Role of the Ca3Co4O9 oxide to enhance the energy density and capacitance of graphene supercapacitors made with recycled polypropylene

Abstract

Recycling wasted plastics from daily use products is of current interest to avoid the contamination of oceans and rivers by microplastics. For this reason, we designed in this work graphene supercapacitors (SCs) made with recycled polypropylene (PP) and studied their electrochemical performance. The PP was recycled from wasted coffee capsules, molded and coated by graphene (G) to make it conductive. SCs made with electrodes of PP + G had an energy density and capacitance of 27.3 Wh kg−1 and 162.6 F g−1, respectively. After the incorporation of Ca3Co4O9 (CCO) microparticles with plate-like morphology to the SC electrodes, the energy-density and capacitance raised up 73.7 Wh kg−1 and 484.5 F g−1, that is, an enhancement of ≈200% and ≈170% for the capacitance and energy density, respectively. Impendance spectroscopy was performed to elucidate the storage mechanisms in the devices and found that the series and charge-transfer resistances were lower in the device made with CCO, therefore, the ion storage/diffusion was more efficient in such device. Additionally, analysis by XPS, optical-absorbance and Raman were achieved and found on the SC electrodes made with the CCO microparticles the existence of oxygen-vacancy defects and Co4+/Co3+/Co2+ species, which were formed during the SC operation. Those species and defects worked as active redox elements for the storage of charge. Overall, the findings of this research suggest that making SCs from recycled plastics is viable and those devices could be used to provide energy to portable equipments.