Abstract: Proton conducting ceramic cells (PCCs) are an attractive emerging technology operating in the intermediate temperature range of 500 to 700 °C. In this work, we evaluate the production of hydrogen at intermediate temperatures by proton conducting ceramic cell electrolysis (PCCEL). We demonstrate a high-performance steam electrolysis owing to a composite positrode based on BaGd_0.8La_0.2Co₂O_6-δ (BGLC1082) and BaZr_0.5Ce_0.4Y_0.1O_3-δ (BZCY541). The high reliability of PCCEL is demonstrated for 1680 h at a current density as high as -0.8 A cm^-2 close to the thermoneutral cell voltage at 600 °C. The electrolysis cell showed a specific energy consumption ranging from 54 to 66 kW h kg^-1 that is comparable to state-of-the-art low temperature electrolysis technologies, while showing hydrogen production rates systematically higher than commercial solid oxide ceramic cells (SOCs). Compared to SOCs, the results verified the higher performances of PCCs at the relevant operating temperatures, due to the lower activation energy for proton transfer comparing with oxygen ion conduction. However, because of the p-type electronic conduction in protonic ceramics, the energy conversion rate of PCCs is relatively lower in steam electrolysis. The faradaic efficiency of the PCC in electrolysis mode can be increased at lower operating temperatures and in endothermic conditions, making PCCEL a technology of choice to valorize high temperature waste heat from industrial processes into hydrogen. To increase the faradaic efficiency by optimizing the materials, the cell design, or the operating strategy is a key challenge to address for future developments of PCCEL in order to achieve even more superior techno-economic merits.

Key words: Steam electrolysis, Hydrogen production, Proton conducting ceramics, Intermediate temperature, Energy efficiency