Tailoring acidic microenvironments for carbon-efficient CO2 electrolysis over a Ni–N–C catalyst in a membrane electrode assembly electrolyzer

Abstract

CO₂ electrolysis converting CO₂ into valuable fuels and chemicals powered by renewable electricity shows great promise for practical applications. However, it suffers from low energy efficiency and carbon efficiency due to severe carbon loss in alkaline and neutral electrolytes. Here we present a carbon-efficient CO₂ electrolysis strategy using a zero-gap acidic membrane electrode assembly electrolyzer. The microenvironments of a Ni–N–C catalyst (such as local concentrations of H⁺/K⁺ and CO₂) are turned by optimizing the anolyte composition (pH, K⁺) and input CO₂ pressure. Under optimal conditions, acidic CO₂ electrolysis over the Ni–N–C catalyst achieves a CO faradaic efficiency of 95% at a total current density of 500 mA cm⁻², corresponding to a CO production rate as high as 13 mL min⁻¹. An energy efficiency of 45% for CO production is obtained at pH 0.5 and the CO₂ loss is reduced by 86% at 300 mA cm⁻², compared to alkaline CO₂ electrolysis. Density functional theory calculations reveal that the co-existence of H⁺ and K⁺ plays a crucial role in stabilizing the initial *CO₂ intermediate, resulting in enhanced CO formation.