The development of energy storage and conversion techniques with high efficiency and power density is of great importance for the sustainable development of our green world. Li-O₂ batteries with high theoretical energy density has attracted extensive attention. However there are still many issues waiting to be solved, such as low stability of cathode catalyst, as well as the deactivation of cathode by H₂O and CO₂ from air. Reversible solid oxide fuel cells can be used for electricity production by SOFCs and fuel production (H₂ and O₂) by SOECs. Thus, oxygen storage materials can bridge Li-O₂ batteries and reversible SOFCs with the purpose of increasing the whole efficiency of the system. The discovery of oxygen storage materials with reversible oxygen release/storage behaviours and high oxygen storage capacities dependent on temperature or oxygen partial pressures (e.g., inert and oxidation gases) still needs further research. The work in this thesis mainly focuses on the preparation of transition-metal based oxides (such as perovskite oxides, brownmillerite-type oxides, layered-perovskite oxides, coated β-MnO₂ nanorods, transition-metal doped CeO₂ nanocrystals) as oxygen storage materials and their energy-related applications, seeking to discover the principles for oxygen storage/release properties and their performance in energy conversion and storage applications. The prepared materials included nanostructured and bulk materials via various synthesis methods, including citrate-modified evaporation-induced self-assembly method, hydrothermal method, pechini method, as well as solid state method. This work investigated the oxygen storage capacities of several crystal structure types oxides based on transition-metals. Nanostructured La₀.₆Ca₀.₄Fe₁₋ₓCoₓO[sub](3-δ) and La₀.₆Ca₀.₄Mn₁₋ₓFeₓO[sub](3-δ) exhibit high oxygen storage capacities and stability under reductive 5%H₂/Ar, but the oxygen-storage content under inert argon is low, just about 0.2 wt%. Brownmillerite-type Ca₂AlMnO₅ is demonstrated to possess a large amount of oxygen release/storage capacities depending on temperature even under flowing oxygen, as well as high oxygen storage/release properties and reversibility under alternating inert and oxygen gases at 500 °C. Substituting Ga on the Al-site would reduce the oxygen storage capacities, even though these substituted samples still posses good reversibility. The effect of A-site species (Mg, Ca, Sr) have been also investigated and demonstrated. It can't obtain pure brownmillerite-type crystal structure when Ca is partially or totally substituted by Mg or Sr, resulting in poor reversibility and low oxygen storage capacities. Nanostructured layered-perovskite La₁.₇Ca₀.₃M₁₋ₓCuₓO[sub](4-δ) (M = Fe, Co, Ni, Cu) have also been investigated for oxygen storage and as potential cathodes for IT-SOFCs. Even though the as-prepared layered-perovskite oxides have been demonstrated to be good candidates as cathode materials for IT-SOFCs with high performance, they do not possess high amount of oxygen storage/release ability under inert atmospheres because of the robust phase stability. β-MnO₂ nanorods can release large amount of oxygen (ca. 9.2 wt%) with increasing temperature at about 560 °C under various gases (air, N₂). Coating β-MnO₂ nanorods with CeO₂ nanocrystals could result in lower temperatures for oxygen mobility and removal under N₂ because of the enhanced oxygen mobility between CeO₂₋ₓ and β-MnO₂, while coating β-MnO₂ nanorods with SnO₂ nanocrystals have no enhanced oxygen mobility behaviours. The results demonstrate the positive and negative synergetic effect between other metal oxides and β-MnO₂ on the oxygen migration. Cr- and Cu-doped CeO₂ nanocrystals (i.e. nanorods, nanocubes and nanoparticles) were chosen to investigate the effect of transition-metal doping on CeO₂ and their valence changes with temperature and various atmospheres, as well as their oxygen storage capacities. The effect of Cr- or Cu- doping on CeO₂ nanocrystal morphology and oxygen storage capacities have been investigated and demonstrated. This provides some basic information for transition-metals doped CeO₂ nanocrystal evolution and stability, as well as further applications in energy-related fields, such as three-way catalysts, electrode materials in solid oxide fuel cells and Li-air batteries.

