Storage of hydrogen at 303 K in graphite slitlike pores from grand canonical Monte Carlo simulation.
Storage of hydrogen at 303 K in graphite slitlike pores from grand canonical Monte Carlo simulation.
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DOI：
10.1021/jp0529063
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发表时间：
2005-08
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影响因子：
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通讯作者：
P. Kowalczyk;Hideki Tanaka;R. Hołyst;K. Kaneko;T. Ohmori;J. Miyamoto
中科院分区：
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作者：
P. Kowalczyk;Hideki Tanaka;R. Hołyst;K. Kaneko;T. Ohmori;J. Miyamoto
采用巨正则蒙特卡罗（GCMC）方法模拟了氢在理想石墨狭缝孔中的吸附。在所有的模拟中，量子效应通过费曼和希布斯二阶有效势被包括在内。模拟的表面过量氢等温线用于测定沥青基活性炭纤维的总储氢量、石墨狭缝状孔中的氢密度、孔径和体积分布、每摩尔吸附焓、总表面积、总孔体积和平均孔径。结合实验结果和模拟结果表明，在303 K时，石墨狭缝状孔隙中的氢密度不超过0.014 g/cm（3），即三相点处液氢密度的21%。在所考虑的孔隙几何形状中，在303 K下储存氢的最佳孔隙尺寸取决于储存压力。对于较低的储存压力，p <30 MPa，最佳孔宽度等于氢的2.2碰撞直径（即，0.65 nm），而对于与50 MPa一致的p，孔宽度等于氢的约7.2碰撞直径（即，2.13 nm）。对于较宽的孔，即，孔宽度超过氢的7.2碰撞直径，氢吸附的表面过量是恒定的。量子效应的重要性是公认的窄石墨狭缝状孔隙在整个范围内的氢压力，以及在更广泛的在高压散装氢。对于所考虑的碳质材料，每摩尔的吸附量实际上随氢负载量而恒定，并且在与7.28-7.85 kJ/mol一致的窄范围q（st）内变化。我们在303 K下对石墨狭缝状孔隙中氢吸附的系统研究，使我们深入了解了作为最有前途的清洁能源的氢储存的及时性问题。计算的氢的最大储存量等于约1.4wt%，这远低于美国能源部（DOE）的目标（即，6.5 wt %），从而得出结论，在303 K下在碳纤维的石墨狭缝状孔中获得的氢的总储存量还不够。
Grand canonical Monte Carlo (GCMC) simulations were used for the modeling of the hydrogen adsorption in idealized graphite slitlike pores. In all simulations, quantum effects were included through the Feynman and Hibbs second-order effective potential. The simulated surface excess isotherms of hydrogen were used for the determination of the total hydrogen storage, density of hydrogen in graphite slitlike pores, distribution of pore sizes and volumes, enthalpy of adsorption per mole, total surface area, total pore volume, and average pore size of pitch-based activated carbon fibers. Combining experimental results with simulations reveals that the density of hydrogen in graphite slitlike pores at 303 K does not exceed 0.014 g/cm(3), that is, 21% of the liquid-hydrogen density at the triple point. The optimal pore size for the storage of hydrogen at 303 K in the considered pore geometry depends on the pressure of storage. For lower storage pressures, p < 30MPa, the optimal pore width is equal to a 2.2 collision diameter of hydrogen (i.e., 0.65 nm), whereas, for p congruent with 50MPa, the pore width is equal to an approximately 7.2 collision diameter of hydrogen (i.e., 2.13 nm). For the wider pores, that is, the pore width exceeds a 7.2 collision diameter of hydrogen, the surface excess of hydrogen adsorption is constant. The importance of quantum effects is recognized in narrow graphite slitlike pores in the whole range of the hydrogen pressure as well as in wider ones at high pressures of bulk hydrogen. The enthalpies of adsorption per mole for the considered carbonaceous materials are practically constant with hydrogen loading and vary within the narrow range q(st) congruent with 7.28-7.85 kJ/mol. Our systematic study of hydrogen adsorption at 303 K in graphite slitlike pores gives deep insight into the timely problem of hydrogen storage as the most promising source of clean energy. The calculated maximum storage of hydrogen is equal to approximately 1.4 wt %, which is far from the United States Department of Energy (DOE) target (i.e., 6.5 wt %), thus concluding that the total storage amount of hydrogen obtained at 303 K in graphite slitlike pores of carbon fibers is not sufficient yet.