Proton-conducting solid oxide electrolysis cells: Relationship of composition-structure-property, their challenges, and prospects

Proton-conducting solid oxide electrolysis cells (H-SOECs) have attracted significant attention in recent years. This is due to their advantageous nature compared with the popular ion-conducting SOECs (O-SOECs). Progress in H-SOECs is, however, lagging compared with O-SOECs. This is primarily due to the low stability of these electrolytes in environments that contain H₂O and CO₂. Here, we present a critical evaluation, recent developments, overview of advancements, and future perspective for H-SOECs (emphasizing the last decade of work on H-SOECs). We focus on the design and advanced interface architecture of electrodes and the composition-structure-property relationship of the most popular Ba(Ce, Zr)_1−x−yY_xYb_yO_3−δ and Sr(Ce, Zr)_1−x−yY_xYb_yO_3−δ materials. We also present the latest innovative electrolyte materials applicable to H-SOECs and introduce the latest reported modification techniques for enhancing overall H-SOEC performance. Finally, we assess the prospects and potential direction of research for the near future.