Electrochemical reduction of carbon dioxide (ECR-CO₂) to formate is a valuable process due to its significance in the net-zero carbon and energy storage cycle, when coupled with renewable energy sources for electricity generation. While the process suffers from the scarcity of CO₂ supply to the electrode surface in a conventional liquid phase system limiting the efficiency to only low operating current density (typically less than 20 mA/cm²), the porous gas diffusion electrode assembly provides the continuous delivery of CO₂ at the catalyst-electrolyte interface thereby enabling the operation at higher current density by overcoming the mass transfer limitation^[1]. Since during the ECR process, CO₂ is known to transform through both the catalytic (electrochemical reaction at the electrode surface) and the non-catalytic (homogeneous acid-base reaction in an aqueous electrolyte) pathways^[2], it is imperative to deduce the true mass transfer characteristics of CO₂ at the gas diffusion layer containing porous catalyst layer in the gas and electrolyte phase, respectively.

In this work, the mass transfer coefficient of CO₂ in a single and two-phase system is experimentally determined using a limiting current technique. The experimentally deduced parameters are used to construct a simple one-dimensional (1D) steady-state mathematical model to study the mass transfer and kinetics effects during CO₂ electroreduction to formate. In the first phase of study, the computed current density and Faradaic efficiency of formate will be validated against the experimental data. The model will then be extended to investigate the effects of operating parameters and the gas diffusion electrode properties on the overall performance. Once optimized, the model, under given assumptions, will help in predicting the true behavior of the CO₂ electroreduction system.

References

[1] Rabiee, H.; Ge, L.; Zhang, X.; Hu, S.; Li, M. and Yuan, Z., Energy Environ. Sci., 2021, 14, 1959-2008

[2] Gupta, N.; Gattrell, M. and Macdougall, B., J. App. Electrochem., 2006, 36, 161-172

Acknowledgment

The authors gratefully acknowledge the financial support from Mitacs Accelerate Ph.D. Fellowship and Agora Energy Technologies Ltd.