First row transition metal dinuclear complexes for H2 production and CO2 reduction: from homogeneous to heterogeneous conditions

The hydrogen evolution reaction (HER) and the electrochemical reduction of carbon dioxide (CO 2 RR) are key processes for the development of sustainable energy and carbon-neutral technologies. Molecular catalysts based on earth-abundant metals offer unique opportunities to address these challenges, owing to their well-defined structures and tunable reactivity. In particular, bio-inspired dimetallic complexes have emerged as powerful platforms for promoting HER and CO 2 RR through metal-metal cooperativity, as exemplified by natural hydrogenases and carbon monoxide dehydrogenases. This review summarizes recent advances in molecular HER and CO 2 RR electrocatalysis based on bio-inspired dimetallic complexes composed of 3d transition metals. We highlight how dinuclearity, functional differentiation between metal centers, and second-coordination-sphere effects enable reaction pathways inaccessible to mononuclear systems, leading to enhanced activity, lower overpotentials, and improved selectivity. Both homogeneous catalysts and immobilized molecular systems operating under electrochemical conditions are discussed, with immobilization considered as a strategy to stabilize molecular catalysts while preserving their intrinsic reactivity. Overall, this review provides design principles for developing efficient and sustainable molecular electrocatalysts for hydrogen production and CO 2 valorization.