Highly Controlled Nanostructured CuO Photocathodes

Today, Cu-based photocathodes are increasingly employed due to Cu abundance, environmental benefits, and high photoelectrocatalytic activity. However, despite significant advances in this field, the development of controllable methodologies to produce highly crystalline, structurally tailored, and reproducible CuO nanoarchitectures remains challenging. Here, we propose an alternative route for the fabrication of nanostructured CuO photocathodes that can address these goals. We have grown highly controlled CuO nanoparticles onto fluorine-doped tin oxide, FTO, electrodes by using a sputter gas aggregation source. The photoelectrochemical response was optimized by different thermal treatments, tuning the environment, duration, and temperature. We have systematically studied the influence of the treatments on the structure of the films and their correlation with the photoresponse of the photoelectrodes. We showed that the thermal treatments first induced nanoparticle growth, which is subsequently followed by coalescence. The best photoelectrochemical performance was obtained after complete recrystallization in the form of CuO nanocubes (thermal treatment in vacuum, 18 h, 500 °C), resulting in a porous film photocathode. This electrode presents maximum current densities of -1.2 mA/cm², an applied bias photon-to-current efficiency of 1.4%, and a moderate operational stability for bare CuO photocathodes operating in aqueous electrolyte. The structural changes with improved crystallinity play a crucial role in favoring charge transport and reducing the recombination of photogenerated electron-hole pairs, thereby enhancing the photocurrent generated by the photocathode. Therefore, this methodology for producing CuO nanostructured films emerges as an alternative approach for fabricating photoelectrocathodes.