A bifunctional cobalt bis(terpyridine) complex for efficient water splitting to green hydrogen generation

Photocatalytic hydrogen evolution is considered to be the holy grail of artificial photosynthesis. Here, we report a novel bifunctional Cobalt bis-(terpyridine) complex on dual role in photocatalytic and electrocatalytic hydrogen generations. The integrated Co-complex as photosensitizer attached to TiO₂ shows an impressive hydrogen evolution reaction rate of 715 µmol g⁻¹ h⁻¹ with a high turnover number of 5718 and apparent quantum yield of 5.34%. The co-functionalized electrode shows significantly enhanced electrocatalytic activity through proton-coupled electron transfer path in CH₃CN/trifluoroacetic acid at 0.63 V with a turn-over frequency of 18.64 s⁻¹ at an optimal acid to catalyst ratio of 8:1. The electron-rich 4′-(5-(4-diphenylamino)phenylthiophen-2-yl)-2,2′:6′,2″-terpyridine π-conjugation synergistically enhances the catalytic performances and effectively transmits electronic charge to the terpyridine core via the thienyl spacer and supports mechanistic insight of the Co-center in the catalytic cycle. The simple design strategy of molecular catalysts with structural integrity is expected to offer an economically viable approach for practical energy conversion applications.