Strong cation concentration effect of Ni–N–C electrocatalysts in accelerating acidic CO2 reduction reaction

Abstract

Understanding the intricacies of electron and proton transfer steps is imperative to exploiting the CO₂ reduction reaction (CO₂RR). Here, we highlight the significance of proton transfer by demonstrating that switching the proton supplier from H₂O to H₃O⁺ in a strongly acidic electrolyte (pH < 2) accelerates CO₂RR kinetics and allows Ni–N–C to achieve higher CO activities. Conversely, under mildly acidic conditions, CO production rate remains similar even with concentrated K⁺. Operando infrared spectroscopy supports pH-dependent changes in interfacial water structures, and density function theory simulations reveal a synergistic effect of cations and H₃O⁺ to stabilize intermediates. Ni–N–C, exhibiting a large overpotential for hydrogen evolution, promotes CO₂RR with prominent ^∗CO adsorption at pH 1.7 under higher cation concentrations. Its membrane electrode assembly (MEA) system achieves 95% CO₂ conversion efficiency and high CO selectivity for 50 h by optimizing proton and cation transport. This study presents opportunities to accelerate CO₂RR in acidic environments by H₃O⁺.