Green hydrogen production by intermediate-temperature protonic solid oxide electrolysis cells: Advances, challenges, and perspectives

Protonic solid oxide electrolysis cells (P-SOECs) operating at intermediate temperatures, which have low costs, low environmental impact, and high theoretical electrolysis efficiency, are considered promising next-generation energy conversion devices for green hydrogen production. However, the developments and applications of P-SOECs are restricted by numerous material- and interface-related issues, including carrier mismatch between the anode and electrolyte, current leakage in the electrolyte, poor interfacial contact, and chemical stability. Over the past few decades, considerable attempts have been made to address these issues by improving the properties of P-SOECs. This review comprehensively explores the recent advances in the mechanisms governing steam electrolysis in P-SOECs, optimization strategies, specially designed components, electrochemical performance, and durability. In particular, given that the lack of suitable anode materials has significantly impeded P-SOEC development, the relationships between the transferred carriers and the cell performance, reaction models, and surface decoration approaches are meticulously probed. Finally, the challenges hindering P-SOEC development are discussed and recommendations for future research directions, including theoretical calculations and simulations, structural modification approaches, and large-scale single-cell fabrication, are proposed to stimulate research on P-SOECs and thereby realize efficient electricity-to-hydrogen conversion.