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 CO 2 electroreduction reaction (CO 2 RR) 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 CO 2 RR by tuning pH and concentration of a K 2 SO 4 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 K 2 SO 4 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 CO 2 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 CO 2 accessibility and adsorption over Fe sites, resulting in improved CO selectivity in acidic media.