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Unveiling the Electrochemical Characteristics of Na-CO2 battery Catholytes through NASICON-Based Hybrid cells
Get PDFSchool of Energy and Chemical Engineering (Energy Engineering (Battery Science and Technology))The high levels of greenhouse gases in the atmosphere are leading to climate change. To address this problem, the concept of "net zero" has been introduced. Achieving net zero means balancing the amount of greenhouse gas emissions produced with the amount removed from the atmosphere. To achieve net zero, it is essential to focus on reducing emissions to the greatest extent feasible. This can be accomplished through various measures such as adopting cleaner technologies, improving energy efficiency, and promoting sustainable practices across different sectors. Net zero is an important goal in the fight against climate change as it aims to limit global temperature increases and negative impacts on the environment and human well-being.
Alkali metal-CO2 batteries have the potential to help address the energy problem and climate change by combining CO2 utilization with energy storage. Among them, Na-CO2 batteries are particularly promising for achieving net-zero because they can address both the energy and environmental crises. The use of Na-CO2 batteries can help capture and store CO2, which is a greenhouse gas that contributes to climate change. Furthermore, Na-CO2 batteries offer a high theoretical energy density and are cost-effective compared to other energy storage technologies. Nevertheless, while Li-CO2 batteries have been extensively researched, Na-CO2 batteries are still in the early stages of exploration. Challenges such as short-term cycle life, low reversibility, and high overpotentials have hindered their commercial viability. To address these limitations and advance the development of Na-CO2 batteries, it is crucial to gain a comprehensive understanding of the underlying electrochemistry that govern their working, as well as establish the relationship between cell configurations and functionality.
To enhance the development of Na-CO2 batteries, The new-type of electrolytes have been investigated to enhance their electrochemical characteristics. One type of solid-state electrolyte, NASICON, was effective in protecting the Na metal anode and preventing dendrite growth that can cause a short circuit. In addition, the use of different electrolyte systems, such as the water-in-salt (WiS) electrolyte and acetonitrile (MeCN) electrolyte with NASICON, was explored in Chapters 2 and 3, respectively.
In the Chapter 2, the WiS (water-in-salt) electrolyte concept was introduced. This innovative electrolyte consists of saturated concentration of salt that enables the solubility of water within it. The WiS electrolyte system offers several advantages, including improved stability, a wider electrochemical stability window, and higher conductivity compared to traditional electrolytes. To enhance the electrochemical properties of Na-CO2 batteries, nano-sized ruthenium was utilized as a cathodic catalyst. The incorporation of Ru@carbon current collectors in Na-CO2 batteries led to reduction in the overpotential gap, which refers to the excess voltage needed to initiate a desired electrochemical reaction. Additionally, the batteries demonstrated a cycling endurance of over 75 cycles, equivalent to 50 days, with minimal degradation. These findings indicate that the implementation of WiS-based Na-CO2 batteries, which utilize CO2 as a reactant, could be a cost-effective solution for energy storage applications. The combination of the WiS electrolyte and ruthenium catalyst contributes to improved battery performance, making it a promising option for efficient and sustainable energy storage.
Chapter 3 focused on investigating acetonitrile (MeCN) as a catholyte in conjunction with NASICON electrolyte for Na-CO2 batteries. While acetonitrile exhibits favorable characteristics such as a high dielectric constant and low viscosity, it reacts with Na metal and cannot be directly used in Na-CO2 batteries. To overcome this challenge, a NASICON-based hybrid cell configuration was developed to enable the utilization of MeCN-based electrolyte. Additionally, the previously reported glyme-based electrolyte was employed in the same system to assess the impact of different electrolytes on Na-CO2 batteries. Electrochemical properties of both electrolytes were thoroughly examined, and computational simulations, including Density Functional Theory (DFT) and Molecular Dynamics (MD), were conducted to provide insights into the effects of electrolytes on Na-CO2 batteries. The simulation results indicated that the diffusion barrier, which represents the resistance to ion movement, was lower for the MeCN-based catholyte compared to the electrolyte employing tetraethylene glycol dimethyl ether (TEGDME). This lower barrier facilitated faster movement of sodium ions due to the solvation structure of Na+ ions in MeCN. As a result, the Na-CO2 battery operated successfully, demonstrating the higher efficiency of the MeCN-based electrolyte in terms of ion movement compared to the TEGDME-based electrolyte.clos
Investigating the surface decomposition of the Argyrodite (Li6PS5Cl) in the dry room
No full textSchool of Energy and Chemical Engineering (Energy Engineering (Battery Science and Technology))clos
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No full textSchool of Energy and Chemical Engineering (Energy Engineering (Battery Science and Technology))clos
Sacrificial Catalyst of Carbothermal-Shock Synthesized 1T-MoS2 Layers for Ultralong-Lifespan Seawater Battery
Get PDFSchool of Energy and Chemical Engineering (Energy Engineering (Battery Science and Technology))The development of efficient electrochemical catalysts for seawater batteries has been of great interest to improve its battery performance with long service life. However, the escalating charge potentials during the battery cycle erode the cell performance and remain a huge challenge. In this work, we demonstrate the sacrificial electrocatalyst of Pt nanoparticles decorated 1T-MoS2 layer triggered by carbothermal shock (CTS) treatment for improving the charge/discharge overpotential and the lifespan of the seawater battery. The simple but potent process of CTS treatment enables us to observe the phase transition of MoS2 crystal from semiconducting 2H to metallic 1T phase, resulting in improved ORR activity under seawater catholyte. In particular, the sacrificial catalyst of MoS2 during the charging process effectively reduces the charging potential due to the oxidation of MoS2, which extends the cycle stability. Furthermore, the increasing portion of 1T-MoS2 induced by the subsequent CTS process of developing Pt nanoparticles on CTS treated MoS2 exhibits a significantly low charge/discharge potential gap of ??0.39 V, a high power density of 6.56 mW cm???2, and long cycle life of up to approximately 800 hours. Thus, high throughput CTS triggered Pt decorated 1T-MoS2 offers a novel strategy for developing efficient bifunctional electrocatalysts to facilitate the long service life of seawater batteries.clos
