How can current leakage be reduced in protonic ceramic electrolysis cells? Insights from thermo-electrochemical modeling

Abstract

Current leakage, affected by a complex interplay of variables in protonic ceramic electrolysis cells (PCECs), undermines its faradaic efficiency (FE), of which comprehensive understandings are still lacking. Here, a tubular PCEC model is developed to systematically investigate the effects of temperature, current density, and gas composition on cell performance with the focus on the current leakage issue enabled by considering defect chemistry in the model. A non-linear relationship between the FE and the current density is discovered, where the FE is found to be collectively affected by the H<inf>2</inf> production rate, the local temperature, the O<inf>2</inf> accumulation, and the H<inf>2</inf>O depletion. With the consideration of defect reaction heat, a reduction in thermoneutral voltage due to the intensified heat derived from defect reactions is also observed. Furthermore, the model demonstrates that an increase of cathodic H<inf>2</inf>O reduces the electrolysis voltage and results in a reduced FE. This study also highlights the impact of anodic gas composition, where an increased H<inf>2</inf>O fraction and a decreased O<inf>2</inf> fraction can effectively suppress current leakage. Findings from this modelling work offer comprehensive understandings of the low FE issue in PCECs, and thus being potential as a useful tool for both material design and thermodynamical optimization of multiple proton conductor-based electrochemical devices.