Synergistic effect between MoS2/WS2 composite and ecofriendly electrolytes for the fabrication of graphene supercapacitors with high energy density

Ecofriendly electrolytes such as fresh coconut water and oral rehydration salts were employed as novel electrolytes for graphene supercapacitors (SCs). To increase the capacitance of SCs, MoS2/WS2 (MWS) composite was added on their electrodes. SCs were malleable because their electrodes were made of graphene/flexible-metals. For comparison purposes, SCs were also made with an acidic electrolyte (AC) of PVA/H3PO4. The SCs constructed with MWS/acidic electrolyte, MWS/oral-rehydration-salts (ORS), and MWS/fresh-coconut-water (FCW) exhibited capacitance/energy density (Cp/Eden) values of 1693.6F g-1/381 Wh kg-1, 912.1 F g-1/205.2 Wh kg- 1, and 632.16F g- 1/142.2 Wh kg-1, respectively. SCs were also bent, in this case, Cp/Edenvalues of 1290.6 F g- 1/290.1 Wh kg-1, 527.3 F g-1/105.5 Wh kg- 1, and 405.7 F g-1/81.1 Wh kg- 1 were obtained for the devices made with AC, ORS and FCW electrolytes. In addition, the devices made with AC and ORS were bent, despite this deformation, those ones produced high Cp/Edenof 1290.6 F g- 1/290.1 Wh kg-1, 527.3 F g- 1/105.5 Wh kg- 1, respectively. The diffusion coefficient (measured by photoacoustic method) was higher for the ORS electrolyte (2.127 x 10-10 m2 s- 1) in comparison with the FCW electrolyte (1.656 x 10- 11 m2 s-1), therefore, devices made with ORS had higher Cp/Eden. Additionally, Raman, UV-Vis, and XPS experiments were performed on the electrodes. Consequently, Mo0, Mo4+, Mo5+, S2- /S22- , W0, W5+, and W6+ species were identified as the redox centers to store charge, together with oxygen vacancy defects. This research suggests that ecofriendly ORS and FCW electrolytes could be used in SCs, which benefits the environment.