Stabilizing Cu-Based Photocathodes: From Interfacial Engineering to Advanced Architectures

Copper-based oxides, including Cu₂O, CuO, CuBi₂O₄, CuFeO₂ and CuFe₂O₄ have emerged as promising photocathode materials for solar-driven photoelectrochemical (PEC) reduction reactions such as hydrogen evolution (HER), carbon dioxide reduction (CO₂RR), and nitrogen reduction (NRR). Their appeal lies in the combination of their earth-abundance, low toxicity, and suitable optoelectronic properties. However, the practical deployment of these materials is hindered by their intrinsic instability under operating conditions, primarily due to photocorrosion, interfacial charge recombination, and limited carrier transport. This review provides a comprehensive overview of recent strategies developed to improve the stability of the most studied Cu-based photocathodes in relevant reported works. Specifically, seven key approaches are discussed: (i) optimization of electrical contact with the substrate, (ii) use of hole-selective layers, (iii) electron-extraction overlayers, (iv) protective coatings, (v) surface passivation strategies, (vi) integration of co-catalysts, and (vii) synergistic strategies. Particular emphasis is placed on how each strategy addresses specific degradation mechanisms, and how synergistic combinations can enable durable and efficient PEC operation. Finally, the present review outlines current challenges related to scalability, fabrication compatibility, and real-world durability, and highlights emerging directions in materials design and device integration. Unlike previous reviews that predominantly compare device efficiencies, this work places stability at its core, providing a strategy-oriented perspective on how Cu-based photocathodes can be made durable under operational conditions. By systematically connecting structure, interface, and function, this work aims to guide the development of robust Cu-based photocathodes for sustainable solar fuel production.