Toward Simultaneous Achievement of Outstanding Durability and Photoelectrochemical Reaction in Cu₂O Photocathodes via Electrochemically Designed Resistive Switching

Photoelectrochemical (PEC) cells using Cu₂O, semiconductor photoabsorbers passivated by protection layers, show a trade-off between high photocurrent and stability because of the thickness of the energy band transport along the conduction band. Based on nanofilaments with non-volatile metal-like current flow characteristics in resistance-change memory devices, a strategically advanced conducting filament transport mechanism for vigorous and robust PEC operation is proposed. The breakdown-like electrochemical forming behavior effectively occurs with a rapid increase in current at ≈2 V (vs RHE). The fundamental properties of filaments, such as diameter, density, and conductivity, are controlled by varying the artificial compliance currents. This process does not require any top electrodes that obstruct light-harvesting and the injection of photo-charges into electrolytes or individual forming process with point-by-point sweeping, and provides electrochemical forming sites with homogeneous and dense distribution. Additionally, some photocorrosive sites that induce photocurrent degradation are passivated by the preferential photoelectrodeposition of co-catalysts. From the electrochemical filament forming process and selective Pt-photoelectrodeposition on filaments, the Cu₂O/AZO/TiO₂ photocathodes exhibit an unprecedented photocurrent density of ≈11.9 mA cm⁻² and open-circuit potential of 0.73 V and produce vigorous hydrogen and oxygen evolutions for over 100 h, even when the TiO₂ passivation film exceeds 100 nm in thickness.