Decoupling Catalyst and Electrolyte Temperatures to Steer Activity and Selectivity of Electrochemical CO2 Reduction
Authors: Lee Sang-Won , Matthews Jesse E. , Cho Ara , Lin Tiras Y , Yap Kyra M. K. , Oh Dongrak , Xu Yi , Yan Katherine , Nielander Adam C. , Ablid-Pedersen Frank , Bajdich Michal , Lee Dong Un , Jaramillo Thomas F. 
Published: December 2024

Despite global initiatives to address climate change, the year 2023 was the hottest year ever recorded in history. The need for technologies to lower carbon emissions and to remove already emitted greenhouse gases is immense. There have been massive efforts to electrochemically drive CO2 conversion to value-added chemicals such as ethylene, ethanol, and acetone using renewable energy.(1) Copper (Cu) is notable for its ability to form high-value C-C bond compounds; however, selectivity and activity challenges remain. Efforts to tackle these issues have focused on catalyst, system and micro-environment developments,(2, 3) and among the critical factors, temperature plays an important role. Of reports that study temperature effects on CO2 reduction (CO2R), usually the entire system is controlled at the same temperature, including the working electrode, electrolyte, and reference electrode. Further, the range of accessible temperatures is usually limited to a range of 10 – 70°C due to the aqueous electrolyte freezing or evaporating.(4, 5)
This study focuses on the development and demonstration of an electrochemical system for decoupling the temperatures of the CO2R cathode and the electrolyte. This allows independent optimization of thermodynamic, mass transport, and kinetic, to improve both activity and selectivity of CO2 reduction. The temperatures are separately controlled from 0 – 140 °C for the working electrode, and from 0 – 70°C for the electrolyte. These temperature gradients result in clearly different activity/selectivity trends compared to when a single temperature controls the entire system. While maintaining electrolyte temperature and current density, a lower cathode temperature favored methane formation, whereas a higher cathode temperature favored CO formation. The Faradaic efficiency of ethylene was maintained at 20% despite the changes in the temperature of the cathode. Furthermore, reducing the working electrode temperature effectively restricted H2 formation down to 15%. We attributed this selectivity and activity change to the control of adsorption and desorption energies, thermal and chemical processes of CO2 conversion, and changopanoles in the CO2 solubility in the electrolyte through density function theory and computational fluid dynamics simulations.(6, 7) The system and method developed in this study can be translated to understanding the effects of mass transport and kinetics in other emerging electrochemical conversions for accelerating clean energy generation and achieving global sustainability goals
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