Faceted Colloidal Metallic Ni₃N Nanocrystals: Size-Controlled Solution-Phase Synthesis and Electrochemical Overall Water Splitting

We report a size-tunable synthesis of faceted Ni3N nanocrystals (NCs) at low temperatures (210-230 °C) via a solution processing route for the first time and demonstrate their viability as an efficient electrocatalytic material for overall water splitting. The high carrier density of Ni3N NCs combined with the faceted morphology is shown to render a broadband absorption in the infrared range attributed to the energy-dispersed localized surface plasmon excitation. The Ni3N NCs show an efficient electrocatalytic activity with impressively low overpotentials of ∼74 and 142 mV for the hydrogen evolution reaction (HER) and 190 and 270 mV for the oxygen evolution reaction (OER), with current densities of 10 and 100 mA/cm2, respectively. The Tafel slopes for HER and OER are 49 and 56 mV/dec, respectively, which are quite small. Furthermore, these Ni3N NCs require a small voltage of 1.48 V to produce a current density of 10 mA/cm2 for overall water splitting conducted in an alkaline electrolyzer when they are used both as a cathode and an anode.