Focusing Grade as a Measure for Graded Approaches to Safety Culture Management in the Nuclear Industry
No full textDepartment of Nuclear Engineeringclos
Development of a Nodal Diffusion Code for Fast Reactor Analysis and Design
No full textDepartment of Nuclear EngineeringThis thesis focuses on the development and application of a new code, RAST-F, for the design and optimization of cutting-edge fast reactor cores. RAST-F is a diffusion nodal code, purposefully designed for fast reactor analysis. Its capabilities include critical aspects such as steady-state neutronics, fuel burnup for multicycle simulations, thermal-hydraulic feedback, and transient behavior. To enable precise calculations, the RAST-F code utilizes the Monte Carlo simulation code MCS for generating cross-sections required for whole core computations. The accuracy and reliability of RAST-F are extensively examined through a verification and validation process involving three distinct benchmarks of fast reactor cores. The achieved results demonstrate a keff error of less than 150 pcm, power error within 2 %, and root mean square error (RMSE) below 1.5 %. Significant contributions have been made in this research, including the development of an approach for generating cross-sections to address the challenges posed by strong leakage effects. This approach has reduced the keff error from more than 600 pcm to approximately 60 pcm, indicating a substantial improvement. The results and findings of this research contribute to the advancement of fast reactor analysis by providing a comprehensive and validated code, RAST-F, which enables efficient and accurate design and optimization of fast reactor cores. The proposed approaches for cross-section generation and addressing fuel-reflector effects offer valuable insights for future studies in this field.clos
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No full textDepartment of Electrical Engineeringclos
Theoretical and Computational Description of Excited-state Phenomena in Condensed Phase
No full textDepartment of ChemistryTheoretical and computational approaches are employed to study excited condensed systems using static DFT calculations and nonadiabatic molecular dynamics (NAMD) simulations. A novel NAMD method for condensed systems is developed using a trajectory-based NAMD approach. Conventional trajectory-based NAMD methods, such as the surface hopping method, have proven successful for predicting excited-state phenomena but are nearly infeasible for studying condensed systems due to the computational demands of calculating many-body excited states and nonadiabatic couplings. Real-time time-dependent density functional theory (RT-TDDFT) is a common and powerful alternative, with the governing equation being the one-body time-dependent Kohn-Sham (TDKS) equation. In this study, a modified form of the TDKS equation, derived from the electronic equation of the exact factorization (XF) formalism, provides a basis for the new orbital-based method called orbital-based surface hopping through XF (OSHXF). This method is able to explain electron-nuclear correlation missing from the original RT-TDDFT framework. From a simulation of a simple model system, charge carrier dynamics for molecular hole transfer materials are studied. The hole transfer dynamics are efficiently executed within the hopping picture of orbitals, and the size of the hole can be monitored. On the other hand, the hopping picture is not intuitive when the charge carrier is delocalized over space. In this case, the traditional band description is more suitable. In addition to molecular crystals, which consist of localized molecular units, a DFT analysis of hexagonal boron-carbon-nitride (BCN) monolayers is conducted. Through the band description, the carrier mobility of BCN compounds is successfully estimated, and they exhibit an asymptotic behavior towards graphene.clos
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Get PDFDepartment of ChemistryHeteroatom-containing molecule chemistry is one of the important sources of novel compounds with various biological activities, especially due to the unique ability of the resulting compounds to bind reversibly to proteins, like the structure of peptides.1 Because of this importance, the synthetic community has been focused on developing various synthetic methodologies in simpler and milder reaction pathways compared to previously reported methodologies.
In Chapter 1, the synthesis of cyclobutenes using alkyne-alkene [2+2] cycloaddition based on visible light photosynthesis is described. Compared to previously reported UV-activated alkyne-alkene [2+2] cycloaddition reactions, this study proceeded under much milder conditions using blue light in the visible light region. Diverse cyclobutenes were synthesized based on intermolecular [2+2] cycloaddition using alkynes and alkenes. Furthermore, 1,3-dienes were also generated via intramolecular [2+2] cycloaddition using various enynes.
In Chapter 2, the synthesis of ?????lactams using electrochemical C(sp3)-H functionalization based on hydrogen atom transfer is described. The typical synthesis of ?????lactams is nucleophilic addition to N-acyliminium (NAI) intermediates generated by the elimination of leaving groups at the nitrogen???s alpha positions of lactams. Unlike the previous typical synthesis, this study describes a coupling reaction with electron-deficient alkenes or N-sulfonyl imines and nitrogen???s alpha radical on lactams to generate various functionalized ?????lactams.
In Chapter 3, the synthesis of dithioacetals using a gold catalyst via hydrothiolation of vinyl sulfides is described. This method not only produces symmetrical dithioacetals, but also unsymmetrical dithioacetals with broad substrate scope. In this study, both activated and unactivated vinyl sulfides were demonstrated for hydrothiolation. Moreover, the reaction is not limited to aryl thiols, as aliphatic thiols were also used to display broad compatibility for reaction conditions.ope