Molecular copper systems for hydrogen production: from pre-catalyst activation to catalytic function
(2026) EES Catalysis — Vol. 4, n° 5, p. 1036-1077 (2026)
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Abudayyeh, Abdullah 
Llobet, Antoni
- Abstract
- The transition toward a carbon-neutral energy future places green hydrogen (H 2) at the forefront of sustainable fuel strategies. However, the large-scale deployment of hydrogen remains constrained by high production costs, underscoring the urgent need for the development of efficient and robust catalysts for the hydrogen evolution reaction (HER). Copper has played a role in hydrogen evolution research since the 1950s, when metallic copper electrodes were employed to probe the kinetics and mechanisms of hydrogen evolution in aqueous electrolytes. Despite this early involvement, systematic development of copper-based HER catalysts has emerged only in the past decade, driven largely by advances in CuO and Cu 2 O nanomaterials for photo-and electrocatalytic hydrogen production. More recently, molecular copper complexes have gained attention as catalysts or pre-catalysts for hydrogen evolution, revitalizing interest in copper-centered HER chemistry. This review surveys recent progress in molecular copper catalysts and pre-catalysts operating under photo-and electrocatalytic conditions. We first outline the key metrics used to benchmark HER performance. We then summarize the principal methods used to probe catalyst homogeneity and critically assess the evidences commonly employed to distinguish molecular from heterogeneous active species. Finally, we discuss current challenges and future prospects for molecular HER catalysts in general, and copper-based systems in particular. Broader context The development of sustainable hydrogen production technologies is central to the global transition toward carbon-neutral energy systems. Molecular electrocatalysts offer unique opportunities for understanding and improving hydrogen evolution reaction (HER) mechanisms through precise control of catalyst structure, electronic properties, and reaction environments. While cobalt, nickel, and iron molecular catalysts have been extensively explored, molecular copper systems remain comparatively underdeveloped despite copper being earth-abundant, inexpensive, and capable of rich redox and coordination chemistry. Recent years have witnessed growing interest in copper-based molecular catalysts for both electro-and photocatalytic hydrogen production, driven by advances in ligand design, mechanistic understanding, and catalyst integration strategies. At the same time, distinguishing true molecular catalysis from catalytically active heterogeneous species formed in situ has emerged as a critical challenge across the field. This review provides a comprehensive overview of molecular copper systems for HER, emphasizing the relationship between catalyst structure, catalytic performance, and catalyst integrity. By critically discussing benchmarking metrics, mechanistic pathways, and homogeneity assessment methods alongside recent catalytic examples, this work aims to support the rational development of next-generation copper-based HER catalysts and contribute to the broader advancement of sustainable hydrogen production technologies.
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Citations
Abudayyeh, A., Troian-Gautier, L., & Llobet, A. (2026). Molecular copper systems for hydrogen production: from pre-catalyst activation to catalytic function. EES Catalysis, 4(5), 1036-1077. https://doi.org/10.1039/d6ey00102e (Original work published 2026)