Electrolyzer energy dominates separation costs in state-of-the-art CO2 electrolyzers: Implications for single-pass CO2 utilization

In low-temperature CO2 electrolysis, a fundamental trade-off exists between maximizing electrolyzer performance and minimizing downstream CO2 recovery. By coupling a down-the-gas-channel electrolyzer model with a techno-economic analysis, we find that the optimal single-pass CO2 conversion for ethylene production is typically low-on the order of 5%-10%-although larger optima are found if the H2 faradic efficiency is very low. Similarly, strategies for eliminating carbonate crossover require more energy than downstream gas separation if they increase the cell potential by X0.2 V; however, when CAPEX are accounted for, this break-evenvoltage increases to -0.4 to 0.8 V for electricity prices vary-ing from 6c/kWh to 1.5c/kWh. These findings are a consequence of the low energy requirements of industrial gas separation relative to electrochemical CO2 reduction. Under most circumstances, main-taining near-optimal electrolyzer performance is more important than reducing or eliminating downstream gas separations.

Automated summary

In low-temperature CO2 electrolysis, the optimal single-pass CO2 conversion for ethylene production is typically low, around 5%-10%, but larger optima can be found with very low H2 faradic efficiency. Eliminating carbonate crossover strategies require more energy than downstream gas separation if they increase the cell potential by X0.2 V. However, when considering CAPEX, the break-even voltage increases to -0.4 to 0.8 V for electricity prices ranging from 6c/kWh to 1.5c/kWh. These findings highlight the importance of maintaining near-optimal electrolyzer performance over reducing or eliminating downstream gas separations.