A membrane electrode assembly-type cell designed for selective CO production from bicarbonate electrolyte and air containing CO₂ mixed gas

The electrochemical CO₂ reduction reaction (CO₂RR) combined with direct air capture (DAC) based CO₂ is a promising method for terrestrial carbon cycling. In this study, we have designed an all-Ag cathode and constructed a membrane electrode assembly (MEA) cell to utilize CO₂ capture solution, which can be produced by flowing air containing CO₂ mixed gas into an alkaline solution. A MEA consisting of a Ag nanoparticle catalyst sprayed on a Nafion membrane and a Ag electrode were used to construct a MEA cell (Ag MEA-cell). The Ag MEA-cell exhibited selective CO production without severe side reactions, such as the hydrogen evolution reaction, even when an aqueous electrolyte was used. The operation of the Ag MEA-cell using CO₂ capture solution, which was prepared by bubbling 60% air containing CO₂ mixed gas (40% CO₂ and 60% air, air-CO₂) into 1 M KOH, achieved CO production with 86% faradaic efficiency (FE_CO). Furthermore, the Ag MEA-cell significantly suppressed O₂ reduction and achieved FE_CO of 74% even when air-CO₂ was used as a CO₂ source.