Metastable CuFe Solid-Solution Nanocrystals with Fe Active Sites for Efficient CO2 to CO Electroreduction

Abstract Owing to its tunable electronic structure, the CuFe alloy demonstrates significant potential as a catalyst for the CO2 reduction reaction (CO2RR). However, the thermodynamic and kinetic incompatibility between Cu and Fe poses a challenge to the controlled preparation of CuFe solid-solution nanocrystals. In this work, metastable CuFe solid-solution nanocrystals are prepared via a polyol method to overcome the lattice mismatch between Cu and Fe at room temperature. 57Fe Mössbauer spectroscopy combined with electron microscopy supports a uniform distribution of Fe within the Cu matrix. Among all samples, Cu-0.4 at.% Fe exhibits the highest Faradaic efficiency (FE) of 91.8% toward CO at a current density of 75 mA cm–2 in a flow cell, which is higher than those of Cu (65.1%) and Cu-1.1 at.% Fe (75.6%) nanocrystals. It also retains a CO FE above 85% during an 11 h stability test. Impressively, the active sites for CO2RR are Fe rather than the well-known Cu. In situ Raman spectroscopy, KSCN poisoning experiments, and density functional theory (DFT) calculations reveal that Fe-centered active sites in the CuFe solid-solution nanocrystals play a dominant role during CO2RR and alter the reaction pathway by regulating the adsorption behavior of key intermediates, thereby promoting the highly selective formation of CO. This work provides a new design strategy for developing low-cost, highly CO-selective electrocatalysts and offers important insights into the synergistic effects of metastable CuFe solid-solution alloys.