The Research On The Electrochemical Hydrogen Storage Properties Of Carbon Nanotubes

The application of CNTs in the electrodes of hydrogen storage battery were carried out to improve the electrochemical hydrogen storage ability.The electrochemical hydrogen storage capacities of CNTs-Ni and CNTs-LaNi₅ electrodes were studied.The effect of CNTs treated with different temperature on the electrochemical Properties of CNTs-Ni and CNTs-LaNi₅ electrodes were investigated.The effect of CNTs with different diameters on the electrochemical Properties of electrodes were researched.The effect of LaNi₅ electrodes mixing 3% CNTs and cathodes mixing Ni powder or Ca(OH)₂ in a different weight ratio on the electrochemical Properties were investigated.(1)The effect of MWNTs treated with different temperature in vacuum on the electrochemical Properties of CNTs-Ni electrodes were investigated.The MWNTs were synthesized by chemical vapor deposition(CVD)using LaNi₅ alloy particles as catalyst,the purified CNTs were treated with a different temperature for 1.5 h in vacuum.Three-electrode system was introduced.The CNTs-Ni electrodes were used as the working electrode,which were prepared by mixing carbon nanotubes(CNTs) and Ni powder in a weight ratio of 1:10.Ni(OH)₂/NiOOH worked as the counter electrode and Hg/HgO as the reference electrode.6 mol/L KOH solution acted as the electrolyte.Results showed that the MWNTs heated with different temperature in vacuum represented a great discrepancy in the electrochemical hydrogen storage capability under the same testing condition.The CNTs-Ni electrode with 40-60nm diameter CNTs treated 800℃in vacuum has the best electrochemical hydrogen storage capacity with a highest capacity of 580.3 mAh/g and a corresponding discharging plateau voltage of 1.10 V,which were gained with 100 mA/g charge current density and 60mA/g discharge current density 0.1V discharge voltage limit. From 500℃to 800℃,the higher temperature MWNTs heated with in vacuum,the better the electrochemical hydrogen storage property of them is.However,CNTs-Ni electrode with the CNTs treated 900℃in vacuum has the lower capacity under the same testing condition.This shows that the temperature of CNTs heated in vacuum is an important factor that influences its electrochemical hydrogen storage performance. The biggest discharging capacity of the Ni electrode is only 18.0 mAh/g.Its effect on the discharging capacity of CNTs can be neglected,because the Ni electrode has such a small discharging capacity.So,the CNTs in the CNTs-Ni electrodes are mainly responsible for their discharging ability.(2)The effect of MWNTs treated with different temperature in vacuum on the electrochemical Hydrogen storage properties were studied.The MWNTs were synthesized by chemical vapor deposition(CVD).The CNTs-LaNi₅ electrodes were prepared by mixing MWNTs and LaNi₅ Alloy in a weight ratio of 1:10. Three-electrode system was introduced.The CNTs-LaNi₅ electrodes were used as the working electrode.Ni(OH)₂/NiOOH worked as the counter electrode and Hg/HgO as the reference electrode.6 mol/L KOH solution acted as the electrolyte.Results showed that the CNTs-LaNi₅ electrode with CNTs treated 850℃in vacuum has the best electrochemical hydrogen storage capacity with a highest discharging capacity of 503.6 mAh/g and a corresponding discharging plateau voltage of 1.18 V under the same testing condition.From 500℃to 850℃,the higher temperature MWNTs heated with in vacuum,the better the electrochemical hydrogen storage property of them is. However,CNTs-LaNi₅ electrode with CNTs treated 950℃in vacuum has the lower discharging capacity under the same testing condition.The MWNTs heated with different temperature in nitrogen represented a great discrepancy in the electrochemical hydrogen storage capability under the same testing condition.(3)The effect of MWNTs treated with different temperature in nitrogen on the electrochemical Properties of CNTs-Ni electrodes were researched.,the purified CNTs were treated with a different temperature for 1.5 h in nitrogen.Three-electrode system was introduced.The CNTs-Ni electrodes were used as the working electrodes,which were prepared by mixing carbon nanotubes(CNTs)and Ni power in a weight ratio of 1:10.Results showed that MWNTs heated with different temperature in nitrogen represented a great discrepancy in the electrochemical hydrogen storage capability under the same testing condition.The CNTs-Ni electrode with CNTs treated 800℃in nitrogen has the best electrochemical hydrogen storage capacity with a highest capacity of 588.1 mAh/g and a corresponding discharging plateau voltage of 1.18 V, which were gained under the same testing condition.Both the discharging capacity and discharge plateau voltage of CNTs-Ni electrodes with CNTs heated 500℃in nitrogen are a little superior to that of CNTs-Ni electrodes with CNTs unheated.From 500℃to 800℃,the higher temperature MWNTs heated with in nitrogen,the better the electrochemical hydrogen storage property of them is.However,CNTs-Ni electrode with CNTs treated 900℃has the lower capacity under the same testing condition.