Co-electrolysis of Water and Carbon Dioxide by Gadolinia Doped Ceria using Electrochemical Perturbations and Differential Frequency Resolved Mass Spectrometry

Abstract

Co-electrolysis of steam and CO2 provides a route to producing fuel for seasonal energy storage or commodity chemicals via Fischer-Tropsch reaction from renewable energy. High temperature co-electrolysis with solid oxide electrolyzer cells (SOEC) is one of the most efficient and economically viable technological options. SOECs are not in widespread use thanks to a myriad of challenges, one of which is the development of a stable catalyst.Ni mixed with yttria stabilized zirconia (Ni-YSZ) is the standard catalyst for co-electrolysis but faces deactivation from carbon deposition, redox cycle oxidation, poisoning, and agglomeration. Alternatives to Ni-YSZ have been explored, particularly mixed ionic and electronic conductors (MIEC) such as gadolinium doped ceria (GDC). Regardless of catalyst, there exists a lack of understanding surrounding the degree to which steam and CO2 are simultaneously electrochemically reduced or if much of the CO2 is reduced by the chemical reverse water gas shift reaction (RWGS). The current toolset of electrochemical and chemical analysis tools may be insufficient to resolve the discrepancy due to the complexity of thermodynamics, geometry, flow rates, inlet gas compositions, temperature, and multiple reaction pathways available. An additional complexity is current distribution. This effect was studied using CO2 electrolysis on MIEC 10% doped GDC (GDC10) with and without a gold porous current collecting layer. Results, complemented with COMSOL modeling, show that relying on metal meshes for current distribution risks misinterpretation of electrochemical impedance spectra. Finally, the new tool presented here is frequency resolved mass spectrometry (FRMS). FRMS applies voltage or current perturbations to an electrode in a low vacuum environment while collecting the perturbations of the gaseous species with a mass spectrometer. FRMS has the potential to provide new insights into the relationships between current, voltage, and gas species by isolating phenomena at different timescales to be analyzed in the mass spectrum. The data presented here suggests that co-electrolysis occurs while RWGS is negligible under the conditions studied.