COMPUTATIONAL AND EXPERIMENTAL STUDIES ON ENERGY STORAGE MATERIALS AND ELECTROCATALYSTS

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COMPUTATIONAL AND EXPERIMENTAL STUDIES ON ENERGY STORAGE MATERIALS AND ELECTROCATALYSTS is a well-researched Physical Sciences and Mathematics Thesis/Dissertation topic, it is to be used as a guide or framework for your Academic Research.

Abstract

Energy storage materials are a critical component of society in their fundamental operation, from cell-phones and portable devices to powering cities and reducing greenhouse gas emissions.

This thesis focuses on selected energy storage materials along with electrocatalysts as an attractive technology for sustainable and benign renewable energy chemistry, specifically: (1) theoretical studies on magnesium chloride/aluminum chloride electrolytes to gain an in-depth understanding of this simple electrolyte system for MG batteries; (2) theoretical and experimental studies on viologen derivatives for organic redox flow batteries (RFBs); and (3) a new iron(II) polypyridine-based electrocatalyst that exhibits the ability to reduce CO2 to renewable fuels.

Comprehensive density functional theory (DFT) calculations were conducted to provide insightful and unprecedented thermodynamic information on tetrahydrofuran (THF) solvation, isomerization, chloration, and dimerization of possible Mg-Cl species for popular Mg-Cl complex electrolytes. The results give an indication to the likely stripping/deposition active species and solution chemistry in electrolyte solutions.

The DFT states that the dimer, [(µ-Cl)3Mg2(THF)6]+, is the most abundant species present in electrolyte solutions and is the likely Mg deposition active species. The theoretical study of designed viologen derivatives for RFBs was done using the M06-2x functional and 6-31+G(d) basis set to demonstrate that rational molecular engineering can yield a series of efficient two-electron storage viologen molecules as anolyte materials for aqueous organic RFBs.

Electrostatic potential surfaces suggest good membrane compatibility for viologen derivatives. Calculations of the frontier HOMO or SOMO indicate high charge delocalization allowing high redox stabilities. Furthermore, calculated redox potentials have aided in the experimental design of high-powered aqueous organic RFBs.

The synthesis and characterization of the Fe(bapbpy)(OTf)2 catalyst is reported. This complex and was found to exhibit the ability to electrochemically reduce CO2 to renewable fuels such as carbon monoxide (CO), dihydrogen (H2), and even methane (CH4) making it an attractive electrocatalyst. Furthermore, the iron(II) catalyst achieved the photochemical CO2-to-methane conversion with high selectivity over CO production using visible light.

INTRODUCTION

Background To meet increasing energy demands, advanced batteries are greatly desired for powering portable devices and electric vehicles (EVs) that are pivotal to our daily life and the economic development of modern society.1-3 In addition,

to address the global problems of escalating energy demand and increasing emissions of CO2, it is critical to developing effective approaches to converting and storing renewable but intermittently available energy sources (e.g. solar, wind, etc.) into reliable energy forms.4-5 Battery systems with low cost, high energy density, and long cycling lifetime have been suggested as viable technologies for storing sustainable energy.4-5

In addition to batteries as energy storage devices, catalytic energy conversion systems can enable the reduction of CO2 to energy-rich fuels to remediate unsustainable energy sources through a renewable carbon cycle . 6 Solid-State Batteries. Rechargeable Li-ion batteries have shown tremendous success in portable electronic devices, power tools, and electric vehicles.

1-3 Moreover, rechargeable Li-ion batteries have been recently employed as a power source for electrical vehicles (EVs) and have been helping reduce the use of fossil fuels and emission of CO2. 1-3 However, technological limitations of Li-ion batteries including low energy density, high cost, and safety issues have stimulated the development of the next generation of battery technology.

1-3 Beyond Li-ion batteries, pure metal battery systems such as Li batteries and Na batteries are highly attractive and have been regarded as power sources for portable devices and electric vehicles (EVs) because of their high energy densities and as a potential strategy for grid-scale energy storage.

1-3 However, they have not been implemented due to a number of technical issues associated with these highly reactive pure metals, including severe dendrite formation, and irreversible depletion of electrolyte solvents.7-8 Recently, rechargeable Mg batteries have been advocated as promising battery systems alternative to Li- or Na-based batteries for powering portable devices and electric vehicles, and grid-scale energy storage.7, 9-13 There are several technical advantages of Mg batteries over Li batteries and Na batteries.

Mg is earth-abundant and low cost (ca. 24 times cheaper than Li). As an anode material, Mg is safe to use without dendrite formation (vs Li, Li-ion, or Na batteries) and also due to its milder reactivity compared to Li and Na. Mg has a high volumetric capacity (3832 Ah/L vs 2062 Ah/L for Li and 1165 Ah/L for Na) due to the two-electron redox chemistry of the Mg2+/0 redox couple. Mg-based electrolytes are environmentally benign.

Furthermore, Mg possesses a sufficient high reduction potential (-2.37 vs SHE) amenable for assembling high voltage and high energy density batteries with suitable cathode materials. However, the biggest roadblock in its development is the electrolyte as it experiences low stability and slow electrochemical cycling kinetics.

14 The development of the Mg-Cl/Al-Cl electrolyte system proved to be a major milestone for Mg batteries, however, optimization is still required to reach satisfactory performance.14-15 Investigations through density functional theory would be an effective strategy to overcome these barriers by deepening our understanding of the electrolyte solution chemistry

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Type

Thesis/Dissertation topic

Category

Physical Sciences and Mathematics

No of Chapters

5

Reference

Yes

Format

PDF

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