Enhancing the electrochemical properties of a Nickel-CobaltManganese ternary hydroxide electrode material using graphene foam for supercapacitors applications

Sustainable, environmentally friendly, and renewable energy sources are urgently needed as concerns about carbon emissions and the depletion of fossil fuels are becoming worrying. It is vital to explore cost-effective and environmentally sustainable energy sources to ensure adequate provision for the ever-increasing energy demand. Supercapacitor devices enable storage of energy and its delivery at high power over a short period. These devices have the advantage of being manufactured at low cost, being safe to use, and having a long-life cycle. This study investigated the effect of incorporating a carbon-based material (graphene foam) within a ternary transition-metals hydroxide (Nickel, Cobalt, and Manganese) to obtain its optimal electrochemical properties for supercapacitors applications. It involved a low-cost and environmentally sustainable synthesis method whereby a constant quantity of the ternary metal hydroxides (NiCoMnTH) was loaded onto various amounts of graphene foam (GF). Typical energy storage characterisation techniques were performed on the synthesised material. The physical characterisation provided results regarding the structural, morphological and surface particularities of the different nanostructured materials. The electrochemical characterisation (EC) allowed the evaluation of the materials' electrochemical behaviours and performances. The EC results also revealed the optimised composite, which demonstrated outstanding electrochemical performances. The integration of graphene foam within the pristine material enhanced its surface area improving its specific capacity to about 178,6 mAh g-1. This specific capacity was close to the triple of the initial value having a specific capacity value equivalent to 76,2 mAh g-1 when evaluated in the same configuration and under the same settings. The improved nanomaterial was then utilised as a positive electrode material for the design of a novel hybrid device. The hybrid device was assembled with the optimised material (NiCoMnTH/GF) on the positive end and activated carbon on the negative end. The device demonstrated a sustaining specific capacity of 23,4 mAh g-1at a specific current of 0,5 A g-1. The device also yielded sustaining specific energy and power densities of values of 22,32 Wh kg-1 and 439,7 W kg-1 respectively at the same specific current. The battery-supercapacitor materials combination developed a synergetic effect on the electrochemical properties, thereby enhancing the specific energy and power densities. After a 15000 cycles stability test, the device displayed an outstanding Coulombic efficiency of 99,9 % and capacity retention of 80 % within a potential range of 1,6 V at a specific current of 3 A g−1. These results have demonstrated the prodigious electrochemical potentials of the as-prepared novel nanomaterial and its capability to be utilised as a positive electrode for energy storage applications.Dissertation (MSc (Chemical Technology))--University of Pretoria, 2020.National Research FoundationChemical EngineeringMSc (Chemical Technology)Unrestricte