Photoelectrochemical Water Splitting with ITO/WO₃/BiVO₄/CoPi Multishell Nanotubes Enabled by a Vacuum and Plasma...

A common approach for the photoelectrochemical (PEC) splitting of water relies on the application of WO₃ porous electrodes sensitized with BiVO₄ acting as a visible photoanode semiconductor. In this work, we propose a new architecture of photoelectrodes consisting of supported multishell nanotubes (NTs) fabricated by a soft-template approach. These NTs are formed by a concentric layered structure of indium tin oxide (ITO), WO₃, and BiVO₄, together with a final thin layer of cobalt phosphate (CoPi) co-catalyst. The photoelectrode manufacturing procedure is easily implementable at a large scale and successively combines the thermal evaporation of single crystalline organic nanowires (ONWs), the magnetron sputtering deposition of ITO and WO₃, and the solution dripping and electrochemical deposition of, respectively, BiVO₄ and CoPi, plus the annealing in air under mild conditions. The obtained NT electrodes depict a large electrochemically active surface and outperform the efficiency of equivalent planar-layered electrodes by more than one order of magnitude. A thorough electrochemical analysis of the electrodes illuminated with blue and solar lights demonstrates that the characteristics of the WO₃/BiVO₄ Schottky barrier heterojunction control the NT electrode efficiency, which depended on the BiVO₄ outer layer thickness and the incorporation of the CoPi electrocatalyst. These results support the high potential of the proposed soft-template methodology for the large-area fabrication of highly efficient multishell ITO/WO₃/BiVO₄/CoPi NT electrodes for the PEC splitting of water.