Design and Diagnosis of high-performance CO2-to-CO electrolyzer cells

This work reports the design of a highly efficient neutral-pH CO2-to-CO zero-gap electrolyzer incorporating a new family of 2D layered framework-derived mesoporous single atom NiNC catalysts. What sets its performance apart from previous reports is not only the ~100% CO faradaic efficiency at applied current densities of up to 300 mA cm-2 at just above 3 V cell voltage and 40% total energy efficiency, but the uniquely low stoichiometric CO2 excess, stoich, of 1.2 that yields a molar CO concentration of around 70%Vol in the electrolyzer exit stream at 40% single pass CO2 conversion. This CO-rich exit stream and the low cost catalyst makes this electrolyze design ideally suited for cost-effective and energy efficient tandem cell configurations for high C2+ product yields. We also propose and validate a new kinetic diagnostic tool to help resolve mechanisms of undesired CO2 loss. We introduce an experimentally accessible carbon crossover coefficient, CCC, that describes the ratio between non-catalytic acid-base CO2 consumption and catalytically generated alkalinity. It offers an intuitive insight into the nature of the prevalent ionic transport. Combined with the stoich and the faradaic CO efficiency data, the CCC analysis offers practical guidelines toward improved electrolyzer designs. Our CCC-based cell diagnosis can be applied more broadly to all CO2 electrolyzers