Cobalt oxide decorated zirconium oxide immobilized multiwalled carbon nanotubes as scaffolds for supercapacitors and the CO₂ reduction reaction

In the field of renewable energy research, the development of materials for use as highly efficient supercapacitors and designing electrocatalytic materials for the reduction of CO₂ to produce useful chemicals are envisaged as two important sustainable routes. However, developing stable, selective, and efficient materials for these purposes is a highly challenging task requiring numerous design attempts. In this work, cobalt oxide decorated zirconium oxide immobilized multiwalled carbon nanotubes (MWCNTs-ZrO₂-Co₃O₄) is reported as a catalyst and battery electrode material for the electrochemical reduction of CO₂ and supercapacitor applications, respectively. The MWCNTs-ZrO₂-Co₃O₄ electrode assembled for the supercapacitor shows a specific capacity of 258.9 C/g at a current density of 1.0 A/g. The MWCNTs-ZrO₂-Co₃O₄ and activated carbon (AC) based asymmetric supercapacitor (MWCNTs-ZrO₂-Co₃O₄//AC) displays specific energy in the range of 8.9 Wh/kg (at 837.2 W/kg) to 6.23 Wh/kg (at 1674.4 W/kg). The device, MWCNTs-ZrO₂-Co₃O₄//AC displays high cycling stability with 97% capacity retention after 7000 cycles at a current density of 1.0 A/g. In the electrocatalytic reduction of CO₂, the MWCNTs-ZrO₂-Co₃O₄ scaffold produces selectively formic acid during the electrolysis at -1.1 V (vs. Ag/AgCl) in 0.1 M aqueous KCl solution. These results indicate that MWCNTs-ZrO₂-Co₃O₄ can serve as a bifunctional material.