Cation-Directed Mechanistic Bifurcation in Electrochemical CO2 Reduction: Rate-Determining Step Switching and Opposite Temperature Dependencies on Ni Single-Atom Catalysts

Abstract While electrolyte cations are widely recognized as a key regulator of electrochemical CO2 reduction (CO2RR) activity, whether different cation classes merely modulate reaction rates or fundamentally redirect the underlying rate-determining step (RDS), and consequently the system's response to environmental variables, remains mechanistically unresolved. Herein, we elucidate the distinct CO2RR kinetic dependencies on a Ni-nitrogen-doped carbon single-atom (Ni–NC) catalyst using a systematic series of alkali-metal, organic quaternary ammonium, and ammonium cations. Using electrochemical analyses and in situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy, we reveal a cation-induced switch in the RDS, supported by differences in intermediate distributions and protonation on Ni–NC. These divergent mechanistic pathways dictate opposite temperature depend…