Mesoporous Ni-Co based nanowire arrays supported on three-dimensional N-doped carbon foams as non-noble catalysts for efficient oxygen reduction reaction

Homologous Ni-Co based mesoporous nanowire arrays, involving nickel cobalt oxide (NiCo₂O₄) and nickel cobalt sulfide (NiCo₂S₄), are successfully grown on three-dimensional (3D) nitrogen-doped carbon foam (NDCF) via a facile hydrothermal reaction followed by annealing and sulfurization treatment, respectively. The NiCo₂O₄ nanowires in the obtained NiCo₂O₄/NDCF composites are composed of numerous small nanoparticles with the presence of mesopores, while the NiCo₂S₄ nanowires of NiCo₂S₄/NDCF composites exhibit unique hollow structures with mesoporous walls. When served as non-noble catalysts for oxygen reduction reaction (ORR), the homologous NiCo₂O₄/NDCF and NiCo₂S₄/NDCF composites exhibit a comparable catalytic activity with a four-electron pathway, superior selectively and methanol tolerance over commercial Pt/C catalyst. Especially, the NiCo₂S₄/NDCF composites possess much higher stability than the Pt/C catalyst in alkaline electrolyte, thus holding great promise in practical application. The impressive performance may originate from the hollow nanowire morphology and the unique mesoporous structure which provide a high surface density of catalytic active sites exposed to oxygen molecules and facilitate the efficient transport of reactant species. Meanwhile, the introduced NDCF with enhanced catalytic activity from the incorporation of the N element generates synergistic effect with NiCo₂O₄ and NiCo₂S₄, and enhances their conductivities, therefore playing a significant role in improving their catalytic performance.