Low-Spin State Single-Atom Ni Catalyst for Electrochemical Carbon Dioxide Reduction at Ampere-Level Current.

Developing earth-abundant, selective, and low-overpotential electrocatalysts for the reduction of carbon dioxide represents a novel paradigm for a sustainable carbon economy. Here, we present advances in the understanding of trends in the reduction of CO2 to CO of Ni single-atom catalysts (SACs) supported by ordered mesoporous carbon (OMC). Characterizations using X-ray absorption spectroscopy (XAS), temperature-dependent magnetic susceptibility (M-T), and density functional theory (DFT) calculations show that the spin-state transitions from high-spin (HS) to low-spin (LS) for Ni SACs are induced by an asymmetric trigonal bipyramidal NiN2O3 configuration. Combined with surface-enhanced infrared absorption spectroscopy in the attenuated total reflection mode (ATR-SEIRAS), kinetic isotope effect (KIE), and density functional theory calculations, the rate-determining step is demonstrated to be the formation of *COOH. The unique NiN2O3 structure with a low-spin state significantly enhances the adsorption of *COOH due to the formation of stable Ni-C bonds and intermolecular hydrogen bonding. In electrocatalytic CO2 reduction to CO, the low-spin Ni SAC achieved an industrial-level performance, with a current density toward the CO product (JCO) up to 1 A cm-2, a turnover frequency (TOF) of 107,200 h-1 at ∼99% Faradaic efficiency (FE), and a half-reaction energy efficiency of 66%. This study establishes an electronic structure mechanistic framework for CO production from M-N/Ox moieties, thereby providing guidelines for the design of CO2 reduction catalysts.