Design of hybrid Au grating/TiO2 structure for NIR enhanced photo-electrochemical water splitting

Abstract

Titanium oxide is commonly considered as an effective catalyst for photo-electrochemical water splitting due to its low cost, high activity, and perfect stability. However, a wide bandgap of TiO2 prevents the utilization of visible and near-infrared photons in the photo-electrochemical process. Photosensitization of TiO2 with plasmon active nanostructures was proposed as a way to solve this problem but the optimal design of coupled TiO2-plasmonic nanostructures, as well as the exact mechanism of plasmon triggering, are still under debate. In this work, we propose a plasmon-based TiO2 photosensitization, using the gold grating, covered by homogenous TiO2 layer. The gold grating supports the excitation and propagation of surface plasmon polariton wave (SPP), which is responsible for TiO2 triggering (unlike common localized plasmon resonance commonly used for TiO2 activation). For the optimization of the present structure design, we studied the impact of TiO2 layer thickness, illumination regime, and spatial distribution of plasmonic evanescent wave energy with regards to the mechanism of TiO2 activation. Obtained results proved that the proposed structure can be used for efficient photo-electrochemical water splitting and hydrogen production under irradiation with NIR photons of 700–1000 nm wavelengths. It was also verified that for a certain TiO2 layer thickness the activation of catalytic activity is mostly due to the plasmon electric field, which is concentrated at the electrolyte/catalyst surface.