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 Niδ+–Pδ− active pairs, in which Niδ+ species are highly active for the NO3–RR and Pδ− 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.