碳基吸附剂储氢吸附热的密度泛函理论

DETERMINATION OF ISOSTERIC HEAT OF ADSORPTION OF HYDROGEN ON CARBON-BASED ADSORBENTS WITH NONLOCAL DENSITY FUNCTIONAL THEORY APPROACH

为比较狭缝孔、纳米管两种典型碳基吸附剂的储氢性能 ,应用非局域密度泛函理论、微观物理学、吸附平衡原理、典型吸附剂储氢试验结果计算并分析了典型碳基吸附剂的氢等量吸附热 .结果表明 ,两类吸附剂的氢等量吸附热相差不大 ,等温线变化规律相似 ,并且只有在低温 (液氮 )、适度压力时吸附储氢的质量密度才有望达到DOE标准 .

To evaluate the hydrogen adsorption performance of the typical carbon based adsorbents from the aspect of adsorption heat, nonlocal density functional theory (NDFT), Carnahan-Starling, MBWR equations of state and the mean-field theory are used to determine the bulk density and density profiles of hydrogen molecules within the adsorption space. The adsorption density is obtained from the weighted average of the density profile calculated with NDFT in the width (or radial) direction of adsorption space. The maximum physical adsorption capacities of hydrogen molecules in the close-packing state are used to calculate the isosteric heat of adsorption. The adsorption isotherms at 77-297 K with a step of 10 K and 1-l0 MPa with a step of 1 kPa are first determined, then, the isosteric heat of adsorption on three typical carbon based adsorbents are ascertained by the adsorbed phase volume and the bulk gas volume in thermodynamic equilibrium during the adsorption process. From the comparisons among the results from the NDFT calculation and experimental data, not only the isotherms of hydrogen adsorption on carbon nanotubes have similar figure to those of activated carbon, but also the values of isosteric heat of adsorption on these adsorbents are within the same range. Finally, the measure that the accurate hydrogen adsorption experiments on pure carbon nanotubes should be carried out to verify their physical adsorption performance, and the effective measures for the management of adsorption heat should also be emphasized while considering the cryogenic adsorption of hydrogen in carbon nanotubes.