High carbon efficiency in CO-to-alcohol electroreduction using a CO reservoir

The electrochemical CO₂ reduction reaction (CO₂RR) has progressed but suffers an energy penalty from CO₂ loss due to carbonate formation and crossover. Cascade CO₂ to CO conversion followed by CO reduction addresses this issue, but the combined figures of carbon efficiency (CE), energy efficiency (EE), selectivity, and stability require improvement. We posited that increased CO availability near active catalytic sites could maintain selectivity even under CO-depleted conditions. Here, we present a heterojunction carbon reservoir catalyst (CRC) architecture that combines copper nanoparticles with porous carbon nanoparticles. The pyridinic and pyrrolic functionalities of CRC can absorb CO enabling high CE under CO-depleted conditions. With CRC catalyst, we achieve ethanol FE and CE of 50% and 93% (CE∗Faradaic efficiency [FE] = 47%) in flow cell at 200 mA cm⁻², fully doubling the best prior CE∗FE to ethanol. In membrane electrode assembly (MEA) system, we show sustained efficiency over 85 h at 100 mA cm⁻².