Improved hydrogen sorption/desorption capacity of exfoliated NiCl2-graphite intercalation compound effected by thermal treatment

In the present work an advantageous effect of thermal exfoliation of graphite intercalation compound with nickel chloride (NiCl2-GIC) on the kinetics of the reaction of hydrogen sorption/desorption occurring in alkaline solution in electrodes made of exfoliated material is proven. The electrochemical investigations were carried out using the cyclic voltammetry method. It was shown that the changes occurred in the crystalline and chemical structure and morphology due to the subsequent thermal exfoliation of NiCl2-GIC primarily exfoliated by chemical method give rise to the increase of the anodic charge associated with both the recovery reaction of hydrogen stored in the electrode material during the precedent process of hydrogen adsorption/absorption and the oxidation reactions of metallic nickel. The improvement of the reversible hydrogen storage capacity is attributed to both the porous structure of graphite and the presence of nickel oxide highly dispersed in the exfoliated graphite matrix. The anodic charge corresponding to the recovery reaction of hydrogen stored in the electrode material appeared to be the highest for NiCl2-GIC subjected to chemical exfoliation in hydrogen peroxide solution followed by heattreatment at 800 °C in air. After this process a two-fold enhancement of the hydrogen storage capacity was noted.