Sodium-ion hybrid capacitors are
attracting great attention and
are emerging as promising energy storage devices, with their remarkable
footsteps in energy and power densities. However, the development
of efficient electrode materials that result in a minimum trade-off
between their energy and power densities, and that allow long-term
cycling stability, still remains a challenge for realizing their full
potential as an alternate energy storage system for commercial applications.
Herein, for the first time, we study the sodium-ion intercalation
pseudocapacitance behavior of brown TiO2 nanotubes for
their application as an efficient anode material for Na-ion hybrid
capacitors. We synthesized semicrystalline and crystalline anatase
brown TiO2 nanotubes, aggregated in a flowerlike morphology,
through a hydrothermal route, and performed detailed electrochemical
studies. The kinetic studies reveal that semicrystalline brown TiO2 exhibits a Na-ion intercalation pseudocapacitive behavior
with 57% of capacitive storage at 1.0 mV s–1, whereas
crystalline brown TiO2 is more faradaic in nature. Further,
hybrid Na-ion capacitors are fabricated with brown TiO2 materials as an anode and activated carbon as a cathode, and the
fabricated device showed an excellent electrochemical performance
with a high energy density of ∼68 Wh kg–1 and a high power density of ∼12.5 kW kg–1 and with a good cycling stability up to 10 000 cycles with
∼80% capacitive retention. The obtained results represent a
promising approach toward developing efficient electrodes for hybrid
Na-ion capacitors.
Incorporation of MnO2 nanostructures as spacers enhances the electrochemical energy storage performance of g-C3N4. The g-C3N4/MnO2 composite electrode exhibited a specific capacitance of 174 F g−1.
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