Kinetics and highly selective N2 conversion of direct electrochemical ammonia oxidation in an undivided cell using NiCo oxide nanoparticle as the anode and metallic Cu/Ni foam as the cathode

Abstract

Ammonia oxidation and selectivity of nitrogen conversion were investigated over an Ni foam-supported NiCo oxide electrode synthesized using chemical precipitation and calcination. Characterization using XRD, SEM, and XPS determined the crystal phase and oxdiation state of the nano-textured particulate metal oxides. A voltammetry analysis showed that a M(II)/(III) (M = Ni and Co) redox reaction couple mediated the direct electron transfer of the nitrogen species. Batch electrochemical parameters, including the initial concentration of NH3 and the current density, were studied to evaluate the performance of the tested electrodes in the absence of chloride ions. The best N2 selectivity (40%) was obtained on the oxyhydroxide anode (H-Ni50Co50/Ni); further, as paired with an electroless Cu/Ni cathode, the total nitrogen (TN) loss in terms of gaseous nitrogen evolution was 76%. Consecutive kinetics was derived to assess the pathways of the NH3 conversion and the rates of the nitrogen cycle on different electrode pairs, such as Ni – Ni, Ni – Cu/Ni, and H-NiCo/Ni – Cu/Ni sets.