N-doped ordered mesoporous carbons with improved charge storage capacity by tailoring N-dopant density with solvent-assisted synthesis

We report a facile, nanocasting synthetic method that results in nitrogen-doped mesoporous carbons with tailorable density of N-dopants and high charge storage capacity. The key step in the synthesis of the materials is the preparation of different nitrogen-functionalized SBA-15 mesoporous silicas with tunable density of organoamine groups using a simple solvent-assisted post-grafting method, and the use of the resulting materials both as hard templates as well as N-doping agents for the carbon materials forming inside the pores of SBA-15 via nanocasting. Accordingly, the carbonization of common carbon sources within the organoamine-functionalized SBA-15 produces mesostructured carbons containing different densities of nitrogen dopant atoms. Specifically, a polar protic solvent (ethanol) and a non-polar solvent (toluene) are used for grafting the organoamine groups, ultimately producing two different nitrogen-doped mesoporous carbons, labelled here as N-MC-E and N-MC-T, respectively. These materials possess not only different amounts of nitrogen dopant atoms (0.6 and 2.4 atomic%, respectively) but also distinct electrochemical and charge storage properties. Nitrogen sorption measurements indicate that both materials have mesoporous structures with a high surface area (typically, ∼800 m2 g−1) and nanometer pores with an average pore size of ∼5 nm. Electrochemical measurements at 0.5 A g−1 reveal that the N-MC-E and N-MC-T exhibit high capacitance (152.4 F g−1 and 190.2 F g−1, respectively). These values are either better or comparable to some of the highest capacitance values recently reported for related materials synthesized via other methods. In addition, N-MC-E and N-MC-T retain up to 98% of their stored charges or initial capacitance after 1,000 charge–discharge cycles at a current density of 2.0 A g−1. These results clearly show N-MCs' good electrochemical stability as well as potential application in energy storage.