Aerogel Electrocatalysts for Nitrate-to-Ammonia Conversion: Materials Development, Reaction Mechanisms, and Reactor Integration

Electrochemical nitrate reduction can combine nitrogen removal with ammonia recovery, but the contribution of an aerogel network is difficult to separate from changes in catalyst chemistry and electrode preparation. This review examines when the architecture created by gelation and drying remains relevant after electrode fabrication and during nitrate conversion. Metallic, carbon-based, and hybrid aerogels are compared through their preparation, working-state structure, reaction evidence, and operating conditions. Particular attention is given to nitrate activation, downstream hydrogenation, soluble-intermediate retention, and competition with hydrogen evolution and nitrogen formation. Related non-aerogel studies provide mechanistic and reactor comparisons while retaining their distinct material identities. The analysis separates measured responses from proposed pathways and distinguishes peak Faradaic efficiency from sustained conversion and product recovery. Dry surface area, isolated spectroscopic signals, and performance measured under different conditions do not independently establish an aerogel-specific advantage. Priorities emerging from the literature are comparisons of retained and fragmented networks, coupled measurements of intermediate transport and catalyst reconstruction, and nitrogen balances under defined feed and recovery conditions. These comparisons provide a basis for evaluating which aerogel design features remain useful in a working nitrate-conversion device.