One-Step Synthesis of Highly Active and Conductive Transition Metal Nitride for Oxygen Evolution in Alkaline Anion Exchange Membrane Electrolysis

The kinetic bottleneck of electrocatalytic water splitting is the oxygen evolution reaction (OER). State-of-the-art electrocatalysts for OER include noble metal oxides in acidic electrolytes, as well as non-noble metal oxides in alkaline conditions. Because OER catalyst performance in alkaline anion exchange membrane electrolysis (AEMEL) is limited by the bulk electrical conductivity of the catalyst material, alternatives to metal oxides are desired. This study introduces an efficient single-step synthesis of heterogeneous transition metal nitrides (TMNs) using metal salts in anhydrous NH3, yielding quantitative amounts of the catalyst and volatile byproducts without the necessity for purification steps, while preventing metal-contaminated waste. Extensive characterization of TMNs based on Co, Ni, and Fe demonstratess that such mixed metal nitrides particles with partially oxidized surface outperform benchmark catalysts IrOx and NiCoFeOx in a three-electrode configuration, exhibiting optimum performance for the Co57Ni14Fe29Nx composition. When incorporated onto gas diffusion electrodes in a 5 cm2 AEMEL electrolyzer, Co57Ni14Fe29Nx achieved a cell potential of 2.05 V at 1Acm−2, with sustained stability for more than 240 h of continuous electrolysis. The one-step synthesis of high-performing TMNs marks a pivotal step in sustainable hydrogen production, heralding them as impactful alternatives to metal oxides for bolstering green energy technologies.