Highly efficient and biodegradable flexible supercapacitors fabricated with electrodes of coconut-fiber/graphene nanoplates

We report the fabrication and electrochemical characterization of biodegradable and flexible supercapacitors (SCs). The conductive electrodes of these SCs were pieces of compacted coconut fibers coated by graphene nanoplates. An oral electrolyte solution (OES) and rice paper were used as electrolyte and separator, respectively. The SCs' encapsulation was made of gelatin/pectin. According to the electrochemical tests, the maximum capacitance and specific energy of the cell made with the biodegradable components were 670.8 F g(-1) and 134.2 Wh kg(-1), respectively. After adding MgTiO3 nanoparticles (NPs) to the anode, both, the capacitance and specific energy were enhanced by approximate to 37% and by approximate to 20%, respectively. For comparison purposes, the OES electrolyte was substituted by a conventional acidic electrolyte (PVA/H3PO4) in the SCs, but the capacitance and specific energy obtained were lower (175.9 F g(-1) and 35.2 Wh kg(-1)). Interestingly, the biodegradable cells exhibited very long discharge times of 550-600 min and a stable output voltage in the range of 0.54-0.71 V, which has not been observed previously for biodegradable SCs. The SCs made with MgTiO3 NPs stored charge by redox reactions and the redox centers were oxygen vacancies (defects), Mg2+/Mg-0 and Ti3+/Ti-4 (the presence of such centers was confirmed by x-ray photoelectron spectroscopy, Raman and absorbance measurements). In general, we demonstrated that the biodegradable SCs are sustainable/eco-friendly energy sources that are promising to substitute the conventional technologies of Li or alkaline batteries made with toxic/corrosive components that contaminate the environment.

Automated summary

We report on the fabrication and electrochemical characterization of biodegradable and flexible supercapacitors. These supercapacitors use graphene nanoplates coated coconut fibers as conductive electrodes, an oral electrolyte solution and rice paper as electrolyte and separator. By adding MgTiO3 nanoparticles to the anode, the capacitance and specific energy of the supercapacitors were enhanced. The biodegradable cells exhibited long discharge times and stable output voltage, which have not been observed previously for such supercapacitors.