Steering CO ₂ Electroreduction to Methane via Secondary‐Sphere Noncovalent Interactions in NHC‐Protected Copper Clusters

Copper‐based catalysts are promising for CO 2 reduction to hydrocarbons; however, selective CH 4 generation remains challenging because of the presence of competing pathways and an insufficient understanding of active site control. Herein, we develop a ligand‐microengineering strategy to synthesize a series of fully N‐heterocyclic carbene (NHC)‐protected Cu 4 O clusters, [Cu 4 ( μ 4 ‐O)] L 2 (PF 6 ) 2 ( L = 1a–1d , denoted as 2a–2d ), via a green and efficient ball‐milling approach. Of the four evaluated preparations, cluster 2c exhibits the optimal CH 4 Faradaic efficiency (), with a value of 67.5% ± 2.1% at –1.4 V versus RHE. Integrated in situ spectroscopy and density functional theory (DFT) calculations reveal that unique secondary‐sphere noncovalent interactions (hydrogen‐bonding and C–H···π) present in 2c provide additional stabilization for the key *CHO intermediate, maximizing CH 4 selectivity. This study not only demonstrates the unique advantages of NHC ligands in constructing stable and efficient copper cluster catalysts but also establishes a new paradigm for precisely steering CO 2 electroreduction selectivity through the rational design of noncovalent interactions within the secondary coordination sphere.