<p>  </p> <p>Nowadays, clean and renewable energy sources like wind and solar power have been rapidly growing for the goal of phasing out traditional fossil fuels, achieving carbon neutrality, and realizing sustainable development. Long-duration and large-scale energy storage is needed to address the intermittent nature of these sources. Especially, redox flow battery (RFB) is an attractive energy storage device for large scale applications because of its high scalability, design flexibility, and intrinsic safety. The all vanadium redox flow battery stands for the state-of-the-art system, but the high vanadium cost and limited energy density are among the limiting factors for wide commercialization. Therefore, it is necessary to develop new RFB materials that are cost-effective and highly soluble. Organic redox-active molecules (redoxmers) hold great potential to satisfy these requirements due to structural diversity, tunable chemical and electrochemical properties, and earth-abundant sources. With rational structural design, organic redoxmers can show favorable properties such as high solubility, suitable redox potential, and good chemical stability. However, current efforts are mainly on the development of anolyte redoxmers, e.g. phenazine, anthraquinone and viologen. Only limited types of catholyte candidates have been reported such as ferrocene and TEMPO. The major reason for such slow-paced progress is the limited chemical stability of these catholyte redoxmers. To bridge this critical gap, my efforts are focused mainly on the design and development of promising catholyte redoxmers for both aqueous organic (AORFBs) and non-aqueous organic redox flow batteries (NRFBs).</p> <p>Phenoxazine functionalized with a hydrophilic tetraalkylammonium group demonstrates good water solubility and suitable redox potential. Cyclic voltammograms (CV) and flow cell testing were used to evaluate the electrochemical properties and battery performance, respectively. Besides, the battery fading mechanism was systematically investigated by CV, liquid chromatography mass spectra (LC-MS) and electron paramagnetic resonance (EPR) spectroscopy. The redoxmer decomposition mechanism analysis will benefit future redoxmer development by guiding the molecular design of more stable structure candidates. </p> <p>A structural design strategy for the development of novel TMPD-based (tetramethyl-<em>p</em>-phenylenediamine) catholyte redoxmers for NORFBs is presented. Two categories of functional groups, including oligo(ethylene glycol) (EG) either chains and phenyl rings, were incorporated into the TMPD core to improve solubility and stability in non-aqueous electrolytes, respectively. EPR characterization and bulk electrolyte (BE) analysis were carried out to evaluate the redoxmers stability. In addition, DFT studies were conducted to understand the impacts of functional groups on redox potential and chemical stability. The present work demonstrates the feasibility of constructing promising redoxmers from TMPD and provides insights into molecular designing of catholytes to achieve high solubility and excellent stability for non-aqueous redox flow batteries.</p>

<p>Li-ion batteries (LIBs) are currently pervasive across portable electronics and electric vehicles and are on the ascent for large-scale applications such as grid storage. However, commercial LIBs based on intercalation chemistries are inching toward their theoretical energy density limits. Consequently, the rapidly growing demands of energy storage have necessitated a recent renaissance in exploring battery systems beyond Li-ion chemistry. Next-generation batteries that utilize Li metal as the anode can improve the energy density and power density of LIBs. Despite the theoretical promise, the commercialization of metal-based batteries requires overcoming several hurdles, stemming from the unstable nature of Li in liquid electrolytes. Upon repeated charging, the metal anode undergoes unrestricted growth of dendrites, devolving to a thermal runaway in extreme circumstances. By replacing the organic liquid electrolyte with a non-flammable solid electrolyte, solid-state batteries (SSBs) can potentially provide enhanced safety attributes over liquid electrolyte cells. Upon pairing of solid electrolytes with a Li metal anode, such systems present the unique possibility of engineering batteries with high energy density and fast charging rates. However, there are a number of technical challenges and fundamental scientific advances necessary for SSBs to achieve reliable electrochemical performance. The formation of dendritic morphologies during charging and the loss of active area at the anode-electrolyte interface during discharging are two critical limitations that need to be addressed.</p> <p>In this thesis, the morphological stability of the Li metal anode is examined based on the mechanistic interaction of electrochemical reaction, ionic transport and surface self-diffusion, that is further dependent on aspects including the thermal field and electrolyte composition. The origin of electrochemical-mechanical instability and metal penetration due to heterogeneities in solid-state electrolytes such as grain boundaries will be analyzed. The phenomenon of contact loss at solid-solid interfaces due to the competing interaction between electrochemical dissolution and Li mechanics will be studied. Lastly, the mechanistic attributes governing the thermal stability of solid-solid interfaces in solid-state batteries will be examined. Overall, the dissertation will focus on understanding the fundamental mechanisms underlying the evolution of solid-liquid and solid-solid interfaces in energy storage and derive potential design guidelines toward achieving stable morphologies in metal-based batteries.</p>

