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 (FECO). Furthermore, the Ag MEA-cell significantly suppressed O-2 reduction and achieved FECO of 74% even when air-CO2 was used as a CO2 source.