Breaking Supercapacitor Symmetry Enhances Electrochemical Carbon Dioxide Capture

Abstract

Electrochemical CO2 capture using supercapacitors offers an energy-efficient approach for mitigating CO2 emissions, but its performance is thought to be hindered by competing CO2 capture and release processes at two identical porous carbon electrodes. To address this, we introduce an asymmetric supercapacitor-battery hybrid system with porous carbon and nonporous metallic zinc as the working and counter electrodes, respectively. The CO2 capture capacity continuously increases as the charging rate decreases with a maximum capacity of 208 mmolCO2 kg−1, surpassing that of an analogous symmetric supercapacitor. Our findings suggest that breaking device symmetry enhances CO2 uptake in capacitive systems by suppressing competing processes, while the noncapacitive zinc counter electrode simplifies the mechanistic picture of capacitive CO2 capture. Extending this approach, we develop asymmetric supercapacitors with two different porous carbon electrodes, demonstrating a 200% increase in CO2 capture capacities at low charging rates. In summary, this study pioneers asymmetric systems for electrochemical CO2 capture and establishes a general strategy to enhance both understanding and performance.