<p dir="ltr">The thesis goal was to design a quasi-solid-state battery electrolyte, which was optimized to function at ambient as well as low temperatures. In the first project, an array of quasi-solid-state electrolytes were developed and compared. A series of electrochemical, spectroscopic, and thermal experiments in addition to imaging techniques determined a top performer as well as elucidated possible mechanistic explanations. This systematic study attempted to validate literature conclusions about the failure mechanisms governing batteries (solid-state batteries) at ultralow temperatures, while also offering hypothesis driven additional insight. The optimized electrolyte, which will be deemed as CSPE@2MMeTHF, performed well for several key reasons, traced to the co-solvent used (Me-THF), the salt concentration, and its formation of a stable and suitable cathode-electrolyte interphase. It was able to perform well at 25 °C, and down to -25 °C. The second part of the work, focused on further optimizing the electrolyte by removing a ‘polymer wetting/soaking’ step, removing a ceramic component, and pairing it with a recently discovered anodic electrode material. Given that narrowing the research gap for low temperatures requires both electrolyte and electrode design, it was important to consider this aspect of the problem as well. The cathodic electrode used for the first project, traditionally performs poorly at low temperatures, allowing for a suitable experimental control for the electrolyte. However, the new anodic electrode had two ways of storing lithium ions, as opposed to just one in the former, making it an attractive option for the stated goal of a low-temperature solid-state battery. This second project is akin to a ‘proof-of-concept’ work and there is much more room for further study, especially in preparing a full cell with the aforementioned electrodes cathode (LFP) and anode (NbWO) with the second SPE@51DMMeT electrolyte. In summary, this thesis shows method design to prepare solid-state electrolytes with portion of liquid, two successfully developed electrolyte systems for low temperatures, and a rigorous discussion of factors that affect electrochemical performance. Demonstrated research activities are of great value to defense as the current lithium-ion batteries does not perform well at subzero temperatures.</p>

In the pursuit of renewable and sustainable energy sources, this century presents humanity with an imperative driven by the crisis of conventional energy shortages and environmental pollution. Clean electrochemical energy storage and conversion technologies play a pivotal role in shaping the future landscape of power generation and energy utilization. However, the judicious design of the catalysts capable of efficiently and robustly driving electrochemical conversion remains a pressing challenge. In my dissertation, I addressed the critical challenges related to enhancing energy conversion efficiency in zinc-air batteries (ZABs) and electrocatalytic carbon dioxide reduction (CO2RR). These innovations show promise in utilizing renewable electricity to generate power and actively contribute to decarbonization efforts. The core focus of my dissertation revolves around the strategy of interface engineering for materials design and characterization. It is coupled with an in-depth mechanistic investigation of structure-property relationship at the interface level. The construction of a strong metal-support oxide interaction (SMMOI) has been demonstrated in the PdNiMnO porous film and has shown promising results. This interaction significantly enhances the activity of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) through electronic perturbation of Pd, reducing the reliance on precious metals and substantially improving the ZAB performance. On the other hand, my dissertation expands the decarbonization concept of electrocatalytic CO2RR towards value-added chemical production such as CO and formate. By designing bio-inspired tin oxide (SnOx) porous films through multiscale approaches of morphology engineering, surface chemistry, and phase transformation, the CO2RR Faradaic efficiency can be significantly improved. This is achieved by establishing a triple-phase interface and preserving the active phase through controlled pulsed electrochemical potentials during reactions. This innovative approach effectively addresses limitations associated with CO2 capture on the electrode and CO2 solubility issues in the electrolyte. The interface engineering strategies outlined in this dissertation illuminate the path toward next-generation catalyst designs that are highly efficient and tailored for sustainable and renewable energy applications.

In this dissertation, density functional theory calculations are performed to calculate the thermodynamic and electrochemical properties of metal coordinated frameworks for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Gibb's free energy, overpotential, charge transfer and ligands effect are evaluated. The charge transfer analysis shows the positive charges on the metal coordinated frameworks play an essential role in improving the electrochemical properties of the metal coordinated frameworks. Based on the calculations, design principles are introduced to rationally design and predict the electrochemical properties of metal coordinated frameworks as efficient catalysts for ORR and OER. An intrinsic descriptor is discovered for the first time, which can be used as a materials parameter for rational design of the metal coordinated frameworks for energy storage and conversion. The success of the design principles provides a better understanding of the mechanism behind ORR and OER and a screening approach for the best catalyst for energy storage and conversion.

