Bio-inspired Cobalt Catalyst Enables Natural-Sunlight-Driven Hydrogen Production from Aerobic Neutral Aqueous Solution

Hetero-axial cobalt complexes are known for their oxygen-tolerant photocatalytic hydrogen production activity, mostly in organic solvents. Here, variable combinations of peripheral basic groups are explicitly positioned around an existing complex framework to generate an enzyme-inspired minimal outer coordination sphere (OCS) scaffold. This catalyst design strategy yields a series of water-soluble, upgraded versions of imidazole-linked cobaloximes. The presence of fringe protic functionalities ensures the formation of a dynamic and water-mediated proton relay. This appended proton relay allows us to probe imidazole-bound cobaloxime in pure aqueous conditions. It exhibits highly efficient electrocatalytic (TOF ∼4,900 s−1) and photocatalytic (TON ∼12,000) hydrogen production in neutral water compared to its relatively moderate performance in organic media. The catalyst retains its activity (TON ∼22), even under natural sunlight (sunny day in Gandhinagar) in aerobic aqueous solution, emphasizing the importance of OCS features for producing robust, natural-condition-ready, synthetic catalysts.