# Stabilizing Cu‐Based Photocathodes: From Interfacial Engineering to Advanced Architectures

## TL;DR

This review explores strategies to improve the stability of copper-based photocathodes for solar fuel production, focusing on methods to enhance their durability and performance.

## Contribution

The paper uniquely emphasizes stability over efficiency, offering a strategy-oriented perspective for durable Cu-based photocathodes.

## Key findings

- Seven key strategies are identified to improve the stability of Cu-based photocathodes.
- Synergistic combinations of strategies enable durable and efficient photoelectrochemical operation.
- Current challenges include scalability, fabrication compatibility, and real-world durability.

## Abstract

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.

This review examines the instability challenges of Cu‐based oxide photocathodes and presents several strategies that enhance their durability and performance in solar‐driven photoelectrochemical reactions. By linking structural, interfacial, and functional considerations, the article highlights how protective, selective, and synergistic approaches improve operational robustness and outlines future directions for scalable and practical solar‐fuel technologies.