Enhancing the capacitance and tailoring the discharge times of flexible graphene supercapacitors with cobalt ferrite nanoparticles

This work reports the use of cobalt ferrite nanoparticles (NPs) for the fabrication of flexible supercapacitors (SCs). According to the microscopy analysis, the cobalt ferrite NPs have quasi-spherical shapes and their average sizes were 10.2 +/- 1 nm, 12.3 +/- 1 nm and 8.8 +/- 1 nm when they are synthesized with cobalt concentrations of 0, 25 and 33 mol%, respectively. Moreover, the X-ray diffraction patterns indicated that all the cobalt ferrite NPs presented a cubic phase. Flexible supercapacitors were made with two flexible graphene electrodes (FGEs) and one of them (anode) was coated with different cobalt ferrite NPs (the FGE electrode had 5 wt percent (wt%) of NPs) synthesized with several cobalt concentrations. The electrochemical characterization of these flexible SCs revealed that not only the capacitance was enhanced from 77.8-337.1 F g(-1) (at 1 A g(-1)) when the cobalt concentration increases from 0 to 33 mol% but also the discharge times from 1650 to 4957 s. Moreover, other SCs devices were fabricated using different wt% of the cobalt ferrite synthesized with a cobalt concentration of 33 mol%. As a result, the capacitance increases from 337.1-835.7 F g(-1) (at 1 A g(-1)) and the discharge times from 4957 to 21969s when the content of cobalt ferrite increases from 5 to 10 wt%. The enhancement of capacitance and discharge times was associated to the increase of the surface area and electrical conductivity of the anodes, which was caused by the presence of cobalt ferrite NPs on them.