Cobaloxime coenzyme catalyzing artificial photosynthesis for hydrogen generation over CdS nanocrystals

Inspired by the natural photosynthesis, artificial photosynthesis (AP) systems comprised of light harvesters and redox catalysts have been widely investigated for photocatalytic H₂ generation. Here we report an artificial photosynthesis system composed of CdS nanocrystals as photosensitizer, cobaloxime coenzyme (Co(dmgBF₂)₂(H₂O)₂, Co) as catalyst, and lactic acid (LA) as electron donor for H₂ generation in a fully aqueous solution. This CdS/Co/LA system exhibits exceptional high photocatalytic activity under visible light, with initial H₂ generation rate increased by 4000% compared to CdS/LA, which is even 700% as high as that of CdS/Pt/LA. The excellent photocatalytic performance of CdS/Co/LA should be attributed to the efficient electron transfer from CdS to Co, leading to the reduced charge recombination, as well as the positively shifted Fermi level of CdS, decreasing the overpotential for H₂ generation. Moreover, the electron-coupling-electron-coupling (ECEC) mechanism, involving with the reduction of Co coenzyme followed by protonation and then reduction again, was supposed to produce the Co(II)-H intermediate active for catalyzing H₂ evolution from aqueous solution.