Abstract
A two-step hydrothermal process was developed to synthesize hydrous 30RuO 2 -70SnO 2 composites with much better capacitive performances than those fabricated through the normal hydrothermal process, co-annealing method, or modified sol-gel procedure. A very high specific capacitance of RuO 2 (C S,Ru ), ca. 1150 F g -1 , was obtained when this composite was synthesized via this two-step hydrothermal process with annealing in air at 150 °C for 2 h. The voltammetric currents of this annealed composite were found to be quasi-linearly proportional to the scan rate of CV (up to 500 mV s -1 ), demonstrating its excellent power property. From Raman, UV-vis spectroscopic and TEM analyses, the reduction in mean particulate size is clearly found for this two-step oxide composite, attributable to the co-precipitation of (Ru δ Sn 1-δ )O 2 ·xH 2 O onto partially dissolved SnO 2 ·xH 2 O and the formation of (Ru δ Sn 1-δ )O 2 ·xH 2 O crystallites in the second step. This effect significantly promotes the utilization of RuO 2 (i.e., very high C S,Ru ). The excellent capacitive performances, very similar to that of RuO 2 ·xH 2 O, suggest the deposition of RuO 2 -enriched (Ru δ Sn 1-δ )O 2 ·xH 2 O onto SnO 2 ·xH 2 O seeds as well as the individual formation of (Ru δ Sn 1-δ )O 2 ·xH 2 O crystallites in the second hydrothermal step. © 2007 Elsevier Ltd. All rights reserved.