A physical model for redox flow batteries is developed to estimate performance for any chemistry using parameters such as electrolyte conductivity and kinetic rate constants. The model returns the performance as a function of flow rate, current density, and state of charge. Two different models are developed to estimate the current density distribution throughout the electrode in order to evaluate physical performance of the battery. This is done using electrochemical parameters such as conductivity and kinetic rate constant. The models are analytical in order to produce a computationally cheap algorithm that can be used in optimization routines. This allows for evaluating the economic performance of redox flow batteries, and optimization of cost. The models are validated vs data and found to accurately predict performance in a V-V system for a wide variety of operating conditions.

No description available.

A redox flow battery (RFB) is an electrochemical energy storage device in which the storage medium is in the form of liquid electrolyte, which is stored in external reservoirs separate from the cell stack. The storage capacity of such systems is limited by the size of the external tanks, making the RFB an ideal technology for grid level energy storage. The vanadium redox flow battery (VRB) is a particularly attractive variant of the RFB, due to its use of a single transition-metal element in both the positive and negative electrolytes. However, the performance of the VRB is affected by the cross-over of electrolytes through the ion-exchange membrane which separates the positive and negative electrolytes. Cross-over causes degradation of energy storage efficiency and long term capacity loss. Previous studies of ion cross-over have focused primarily on the measurement of ion diffusion across ion exchange membranes in the absence of electrical current. In this work a novel VRB cell is described in which ion cross-over can be measured directly in the presence and absence of electrical current. Measurements are made of cross-over using this cell with three different types of ion exchange membrane in both charge and discharge modes. The results reported in this work show that the rate of ion cross-over can be greatly enhanced or suppressed depending upon the magnitude of the current flow and its direction relative to the ion concentration gradient. / text

<p dir="ltr">Energy storage has become a promising solution to stabilize renewable energy outputs and to solve the peak/off-peak issues of the power grid. Redox flow battery (RFB) possesses separated energy and power, high capacity, long cycle life and safety, and therefore is regarded as a potential candidate of energy storage. In this thesis, we have researched the degradation pathway of TEMPO derivative redoxmers, obtained long-time stable cycling of a non-aqueous RFB with synthetic redoxmers and permselective ceramic membranes, and extended the redox flow approach to the field of water desalination.</p><p dir="ltr">The properties of redoxmers are the main elements that affect RFB performance. Organic redoxmers come to sight due to their facile property improvement based on structural diversity and molecular tailorability. But the majority of reported redoxmers are anolytes; catholytes are less developed. Also, the mechanism of limited long-time cycling stability is still not well understood. In our experiment, we have progressively unraveled a series of degradation mechanisms of TEMPO-based redoxmers, including oxidation, crossover, ring-opening and possibly deoxygenation. The initial candidate, 4-hydro-TEMPO (TEMPOL), presents combined decomposition pathways. The charged oxoammonium species oxidizes the alcohol group (-OH) in its structure to a ketone (C=O) bond and also undergoes a protonation-induced ring-opening side reaction forming an alkene structure, evidenced by the characteristic 13C NMR chemical shifts of C=O and C=C groups. Due to its non-ionic structure, crossover through the anion exchange membrane used in flow cells is another issue that causes capacity loss. A hydroxyl-free TEMPO derivative bearing an anionic sulfonate group (‒SO3‒) also suffers from deprotonation-induced ring opening. By eliminating nucleophilic moiety, we have designed the third TEMPO derivative that has a cationic tetraalkylammonium end group. This molecule exhibits greatly improved cycling stability in flow cells, yet still with slow capacity fading that may hypothetically be a result of parasitic deoxygenation reaction. With the carefully designed analyses, the obtained mechanistic understanding of molecular decomposition has paved the way for rationale structural design toward stable TEMPO catholyte candidates.</p><p dir="ltr">Nonaqueous RFBs hold promise for higher cell voltage and energy density given their wider electrochemically stable voltage windows, but their performance is often plagued by the crossover of redox compounds. In this study, we used permselective lithium superionic conducting (LiSICON) ceramic membranes to enable reliable long-term cycling of organic redox molecules in nonaqueous flow cells. With different solvents on each side, enhanced cell voltages were obtained for a flow battery using viologen-based negolyte and TEMPO-based posolyte molecules. The thermoplastic assembly of the LiSICON membrane realized leakless cell sealing, thus overcoming the mechanical brittleness challenge. As a result, stable cycling was achieved in the flow cells, which showed good capacity retention over an extended test time (e.g. two months).</p><p dir="ltr">Desalination of saline water is becoming an increasingly critical strategy to overcome the global challenge of drinkable water shortage, but current desalination methods are often plagued with major drawbacks of high energy consumption, high capital cost, or low desalination capacity. To address these drawbacks, we have developed a unique continuous-mode redox flow desalination approach capitalizing on the characteristics of redox flow batteries. The operation is based on shuttled redox cycles of very dilute Fe2+/Fe3+ chelate redoxmers with ultralow cell overpotentials. The air instability of Fe2+ chelate is naturally compensated for by its in situ electrochemical generation, making the desalination system capable of operations with electrolytes at any specified state of charge. Under unoptimized conditions, fast desalination rates up to 404.4 mmol·m−2·h−1 and specific energy consumptions as low as 7.9 Wh·molNaCl−1 have been successfully achieved. Interestingly, this desalination method has offered an opportunity of sustainable, distributed drinkable water supplies through direct integration with renewable energy sources such as solar power. Therefore, our redox flow desalination design has demonstrated competitive desalination performance, promising to provide an energy-saving, high-capacity, robust, cost-effective desalination solution.</p>

