Enhancement of mass transfer efficiency and photoelectrochemical activity for TiO2 nanorod arrays by decorating Ni3+-states functional NiO water oxidation cocatalyst

Abstract Photoelectrochemical (PEC) water splitting is a promising technology to use solar energy. However, current metal oxides photoanode face the problem of sluggish water oxidation kinetic. In this study, we propose that the sluggish water oxidation process will cause slow mass transfer efficiency, which are rarely considered previously, especially at large bias and strong illumination. Mass transfer refers to the migration of reactants (like H2O, OH-) to the photoanode surface, reaction with holes, and diffusion of products (like radical and O2) to the bulk of the electrode. If the migration and diffusion are not fast enough, the mass transfer will inhibit the increase of PEC activity. This problem will be more apparent for nanorod arrays (NRAs), where the space among the NRAs is related narrow. Herein, we solve this problem by decorating the surface of the photoanode by NiO clusters with Ni3+ state as water oxidation cocatalysts. This work studies the PEC process from the viewpoint of mass transfer and firstly demonstrates that mass transfer in NRAs structure can be promoted by using Ni-based water oxidation cocatalyst.