A Coupled System of Ni₃S₂ and Rh Complex with Biomimetic Function for Electrocatalytic 1,4-NAD(P)H Regeneration

NAD(P)H cofactor is a critical energy and electron carrier in biocatalysis and photosynthesis, but the artificial reduction of NAD(P)⁺ to regenerate bioactive 1,4-NAD(P)H with both high activity and selectivity is challenging. Herein, we found that a coupled system of a Ni₃S₂ electrode and a Rh complex in an electrolyte (denoted as Ni₃S₂-Rh) can catalyze the reduction of NAD(P)⁺ to 1,4-NAD(P)H with superior activity and selectivity. The optimized selectivity in 1,4-NADH can be up to 99.1%, much higher than that for Ni₃S₂ (80%); the normalized activity of Ni₃S₂-Rh is about 5.8 times that of Ni₃S₂ and 13.2 times that of the Rh complex. The high performance of Ni₃S₂-Rh is attributed to the synergistic effect between metal sulfides and Rh complex. The NAD⁺ reduction reaction proceeds via a concerted electron-proton transfer (CEPT) mechanism in the Ni₃S₂-Rh system, in which Ni₃S₂ acts as a proton and electron-transfer mediator to accelerate the formation of Rh hydride (Rh-H), and then the Rh-H regioselectively transfers the hydride to NAD⁺ to form 1,4-NADH. The artificial system Ni₃S₂-Rh essentially mimics the functions of ferredoxin-NADP⁺ reductase in nature.