3D Melamine Sponge-Derived Cobalt Nanoparticle-Embedded\nN‑Doped Carbon Nanocages as Efficient Electrocatalysts for\nthe Oxygen Reduction Reaction

Abstract

The large-scale and\ncontrollable synthesis of novel N-doped three-dimensional\n(3D) carbon nanocage-decorated carbon skeleton sponges (Co-NCMS) is\nintroduced. These Co-NCMS were highly active and durable non-noble\nmetal catalysts for the oxygen reduction reaction (ORR). This hybrid\nelectrocatalyst showed high ORR activity with a diffusion-limiting\ncurrent of 5.237 mA·cm^–2 in 0.1 M KOH solution\nthrough the highly efficient 4e^– pathway, which\nwas superior to that of the Pt/C catalyst (4.99 mA·cm^–2), and the ORR Tafel slope is ca. 67.7 mV·dec^–1 at a high potential region, close to that of Pt/C. Furthermore,\nCo-NCMS exhibited good ORR activity in acidic media with an onset\npotential comparable to that of the Pt/C catalyst. Most importantly,\nthe prepared catalyst showed much higher stability and better methanol\ntolerance in both alkaline and acidic solutions. The power density\nobtained in a proton exchange membrane fuel cell was as high as 0.37\nW·cm^–2 at 0.19 V compared with 0.45 W·cm^–2 at 0.56 V for the Pt/C catalyst. In Co-NCMS, the\nN-doped carbon nanocages facilitated the diffusion of the reactant,\nmaximizing the exposure of active sites on the surface and protecting\nthe active metallic core from oxidation. This made Co-NCMS one of\nthe best non-noble metal catalysts and potentially offers an alternative\napproach for the efficient utilization of active transition metals\nin electrocatalyst applications.