Development of Transition Metal Oxide and Oxyhydroxides as Electrode Materials for Electrochemical Energy Storage

Koppisetti, Heramba Venkata Sai Rama Murthy (2024) Development of Transition Metal Oxide and Oxyhydroxides as Electrode Materials for Electrochemical Energy Storage. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Heramba Venkata Sai Rama Murthy Koppisetti (18RS106)) 18RS106.pdf - Submitted Version Restricted to Repository staff only Download (14MB)

Abstract

The continuous growth of world population is currently leading to huge increase in energy demand. Majorly relying on energy production and consumption from fossil fuels will have severe effects on global economics and environment. Excessive consumption of fossil fuels will lead to serious problems like global warming and air pollution. In past few years, there has been a surge in global investments in clean and renewable energy technologies. Although, renewable energy technologies like wind, solar and geothermal energy are available, they are highly intermittent in nature and thus require efficient energy storage systems to channel the excess energy. Fuel cells, batteries and supercapacitors are major electrochemical energy storage devices. The common thing among these energy storage systems is, the energy conversion or production reactions take place near the electrolyte electrode interfaces and the ionic/electronic movements occurs in opposite directions. A sustainable approach is to use renewable energy sources to perform water splitting through electrocatalysis to use hydrogen fuel as energy storage medium. The water splitting is comprised of two half reactions oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), which rely on catalysts to overcome the activation energy barrier of these reactions. However, these catalysts require an additional potential than the threshold thermodynamic potential of 1.23 V due to kinetic constraints to generate a reasonable amount of current. The OER is generally considered as a bottle neck of water splitting due to the complicated mechanism and till date expensive catalysts like RuO₂/IrO₂ are regarded as benchmark catalysts. Hence, it is highly envisaged to develop abundant and efficient transition metal catalysts for OER. Other conventional energy storage systems are batteries and supercapacitors, where charge storage happens through ionic movements. From the Ragone plot which demonstrates the energy and power capabilities of EESs, super capacitors have high power densities and batteries possess high energy densities. The SCs lack behind in energy outputs due to restriction of charge storage kinetics to surface. This requires development of electrode materials with improved porous features to improve energy density and construction of hybrid device for increased voltage window to improve energy density. On the other hand, batteries are way ahead of any other EES, and find applications in portable electronics to EV industry. However, the sky rocketing price of lithium and supply chain issues of raw materials lead to increase in cost of batteries and are also associated with safety issues. Hence, there is a quest for beyond LIB technology and due to abundance of sodium and similar kinetics to LIBs, sodium ion batteries are emerging as potential storage devices. However, the SIBs have low intrinsic energy density, still in premature stage and there are fewer reports on low temperature storage. Hence the key factor to improve energy storage is development of efficient electrode materials for water splitting, supercapacitors, and batteries. Chapter 1 gives general introduction to the energy storage systems i.e. fuel cells, batteries, and supercapacitors. The current state of renewable energies, requirement of energy storage systems, electrochemical water splitting, supercapacitor and battery mechanisms for energy storage systems are comprehensively discussed. Further, a brief discussion on previous literature reports on transition metal-based electrode materials for energy storage applications is provided. Finally, the challenges and motivation behind the working chapters are discussed in detail. Chapter 2 demonstrates the development of earth abundant iron rich catalysts for oxygen evolution reaction. Briefly, a one pot synthesis was employed to obtain iron rich nickel composed catalysts using polyethyleneimine as mild base. The optimized catalysts with minuscule amount of nickel incorporation displayed excellent OER activity and stability. The results revealed that nickel incorporation leads to increased oxygen vacancies, more catalytic active centers, thereby facilitating the higher activity. Chapter 3 illustrates the structural engineering approach to improve the geometric OER activity. The geometric OER activity of the crystalline Co3O4 always become inferior to its amorphous precursors upon calcination. In this chapter, we have shown that incorporation of sulfate in pre-annealed materials plays a pivotal role in boosting the OER activity of annealed Co₃O₄ irrespective of the pre-annealed phase. This was due to the “pore-alteration ability” and “crystallization hindrance effect” of sulfate ions that significantly alter the microstructure of the resulting Co₃O₄ during annealing process by dramatically improving the surface area, pore size, and pore volume. To our knowledge, this is the first report where the geometric electrocatalytic OER activity of an annealed Co₃O₄ is significantly better compared to its pre-annealed phase and is in fact comparable to the activity of amorphous Co-hydroxide based compounds. Chapter 4 discusses the nanostructural engineering of Cobalt phosphate micro belts into cobalt oxyhydroxide/hydroxide nano discs with improved specific area and abundant active sites. The improved access to redox sites that lay inaccessible in bulk structures aided in improved specific capacitance. The synthetic conditions like pH and solvent of the reaction medium have tremendous control over the phases of the obtained products. A hybrid device was constructed with activated charcoal as a negative electrode to further improve the energy density of the supercapacitors. Chapter 5 focuses on development of stable cathodes for emerging technology sodium ion batteries (SIBs). SIBs are highly explored in the beyond lithium class technologies due to the high abundance and cost effectiveness of the former. Though transition metal based layered oxides are well explored as cathode materials for SIBs, they suffer from structural instabilities and poor cycling performance in long run. LiF was incorporated into the sodium manganese cobalt oxide cathode and the optimized cathode demonstrated excellent capacity retention and cyclic stability at both ambient temperature and sub-zero temperature.

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