Design and Optimization of Commercially-Relevant CO₂ Electrolyzers

The electrochemical reduction of CO 2 (CO 2 R) to value-added products is an attractive technology for tackling the rising atmospheric CO 2 levels and storing intermittent renewable energy into chemical bonds. Fundamental understanding of CO 2 R has progressed significantly in recent years and is critical in the development of industrial scale CO 2 R electrolyzers. 1 However, most of our understanding has been drawn from experiments optimized for aqueous-phase CO 2 R systems. These systems can be limited by mass transfer at fairly low current densities (~10 mA cm -2 ) due to unfavorable CO 2 /OH - interactions and large diffusion lengths. 2 To achieve commercially-relevant CO 2 R rates (> 100 mA cm -2 ), gas-diffusion electrodes (GDEs) play an important role as they can decrease the diffusion length of CO 2 to as small as 10 nm. 3 The thin diffusion boundary layers in GDEs allow higher CO 2 R current densities and CO 2 R to occur under environments with higher OH - concentrations. 4 However, with such drastic changes in operating condition and local environment, it is necessary to explore and better understand the transport and reaction overpotential intricacies in GDEs. For instance, conventional cell designs optimized for planar electrodes will suffer from large ohmic drops across the cell due to the higher current density; product distribution will also vary arising from higher CO 2 and OH - concentrations near the catalyst. 5 In this talk, we present a multiphysics modelling framework to design and optimize GDE systems performing CO 2 R. We then explore the performance and limitations of various cell designs guided by simulation results and examine potential methods for improving water management and tuning catalyst selectivity. Finally, we discuss the disparities in local environments between aqueous and GDE devices and propose strategies to reduce the gap in knowledge between the two systems. Acknowledgements This material is based upon work performed by the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy under Award Number DE-SC0004993. We thank David Larson for providing experimental data for CO 2 reduction on membrane-electrode assembly devices. D. Raciti and C. Wang, ACS Energy Lett. , 2018, 3 , 1545-1556. T. Burdyny and W. A. Smith, Energy Environ. Sci. , 2019, DOI: 10.1039/c8ee03134g. L. C. Weng, A. T. Bell and A. Z. Weber, Phys. Chem. Chem. Phys. , 2018, 20 , 16973-16984. S. Verma, X. Lu, S. Ma, R. I. Masel and P. J. Kenis, Phys. Chem. Chem. Phys. , 2016, 18 , 7075-7084. C. T. Dinh, T. Burdyny, M. G. Kibria, A. Seifitokaldani, C. M. Gabardo, F. P. G. de Arquer, A. Kiani, J. P. Edwards, P. De Luna, O. S. Bushuyev, C. Q. Zou, R. Quintero-Bermudez, Y. J. Pang, D. Sinton and E. H. Sargent, Science , 2018, 360 , 783-787.