Synergy Between Metal and Molecular Catalysts for (Photo)electrocatalytic 1,4-NADH Regeneration

(Photo)electrocatalytic NAD(+) reduction provides a promising approach for 1,4-NADH regeneration, but it remains challenging to achieve both high activity and selectivity. Here, we found prominent synergetic effects between various metals (Cu, Fe, Co, and Ni) and Rh-based complexes (M and M') for electrocatalytic NAD(+) reduction, promoting the activity and selectivity simultaneously. Typically, the normalized activity of the Cu and M coupled system is 15.6 times that of M, while Cu alone shows negligible activity at the same potential. Meanwhile, the selectivity of 1,4-NADH is enhanced from 63.3% for Cu alone to as high as 95.3% for the coupled system. We found that the transfer of hydrogen atoms from the metal electrode to the M complex accelerates the formation of metal-hydride active species, which catalyzes the regioselective production of 1,4-NADH. This work provides a universal strategy of coupling proton-reduction electrocatalysts and regioselective molecular catalysts for efficient (photo)electrocatalytic 1,4-NAD(P)H regeneration.