Strategies for d-band center control in nickel based electrocatalysts for efficient nitrate-to-ammonia reaction

The electrochemical nitrate (NO 3 − ) reduction reaction to ammonia (NH 3 ) offers a sustainable route for simultaneous wastewater remediation and green ammonia synthesis. Among non-precious metal catalysts, nickel (Ni)-based systems have emerged as particularly promising, with their catalytic performance intimately governed by the position of the Ni d -band centre, as reflected in well-established activity volcano relationships. This review provides a comprehensive and critical analysis of how modulation of the Ni d -band centre controls the adsorption and activation of nitrate-derived intermediates, as well as the hydrogenation kinetics through regulation of adsorbed hydrogen ( H ads ) binding strength. We examined recent strategies for tuning the electronic structure of Ni catalysts, including single-atom design, coordination modulation (e.g., Ni–N 4 and Ni–O 4 ), defect engineering, heterostructure formation, and bimetallic alloying. Emphasis is placed on synergistic interactions in Cu–Ni and Fe–Ni systems, which enable precise tuning of the d -band center to enhance activity, selectivity toward NH 3 , and suppression of competing HER and undesired byproducts. State-of-the-art experimental techniques such as in-situ Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray absorption spectroscopy (XAS) combined with density functional theory (DFT) calculations are highlighted as indispensable tools for elucidating reaction pathways, identifying true active sites, and correlating electronic structure descriptors with catalytic performance. By linking reaction mechanisms with electronic structure engineering, this review outlines clear design guidelines for developing efficient and selective Ni-based electrocatalysts for nitrate-to-ammonia conversion.