Hierarchically porous carbons derived from nonporous metal-organic frameworks: Synthesis and influence of struts

It is challenging to synthesize low cost hierarchically structured porous carbons of high surface area and narrow mesopore-size distribution. In this paper we report a series of hierarchically porous carbons (HPCs) with the same mesopore size distribution but varied micropore sizes and surface areas. These HPCs were fabricated by one-pot thermal conversion of Zn-containing metal-organic framework (MOF) crystals with different “strut lengths” at high temperatures. Struts with different lengths were used as 'modulators' for controlling the surface area, porosity, morphology, structural ordering and conductivity of the HPCs derived, by pyrolysis of Zn-containing MOFs constructed with different linear or trident aromatic acids. The correlation between the properties of the end carbon products and the capacitive performance was studied. It is found that all MOFs-derived HPCs had higher the gravimetric specific capacitance compared to activated carbon. Among the HPCs synthesized, hierarchically porous carbon-bdc (HPC-bdc) derived from Zn-bdc (zinc benzene-1,4-dicarboxylate) exhibited the largest gravimetric specific capacitance (170 F/g). This HPC can be cycled up to 5000 times with a capacitance retention ratio of 98%. This is attributed to its long-range ordered structure, largest surface area (2816 m2/g) and highest porosity, and best conductivity.