Subnanometric Nickel Phosphide Heteroclusters with Highly Active Niδ+–Pδ− Pairs for Nitrate Reduction toward Ammonia

The development of efficient electrocatalysts for the neutral nitrate reduction reaction (NO₃^–RR) toward ammonia (NH₃) is essential to address the environmental issues caused by NO₃^– but remains considerably challenging owing to the sluggish reaction kinetics of NO₃^–RR in neutral media. Herein, we report subnanometric heteroclusters with strongly coupled nickel–phosphorus (Ni–P) dual-active sites as electrocatalysts to boost the neutral NO₃^–RR. Experimental and theoretical results reveal that the subnanometric feature of Ni–P heteroclusters promotes the electron transfer from Ni to P, generating Ni^δ+–P^δ− active pairs, in which Ni^δ+ species are highly active for the NO₃^–RR and P^δ− tunes the interfacial water hydrogen bonding network to promote the water dissociation step and accelerate proton transfer during the NO₃^–RR. Consequently, in the neutral NO₃^–RR, Ni–P heteroclusters exhibit a large NH₃ yield rate of 0.61 mmol h^–1 cm^–2 at −0.8 V versus reversible hydrogen electrode, which is 2.8- and 3.3-fold larger than those on Ni–P nanoparticles and Ni clusters, respectively, and the generated NH₃ exists as NH₄⁺ in electrolytes. This study offers an efficient approach to boosting electrocatalytic reactions with multiple intermediates by designing subnanometric heteroclusters with strongly coupled active sites.