraction in the nanowire center that mitigates losses due to charge recombination while optimizing light absorption within the SiNW, as revealed by three-dimensional electromagnetic simulations.