Stable radicals have enjoyed widespread use in a variety of fields including synthetic chemistry, materials chemistry, energy storage, and biochemistry. This thesis outlines our investigations of cyclopropenium-based stable radicals and their application as redox mediators, redox-active ligands, catalysts, and materials for energy storage. The first chapter gives a brief overview of the use of radicals in synthetic chemistry. The principles that govern the stability of radicals is discussed and notable examples are highlighted. The second section of the first chapter reviews the aromatic platforms that have been developed by the Lambert group and how they might be converted into stable radical species. The second chapter details our study of 2,3-diaminocyclpropenones as stable radicals. These electron rich cyclopropenium derivatives undergo facile oxidation to yield a radical cation species. The origin of the stability of this oxygen-centered radical was elucidated by density functional theory calculations and analysis of the crystal structure. Diaminocyclopropenones were also found to be effective neutral L-type ligands in Ce(IV) complexes. EPR and UV-VIS experiments revealed that these complexes exhibited reversible homolytic dissociation of their diaminocyclopropenone ligands. The third chapter describes the use of trisaminocyclopropeniums as catholytes for nonaqueous redox flow batteries. A newly designed trisaminocyclopropenium structure could be accessed in large quantities and showed long lasting stability in its oxidized state. A new composite polyionic material was developed for use as a membrane suitable for organic solvent and high voltages. Cycling in combination with a perylenediimide anolyte yielded a 1.7 V battery that exhibited excellent coulombic efficiency and capacity retention. Using a spiro-bis(phthalimido) anolyte afforded a battery with an open circuit voltage of 2.8 V. The fourth chapter details how our battery studies with trisaminocyclopropenium radical dications led us to discover their photoinduced reactivity. We developed an electrophotocatalytic platform using trisaminocyclopropeniums as a species capable of being activated by both photochemical and electrochemical energy. The excited state oxidation potential of the doubly activated species was found to be +3.33 V, which was capable of effecting oxidative coupling reactions using both arenes and ethers as substrates. Density functional theory calculations and spectroscopic experiments revealed that the photoreactivity was due to a SOMO-inversion event. The trisaminocyclopropenium radical dication could be prepared on scale via direct electrolysis and subsequently used in high throughput screening.

