Effect of Mn Doped Ni−Co Mixed Oxide Catalysts on Urea Oxidation

Urea as an energy generation and storage fuel has attracted increased attention for its stability, non-toxicity, and availability. Urea possesses 10.1 wt.% of hydrogen. Nevertheless, its electrochemical oxidation is generally sluggish and inefficient. Ni-based catalysts which showed efficient activity towards urea electrooxidation in the alkaline medium were studied for Direct Urea Fuel Cell (DUFC) anodes. In the present study, we investigated urea oxidation on a novel three-dimensional mixed oxide catalyst, NiCo₂O₄. Mn-doped NiCo₂O₄ catalyst exhibited urea oxidation activity of 45.88 mA cm⁻² (at 1.30 V vs SHE), fifteen times higher than NiO and Co₃O₄ and twice that of bare NiCo₂O₄ spinel. Chronoamperometry curves of the Mn-doped NiCo₂O₄ catalyst demonstrated stable urea oxidation for over 3 hours. The significantly higher mass activity of Mn-doped NiCo₂O₄ catalyst is attributed to the least nano-crystallite size, better dispersion of Ni nuclei onto the spinel crystal matrix, enhanced Ni electrochemical active surface area, and lower bandgap.