Co-doped Ni–Fe spinels for electrocatalytic oxidation over glycerol

A series of Co-doped Ni–Fe spinels (NiCoxFe(2-x)O4, x = 0.2, 0.4, 0.6, 0.8, 1.0, 1.4, 1.8, 2) were prepared at optimum calcination temperature (700 °C) by the sol-gel method and then applied for the electrocatalytic oxidation over glycerol. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), Tafel curve, and chronoamperometry (i-t) were performed to investigate electrochemical performance of as-prepared spinel catalysts. The results showed that NiCo0·8Fe1·2O4 exhibited distinct redox peaks and the larger CV area (626.2 ± 0.03 μV A cm−2), lower Rct (42.42 ± 0.03 Ω) and Tafel slope (21 mV dec−1) than that of pristine NiFe2O4 and NiCo2O4, signifying Co-doped NiFe2O4 is beneficial to accelerate the catalytic oxidation of glycerol. Moreover, the ECSA and stability of NiCo0·8Fe1·2O4 were also observably improved. This excellent performance is comparable to that of commercial Pt/C (20 wt.%)-SA. The enhanced electrocatalytic property of NiCo0·8Fe1·2O4 is ascribed to the uneven distribution of oxygen in NiFe2O4 structure caused by Co doping, thus forming oxygen defect sites.