Highly Dense Atomic Fe-Ni Dual Metal Sites for Efficient CO2 to CO Electrolyzers at Industrial Current Densities

Abstract

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, 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.%). We developed a gas-phase chemical vapor deposition (CVD) approach to introduce single Ni sites into 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 (FECO) 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 FECO 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.