The electrochemical properties of LaNi 5 electrodes doped with multi-walled carbon nanotubes synthesized by chemical vapor deposition and treated at different temperatures in a nitrogen atmosphere

Abstract

The electrochemical properties of LaNi 5 electrodes doped with multi-walled carbon nanotubes (MWNTs) treated at different temperatures in a nitrogen atmosphere were investigated. The MWNTs were synthesized by chemical vapor deposition (CVD). The purified carbon nanotubes (CNTs) were annealed during 1.5 h in a nitrogen atmosphere at different temperatures. A three-electrode system was applied. The CNTs-LaNi 5 electrodes were prepared by mixing CNTs and LaNi 5 in a weight ratio of 1:10, and used as the working electrode; Ni(OH) 2/NiOOH worked as the counter electrode and Hg/HgO as the reference electrode. A 6 mol/L KOH solution acted as the electrolyte. MWNTs annealed at different temperatures in a nitrogen atmosphere showed large differences in the electrochemical hydrogen storage capability under the same testing condition. The CNTs-LaNi 5 electrodes with 20–40 nm diameter CNTs heated at 800 °C in nitrogen proved to have the best electrochemical hydrogen storage capacity, with a discharging capacity of 519.1 mAh/g and a corresponding discharging plateau voltage of 1.18 V, at a 200 mA/g charge current density and a 60 Ma/g discharge current density with a 0.2 V discharge voltage limit. From 500 to 800 °C, the higher the annealing temperature,the better the electrochemical hydrogen storage property. However, CNTs-LaNi 5 electrodes with 20–40 nm diameter CNTs heated at 900 °C in nitrogen have a lower capacity of 476.2 mAh/g under the same testing condition. This shows that the annealing temperature of CNTs is an important factor that influences their electrochemical hydrogen storage performance.