Extension of charge separation distance over isolated dual-metal sites in metal-organic frameworks for efficient CO₂ photoreduction

Solar-driven photocatalytic CO₂ reduction receives intensive attention while facing the challenge of achieving a single product with high conversion efficiency. Herein, we report a feasible strategy for regulating isolated dual-metal sites on semiconductive metal-organic frameworks (MOFs) for efficient CO₂ photoreduction. The atomically isolated CuM dual-metal (M = Co, Ni, Fe) sites on two-dimensional CuM-THQ (THQ = tetrahydroxyquinone) with high activity are obtained. Impressively, the CuCo dual-metal sites present a CO production rate of 1626 µmol g⁻¹ h⁻¹ and near 100 % selectivity under visible-light irradiation. The presence of Co sites induces the metal-to-metal charge transfer (MMCT) process in CuM dual-metal sites, enabling the extension of charge separation distance and thereby accelerating reacting kinetics. Moreover, the declined 3d-orbital occupancy on CuCo dual-metal sites facilitates CO₂ adsorption and reduces the energy barrier of the rate-determining step (*CO₂ to *COOH). Meanwhile, the isolated Cu sites provide a weak desorption of *CO intermediates to produce exclusive CO. As a result, the synergist effect of isolated dual-metal sites on MOFs contributes to the high performance of CO₂-to-CO.