Industrial amine blends enable efficient CO electrosynthesis in reactive capture

Abstract

Reactive capture of CO₂ (RCC) integrates CO₂ capture and electrochemical conversion into carbon monoxide (CO), avoiding the energy-intensive CO₂ regeneration required in conventional CO₂ electrolysis. While single-component amines have been used in prior RCC systems, they suffer from limited CO energy efficiency (<15%) due to sluggish CO₂ release. In contrast, the norm in industrial CO₂ capture is to blend amines for a favorable combination of absorption rate, CO₂ loading capacity, and release energetics. Here, we explore whether blending amines could likewise benefit reactive capture. Using aqueous blends of monoethanolamine (MEA) and methyldiethanolamine (MDEA), we find a strong correlation between bicarbonate concentration in the post-capture solution and CO faradaic efficiency (FE). However, under industrial absorption conditions, the blend with the highest bicarbonate content did not always yield the best CO FE: although MDEA increased bicarbonate concentrations, it also increased the viscosity, hindering CO₂ mass transport and increasing cell resistance. These competing effects highlight that, for efficient RCC, the composition must balance CO₂ absorption kinetics and capacity for capture, as well as CO₂ availability and transport properties for conversion. Screening the performance of binary and commercial amine blends, we find a CO energy efficiency (EE) of 31% at 50 mA cm⁻²—a 2.4-fold improvement over single-amine systems.