General synthesis of zeolitic imidazolate framework-derived planar-N-doped porous carbon nanosheets for efficient oxygen reduction

High cost and scarcity of graphene boosts the great interests in seeking for its low-cost substitute, e.g., 2D carbons, for upcoming energy applications where extreme physical properties are not absolutely critical. Metalorganic frameworks (MOFs) are very convenient self-templated precursor towards carbon-based materials with tunable functionalities. However, the morphology of most MOF-derived carbons is largely limited to solid particles with limited active surface and diffusion kinetics. The morphology control is still remained the bottleneck for developing high-performance MOF-derived carbons with widespread applications until now. Here we report a general strategy for morphology control of zeolitic imidazolate framework (ZIF)-derived 2D carbon nanostructures by layered-nanospace-confinement growth of 2D ZIFs and in-situ carbonization. The process yields ZIF-derived porous carbon nanosheets with high level of planar N doping (over 93% in total N content) and highly tunable chemical compositions (pure carbon or decorated with various metals such as Co, Fe, Ni, NiCox, etc.). Unique 2D nanostructure renders them with extra exposed active surface area, more accessible porosity with much higher pore volume and shorter diffusion distance as compared to the particulate counterparts. Benefited from enhanced activity and diffusion kinetics, the ZIF-derived porous carbon nanosheets exhibit superior onset potential, current density and durability to commercial Pt catalyst and their particulate counterparts for oxygen reduction reactions in both alkaline and acidic medium.