<p dir="ltr">This dissertation addresses the significant challenge of enhancing the performance of lithium-ion batteries (LIBs) in extremely low-temperature environments, which is critical for applications in defense and space exploration. By innovating both electrolyte formulations and electrode materials, this research extends the operational boundaries of LIBs to temperatures below -100 ℃. </p>

Le développement durable nécessite des investissements massifs pour l'exploration et l'utilisation des sources d'énergie renouvelables dans le bilan énergétique. Parmi diverses formes de l’énergie, l'électricité est sans doute la forme la plus souhaitable pour les usages quotidiens. Cependant, en raison de l'intermittence des sources d’énergie renouvelables, l'électricité doit être stockée sous d'autres formes afin de corréler la production éphémère et la consommation en continue. Malgré la présence des systèmes commerciaux de stockage d'énergie, la recherche de nouveaux matériaux et de nouvelles approches pour résoudre ce problème est toujours en cours et attire également une grande attention. Les récents progrès ont poussé la communauté scientifique vers l'utilisation de matériaux à l'échelle nanométrique pour des systèmes de stockage et de conversion de l'énergie. Bien que ces derniers offrent des avantages pour réduire les émissions de gaz à effet de serre, leurs performances sont encore inférieures aux valeurs théoriques. Dans ce contexte, l’ingénierie à l'échelle moléculaire devient cruciale non seulement pour créer un nouveau type d'entités moléculaires mais aussi pour augmenter les performances des matériaux existants. Dans ce contexte, nous proposons d’utiliser une nouvelle famille de matériaux à base de liquides ioniques pour diverses d’applications, comprenant celles dans le domaine énergétique et pour le long terme, dans la fabrication de la peau artificielle, ces objectifs font l’objet de ces travaux de thèse. Cette dissertation est composée de cinq chapitres. Le chapitre 1 présente différents aspects des liquides ioniques (LIs) et des polymères à base de LI décrites dans la littérature. Via ce chapitre, nous envisageons d’atteindre les points suivants : (1) Décrire les utilisations possibles des liquides ioniques en électrochimie ; (2) Discuter des comportements physico-chimiques de ces composés en solution, (3) Montrer l'immobilisation de liquides ioniques (Redox-actifs) sur différents substrats : de couches minces aux polymères et (4) Mettre en évidence les travaux marquant portant sur l’utilisation des polymères ioniques liquides dans diverses applications. Le chapitre 2 présente différentes approches électrochimiques pour l'immobilisation de liquides ioniques rédox à la surface de l'électrode. De plus, les différentes caractéristiques des nouvelles interfaces seront reportées. Le chapitre 3 se concentre sur l'utilisation des polymères LIs comme catalyseurs émergents et comme matrices pour la génération de matériaux hybrides vers l'activation de petites molécules (ORR, OER, HER). Le chapitre 4 étudie la réactivité à l'échelle micro / nanométrique de divers matériaux, y compris les polymères liquides ioniques électro-actifs, en utilisant la microscopie électrochimique à balayage (SECM). Le chapitre 5 présente les résultats préliminaires de la fabrication de substrats flexibles avec des fonctionnalités intéressantes : possibilité de convertir le frottement en électricité et stockage d'énergie en utilisant des liquides ioniques redox polymériques. Ces études ouvrent de nouvelles opportunités pour élaborer des dispositifs flexibles, portables et implantables. / Increasing demand of energy requires massive investment for exploration and utilization of renewable energy sources in the energy balance. However, due to the intermittence of the current renewable sources, the generated electricity must be stored under other forms to correlate the fleeting production and the continuous consumption. Despite available commercialized systems, seeking for new materials and new approaches for resolving this problem is still matter of interest for scientific researches. Highlighted advancements have recently oriented the community towards the utilization of nanoscale materials for efficient energy storage and conversion. Although the advantages given by existing nanomaterials for diverse applications, especially in the energy field, their performance is still lower than theoretical purposes. Consequently, tailoring the physical-chemical properties at the molecular scale becomes crucial not only for boosting the activities of the existed materials but also for creating a new type of molecular entities for storing and releasing the energy. Accordingly, this PhD work aim to develop new family of materials based on ionic liquid that exhibits a multifunctionality towards energy applications. Our work is based on the knowhow in surface functionalization and material preparation by simple methods to build up electrochemical systems that can be utilized in various applications. Thus, this thesis will report different results obtained by following this direction and is composed of six chapters: Chapter 1 reports an overview of ionic liquid and polymeric ionic liquid. We propose to review the available literature on the redox-IL from solution to immobilized substrates. Through this chapter, we will achieve the following points: (1) Report the possible uses of ionic liquids in electrochemistry; (2) Discuss about the physical-chemical behaviors of these compounds in solution, (3) Show the immobilization of (Redox-active)–ionic liquids onto different substrates: from thin layer to polymer and (4) Highlight recent advances using polymeric ionic liquids for diverse applications. Chapter 2 will be devoted to different electrochemical assisted approaches for the immobilization of (redox)-ionic liquids to the electrode surface. We will focus on generating a thin layer and polymeric film based ionic liquid. Furthermore, the different characteristics of the new interfaces will be reported. Chapter 3 concentrates on the use of the polymer ionic liquid modified electrodes as emerging catalyst and as template for the generation of hybrid materials towards activation of small molecules. Chapter 4 studies the reactivity at micro/nanometer scale of diverse materials, including single layer graphene, polymeric redox – ionic liquid, using the scanning electrochemical microscopy (SECM). Chapter 5 reports the potential applications of redox ionic liquid and focus on providing the preliminary results towards the fabrication of flexible substrates with interesting functionalities: possibility to convert the friction to electricity and energy storage by using polymeric redox ionic liquids. These studies open a new opportunity to elaborate flexible, wearable and implantable devices. Finally, some concluding remarks are given to summarize different results obtained in the previous chapters. Besides, different perspectives will be given by using ionic liquid as main material for developing different energy storage and conversion systems.

