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. A novel approach for enhancing the charge conductivity in photoelectrodes is proposed. It is designed for completely solving the trade‐off issue between photo‐charge transport and stability originating from the use of insulating protection layers. The electrochemical forming process suggested for the TiO2 protection layer on photocathodes draws inspiration from typical resistive switching behaviors in resistive‐type memory with metal/insulator/metal structures.