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We successfully synthesized a novel core-shell hybrid metal oxide via a simple one-step hydrothermal method without annealing. This composite of Co 3 O 4 particles covered with SnO 2 –SnO (Co 3 O 4 @SnO 2 –SnO) predicted better performance compared to pure Co 3 O 4 , which strongly depends on the synthetic temperature. The Co 3 O 4 @SnO 2 –SnO prepared at a temperature of 250 °C (labeled Co 3 O 4 @SnO 2 –SnO-250) exhibited an outstanding specific capacitance of 325 F g−1 under the current density of 1 A g−1, which was much higher than those of Co 3 O 4 (12.6 F g−1) and other composites. Additionally, the sample also exhibited good cycle stability performance with a retention rate of 100% after 5000 cycles at a current density of 5 A g−1. Through X-ray photoelectron spectroscopy analysis, the presumed mechanism was that Sn-O x decreases the surface electron densities of Co 3 O 4 , which is beneficial to OH− adsorption and specific capacitance improvement, and the synthetic temperature had a strong impact on the microstructure and thus on the surface electron densities. The most. obvious finding to emerge from this study is that the specific capacitance can be improved through adjusting the surface electron densities of transition metal oxides. [ABSTRACT FROM AUTHOR]