Potential Applications of Mesoporous Carbon Materials for Hydrogen Fuel Storage

• Main Authors: Li-Ren Chang, 張立仁
• Other Authors: Shang-Bin Liu
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/00679630747571126078

碩士 === 國立臺灣師範大學 === 化學系 === 93 === ABSTRACT Hydrogen, which can be produced from renewable sources, has emerged as one of the most promising candidates for the replacement of the current carbon-based energy carriers in the twenty-first century. The advantages of hydrogen over other fossil fuels are two folds: first, it is a clean combustion of a nontoxic fuel. Secondly, its high delivered energy per mass. Thus, the utilization of hydrogen fuel is believed to be the solution for today’s continuous shortages in fossil fuel supplies and increasing demands in environmental control issues. Although many advances in hydrogen production, purification and utilization technologies have been made since 1990’s, hydrogen storage technologies must be significantly advanced if a hydrogen-based energy system, particularly in the transportation sector, is to be established. In this context, the search for ideal technologies for hydrogen storage, which requires major advances in storage capacity, energy efficiency, safety and cost, so that the uptake can be rationally optimized to commercially attractive levels is a demanding and challenging task. The objective of this research is to evaluate the potential applications of novel carbon mesoporous materials, CMK-n (n = 1, 3, 5), as supports for hydrogen fuel storage. For comparison, commercially available carbon materials, namely graphite fine powder (GFP) and graphite nano-fiber (GNF), were also examined. The structural and physical-chemical properties of the carbon materials as well as the adsorption dynamics of hydrogen were characterized by a variety of different analytical and spectroscopic techniques. All carbon materials exhibit typical graphitized diamond-like structure with sp2 and sp3 bands, as also confirmed by powdered x-ray diffraction (PXRD) studies. N2 adsorption/desorption isotherm measurements (at 77 K) revealed the textual properties of various carbon materials; their BET surface areas (in unit of m2/g) follow the trend: CMK-5 (1690) > CMK-1 (1263) > CMK-3 (772) >> GNF (65) > GFP (18), whereas their pore diameter (in nm) follow the trend: CMK-3 (3.6) > CMK-5 (3.2) > CMK-1 (2.3), among them, GFP and GNF carbons were found to possess null porosities. Furthermore, unlike deuterium (2D) NMR of pure D2 gas, for which the observed chemical shift (6.2 ppm) was found independent of temperature and pressure, a notable decrease in 2D NMR chemical shift was observed for D2 adsorbed on carbon materials, mainly due to Knight shift effect. The observed chemical shift was also found to increase with increasing D2 loading as well as temperature. However, the linewidths observed for D2 adsorbed in the CMK-n appeared to be much narrower than GFP and GNF, revealing that D2 are in fast exchange in the ordered mesoporous carbon materials. In terms of hydrogen storage capability, various carbons show the following trend for adsorption capacities: follow the following trend: CMK-5 > GNF > CMK-3 > CMK-1> GFP. CMK-5, which has a tubular hollow carbon structure and highest surface area, revealed a hydrogen storage capacity of ca. 3.5 wt% at 273 K, 80 atm, substantially higher than GFP (1.5 wt%) and GNF (1.0 wt%). As expected, the storage capacity increase with decreasing temperature, for example, CMK-5 exhibited a hydrogen storage capacity of ca. 75 wt% at 77 K, 80 atm; a value greater than conventional graphite materials by at least three folds. The results obtained from the present study should promote fundamental understanding and development of novel nanostructured carbon materials and their potential applications in fuel storage and energy related issues.