pH- and Cation-Induced Interfacial Hydrogen-Bond Network Reorganization Governs Acidic CO ₂ Electroreduction over Fe–N–C Catalyst

Beyond catalyst design, electrolyte effects provide an alternative to improve acidic CO2 electroreduction reaction (CO2RR) performance, yet the underlying mechanisms, especially dynamic interfacial behaviors of reactive species, remain unclear. Here we tailor the interfacial microenvironment of an Fe–N–C model catalyst for acidic CO2RR by tuning pH and concentration of a K2SO4 electrolyte, with a CO Faradaic efficiency of 95.7% and a maximum CO partial current density of 103.9 mA cm–2 in 0.6 M K2SO4 with pH 2. Finite element simulations indicate that a delicate balance between the alkaline interfacial microenvironment and acidic bulk electrolyte is favorable for inhibiting HER while maintaining sufficient CO2 availability. In situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) measurements and ab initio molecular dynamics (AIMD) simulations reveal that both pH and cation can reorganize the hydrogen-bond network of interfacial water and thus facilitate CO2 accessibility and adsorption over Fe sites, resulting in improved CO selectivity in acidic media.