<p>Energy storage devices have become an integral part of the digital infrastructure of the 21st century. Li-ion batteries are a widely used chemical form of energy storage devices comprising components with varied chemical, mechanical and electrochemical properties. Over long-term usage, the anode and cathode experience spatially heterogeneous Li reaction, mechanical degradation, and reversible capacity loss. The small particle size and environmental sensitivity of materials used in Li-ion battery materials make investigating electrodes' electrochemical and mechanical properties an arduous task. Nevertheless, understanding the effect of electrochemical fatigue load (during the battery's charging and discharging process) on composite electrodes' mechanical stability is imperative to design and manufacture long-lasting energy storage devices.</p><p>Due to the low-symmetry lattice, Lithium Nickel Manganese Cobalt Oxide (NMC) cathode materials exhibit direction-dependent (anisotropic) mechanical properties. In this Dissertation, we first measure the anisotropic elastic stiffness of NMC cathode material using nano-indentation. We also determine the effect of Ni stoichiometry on the indentation modulus, hardness, and fracture toughness of NMC materials. The complete information on the mechanical properties of cathode materials will enable accurate computational results and the design of robust cathodes.</p><p>Further, using operando optical experiments, we report that NMC porous composite cathode experiences asynchronous reactions only during the 1st charging process. Non-uniform carbon binder network coverage across the cathode and Li concentration-dependent material properties of NMC results in the initial asynchronous phenomenon. The information on the degree of electrochemical conditioning of Li-ion battery cathode obtained from optical microscopy can test the consistency of product quality in the industrial manufacturing process. We also investigate the effects of non-uniform reactions on active material’s local morphology change and study the evolution of particle network over long-term cycling. Reported data from experiments depicts that in the early cycles, individual particles’ characteristics significantly influence the degree of damage across the cathode.</p><p>However, the interaction with neighboring particles becomes more influential in later cycles. Computational modeling uses a multiphysics-based theoretical framework to explain the interplay between electrochemical activity and mechanical damage. The methodology, theoretical framework, and experimental procedure detailed here will enable the design of efficient composite electrodes for long-lasting batteries.</p>

<p>Two studies incorporated providing the groundwork for a blueprint to design sodium sulfur cells from electrode fabrication to choices in electrolyte such as DME, DEGDME, TEGDME and two different salts NaClO4 and NaPF6. First study describes role of the binder within the system comparing carboxymethyl cellulose and carboxymethyl cellulose with a styrene butadiene elastomer addition. The second study focuses on methods to prevent polysulfide shuttling within room temperature sodium sulfur system</p>