Study On Activated Carbon Fiber Modification And Hydrogen Storage

As the population continues to grow,with the dwindling of fossil energy reserves,the greenhouse effect on the climate is obvious,hydrogen as a new type of energy,has the advantages of high calorific value and pollution-free,but the storage conditions of hydrogen are harsh.Activated carbon fiber as a new type of adsorbent material which is known as low cost、strong adsorption capacity.In this paper,activated carbon fiber was used as a precursor to modify by surface-loaded metal、heat treatment、ammonia impregnation、heat treatmentammonia impregnation and other methodsACF modified by nickel nitrate impregnation was investigated by orthogonal analysis,the results show that the influence of B impregnation time >F activation constant temperature >A impregnation concentration >E activation temperature on the hydrogen storage amount,however,C immersion temperature and D activation heating rate had no effect on hydrogen storage.The optimum condition of modification was the nickel salt mass fraction 0.05%、impregnation for 6 h、impregnation temperature 35℃、activation temperature 600℃、constant temperature time 40 min、heating rate 6℃/min.The hydrogen storage capacity of the modified activated carbon fiber reached to 2.33 wt.%,increased by 28.4%.The increase of hydrogen storage in the modified material is the result of the action of the adsorption site provided by the nickel oxide load and the increase of the micro-pore ratio.Other metal salts were modified with optimum conditions,the results also show that ACF modified by samarium nitrate and nickel nitrate can improve the hydrogen storage capacity of ACF.The control variable method was used to investigate the heat treatment modification of ACF.The optimal condition of modification was the heat treatment temperature 600℃、constant temperature time 60 min、heating rate 6℃/min。After heat treatment,the acid functional groups on the surface of the material decreased,the number of basic functional groups was basically unchanged,and the polarity of the material surface decreased.After heat treatment,the number of micro-pores and micro-pores increased,and the hydrogen storage capacity reached to 2.06 wt.%,increased by 17.1%.After the secondary activation of ACF by KOH,the hydrogen storage capacity of the modified material generally decreased until 0,the BET characterization was carried out on the selected materials whose hydrogen storage capacity was exactly 0,and the results showed that the pore size greater than 1.2 nm was not helpful for hydrogen storage.The ACF modified by ammonia was investigated by the method of control variables.The optimum condition of modification was ammonia concentration 25 wt.%、 impregnation temperature 25℃、impregnation for 8 h.After the modification of ammonia treatment,the number of acidic functional groups on the surface of the material decreased,the number of alkaline functional groups increased significantly,and the polarity of the material surface decreased.The BET characterization showed that the number of micropores and extremely micropores of the modified material decreased,and the hydrogen storage amount reached 2.08 wt.%,increased by 18.2%.Because the reduction of ACF surface polarity is beneficial to hydrogen storage,ammonia modification can better reduce the surface polarity compared with heat treatment,but it has certain damage to the micro-porous structure of the material.After heat treatment,the ACF surface polarity decreased less,but the microporous structure of the material became more abundant.ACF modified by heat treatment-ammonia was investigated by orthogonal analysis,the results showed that the effect on hydrogen storage A activation temperature > C ammonia concentration,however,the effect of B activation time and D impregnation time on hydrogen storage could be negligible.The optimum condition for modification was activation temperature 600℃、activation constant temperature time 60 min、heating rate 6 ℃/min、ammonia concentration 25 wt.%、immersion time 8h、immersion temperature 25℃.After the modification,the number of acid functional groups on ACF surface decreased,while the number of alkaline functional groups increased.Moreover,the pore structure parameters of the modified material were basically the same as those of the original ACF.The hydrogen storage capacity of the modified material reached 2.39 wt.%,increased by 35.8%.