钾掺杂多壁纳米碳管储氢性能研究

Hydrogen Storage Capacity of Potassium-doped Multi-walled Carbon Nanotubes

使用自制的钴催化裂解碳氢气法制备多壁纳米碳管 ,并对其进行退火、掺杂等一系列预处理 ,然后使用高压高纯氢源 ,在中压 (12MPa)和室温条件下 ,进行钾掺杂多壁纳米碳管的储氢性能实验 .结果表明 :预处理对纳米碳管的储氢性能有很大影响 .实验条件下 ,经过氮气退火 ,并在 1.0mol/L硝酸钾溶液中掺杂的多壁纳米碳管吸氢量最大 (H/C质量分数为 3.2 % ) .上述样品在室温下的放氢量一般不超过其吸氢量的 5 0 .8% .

Multi - walled carbon nanotubes with diameters of 20 similar to 30nm were synthesized by cobalt - catalytic decomposition of acetylene, which are showed by TEM images. A series of pretreatments including purification, annealing and doping were performed before carrying out hydrogen storage experiments at room temperature and modest pressure ( 12 MPa). For comparison, the annealing treatments were processed under ambient pressure in air and nitrogen atmosphere respectively. KNO3 solutions (0.1 mol/L and 1.0 mol/L) were used to dope carbon nanotubes. The results suggest that both annealing and doping play an important role in the hydrogen storage capacity of carbon nanotubes. Under the same conditions conducted, MWNTs annealed in nitrogen adsorbed more hydrogen than those annealed in air. FTIR spectra of the samples shows that the amount of oxygen functional groups linked to MWNTs after annealed in air is more than that treated in nitrogen. The former treatment may bring about more agglomeration of MWNTs, decrease the specific area and surface activity of MWNTs and eventually lead to lower capacity of hydrogen adsorption. The results also show that with the same dopant, the capacity of hydrogen adsorption has great difference when the concentration of the doping solution changed. Hydrogen adsorption of MWNTs increased not only after doped in KNO3 solution but also with the increase of solution concentration in certain extent. An optimal result(3.2%) was obtained when carbon nanotubes were annealed in nitrogen at 500 degreesC and doped in 1.0 mol/L KNO3 solution. Hydrogen desorption experiments were also carried out at room temperature. It is found that after a typical adsorption/desorption cycle under ambient. temperature, the MWNTs samples still retain significant amount of stored hydrogen. The phenomenon may be attributed to the existence of two types of adsorbed hydrogen in the structure: physical and chemical adsorptions, the former can be released easily and the latter is strongly bound and could be released more difficultly.