氢气在碳纳米管基材料上的吸附-脱附特性

Characteristics of Adsorption and Desorption of Hydrogen on Multi-walled Carbon Nanotubes

利用高压容积法测定多壁碳纳米管(MWCNTs)及钾盐修饰的相应体系(K+-MWCNTs)的储氢容量,并用程序升温脱附(TPD)方法表征研究氢气在MWCNTs基材料上的吸附-脱附特性.结果表明,在经纯化MWC-NTs上,室温、9.0MPa实验条件下氢的储量可达1.51%(质量分数);K+盐对MWCNTs的修饰对增加其储氢容量并无促进效应,但相应化学吸附氢物种的脱附温度有所升高;K+的修饰也改变了MWCNTs表面原有的疏水性质.在低于723K的温度下,H2/MWCNTs体系的脱附产物几乎全为氢气;773K以上高温脱附产物不仅含H2,也含有CH4、C2H4、C2H2等C1/C2烃混合物;H2/K+-MWCNTs储氢试样的脱附产物除占主体量的H2及少量C1/C2烃混合物外,还含水汽,其量与吸附质H2源水汽含量密切相关.H2在碳纳米管基材料上吸附兼具非解离(即分子态)和解离(即原子态)两种形式.

Storage capacities of H 2 in a kind of multi-walled carbon nano tubes(MWCNTs )and its correspond-ing system modified with K + salt were measured using volumetric method,and characteristics of adso rption and desorption of hydrogen on MWCNTs were studied by means of temperature-pr ogrammed desorption(TPD)method.The results showed that the s torage capacities of H 2 in the purified MWCNTs could reach 1.51%(mass fraction)under condition of room temperature and 9.0MPa,with adsorption of ～99%o f the H 2 being re-versible.A comparative study indic ated that the modification of the K + salt to the MWCNTs did not improve its storage capacity of hydrogen,but le d to elevating of desorption tempera ture of adsorbed hydrogen H 2 (a)to a cer-tain extent;in addition,the K + modification resulted also in chang ing of surface property of the MWCNTs from original hydrophobicity to hydroph ilicity.The products desorbed on H 2 /MWCNTs involved exclusively H 2 at T≤723K,and main part of H 2 and small amount of CH 4 ,C 2 H 4 ,and C 2 H 2 at T≥773K;whereas on H 2 /K + -MWCNTs,H 2 O was also involved in the desorbed pr oducts,in addition to H 2 and small amount of C 1 /C 2 -hydrocarbons.The adsorption of H 2 on the MWCNTs-based materials is in t he two models:associative(molecular state)and dissociative(atomic state).