Tuning Nitrate Electroreduction Selectivity via Doping of Nickel Phosphide Nanocrystals

Metal phosphide nanomaterials have been demonstrated as catalysts for various electrosynthetic transformations, where their reactivity is attributed to their surface site heterogeneity. In this study, we modify Ni 2 P’s hydrogen affinity by synthesizing a series of doped Ni 2– x M x P (M = Cu, Co) nanocrystals as catalysts for nitrate electroreduction. We propose that cobalt’s strong hydrogen affinity contributes ≥80% faradaic efficiency for ammonia, nearly a 2-fold increase relative to undoped Ni 2 P, while the weak hydrogen affinity of copper promotes hydrogen and nitrite formation. This work demonstrates how the synthetic tunability of metal phosphide nanocrystals can be leveraged to tune nitrate electroreduction selectivity.