New ideas and solutions are necessary to face challenges in the electricity industry. The application of electricity storage systems (ESS) can improve the quality and stability of the existing electricity network. ESS can be used for peak shaving, instead of installing new generation or transmission units, renewable energy time-shift and many other services. There are few ESS technologies existing today: mechanical, electrical and electrochemical storage systems. Flow batteries are electrochemical storage systems which use electrolyte that is stored in a tank separated from the battery cell. Electrochemistry is very important to understand how a flow battery functions and how it stores electric energy. The functioning of a flow battery is based on reduction and oxidation reactions in the cell. To estimate the voltage of a cell the Nernst equation is used. It tells how the half-cell potential changes depending on the change of concentration of a substance involved in an oxidation or reduction reaction. The first flow battery was invented in the 1880’s, but was forgotten for a long time. Further development was revived in the 1950’s and 1970’s. A flow battery consists of two parallel electrodes separated by an ion exchange membrane, forming two half-cells. The electro-active materials are stored externally in an electrolyte and are introduced into the device only during operation. The vanadium redox battery (VRB) is based on the four possible oxidation states of vanadium and has a standard potential of 1.23 V. Full ionic equations of the VRB include protons, sulfuric acid and the corresponding salts. The capital cost of a VRB is approximately 426 $/kW and 100 $/kWh. Other flow batteries are polysulfide-bromine, zinc bromine, vanadium-bromine, iron-chromium, zinc-cerium, uranium, neptunium and soluble lead-acid redox flow batteries. Flow batteries have long cycle life and quick response times, but are complicated in comparison with other batteries. / Nya idéer och lösningar är nödvändiga för att möta utmaningarna i elbranschen. Användningen av elektriskt lagringssystem (ESS) kan förbättra kvalitén och stabiliteten av det nuvarande elnätet. ESS kan användas till toppbelastningsutjämning, istället för att installera nya produktions eller kraft överförnings enheter, förnybar energi tidsförskjutning och många andra tjänster. I dagsläget finns det få olika ESS: Mekaniska, elektriska och elektrokemiska lagringssystem. Flödesbatterier tillhör kategorin elektrokemiska lagringssystem som använder sig utav elektrolyt som är lagrad i en tank separerad från battericellen. För att kunna förstå hur flödesbatteriernas funktioner och på vilket sätt som dem lagrar elektriskt energi är det viktigt att kunna elektrokemi. Flödesbatteriernas funktion är baserad på reduktions och oxidations reaktioner i cellen. Nernsts ekvation används för att kunna uppskatta voltantalet i en cell. Nernsts ekvation säger hur halvcell potentialen ändras beroende av ändringen av koncentrationen av ämnet involverat i oxidations eller reduktions reaktionen. Det första flödesbatteriet uppfanns 1880-talet, men blev bortglömt under en lång tid. Vidare utveckling förnyades under 1950 och 1970-talet. Ett flödesbatteri består utav två parallella elektroder som är separerade utav ett jonbytes membran vilket formar två halvceller. Dem elektroaktiva materialen är lagrade externt i elektrolyt och är införs bara i anordningen under användning. Vanadium redox batteriet (VRB) är baserat på dem fyra möjliga oxidations tillstånden av vanadium och har en standard potential på 1.23 V. Fullt joniska ekvationer av VRB inkluderar protoner, svavelsyra och deras motsvarande salter. Kapitalkostnaden av ett VRB är ungefär 426 $/kW och 100 $/kWh. Det finna andra flödesbatterier som är polysulfide-brom, zink-brom, vanadium-brom, järn-krom, uran, neptunium och löslig blysyre redox flödesbatterier. Flödesbatterier har en lång omloppstid samt en snabb svarstid men är komplicerade jämfört med andra batterier.

<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>

No description available.

No description available.

No description available.