**4. Carbon-metal oxide composite electrode materials**

Many metal oxide such as RuO2, MnO2, Fe3O4, V2O5, NiO, Co3O4, and TiO2, has been received significant attention and extensive studied as SC electrode materials due to Pseudo capacitance nature, which depends on the fast reversible redox reaction of electroactive species directly as well as in the vicinity of electrode surface [17–20]. The redox behavior is due to the multivalent property of the above oxides which changes their oxidation states by interaction with protons or hydroxide ions reversibly. In spite of their excellent specific capacitance, they still suffer from low conductivity, low rate capability, poor stability and durability during the process of charge/discharge. In contrast carbon materials shows excellent performance in

these regards but suffer from comparatively limited specific capacitance. Hence, the synergic integration of metal oxides with conducting carbon supports may form high potential carbon-metal oxide composite electrodes materials for SCs and hybrid devices because of their enhanced electrochemical performance through the combined effect of pseudocapacitive/faradaic charge storage and electrical double layer capacitance mechanisms [21–23].
