(65c) Design and Development of a Kilowatt Scale Stack for Carbon Dioxide and Carbon Monoxide Electroreduction

The electrochemical conversion of carbon dioxide (CO₂) to value-added products is a developing approach to offset CO₂ emissions. Previous research has driven ambient temperature electroreduction of CO₂ to single carbon products, such as carbon monoxide (CO) and formate, to technology readiness levels > 4. Higher value multi-carbon (C₂₊) products, such as ethylene and acetic acid, still suffer from low durability, low sustainability, and high energy demand when produced via direct CO₂ electroreduction. Therefore, an alternative to direct CO2 reduction is to undergo tandem CO₂-to-CO and CO-to-C₂₊ electroreduction. Tandem systems have been shown to have higher selectivity towards single products, specifically acetate, and improved conversion of CO₂-to-C₂₊ products. Our previous efforts focused on CO electroreduction have demonstrated that specially designed CO electrolyzers can continuously produce >25 wt% acetate and a maximum of 60 wt% acetate stream at >70% molar selectivities. Additionally, we coupled this CO electrolyzer with an ambient CO₂ reduction electrolyzer which converted >25% of fed CO₂ to acetate, a significant improvement over previous CO₂ electrolyzers. While performance metrics for these systems have greatly improved, scaling tandem systems to industrial levels still presents a considerable challenge. Here we present our recent work on scaling this tandem CO₂-to-CO-to-C₂₊ system from the commonly investigated small scale (< 10 W total power) to a more industry viable scale (~ 1 kW). We will first focus on our scaling efforts of the CO electrolyzer from the small scale of 5 cm² to the medium scale of 25 cm², where modification to the cathode and membrane allowed for over 130 hours of continuous operation at a total current of 7.5 A with no degradation in cell performance. We will then highlight our development of a 10 cell stack (1000 cm² total) capable of converting CO₂ to CO, CO to C₂₊ products, or tandem CO₂-to-CO-to-C₂₊ at operating powers >0.5 kW. Our investigation into parameters to improve system durability such as cooling, flow pattern design, gas/liquid feed patterns, membrane, and electrodes will also be discussed. Knowledge gained from the development of this stack system will allow for accelerated future development of tandem CO₂ electroreduction at pilot and industrial scales.