Controlling the morphology and efficiency of nanostructured molybdenum nitride electrocatalysts for the hydrogen evolution reaction

Abstract

Among catalysts based on non-noble metals, Mo-based materials are important for hydrogen evolution because of their low cost, good conductivity, and catalytic efficiency. This study demonstrates a facile two-step synthesis of Mo₂N nanostructures assembled from 5–8 nm particles with graphitic carbon nitride as the nitrogen source. These Mo₂N nanostructures of various morphologies (hexagons, triangles, and nanowires) show a very high activity and stability in acidic media during water electrolysis. Their nanostructures were characterized by using powder XRD, electron microscopy, N₂ gas adsorption analysis, and X-ray photoelectron spectroscopy. Hydrogen evolution reaction parameters, which include the Tafel slope, charge transfer resistance, and stability, were analyzed by using linear sweep voltammetry and electrochemical impedance spectroscopy. Thin hexagonal sheets of Mo₂N show the highest apparent electrocatalytic activity (current density of 197 mA cm⁻²_geometric at −400 mV vs. the reversible hydrogen electrode) and excellent stability in an acidic medium with a small onset potential of 90 mV and a Tafel slope of 145 mV decade⁻¹. The lowest Tafel slope was observed for Mo₂N nanowires.