Effect of Substrate on Active Material and Dynamic Performance Enhancement in Supercapacitor Devices Based on Graphite-Clay Composite Electrodes

Abstract

Graphite-clay composite electrodes are promising candidates for fabricating energy storage devices with Polyaniline (PANI) as the active material. Well-performing homogeneous symmetric supercapacitors made from graphite-clay electrodes open a new pathway to construct heterogeneous symmetric supercapacitors, providing a novel technological perspective on supercapacitors. The present study demonstrates the fabrication of three different supercapacitors, including a PANI-coated graphite-Montmorillonite (MMT) composite electrode and graphite-kaolinite-cement composite electrode-based supercapacitor (PANI-GMMTCE_GKCeCE), a PANI-coated graphite-MMT-cement composite electrode and graphite-kaolinite-cement composite electrode-based supercapacitor (PANI-GMMTCeCE_GKCeCE), and a PANI-coated graphite-kaolinite composite electrode and graphite-kaolinite-cement composite electrode-based supercapacitor (PANI-GKCE_GKCeCE), and their performance evaluation using various electrochemical and analytical techniques. Supercapacitors were constructed based on four different PANI-coated graphite-clay composite electrodes, each consisting of PANI-GKCeCE, with the remaining section from each of the other electrodes. Each electrode surface facilitated the formation of conductive PANI coating via aniline electropolymerization, as evidenced by well-characteristic Cyclic Voltammograms (CV) with dominant peaks. The morphological structures of PANI coating on each electrode are unique from one another, but all have a PANI nanofiber network with uniform or irregular distribution. Synergistic interactions of two different PANI networks in a supercapacitor contribute to the charge transfer and storage mechanisms. Both (PANI-GMMTCE_GKCeCE) and (PANI-GMMTCeCE_GKCeCE) supercapacitors outperformed in capacitance, producing more than 390 F·g^-1 of specific capacitance in CV and charge-discharge tests. All three supercapacitors follow pseudocapacitive behavior in charge-discharge as well as in CVs. However, each supercapacitor displayed combined properties of double-layer and pseudocapacitor, indicating a constant phase element in each impedance spectrum. The ionic diffusion process contributed to the charge transport and storage mechanism due to the heterogeneous nature on both sides, which is similar to previously fabricated PANI-coated graphite-clay-based supercapacitors. Charge-discharge curves of each supercapacitor exhibited cyclic stability with higher Coulombic efficiency, and all supercapacitors achieved considerably higher energy and power densities, indicating the high performance of heterogeneous symmetric graphite-clay-based supercapacitors. Further modifications of heterogeneous symmetric supercapacitors are essential to improve their performance for commercial-scale development.