Toward circular nitrogen: Electrochemical ammonia recovery using redox-active materials

Ammonia (NH₃) recovery plays a pivotal role in closing the nitrogen cycle by recycling ammonia from waste streams and mitigating environmental pollution. Electrochemical ammonia recovery is promising for distributed ammonia recovery, which requires ammonia transport through diffusion and migration or (de)intercalation. Using redox-active materials for ammonia recovery is an emerging strategy that enables selective ammonia uptake without expensive ion-exchange membranes, although ammonium recovery mechanisms and related process design require further exploration. This minireview summarizes the recent developments in ammonia recovery using redox-active materials, especially Prussian blue analogs, through electrochemical and electrochemical-chemical cycles. The working principles of redox-active materials and key evaluation metrics, such as stability, selectivity, and kinetics, are systematically discussed. Redox-active materials allow selective ammonia uptake driven by either renewable electricity or even spontaneously through the oxidation of organic matter in manure wastewater. We also discuss opportunities and challenges for practical ammonia recovery and environmental remediation using redox-active materials.