Second Coordination Sphere-Regulated Nickel Sites Enable Enhanced Photocatalytic Eight-Electron Reduction of Carbon Dioxide to Methane

The photocatalytic eight-electron reduction of CO2 to CH4 holds great promise for fuel production but suffers from sluggish kinetics and poor selectivity due to intricate multiproton/electron transfer. Herein, we report an atomic-scale regulation of nickel sites via constructing a multifunctional second coordination sphere (SCS) by leveraging Fe3+-mediated supramolecular assembly with a metalloporphyrin regulator, dramatically boosting CH4 generation. Specifically, the SCS-tailored catalyst achieves a high CH4 production rate of 420.3 μmol·g–1·h–1 with 91.0% selectivity and suppresses H2 evolution, significantly surpassing the pristine counterpart and ranking among the most efficient systems reported thus far. Fine structural characterizations reveal that SCS, constructed through electrostatic interaction and hydrogen bonding, induces lattice compression and generates lower-valence Niδ+ sites. In situ XAFS, in situ FTIR, and density functional theory calculations demonstrate that the SCS strengthens CO2 binding, stabilizes *CO for protonation, and reduces energy barriers for *COOH formation, thus leading to the significantly enhanced CH4 activity. In addition, SCS-mediated electronic modulation optimizes the conduction band position, enhancing charge separation and transfer efficiency to synergistically accelerate the CO2-to-CH4 conversion. This work establishes an SCS engineering paradigm to atomically master complex multielectron photoreductions, offering a universal design principle for advanced catalysts.