Catalysts for Electrochemical Oxidation of Ammonia: A Comprehensive Review of Fundamentals and Optimization Strategies.

The realization of a hydrogen (H2) economy confronts formidable challenges in storage, transportation, and logistics. To address these challenges, H2 carriers have been proposed as alternative solutions. Ammonia (NH3), as one of the most promising H2 carriers, becomes a game-changer, offering higher volumetric H2 density than compressed H2, simplified logistics, and compatibility with existing infrastructure, which thereby reduces costs and supply chain complexities. However, fully realizing NH3's potential requires overcoming downstream inefficiencies associated with its conversion either back into H2 or into energy. Downstream processes primarily include thermal cracking, NH3 electrolysis, and direct NH3 fuel cells, two of which are electrochemical systems leveraging the NH3 oxidation reaction (AOR). The efficiency of these electrochemical systems is significantly limited by severe surface poisoning and poor AOR catalytic activity, underscoring the urgent need for advanced catalyst design. Here, a comprehensive review of AOR electrocatalysis is provided, with a focus on mechanistic insights into activity-governing steps and surface poisoning pathways. Recent advances in catalyst design are summarized, and overlooked factors are highlighted for performance enhancement. Finally, perspectives on future research directions are presented for AOR catalyst development to accelerate the integration of NH3-based technologies into the hydrogen economy.