Solvothermal Synthesis Of Metal Oxides-activated Carbon Composites And Study On The Electrochemical Performance

Supercapacitor is a new energy storage device between the traditionalcapacitor and lithium battery. Recently, supercapacitor emerge as a competitiveelectrochemical energy storage device due to their fast energy delivery, highpower capability and long life cycle (>105cycles). The electrode is one of themost important factors to determine the properties of supercapacitor.In this paper, we prepared metal oxide and hydroxide/AC composites by afacile solvothermal route with AC, metallic salt, and precipitants. Thecomposites were analyzed using XRD, SEM-EDS, FTIR, N2adsorption-desorption and TG-DSC curves. Electrochemical properties weretested by cyclic voltammogram, chronopotentiometry, electrochemicalimpedance spectroscop in6M KOH aqueous electrolyte. The main contents aresummaried as follows:(1) Fe2O3loaded AC electrode materials for electrochemical capacitorshave been synthesized by a cost-efficient and environmental-friendlysolvothermal process. The Fe2O3/AC composite prepared from Iron (III)chloride hexahydrate (FeCl36H2O), activated carbon (AC, from petroleum coke),and NaOH precipitant exhibited a high specific capacitance of215F/g (at1A/g),and an excellent rate capability (65.1%of capacity retention at40A/g). Suchremarkable electrochemical performances can be primarily ascribed to thecombination between high pseudo-capacitance of Fe2O3nano-particles and highsurface area/conductivity of AC, which provides effective transport/diffusion path for both ions/electrons to achieve high specific capacitance.(2) The electrochemical properties of Fe2O3/AC were effected by fourdifferent precipitants (i.e., NaOH, CH3COONa, HMT, CO(NH2)2). XRD,SEM-EDS, TG analysis show that the products were consisted of nanosizedα-Fe2O3(weight ratios:48.1,47.9,44.2,44.3%) loaded onto AC particles (~20μm). Significantly, both kind and dosage of precipitants exhibited effects on thespecific capacitances of Fe2O3/AC composites. The highest specific capacitancereaches up to240F/g (at a current density of1A/g in6M KOH aqueouselectrolyte) when the molar ratio of CH3COONa: FeCl3is9. On the other hand,the sample prepared with NaOH: FeCl3molar ratio being1.5exhibitedexcellent rate capability with specific capacitance of215F/g at1A/g, and89.3,82.3,78.1,72.6and65.1%capacity retention at2,5,10,20, and40A/g,respectively.(3) Co(OH)2/AC composite electrodes was prepared by a facilesolvothermal synthesis method for electrochemical capacitors withCo(NO3)2·6H2O, CO(NH2)2and AC as raw materials. XRD, SEM-EDS, FTIRand TG show that the products were consisted of~2μm amorphous Co(OH)2sheet-like paticles loaded onto AC particles. Electrochemical tests indicated thehighest specific capacitance reached up to301F/g at a current density of1A/gin a6mol/L KOH electrolyte, and the specific capacitance was164F/g at acurrent density of20A/g. In contrast, pure Co(OH)2and the AC show muchlower specific capacitances of195and33F/g, respectively. The excellentelectrochemical performance of the composite derived from the synergisticeffect which combined the high conductivity of AC with highpseudo-capacitance of Co(OH)2.