A 'Nanopore Lithography' Strategy for Synthesizing Hierarchically Micro/Mesoporous Carbons from ZIF-8/Graphene Oxide Hybrids for Electrochemical Energy Storage

摘要

Porous carbons derived from metal-organic frameworks (MOFs) are promising materials for a number of energy- and environment-related applications, but their almost exclusively microporous texture can be an obstacle to their performance in practical uses. Here, we introduce a novel strategy for the generation of very uniform mesoporosity in a prototypical MOF, namely, zeolitic imidazolate framework-8 (ZIF-8). The process, referred to as "nanopore lithography", makes use of graphene oxide (GO) nanosheets enclosing ZIF-8 particles as masks or templates for the transfer of mesoporous texture to the latter. Upon controlled carbonization and activation, nanopores created in the GO envelope serve as selective entry points for localized etching of carbonized ZIF-8, so that such nanopores are replicated in the MOF-derived carbonaceous structure. The resulting porous carbons are dominated by uniform mesopores similar to 3-4 nm in width and possess specific surface areas of similar to 1300-1400 m(2) g(-1). Furthermore, we investigate and discuss the specific experimental conditions that afford the mesopore-templating action of the GO nanosheets. Electrochemical characterization revealed an improved capacitance as well as a faster, more reversible charge/discharge kinetics for the ZIF-8-derived porous carbons obtained through nanopore lithography, relative to those for their counterparts with standard activation (no GO templating), thus indicating the potential practical advantage of the present approach in capacitive energy storage applications.