Disordered Nickel Oxide Nanostructure-Enriched Bimetallic AuNi Nanoparticles for Methanol Electrooxidation

Herein, we report a facile method for stabilizing highly reactive disordered NiO on tiny AuNi alloy particles anchored by N-doped carbon matrices as efficient electrocatalysts for the oxidation of alcohols such as methanol, ethanol, propanol, and ethylene glycol. Initially, an amorphous nickel-enriched bimetallic AuNi alloy was prepared by annealing a mixture containing a gold precursor, Ni(salen), and DMF at 300 °C. Treatment of the same mixture at 500 and 800 °C results in crystalline and ordered thick NiO on AuNi particles. According to the X-ray diffraction (XRD) results, the bimetallic AuNi alloy structure is highly preserved at all temperatures and acts as a substrate for the growth of amorphous nickel and crystalline thick NiO, which is in sharp contrast to other reported methods. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and extended X-ray absorption fine structure (EXAFS) results reveal that amorphous Ni transformed into highly disordered NiO aggregates, which are in the proximity to AuNi. The close proximity of highly dispersed defect-rich NiO to AuNi results in abundant Ni(OH) 2 /AuNi interfacial sites, which provide more accessible active sites for alcohol molecule adsorption. The as-prepared disordered NiO on AuNi exhibits excellent electrocatalytic activity and stability for methanol electrooxidation by combining the benefits of the electronic structure optimization of disordered NiO on AuNi through the synergistic effects among rich oxygen vacancies and high-concentration nickel valence species, as well as the anchoring effect of the N-doped carbon layer compared to that of crystalline, ordered thick NiO on AuNi. Thus, the highly dispersed defect-rich NiO on AuNi may inspire the development of platinum-free metal catalysts for alcohol fuel oxidation processes.