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

A series of Co-doped Ni–Fe spinels (NiCo_xFe_(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 NiCo_0·8Fe_1·2O₄ 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 NiCo_0·8Fe_1·2O₄ were also observably improved. This excellent performance is comparable to that of commercial Pt/C (20 wt.%)-SA. The enhanced electrocatalytic property of NiCo_0·8Fe_1·2O₄ is ascribed to the uneven distribution of oxygen in NiFe₂O₄ structure caused by Co doping, thus forming oxygen defect sites.