Mo–Ag nanocomposite catalysts for the oxygen evolution reaction

Nanocomposite powders are interesting electrocatalysts for efficient water splitting in alkaline medium. In this work, Mo–Ag nanocomposites were prepared by high energy ball milling of (NH4)6Mo7O24.4H2O and AgNO3 precursors, with subsequent reduction in hydrogen atmosphere. High energy ball milling formed spheres composed of needle-like structures of different sizes. The particle size decreases with increasing the milling time from 20 h to 40 h, with the same trend observed for crystallite sizes. The electrochemical performance for the oxygen evolution reaction (OER) is assessed using linear sweep (LSV) and cyclic (CV) voltammetry, electrochemical impedance spectroscopy (EIS), and chronopotentiometry (CP). The values of overpotential, Tafel slope, double layer capacitance (CDL) and turnover frequency (TOF) of samples milled for 20 h and 40 h are determined to be 350 and 330 mV vs. RHE, 84 and 75 mV dec−1, 5.4 and 6.2 mF cm−2, 3.84 × 10−3 and 6.98 × 10−3 mol O2 s−1, respectively, which suggests an improved electrocatalytic activity for the sample milled for 40 h. The increased surface area dramatically boosts the electrochemical processes with adsorbed species. Chronopotentiometry measurements for 15 h reveal that electrodes exhibit acceptable short-term electrochemical stability. The overall results suggest that Mo–Ag nanocomposites are promising materials for the oxygen evolution reaction, being among the best Mo-based electrocatalysts reported in the literature.