Progress Report on Proton Conducting Solid Oxide Electrolysis Cells

The proton-conducting solid oxide electrolysis cell (H-SOEC) is a promising device that converts electrical energy to chemical energy. H-SOECs have been actively studied in the past few years, due to their advantages over oxygen-ion-conducting solid oxide electrolysis cells (O-SOECs), such as lower operation temperature, relatively lower activation energy, and easier gas separation. A critical overview of recent progress in H-SOECs is presented, focusing particularly on the period from 2014 to 2018. This review focuses on three aspects of H-SOECs, namely, the materials, modeling, and current leakage in proton conducting oxide electrolytes. Specifically, the current leakage in proton conducting oxides, which is often neglected, leads to two problems in the studies of H-SOECs. One is the distortion of the electrochemical impedance spectra and the other is low faradaic efficiency of electrolysis. Based on the comprehensive and critical discussion in these three sections, challenges in the development of H-SOECs are highlighted and prospective research in H-SOECs is outlined.