Effects of carbon nanomaterials on the performance of symmetric pseudocapacitors

Abstract

This thesis reports on the study of carbon nanomaterials integrated with nanostructured birnessite-type MnO2 and tetragonal hausmannite-type Mn3O4 as electrode materials for enhanced performance in symmetric pseudocapacitors. This work further explores the synergistic effect of graphene oxide decorated with particles of nickel (II) tetraaminophthalocyanine as electrode materials for improved performance (power and energy densities) in symmetrical pseudocapacitor device. Physical properties of the synthesised electrode materials were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), gas adsorption technique (BET), infra-red spectroscopy, Raman spectroscopy and thermogravimetric analysis (TGA) techniques. Electrochemical properties of synthesised electrode materials were investigated using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS). From the study of carbon nanomaterials integrated with nanostructured birnessite-type MnO2, it has been discovered that OLC/MnO2 nanohybrid exhibited better performance (regarding specific capacitance, rate capability, and energy density) compared to other nanohybrids such as CNT/MnO2, GO/MnO2, and AC/MnO2. This device gave maximum specific capacitance of 255 F g-1, the specific energy density of 5.6 Wh kg-1 and excellent power density of 74.8 kW kg-1. The CNT/MnO2, exhibited a maximum specific capacitance, energy and power density of 174 F g-1, 4.9 Wh kg-1, and 55.1 kW kg-1, respectively, while, the GO/MnO2 displayed 135 F g-1, 3.9 Wh kg-1, and 35.8 kW kg-1, and AC/MnO2 was 110 F g-1, 3.3 Wh kg-1, and 30.0 kW kg-1, respectively. From the study of carbon nanomaterials integrated with nanostructured tetragonal hausmannite-type Mn3O4, OLC/Mn3O4 nanohybrid exhibited better performance (regarding specific capacitance, rate capability, and energy density) compared to other nanohybrid electrode materials (i.e., CNT/Mn3O4 GO/Mn3O4, and AC/Mn3O4). This device exhibited a maximum specific capacitance of 195 F g-1, the specific energy density of 4.3 Wh kg-1 and power density of 52 kW kg-1. The CNT/Mn3O4 exhibited a maximum specific capacitance, energy and power density of was 180 F g-1, 3.9 Wh kg-1, and 33 kW kg-1, respectively. While the GO/Mn3O4 displayed values of 160 F g-1, 3.6 Wh kg-1, 24 kW kg-1 and AC/Mn3O4 was 124 F g-1, 2.8 Wh kg-1, 18 kW kg-1, respectively. The study on the synergistic effect of graphene oxide (GO) decorated with particles of nickel (II) tetraaminophthalocyanine (NiTAPc) resulted in GO/NiTAPc nanohybrid displaying better pseudocapacitive performance relative to its precursor (i.e., GO and NiTAPc). This pseudocapacitor device exhibited a maximum specific capacitance of 163 F g-1, the specific energy density of 3.6 Wh kg-1 and high-power density of 140 kW kg-1. These values are much higher than those of its individual precursors NiTAPc (60 F g-1 and 1.3 Wh kg-1) and GO (15 F g-1 and 0.3 Wh kg-1). This excellent capacitive performance shows promising opportunities for the development of aqueous-based pseudocapacitors made of carbon nanomaterials with transitional metal oxides and metallophthalocyanine (MPc) complexes (N4-macrocyclic metal compounds). Interestingly, this study also shows the significance of the use of novel carbon nanomaterials apart from the well-studied activated carbon for the development of high-power electrochemical capacitors.