Hierarchically nanoporous carbons: synthesis, characterization and electrochemical application

Abstract

The work presented in this thesis addressed the synthesis, characterization and electrochemical application of carbon materials possessing a mesopore-micropore hierarchy. Nanoporous carbons, a class of non-oxide porous materials, have received a great deal of scientific and technological interest due to their large surface area and tunable porosity as well as the superior physical and chemical properties, such as electrical conductivity, thermal conductivity, chemical stability and light-weight. These advantages make nanoporous carbons significantly desirable for use as electrode materials in energy conversion and storage devices including fuel cells, Li-ion batteries and electrical double layer capacitors (EDLC). In particular, with growing need of the devices capable of supplying high power, extensive studies related to the carbon applications have focused on design of suitable carbon electrodes for high performance of EDLC. In EDLC, where the energy stores by the adsorption of ions on the electrode surfaces, the performance is dramatically affected by the pore size of electrodes. Microporous carbons exhibit higher capacitance at low discharge current density than mesoporous carbons, due to the high surface area. In high current conditions, on the other hand, mesoporous carbons show better performance due to low diffusion resistance of electrolyte. However, neither of these materials can achieve high energy density and high power density simultaneously. To achieve the both, several attempts to synthesize carbon materials with a hierarchically meso-/microporous structure were made in the past. In the present work, a hierarchically meso-/microporous carbon was synthesized via templating the intracrystalline microporous texture of beta zeolite nanocrystals and their intercrystalline mesoporous texture. Various compounds were evaluated as the carbon precursors in the carbon synthesis and resultant carbon products were rigorously characterized by X-ray diffracti...