Molecularly Crosslinked Dense Ni-N4-O/Ni Clusters for Scalable CO2 Electroreduction in Acidic and Alkali-Metal-Free Media.

Electrochemical CO2 reduction (ECO2R) in pure acid or water offers a promising solution to carbon loss and salt precipitation. However, these harsh conditions pose significant challenges, including intensified hydrogen evolution reaction (HER). Herein, guided by density functional theory (DFT) calculations, the Ni-N4-O/Ni clusters are identified as active sites that can simultaneously promote *COOH formation and suppress HER. Based on this insight, a molecular-crosslinking strategy is developed to construct a NiX@NiN4-O catalyst with high-density Ni-N4-O/Ni clusters. The resulting catalyst achieves a high CO Faradaic efficiency (FECO) of 93.6% at an industrial-level current density of 1 A cm-2 in strongly acidic media (0.25 m K2SO4, pH = 1). Even in dilute sulfuric acid (pH = 2) without K+, it retains a FECO of 70.9%. Notably, the catalyst also exhibits remarkable performance in a pure-water-fed membrane electrode assembly (MEA) system using both cation and anion exchange membranes (CEM and AEM), with FECO values of 92.7% and 94.8%, respectively.