Ca2.9La0.1Co4O9/graphene composite electrodes for improved electrochemical performance of cellulose-based supercapacitors

In this study, we report a highly flexible and biodegradable supercapacitor (SC) assembled with electrodes made of cellulose and graphene microplates. The cellulose was extracted from the palocote plant (tithonia tubaeformis), which is considered a weed in Mexico. To enhance the capacitance of the devices, Ca2.9La0.1Co4O9 (CaLaCo) particles with microplate morphology were added to the SC electrodes. The electrochemical characterization indicated that the SCs fabricated without CaLaCo particles exhibited a specific capacitance of 777.3 F/g (at 1 A/ g) and an energy density of 108.1 Wh/kg. When the CaLaCo was introduced into the SC electrodes, the above parameters increased to 1320.3 F/g (at 1 A/g) and 182.3 Wh/kg, that is, the capacitive performance was enhanced by approximate to 70%. Also, the device made with the CaLaCo particles exhibited a high capacitance retention of 95.8% after 1500 continuous charging/discharging cycles. Some advantages in the devices made with CaLaCo in comparison with these fabricated without CaLaCo were: 1) longer discharge times and 2) low loss of capacitance (4.1%) at higher current densities (up to 10 A/g). On the other hand, redox peaks were observed in the cyclic voltammetry curves, suggesting the storage of charge by redox reactions. To find the redox centers responsible for the charge storage, optical absorbance, Raman and XPS measurements were carried out and we found that the oxygen vacancy defects and Co2+/Co3+ species were the main redox centers. Furthermore, EIS measurements showed that the series resistance (Rs) and charge transfer resistance (Rct) decreased by 28% and 80%, respec-tively, after the introduction of the CaLaCo oxide in the SC. The reduction of the Rs and Rct was relevant because it promoted the ion diffusion/storage in the electrodes, which in turn, increased the capacitance of the devices. Thus, the results of this report indicate that our biodegradable and flexible SC could be produced from sus-tainable materials and can be used as energy source for wearable/portable devices.

Automated summary

This study presents a flexible and biodegradable supercapacitor made of cellulose and graphene microplates, with enhanced capacitance through the addition of CaLaCo particles. The introduction of CaLaCo increased the specific capacitance by approximately 70% and resulted in a high capacitance retention of 95.8% after 1500 charging/discharging cycles. The redox peaks observed in the cyclic voltammetry curves indicated the storage of charge through redox reactions, with oxygen vacancy defects and Co2+/Co3+ species identified as the main redox centers. The reduction in series resistance and charge transfer resistance promoted ion diffusion/storage and increased the capacitance of the devices. Overall, this study demonstrates the potential of producing sustainable and flexible supercapacitors for use in wearable/portable devices.