Electrochemical capacitive behavior of RuO2/graphene composites prepared under various precipitation conditions

Using graphene oxide and hydrous ruthenium chloride as starting materials, RuO2/graphene composites were prepared via a hydrothermal reaction under different precipitation conditions by using ammonium carbonate, urea, and sodium hydrate as precipitants. The morphology and structure of the RuO2/graphene composites were characterized by SEM, TEM, XRD. Cyclic voltammetry, galvanostatic charge-discharge, and impedance measurements were carried out to test the electrochemical performance. The results revealed that the veil-like RuO2/graphene composite prepared by sodium hydrate precipitation showed better capacitance performance than a particle-like composite prepared by ammonium carbonate and urea precipitation. A disproportionation reaction from Ru3+ to Ru and RuO2 took place in the RuO2/graphene composite when using CO(NH2)2 as the precipitant. The RuO2/graphene composite using sodium hydrate as the precipitant exhibited the optimum electrochemical performance with superior specific capacitance of 528.5 F g−1 at 0.1 A g−1, minimum resistance (0.4 Ω), and excellent rate performance and cycling stability, suggesting the synergetic effects of the Ru(OH)δCl3−δ precursors and graphene oxide during the hydrothermal process.