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

• The Au grating, covered by ALD with TiO2 layer is proposed for PEC water splitting. • The Au grating supports the excitation of SPP, responsible for TiO2 triggering. • The impact of materials parameters on PEC efficiency is described. • The proposed structure ensures efficient water splitting under NIR irradiation. • A significant increase of evolved hydrogen was observed under NIR illumination. 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 TiO 2 prevents the utilization of visible and near-infrared photons in the photo-electrochemical process. Photosensitization of TiO 2 with plasmon active nanostructures was proposed as a way to solve this problem but the optimal design of coupled TiO 2 -plasmonic nanostructures, as well as the exact mechanism of plasmon triggering, are still under debate. In this work, we propose a plasmon-based TiO 2 photosensitization, using the gold grating, covered by homogenous TiO 2 layer. The gold grating supports the excitation and propagation of surface plasmon polariton wave (SPP), which is responsible for TiO 2 triggering (unlike common localized plasmon resonance commonly used for TiO 2 activation). For the optimization of the present structure design, we studied the impact of TiO 2 layer thickness, illumination regime, and spatial distribution of plasmonic evanescent wave energy with regards to the mechanism of TiO 2 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 TiO 2 layer thickness the activation of catalytic activity is mostly due to the plasmon electric field, which is concentrated at the electrolyte/catalyst surface.