Acidic Electrochemical Reduction of CO₂ Using Nickel Nitride on Multiwalled Carbon Nanotube as Selective Catalyst

Ni3N/MCNT (multiwalled carbon nanotube) nanocomposites fabricated by ammonolysis displayed high CO2 electrochemical reduction reactivity with CO Faradaic efficiencies of 89.0% and current density of 6.5 mA cm–2 at −0.73 V vs reversible hydrogen electrode (RHE). The Ni3N/MCNT catalyst could operate under weakly acidic conditions in the pH range of 2.5–7.2. Even at pH 2.5, the CO Faradaic efficiency remained at 50.1%, demonstrating the high selectivity for CO2 reduction. The high catalyst selectivity could be due to increased adsorption of CO2 on the Ni3N surface, which can compete with hydrogen evolution under acidic conditions.