Combustion-driven synthesis route for tunable TiO2/RuO2 hybrid composites as high-performance electrode materials for supercapacitors

Abstract

Hybrids of micro/nanostructured metals/metal oxides have great potential to provide high performance in electrochemical applications such as supercapacitors. However, their synthesis routes involve complex procedures that limit scalable fabrication. Herein, we report a combustion-driven synthesis route for tunable TiO2/RuO2 hybrid composites as high-performance electrode materials for supercapacitors. Self-propagating combustion waves passing through precursors consisting of TiO2 nanoparticles and combustible nitrocellulose directly fabricated carbon templates as sacrificial layers for the outermost functional metal oxides, while the initial mass loading of nitrocellulose manipulated the residual hybrids. Through substituting the pre-formed carbon templates with RuO2, tunable TiO2/RuO2 hybrid composites of core–shell TiO2@RuO2 nanostructures or RuO2 clusters with embedded TiO2 nanoparticles were selectively obtained. The developed hybrids exhibited outstanding specific capacitances (~1200 F/g at 0.5 A/g) and capacitance retentions (~95.2% after 10,000 cycles) as supercapacitor electrodes, whereas the commercial RuO2-based electrode showed a lower specific capacitance (~600 F/g) and faster degradation of stability (~72%). An optimal thickness of hydrous RuO2 could facilitate inter-diffusion and proton transport for the high specific capacitances, while the amorphous nature of the outermost RuO2 and the inner TiO2 stability could provide robustness against the harsh stresses during charge–discharge cycles. This work can provide new strategies for the scalable fabrication of hybridized metal oxides such as core–shell nanostructures and nanoclusters, which would be useful for electrochemical devices, catalysts, and electromagnetic shielding.