Highly dense atomic Fe-Ni dual metal sites for efficient CO₂ to CO electrolyzers at industrial current densities

Carbon-supported, atomically dispersed, nitrogen-coordinated metal sites (e.g., Fe and Ni) are arguably the most promising catalysts for the electrochemical reduction of CO₂ to CO due to their unique catalytic properties and the use of earth-abundant elements. However, conventional single metal sites are constrained by their structural simplicity, causing either too weak or too strong absorption/desorption of multiple critical intermediates (e.g., *COOH and *CO). Current catalysts also suffer from ultra-low loadings (<1.0 wt%) of atomic metal active sites in catalysts, leading to inadequate performance for CO₂-to-CO conversion. Here, we develop dual Ni/Fe metal site catalysts with significantly increased atomically dispersed metal loadings (up to 4.8 wt%). A gas-phase chemical vapor deposition (CVD) approach to introducing single Ni sites was integrated with Fe₂O₃/ZIF-8 precursors, followed by an optimal thermal activation. The optimized CVD-Ni/Fe-N-C catalyst exhibited remarkable electrocatalytic performance for the CO₂ reduction to CO in a continuous membrane-electrode-assembly electrolyzer, achieving a maximum CO faradaic efficiency (FE_CO) of 96% at a current density of 700 mA cm⁻² in a near-neutral electrolyte. Furthermore, a desirable but challenging acidic flow-cell electrolyzer was designed using this dual metal site catalyst to improve CO₂ utilization, accomplishing a FE_CO of up to 95% at a CO partial current density close to 600 mA cm⁻². Density functional theory (DFT) calculations suggest a synergetic effect between Fe-Ni pairs facilitating *COOH intermediate formation and *CO desorption simultaneously during CO₂ to CO conversion. This is key to breaking the linear scaling relationship of conventional single-metal site catalysts during the CO₂ reduction reaction.