Photoelectrochemical Water Splitting with ITO/WO/BiVO/CoPi Multishell Nanotubes Enabled by a Vacuum and Plasma Soft-Template Synthesis.

A common approach for the photoelectrochemical (PEC) splitting of water relies on the application of WO porous electrodes sensitized with BiVO 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), WO, and BiVO, 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 WO, and the solution dripping and electrochemical deposition of, respectively, BiVO 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 WO/BiVO Schottky barrier heterojunction control the NT electrode efficiency, which depended on the BiVO 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/WO/BiVO/CoPi NT electrodes for the PEC splitting of water.