Copper tungstate photoanodes: recent progress and prospects for efficient solar water splitting

Copper tungstate (CuWO₄) is a ternary metal oxide that has attracted sustained interest as a photoanode material for photoelectrochemical (PEC) water oxidation due to its visible light absorption, favorable band alignment, high theoretical photocurrent density and intrinsic chemical stability in oxidative environments. Despite these advantages, its performance remains limited by poor charge transport, short carrier diffusion lengths and pronounced recombination, making its PEC ability highly sensitive to synthesis-dependent characteristics established during fabrication. In this review, we revisit the evolution of CuWO₄ photoanodes, beginning with earlier studies that established its fundamental activity and examine how subsequent work has clarified the interplay between electronic structure, bulk properties and interfacial processes. Particular attention is given to the role of Cu oxidation states, defect chemistry and emerging insights into surface energetics and water adsorption, which collectively influence charge transfer kinetics at the semiconductor electrolyte interface. We provide a critical assessment of fabrication strategies, including solid-state, vapor phase and solution-based methods with emphasis on how precursor chemistry, stoichiometry and processing conditions govern phase formation, crystallinity and microstructural evolution. The influence of annealing temperature and atmosphere is discussed in relation to phase purity, defect populations and morphological stability, alongside challenges with controlling multiphase formation and compositional gradients. Strategies to improve performance, such as doping, morphology engineering, heterostructure design, and cocatalyst integration, are evaluated in the context of their impact on overall PEC performance and impact on bulk and electronic properties of the material. Through this analysis, key limitations and opportunities are identified, underscoring the need for more studies to advance CuWO₄ toward efficient and scalable PEC systems.