Electrochemical Oxidation of Glycine with Bimetallic Nickel−Manganese Oxide Catalysts

A simple template-free hydrothermal route followed by high-temperature (800 °C) annealing in air forms Ni–Mn bimetallic oxides, namely NiMn₂O₄, Ni_1.5Mn_1.5O_4, and MnNi₂O_4, which are characterized by XRD, Raman, EDS, and SEM analysis. The electrocatalytic activity of these metal oxides toward the oxidation of glycine molecules in alkaline condition was studied by cyclic voltammetry and linear sweep voltammetry methods. Among other nickel manganese bimetallic oxides and monometallic oxides (Mn₂O₃, NiO), Ni_1.5Mn_1.5O₄ shows excellent redox characteristics with high oxidation current density (310 μA cm⁻² at 0.43 V vs. Ag/AgCl) and lower onset potential (0.22 V vs. Ag/AgCl). Additionally, Ni_1.5Mn_1.5O₄ exhibits a moderate Tafel slope (78 mV dec⁻¹) and is electrochemically stable, as confirmed from chronoamperometry, indicating its potential for glycine oxidation. The linear dependence of the oxidation current with glycine concentration signifies that the overall process is diffusion controlled. The electrochemical results suggest that bimetallic mixed Mn and Ni oxides are promising glycine oxidation catalysts, which may be attributed to the cooperative effect between different Ni and Mn elements.