氢在多壁碳纳米管上吸附行为研究

根据热力学平衡原理推导了通用吸附等温方程.通过比较氢在碳纳米管和炭狭缝孔上的高阶维里吸附系数，分析了77～297 K温度区间，温度、管径(孔宽)对碳纳米管、炭狭缝孔吸附空间储氢容量的影响，并由氢在石墨平面上的最大吸附容量计算了本次试验多壁碳纳米管(MWCNTs)在各平衡温度时的最大氢吸附容量.运用确定参数后的吸附等温方程，线性回归分析了氢在本次试验MWCNTs上的吸附数据.结果表明，在160～180 K温度区间，管内被吸附氢分子之间由于吸附受压产生的排斥能出现极大值；随着温度升高，氢分子之间以吸引力为主，提高氢气压力后才发生明显吸附.

Theoretical Study on the Adsorbed Hydrogen Molecules on Multi Walled Carbon Nanotubes

A general model for hydrogen adsorption is derived to discuss the compressibility of the hydrogen molecules on the adsorption surface caused by the strong adsorptive potential exerted by the carbon wall. The mono-layer capacity (see Table 1) inside the tube of the MWCNTs tested in our laboratory is evalued by the comparison studies on the adsorptive performance between the tubular pore and the slit-pore, the results show that better adsorptive performance can only be obtained when temperature is getting lower or the diameter of the tube is getting smaller (see Fig.1). From the model, the strong attraction to the surface may even cause hydrogen molecules to attain much higher densities than that of liquid hydrogen, and this will surely make adsorbed hydrogen molecules to behave as repulsion among each other. This phenomenon is discussed in terms of experimental data and the ascertained model (see Fig.3). A linear form of the model is applied to determine the interaction energy between hydrogen molecules in the adsorbed layer from the experimental data. Analysis of the experimental data of hydrogen adsorption over a wide range of pressure and temperature shows that the energies of hydrogen-hydrogen interactions in the adsorbed phase are positive in low temperature region(< 200 K) and obtain the highest value in the temperature range of 160～180 K, but will be negative when the temperature is above 230 K(see Fig.4), indicating the repulsions among the adsorbed hydrogen molecules are prominent in low temperature, however, the attractions among the adsorbed hydrogen molecules at higher temperature are hard to understand because the pressures are also high in those cases. Comments are made that the chemical adsorption should be included to interpret the experimental data at higher temperatures. The results presented here also show that the concept of ‘maximum capacity’ for hydrogen adsorption should differ from the density of the adsorbed hydrogen molecules.