Novel FexCr2−x(MoO4)3 electrocatalysts for oxygen evolution reaction

Transition metal mixed oxides of Fe, Cr and Mo with nominal compositional formula, FexCr2−x(MoO4)3 (x = 0, 0.25, 0.50 and 0.75) have been obtained by a co-precipitation method and investigated for their structural and electrocatalytic properties by XRD, TEM, XPS, BET, electrochemical impedance spectroscopy and anodic Tafel polarization. Results show that introduction of Fe for Cr from 0.25 to 0.75 mol into the Cr2(MoO4)3 matrix improved the electrocatalytic activity toward the O2 evolution reaction (OER) in 1 M KOH considerably; the magnitude of improvement being maximum with 0.5 mol Fe. Values of the Tafel slope were close to 35 mV at low and 2.303RT/F at high overpotentials on Fe-substituted oxides. The OER follows nearly second order kinetics in OH− concentration at low overpotentials.

► Introduction of Fe for Cr increases the catalytic activity of Cr2(MoO4)3 for OER greatly.
► The Tafel slope of the reaction is ∼35 mV at low overpotentials.
► The crystallites of Fe-substituted product follow the orthorhombic crystal structure.