Recent advances in carbon capture create new opportunities for recycling CO₂ into liquid fuels to store intermittent electrical energy¹. One option is to co-electrolyze CO₂ and H₂O at high temperature using solid oxide electrolysis cells (SOECs). Although promising, the factors controlling rates of CO₂ and H₂O reduction in SOECs are not well understood, hampering development^2,3. Traditional electrochemical techniques have difficulty resolving the various factors and mechanisms governing CO₂ and H₂O reduction. This limitation can potentially be overcome through the use of linear and non-linear electrochemical impedance spectroscopy (EIS and NLEIS) in conjunction with dynamic measurement of gas-phase species using mass spectrometry.

In regards to co-electrolysis, mixed ionic electronic conductors (MIEC) have gained interest as alternatives to nickel-yttria stabilized zirconia (Ni-YSZ) because the active region is not limited to the triple phase boundary and they are more stable in reducing environments³. Gadolinia-doped ceria coupled with perovskite La_1-xSr_xCr_1-yMn_yO_3-δ (GDC-LSCM) has been a particularly well studied MIEC³.

We are currently conducting NLEIS and EIS measurements of CO₂ reduction, water reduction, and co-electrolysis reduction experiments on button cells composed of GDC and LSCM as the working electrode with electrolyte YSZ under various temperatures and gas compositions. Gas atmospheres surrounding the cells contain various mixtures of water, CO₂, CO, H₂, and carrier gas such as Ar or N₂. Currently hypothesized mechanisms/models on H₂O and CO₂ reduction are considered and scrutinized against NLEIS data in order to further reveal the nature of water and CO₂ reduction.

References

1. Graves, C., Ebbesen, S. D., Mogensen, M., & Lackner, K. S. (2011). Sustainable hydrocarbon fuels by recycling CO2 and H2O with renewable or nuclear energy. Renewable and Sustainable Energy Reviews, 15(1), 1–23. https://doi.org/10.1016/j.rser.2010.07.014
2. Graves, C., Chatzichristodoulou, C., & Mogensen, M. B. (2015). Kinetics of CO/CO2 and H2/H2O reactions at Ni-based and ceria-based solid-oxide-cell electrodes. Faraday Discussions, 182(0), 75–95. https://doi.org/10.1039/C5FD00048C
3. Valdes-Espinosa, H., Stuve, E. M., & Adler, S. B. (2015). Modeling Water Reduction on 10 Mole% Gadolinia-Doped Ceria (GDC10) Porous Electrodes. ECS Transactions, 66(2), 229–251. https://doi.org/10.1149/06602.0229ecst