Rewiring Electrocatalytic Nitrate Reduction with Single-Atom-Based Dual Active Sites at the Water-Energy Nexus

Abstract Nitrate electroreduction links water purification with ammonia production, but its use is still limited by sluggish proton-coupled electron transfer, poor product selectivity, and competition from the hydrogen evolution reaction. Single-atom-based dual active sites (SADASCs) address these constraints by coupling atomically dispersed metal centres with adjacent single atoms, clusters, or nanoparticles. Such coupled motifs regulate adsorption, charge redistribution, intermediate stabilisation, hydrogen supply, and product release in a step-specific manner. This review discusses electrocatalytic nitrate reduction according to its elementary sequence: nitrate adsorption and activation, initial N–O bond cleavage, nitrite conversion, deep NOx hydrogenation, active-hydrogen regulation, product desorption, and catalyst reconstruction. SADASCs are then classified into single-atom/single-atom, single-atom/cluster, and single-atom/nanoparticle architectures, with emphasis on how dual-site coupling overcomes the limitations of isolated single atoms. Key challenges in stability, operando identification, selectivity control, benchmarking, matrix tolerance, and device integration are also summarized. This perspective provides design principles for dual-site catalysts that can promote nitrate valorization under complex aquatic conditions.