Performance characteristics of carbon based electrical double layer capacitors with PVA and PVA-Cellulose hybrid electrolytes

Abstract

The main focus of this work is to develop a high conducting solid polymer electrolyte (SPE). Poly(vinyl Alcohol), PVA was used as a host and H3PO4 as the ionic dopant. The highest electrically conducting sample in the PVA-H3PO4 (nonhybrid) electrolyte system has composition PVA + 50 wt% H3PO4 (P50H50). The room temperature electrical conductivity is 9.70 x 10-6 S cm-1. A higher electrical conductivity can be achieved by introducing a Whatman® filter paper which acts as a support to the PVA electrolyte and because of its porous nature allows more H3PO4 acid to be loaded into the system. In the PVA-H3PO4 which is considered as the non-hybrid system, the maximum amount of acid that can be loaded is 50 wt%. For the hybrid system, i.e. PVA-filter paper-H3PO4 70 wt% acid can be loaded into the system. The mechanical strength of the system has improved and the highest electrically conducting sample in the PVA-H3PO4-filter paper system has been designated P30H70-C with conductivity 1.04 x 10-4 S cm-1. Three EDLCs were fabricated using the two polymer electrolyte systems. Using PVAH3PO4 (non-hybrid) electrolyte system with the highest conductivity at room temperature sandwiched between two activated carbon electrodes (BP20) a specific capacitance of 4.89 Fg-1 and the internal resistance of 4.13 Ω cm-2 has been obtained. The second EDLC used the same electrodes but different polymer electrolyte system. Cellulose hybrid electrolyte system was introduced to replace PVA-H3PO4 (non-hybrid) electrolyte system. Cellulose hybrid electrolyte is used because the conductivity is higher than PVA-H3PO4 (non-hybrid system). Chargedischarge characteristics showed the specific capacitance increased to 7.73 Fg-1 and internal resistance reduced to 2 Ω cm-2. The third EDLC used the same cellulose hybrid electrolyte and activated carbon electrodes soaked in H3PO4. Charge-discharge characteristics showed the specific capacitance increased to 31.47 Fg-1 and internal resistance reduced to 1 Ω cm-2. The increase in specific capacitance is contributed by the diffusive layer to the entire electrodes. The double layers formed capacitors which are overall connected in a parallel arrangement such that the total capacitance adds up and contribute to a higher capacity. For a working voltage for this EDLC is 1 V and the efficiency is between 80 to 97 %.