Abstract
In the present work we report on TiO2 nanotube arrays (TNTAs) that were converted to a conductive scaffold established via an optimized reduction treatment in Ar/H2. These conductive TNTAs are then employed for RuO2 nanoparticle decoration. The effect of the Ar/H2 treatment is evaluated by electron energy loss spectroscopy (EELS) and electron paramagnetic resonance (EPR). The results show that, under ideal conditions, buried Ti3+ states are formed, with a higher concentration in the inner shell of the nanotube. Together with the capacitive and conductive performance, investigated by solid-state conductivity and electrochemical measurements, we find that 20 μm long TNTAs, annealed at 550 °C in Ar/H2, yield an optimized and stable structure that provides a remarkably low resistivity of 13.5 KΩ/tube (vs. 70.2 MΩ for non-treated nanotubes). In cycling experiment, with a loading of only 0.048 mg cm−2 RuO2 a specific capacitance of 1297 F g−1 can be reached. The reason for this highly efficient use of RuO2 is that the conducting core-shell scaffold provides a unique, well dispersed RuO2 nanoparticle structure (∼2.8 nm), which is responsible for the high specific capacitance, and moreover yields an excellent long-term cycling stability.
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•Conductive TiO2 nanotube electrode scaffold for efficient RuO2 supercapacitors.•By reducing in an Ar/H2 atmosphere, stable interstitial Ti3+ states are formed.•The high capacitance is based on a conductive/active core/shell structure.