Design and synthesis of ternary Co₃O₄/carbon coated TiO₂ hybrid nanocomposites for asymmetric supercapacitors

Recently, attention has been focused on the synthesis and application of nanocomposites for supercapacitors, which can have superior electrochemical performance than single structured materials. Here, we report a carbon-coated TiO₂/Co₃O₄ ternary hybrid nanocomposite (TiO₂@C/Co) electrode for supercapacitors. A carbon layer was directly introduced onto the TiO₂ surface via thermal vapor deposition. The carbon layer provides anchoring sites for the deposition of Co₃O₄, which was introduced onto the carbon-coated TiO₂ surface by hydrazine and the thermal oxidation method. The TiO₂@C/Co electrode exhibits much higher charge storage capacity relative to pristine TiO₂, carbon-coated TiO₂, and pristine Co₃O₄, showing a specific capacitance of 392.4 F g^-1 at a scan rate of 5 mV s^-1 with 76.2% rate performance from 5 to 500 mV s^-1 in 1 M KOH aqueous solution electrolyte. This outstanding electrochemical performance can be attributed to the high conductivity and high pseudo-capacitive contributions of the nanoscale particles. To evaluate the capacitive performance of a supercapacitor device employing the TiO₂@C/Co electrode, we have successfully assembled TiO₂@C/Co//activated carbon (AC) asymmetric supercapacitors. The optimized TiO₂@C/Co//AC supercapacitor could be cycled reversibly in the voltage range from 0 to 1.5 V, and it exhibits a specific capacitance of 59.35 F g^-1 at a scan rate of 5 mV s^-1 with a specific capacitance loss of 15.4% after 5000 charge-discharge cycles. These encouraging results show great potential in terms of developing high-capacitive energy storage devices for practical applications.