(4)The structure change of multi-wall carbon nanotubes(MWNTs)after heat treatment and the effect of MWNTs treated with different temperature in nitrogen ambient on the electrochemical Properties of CNTs-LaNi₅ electrodes were investigated.The end of MWNTs is more opened,the inside of MWNTs is more unimpeded than that of MWNTs unheated.So the deposition and release of hydrogen are easier.CNTs-LaNi₅ electrodes were prepared by mixing MWNTs and LaNi₅ Alloy in a weight ratio of 1:10.The CNTs-LaNi₅ electrode with MWNTs treated 800℃in nitrogen has the best electrochemical hydrogen storage capacity with a highest capacity of 519.1 mAh/g and a corresponding discharging plateau voltage of 1.19 V.From 500℃to 800℃,the higher temperature the MWNTs heated,the better the electrochemical hydrogen storage property of them is.However,CNTs-LaNi₅ electrode with MWNTs treated 900℃has the lower capacity.The structure of multi-wall carbon nanotubes(MWNTs)has changed after heat treatment,the deposition and release of hydrogen are easier.The MWNTs heated with different temperature in nitrogen represented a great discrepancy in the electrochemical hydrogen storage capability.(5)The effect of MWNTs with different diameters on the electrochemical Properties of LaNi₅ Alloy were discussed(unheated).The CNTs-LaNi₅ electrodes were prepared by mixing carbon nanotubes(CNTs)and LaNi₅ Alloy in a weight ratio of 1: 10.Results showed that MWNTs with different diameters represented a great discrepancy in the electrochemical hydrogen storage capability under the same testing condition.20-40 nm CNTs-LaNi₅ electrode has the best electrochemical hydrogen storage capacity with a highest capacity of 381.3 mAh/g.However,10-20 nm CNTs-LaNi₅ electrode has the lowest capacity of 315.7 mAh/g under the same testing condition.The CNTs-LaNi₅ electrodes with different diameters exhibit different discharge performance under the same charge/discharge current density and discharge voltage limit.It is not that the bigger the diameter of MWNTs is,the better the electrochemical hydrogen storage property of MWNT is,and nor is the opposite.The 20-40 nm CNTs-LaNi₅ electrode represents the best discharge ability,and has a higher and steadier discharge characteristic and capacity.(6)The effect of MWNTs with different diameters on the electrochemical Properties of LaNi₅ Alloy were investigated,the purified CNTs were treated with a temperature of 500℃for 1.5 h in vacuum.Results showed that MWNTs with different diameters represented a great discrepancy in the electrochemical hydrogen storage capability under the same testing condition.20-40 nm CNTs-LaNi₅ electrode has the best electrochemical hydrogen storage capacity with a highest capacity of 425.9 mAh/g and a corresponding discharging plateau voltage of 1.07 V.However,60-100 nm CNTs-LaNi₅ electrode has the lowest capacity of 340.5 mAh/g under the same testing condition.The CNTs-LaNi₅ electrodes with different diameters exhibit different discharge performance,The MWNTs with a diameter of 20-40 nm and 40-60nm are good hydrogen storage material compared with the other diameter distribution.(7)The effect of LaNi₅ electrode mixing 3%CNTs and cathode mixing Ni powder in a different weight ratio on the electrochemical Properties of cathode were investigated.Results showed that the LaNi₅ electrode doping 3%CNTs showed higher electrochemical hydrogen storage capacities and a longer cycle life than un-mixing CNTs.The cathode mixing Ni powder in a different weight ratio represented a great discrepancy in the electrochemical hydrogen storage capability under the same testing condition.The cathode mixing Ni powder in a weight ratio 7%has the best electrochemical hydrogen storage capacity with a highest capacity of 377.6 mAh/g. From weight ratio 1%to 7%,the higher the cathode mixing Ni powder in weight ratio,the better the electrochemical hydrogen storage property of them is.However, The cathode mixing Ni powder in a weight ratio 9%has the lower capacity under the same testing condition.(8)The effect of LaNi₅ electrode mixing 3%CNTs and cathode mixing Ca(OH)₂ in a different weight ratio on the electrochemical Properties of cathode were investigated.Results showed that The LaNi₅ electrode doping 3%CNTs showed higher electrochemical hydrogen storage capacities and a longer cycle life than un-mixing CNTs.The cathode mixing Ca(OH)₂ in a different weight ratio represented a discrepancy in the electrochemical hydrogen storage capability under the same testing condition.The cathode mixing Ca(OH)₂ in a weight ratio 1%has the best electrochemical hydrogen storage capacity.