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⁺.

more >> https://doi.org/10.1016/j.chempr.2025.102461