Structural Evolution from Metal–Organic Framework to Hybrids of Nitrogen-Doped Porous Carbon and Carbon Nanotubes for Enhanced Oxygen Reduction Activity

A series of hybrids of nitrogen-doped graphitic porous carbon and carbon nanotubes (NGPC/NCNTs) are readily prepared in a stepwise manner by using a typical metal–organic framework (MOF-5) and urea as the carbon and nitrogen precursors, and nickel as the graphitization catalyst, respectively. These NGPC/NCNTs hybrids have demonstrated prominent catalytic activities toward oxygen reduction reaction (ORR) in alkaline medium. Compared to the benchmark Pt/C catalyst, the optimized NGPC/NCNT-900 (annealed at 900 °C) exhibits superior catalytic activity, durability and methanol tolerance, which makes it one of the best ORR electrocatalysts derived from MOFs. The promising properties in NGPC/NCNT-900 are mainly attributed to synergistic contributions of its unique hybrid structure, rich nitrogen doping, high graphitic degree, and large surface area. This attractive route for the preparation of NGPC/NCNTs holds promise for general use of a great number of available and yet rapidly growing MOFs in constructing high-performance carbon-based ORR electrocatalysts.