Direct electrochemical ammonia synthesis from water and air via solid-state protonic electrochemical cells – A critical review

Solid-state protonic electrochemical cells (SSPECs) are gaining attention as a technology that has great potential for sustainable ammonia (NH₃) synthesis, energy storage, and power generation, while providing seamless integration with renewable energy thereby offering a pathway towards a low-carbon economy. However, challenges remain in achieving industrially relevant NH₃ production rates and overall energy efficiencies required for commercial applications. Key barriers are outlined, including the thermodynamically favoured hydrogen evolution reaction (HER) at the cathode, which limits selectivity and lowers efficiencies. Recent advancements are highlighted including the importance of rational catalyst design, often focusing on functionalisation or defect-engineered sites, and integrated systems optimisation. In particular, co-fed electrochemical nitrogen reduction (eNRR) presents a strategy for enhancing NH₃ yields, while plasma-assisted processes also show promise in increasing both NH₃ production rates and selectivity. Furthermore, the lack of consistent ammonia detection methods has been outlined as a critical variable in comparative performance evaluation, which significantly impacts robust benchmarking of new catalyst and system designs. Despite these current limitations, SSPECs present a compelling opportunity for converting renewable electricity into liquid fuels, with significant potential for scaling solid-state protonic eNRR.