Photoilluminated Redox-Processed Rh₂P Nanoparticles on Photocathodes for Stable Hydrogen Production in Acidic Environments

While photoelectrochemical (PEC) cells show promise for solar-driven green hydrogen production, exploration of various light-absorbing multilayer coatings has yet to significantly enhance their hydrogen generation efficiency. Acidic conditions can enhance the hydrogen evolution reaction (HER) kinetics and reduce overpotential losses. However, prolonged acidic exposure deactivates noble metal electrocatalysts, hindering their long-term stability. Progress requires addressing catalyst degradation to enable stable, efficient, and acidic PEC cells. Here, we proposed a process design based on the photoilluminated redox deposition (PRoD) approach. We use this to grow crystalline Rh₂P nanoparticles (NPs) with a size of 5-10 on 30 nm-thick TiO₂, without annealing. Atomically precise reaction control was performed by using several cyclic voltammetry cycles coincident with light irradiation to create a system with optimal catalytic activity. The optimized photocathode, composed of Rh₂P/TiO₂/Al-ZnO/Cu₂O/Sb-Cu₂O/ITO, achieved an excellent photocurrent density of 8.2 mA cm^-2 at 0 V_RHE and a durable water-splitting reaction in a strong acidic solution. Specifically, the Rh₂P-loaded photocathode exhibited a 5.3-fold enhancement in mass activity compared to that utilizing just a Rh catalyst. Furthermore, in situ scanning transmission electron microscopy (STEM) was performed to observe the real-time growth process of Rh₂P NPs in a liquid cell.