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

Abstract

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. Nibased 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, NiCo 2 O 4 . Mn-doped NiCo 2 O 4 catalyst exhibited urea oxidation activity of 45.88 mA cm À 2 (at 1.30 V vs SHE), fifteen times higher than NiO and Co 3 O 4 and twice that of bare NiCo 2 O 4 spinel. Chronoamperometry curves of the Mn-doped NiCo 2 O 4 catalyst demonstrated stable urea oxidation for over 3 hours. The significantly higher mass activity of Mn-doped NiCo 2 O 4 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.

Mesoporous Electrocatalysts with p–n Heterojunctions for Efficient Electroreduction of CO2 and N2 to Urea

“…The d-electron number and d-electron delocalization in transition-metal catalysts play an important regulatory role in electrocatalytic oxidation–reduction reactions . Therefore, the orbital electron occupation state of the transition metals in electrocatalysts can be adjusted to create empty orbitals to receive intermediate σ orbital electrons, thus promoting spontaneous coupling of C–N bonds. ,− Moreover, transition-metal oxide catalysts can increase their specific surface area through metal doping, thereby enhancing its gas adsorption ability and promoting the activation of reaction gases. , …”

“…13,20−24 Moreover, transition-metal oxide catalysts can increase their specific surface area through metal doping, thereby enhancing its gas adsorption ability and promoting the activation of reaction gases. 25,26 Herein, hierarchically ordered mesoporous CeO 2 /Co 3 O 4 with a p−n heterojunction was suggested for efficient electroreduction of CO 2 and N 2 to urea. The adsorption and activation ability of inactive gases were enhanced by the spacecharge regions formed at the heterojunction in CeO 2 /Co 3 O 4 .…”