Impact of pressurized operation on fuel cell and electrolysis performance in a tubular proton-conducting ceramic cell

In this study, tubular proton-conducting ceramic cells (PCCs) were fabricated via easily scalable extrusion and spraying processes. Pressurized operation up to 2.5 bar was found to improve electrochemical performance by reducing polarization and ohmic resistances, consistent with enhanced surface reaction kinetics and more-facile gas diffusion in the porous electrodes and increased proton conductivity in the electrolyte. During electrolysis, pressurization from 1 to 2.5 bar served to enhance faradaic efficiency with a 55 %-gain in hydrogen production rate at −500 mA cm −2 . This gain is consistent with the pressure-dependent defect chemistry, where electronic hole concentration more strongly depends on p H2O than on p O2 , so increasing pressure at constant H 2 O/O 2 ratio lowers hole concentration. Comparative pressure sweeps at fixed p H2O and fixed H 2 O/O 2 ratio further showed that faradaic efficiency can increase even when p H2O is fixed, indicating that fuel side pressurization (higher p H2 ) promotes hydrogen incorporation and proton-defect formation that compensates the leakage promoting rise in p O2 . Finally, pressurization was also shown to reduce electrolyzer degradation rates, when keeping p H2O constant.