Protonic ceramic electrochemical cells: Opportunities and challenges for ammonia synthesis

Electrochemical ammonia synthesis is being widely investigated to couple with renewable electricity for future sustainable ammonia production. Protonic ceramic electrochemical cells (PCECs) possess superior energy transfer efficiency and remarkable flexibility to produce high-demand chemicals such as H₂, CH₄, and NH₃ from readily available feedstocks (e.g., H₂O, CO₂, N₂). Despite recent advances that have been established, the research for the high-efficiency PCECs for practical ammonia synthesis continues. In this review, we summarized the recent progress of PCECs for ammonia synthesis. First, we briefly introduce the basic mechanisms and protocols of the ammonia synthesis. Then, we systemically introduce the cell configurations, representative electrolytes and electrodes of PCECs for the ammonia synthesis. We highlight the strategies to tune the ion/electron mobility and the catalytic performance, which are related to the defect structures and redox properties of the electrolyte/electrode, and the opportunities for next-generation ammonia synthesis. Finally, perspectives on ammonia synthesis in PCECs are proposed consering the current challenges.