Toward sustainable ammonia: Structure-activity relations and reaction-system engineering for electrocatalytic nitrate...

Electrochemical nitrate reduction (NO₃RR) to ammonia could couple nitrate removal with lower-carbon nitrogen recovery, but its eight-electron pathway makes activity and selectivity hard to control. A material-by-material view can hide how active-site structure, mass transfer and operating conditions work together. Here we assess NO₃RR through a joint structure-activity and reaction-system framework. We compare facet-controlled Pd, evolving Cu/CuO_x interfaces, Cu-Co tandem sites, isolated and symmetry-broken Fe centers, defect-rich Zr supports, metal-organic frameworks and other transition-metal systems. Across these materials, the evidence links selective ammonia formation to a matched sequence of nitrate capture, N-O bond cleavage, proton delivery, intermediate hydrogenation and product release. We also examine pulsed potentials, porous electrodes, flow cells and product recovery as ways to regulate transport and intermediate coverage beyond static catalyst design. However, reported metrics do not support a universal catalyst ranking because studies use different nitrate concentrations, electrolytes, potentials, cell designs and rate units. We therefore identify four priorities: direct tracking of active states during operation, shared testing rules, long-term tests with realistic feeds, and catalyst-reactor co-design at practical current densities. This framework connects atomic-scale catalyst design with device operation and sets clear tests for advancing nitrate-to-ammonia conversion.