The microenvironment modulation enabled by mass transfer control to achieve efficient CO2 electroreduction in acidic membrane electrode assembly electrolyzers

Abstract

The utilization of zero-gap acidic membrane electrode assembly (MEA) electrolyzers for electrocatalytic CO₂ reduction presents a significant potential for practical application, owing to their capability to effectively mitigate salt precipitation on electrodes and minimize voltage losses. However, suppressing the hydrogen evolution reaction (HER) in an H⁺-rich environment remains a great challenge, demanding the development of advanced catalysts and precise modulation of the microenvironment. Here, we present an efficient strategy for converting CO₂ to CO using a Ni single-atom catalyst in acidic MEA-type electrolyzers. By controlling CO₂ and H⁺ mass transfer distance to modulate the microenvironment near the catalyst, a Faradaic efficiency for CO of up to 91.3 % is achieved at 700 mA cm⁻² and a pH of 1. Remarkably, the carbon utilization efficiency reaches 75.9 %, which exceeds the performance of both alkaline and neutral systems. The results reveal that, with high K⁺ concentration, moderate adjustment of mass transfer distance can optimize the distribution of CO₂ and H⁺ within the catalyst layer. This optimization improves the local CO₂ concentration and impedes the H⁺-enrichment, thereby suppressing HER during acidic CO₂ electrolysis. This work may inspire further optimization of the microenvironment within the catalyst layer for electrochemical CO₂ reduction in acidic electrolysis.