Enhanced Areal Capacitance of Solid-State Supercapacitors Based on Graphene Mixed Gel Electrolyte

Abstract

To meet the widely used portable and wearable electronic devices with improved funtionalities, developing flexible energy storage devices with larger energy density is an important issue. To this end, fabricating electrodes with materials that can act well while bending or twisting is necessary. Reduced graphene oxide is a promising candidate because of its outstanding mechanical and chemical properties, easily accessed surface area, and potential to be manufacturable [1]. In this research, we proposed a facile method to fabricate a graphene-based, flexible all solid-state supercapacitors. Briefly in fabrication, reduced graphene oxide (rGO) solution derived from modified Hummers method and hydrazine reduction [2] was directly drop cast on a flexible Au-coated polyimide substrate to form a porous electrode. Then the rGO solution mixed with PVA/H3PO4 was poured onto the electrode and air dried for 12 hours until solidified. Two as-made electrodes were pressed face to face to finish the device encapsulation.SEM images of drop cast rGO electrode show a layered morphology with pores enable the gel electrolyte to inject in. The electrochemical characteristic of the as-made device is investigated by CV measurement. For the device using PVA/H3PO4 as electrolyte, only 41 mF/cm2 is obtained at the scan rate of 100 mV/s, whereas the device with rGO/PVA/H3PO4 as electrolyte shows 130 mF/cm2, about two times larger. We believe that a suitable mass ratio of rGO dispersed in the gel electrolyte forms a continuous 3D network that can contribute to electric double layer capacitance. The CV result shown in figure 2 comes from the sample using PVA/H3PO4 with 0.1 wt% rGO mixed. And the optimization of varied rGO mass ratio is investigated.Reference[1] M. Segal, Nat. Nanotechnol. 2009, 4, 611-613.[2] D. Li, M. B. Muller, S. Gilje, R. B. Kaner, G. G. Wallace, Nat. Nanotechnol. 2008, 3, 101-105