Synergetic effect of eco-friendly carbon compounds over the metal oxide and metal-chalcogenide for energy storage applications

Abstract

Reducing fossil fuel consumption to help the planet gain its deteriorated health back will be the major goal for researchers in this century. Switching to greener energy sources such as solar, wind, hydro, etc. is one of the most viable options to cut down fossil fuel consumption. However, efficient storing mechanisms, as well as the conversion of the energy obtained from the aforementioned sources, is a vital part of the whole green energy solution. Systems for electrochemical energy storage and conversion include batteries, fuel cells, and electrochemical capacitors (ECs). In recent years much attention has been given towards electrochemical capacitors, also known as supercapacitors or ultracapacitors. The engrossment of ECs is because of their attractive specifications such as high-power density, long cycle life, and hybrid nature, that bridge the gap between traditional dielectric capacitors and batteries or fuel cells. In general, according to their charge storage mechanism, supercapacitors are divided into two types: Electric Double-Layer Capacitors (EDLCs) and Pseudocapacitors. Because of the ability of pseudocapacitive materials to store charge in a faradic or redox‐type process like batteries, they possess higher energy density compared to EDLCs. Hence extensive research has been focused on the synthesis and fabrication of pseudocapacitive materials. On the other hand, due to their high energy density, low self-discharge, lightweight, and various other features, lithium-ion batteries are the most sought-after energy storage device for the verity of applications such as electric vehicles and uncountable electronic accessories for a few decades now. Conventional Li-ion batteries (LIBs) use graphite as an anode material. Graphite with a theoretical specific capacity of 372 mAh/g may no longer fulfill the tremendous energy demand of numerous applications in imminent future. Over the past few decades, a worldwide effort has been made to search for alternative anode materials for improving the capacity and cyclability of LIBs. The first half of this thesis work is focused on the synthesis of the pseudocapacitive material, and its practical realization as a supercapacitor device. The other half focused on the synthesis of anode material for LIBs and studied the characteristic of its energy storage by constructing CR2032 coin cells. Supercapacitor electrode was fabricated by growing CoMoO4 nanoplates in the nickel foam substrate, and its pseudocapacitive properties were studied. The specific capacity of 580 F/g was obtained at the current density of the 1 A/g. Glucose was introduced as a carbon precursor to elevate the performance of the aforementioned electrode. The specific capacitance of 1638 F/g was obtained from the glucose treated electrode. Additionally, the carbonaceous electrode performed as an excellent supercapacitor device with 87% capacity retention even after 5000 charge-discharge cycles. On the other hand, cobalt molybdenum sulfide (CoMoS) was synthesized as a novel anode material for LIBs. The CR2032 coin cells were prepared to observe the energy storage characteristics and specific capacity of as-synthesized material. In addition, dopamine was used as a carbon precursor to enhance the performance of the pristine CoMoS. The discharge capacity of 425 mAh/g and 723 mAh/g was obtained from pristine CoMoS, and carbon treated CoMoS, respectively, even after the 100 charge-discharge cycles at a current density of 200 mA/g. Furthermore, both electrodes registered excellent capacity retention ability when subjected to different current densities. In addition to the better electrochemical performance of CoMoS than the traditional graphite, the use of dopamine as a carbon source also increased its performance in each electrochemical test and hence presented itself as a strong LIBs anode material candidate.