Synergistic Effects of Ni and Cu in Morphology-Controlled NiCu Electrocatalysts for Ammonia Electro-oxidation

Abstract

The ammonia electrochemical oxidation reaction (AOR) has recently attracted attention not only for environmental remediation but also for anode reactions in direct ammonia fuel cells and hydrogen fuel production. A deep understanding of the AOR mechanism is of great importance in the design of powerful catalysts. Here, we introduce morphology-controlled electrocatalysts using a facile solvothermal method and dodecylamine as a shape-controlling precipitation agent. Several shapes, including scattering nanoparticles, microspheres, and microcubes, were synthesized by adjusting the ratio of metal precursors to the dodecylamine content. The optimized catalyst, NiCu-D-1:2 with a microsphere shape, showed a hierarchical nanostructure, which provided better contact of the catalyst surface with the reactants and facilitated mass transfer through the reaction. Cyclic voltammetry experiments found that NiCu-D-1:2/CP supplies a current density of 44.9 mA/cm2 at the potential of 0.6 V vs Hg/HgO. Furthermore, NiCu-D-1:2/CP promoted a high Faradaic efficiency of 79% toward N2, which was confirmed using in operando gas chromatography. In addition, a mechanism explaining the synergistic effect of nickel and copper in providing robust AOR activity with a high N2 selectivity is proposed.