Boundary Investigation of High-Temperature Co-Electrolysis Towards Direct CO<sub>2</sub> Electrolysis
Stephanie E. Wolf, Lucy Dittrich, Markus Nohl, Tobias Duyster, Izaak C. Vinke, Rüdiger‐A. Eichel, L.G.J. de Haart
Abstract
In the temperature range of high temperature co-electrolysis of both steam and carbon dioxide, the reverse water-gas shift reaction (RWGS) takes place. Prior studies were conducted with a narrow gas composition range to investigate the role of RWGS during co-electrolysis. The results for steam electrolysis, CO 2 electrolysis, and co-electrolysis caused different conclusions regarding the role of electrochemical CO 2 and H 2 O conversion compared to RWGS during co-electrolysis. This work aims to resolve the role of CO 2 conversion as part of RWGS in co-electrolysis. The boundary is characterized by AC and DC measurements over a broad gas composition range from CO 2 electrolysis towards co-electrolysis with nearly 50% eq H 2 O. Especially, the electrochemical CO 2 reduction and CO 2 conversion in the RWGS are compared to clarify their role during co-electrolysis. The results revealed that gas composition determined the predominant reaction (H 2 O or CO 2 reduction). The cell performance of co-electrolysis in the boundary region up to 5% eq H 2 O was similar to the performance of CO 2 electrolysis. Up to 30% eq H 2 O, the performance increases with H 2 O concentration. Here, both CO 2 and H 2 O electrolysis occur. Above 30% eq H 2 O, steam electrolysis and the RWGS reaction both dominate the co-electrolysis process.