Ultra-stable self-standing Au nanowires/TiO2 nanoporous membrane system for high-performance photoelectrochemical water splitting cells

Abstract

We introduce for the first time a core–shell structure composed of nanostructured self-standing titania nanotubes (TNT, light absorber) filled with Au nanowire (AuNW) array (electrons collector) applied to the photoelectrocatalytic water splitting. Its activity is four times higher than that of reference TNT–Ti obtained with the same anodizing conditions. The composite photoanode brings a distinct photocurrent generation (8 mA cm⁻² at 1.65 V vs. RHE), and a high incident photon to current efficiency of 35% obtained under UV light illumination. Moreover, the full system concept of selected constitutional materials, based on Au noble metal and the very stable semiconductor TiO₂, ensures a stable performance over a long-time range with no photocurrent loss during 100 on–off cycles of light illumination, after 12 h constant illumination and after one-month storage in air. We provide experimental evidence by photoelectron spectroscopy measurements, confirming that the electronic structure of TNT–AuNW is rectifying for electrons and ohmic for holes, while the electrochemical characterization confirms that the specific architecture of the photoanode supports electron separation due to the presence of a Schottky type contact and fast electron transport through the Au nanowires. Although the composite material shows an unchanged electrochemical band gap, typical for plain TiO₂, we find this material to be an innovative platform for efficient photoelectrochemical water splitting under UV light illumination, with significant potential for further modifications, for example extension into the visible light regime.