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The hydrogen–bromine redox flow battery is a promising energy storage technology with the potential for capital costs as low as 220 $ kWh−1 and high operational power densities in excess of 1.4 W cm−2. In this work, enhanced surface area bromine electrodes incorporating carbon black (CB) and graphene nanoplatelets (GnPs) on carbon paper and carbon cloth substrates were investigated, and the effect of electrolyte concentration on performance of the electrodes was studied. Carbon-black-modified electrodes are found to possess the largest electrochemically active surface areas, i.e., up to 11 times that of unmodified materials, while GnP electrodes are shown to have superior kinetic activity towards the bromine electrode reaction. In terms of performance, lower electrolyte concentrations are found to favour the improved kinetic parameters associated with graphene nanoplatelet electrodes, while highly concentrated electrolytes favour the larger electrochemically active surface area of carbon black electrodes. The optimal performance was achieved on a carbon-black-modified carbon cloth electrode in a 6 M HBr/2 M Br2 electrolyte concentration, with polarisation current densities approaching 1.6 A cm−2 at overpotentials of ±400 mV, and mean overpotentials of 364 mV during oxidation and 343 mV during reduction, resulting from bromine oxidation/reduction cycling tests at ±1.5 A cm−2.

To achieve carbon neutrality by mid-21st century, rapid deployment of large-scale electrical energy storage options is required to integrate intermittent renewable energy resources such as solar and wind, and catalyze smart-grid infrastructure. Electrochemical energy storage technologies such as Li-ion batteries (LIBs) and redox flow batteries (RFBs) offer the modularity and scalability required for large-scale energy storage. RFBs operate by spatial separation of electrode and electrolyte, providing energy and power decoupling. This gives them an advantage over conventional LIBs, in terms of long life cycles (>10,000 cycle, 10-20 years) and inherent safety. However, the volumetric energy density of RFBs ( 500 Wh l-1. RTFBs however are in embryonic stages of development. The design principles of electroactive materials and the chemical redox reaction mechanism would need to be established to realize full-scale deployment of RTFBs. To address these challenges, chemical redox kinetics and RTFB design were investigated in this dissertation. In Chapter Ⅱ, chemical redox kinetics were compared to the well-studied electrochemical kinetics of LFP. Chemical redox of LFP by ferrocene-based redox shuttles was evaluated using in-operando UV-Vis spectroscopy, whereas LFP half-cells were potentiostatically charged/discharged. The kinetics and phase transformations of the two redox routes were estimated using Johnson-Mehl-Avrami-Erofeyev-Kolomogorov model (JMAEK). It was revealed that the reaction pathway and phase transformations are different for chemical and electrochemical redox. The first-order rate constants were consistently lower for chemical redox than electrochemical redox. Additionally, apparent activation energy calculations suggested that the low redox shuttle concentrations (

Redox flow batteries (RFBs) are an emerging electrochemical technology suitable for energy-intensive grid storage, but further cost reductions are needed for broad deployment. Overcoming cell performance limitations through improvements in the design and engineering of constituent components represent a promising pathway to lower system costs. Of particular relevance, but limited in study, are the porous carbon electrodes whose surface composition and microstructure impact multiple aspects of cell behavior. Here, we systematically investigate woven carbon cloth electrodes based on identical carbon fibers but arranged into different weave patterns (plain, 8-harness satin, 2 × 2 basket) of different thicknesses to identify structure–function relations and generalizable descriptors. We first evaluate the physical properties of the electrodes using a suite of analytical methods to quantify structural characteristics, accessible surface area, and permeability. We then study the electrochemical performance in a diagnostic flow cell configuration to elucidate resistive losses through polarization and impedance analysis and to estimate mass transfer coefficients through limiting current measurements. Finally, we combine these findings to develop power law relations between relevant dimensional and dimensionless quantities and to calculate extensive mass transfer coefficients. These studies reveal nuanced relationships between the physical morphology of the electrode and its electrochemical and hydraulic performance and suggest that the plain weave pattern offers the best combination of these attributes. More generally, this study provides physical data and experimental insights that support the development of purpose-built electrodes using a woven materials platform.

The following article shows how a simple construction of a hybrid flow battery can be realised with medical technology materials. The implementation of this future-oriented topic is an example of a curricular innovation and should already be included in school curricula, since future generations will have to deal intensively with the energy transition (not only in Germany) and renewable energies. An electrolyte based on ink cartridges was used to motivate the pupils. The use of this 'everyday chemical' creates a real life reference for the students in the classroom, which can increase the popularity of chemistry teaching.

peer-reviewed We report a newadditive,monobasic potassium arsenate (KH2AsO4), for improving the thermal stability of VFB catholytes.Using our standard accelerated testing methodology at 30–70°C, we showed that the effect increases continuously with increasing concentration of arsenate over the range investigated (0 – 0.10 mol dm−3). In comparison to similar experiments with phosphate (H3PO4), the magnitude of the effect was greater for arsenate. A combination of arsenate and phosphate was also effective. Based on these results, we speculate that other Group-V elements in the +5 oxidation state may also stabilize VFB catholytes

This study proposes a novel methodology for optimal sizing of a vanadium redox flow battery (VRFB) aiming at providing the load frequency control (LFC) of power system (PSs) with renewable generation, such as wind generation. This methodology utilises a new optimisation problem, where the optimal size of the VRFB is an endogenous result from the model of optimisation problem. To resolve the new optimisation problem, a hybrid optimisation model (HOM) is employed in order to calculate the optimal investment for the VRFB (optimal size) while taking into account both its impact on the PS costs and on the quality of the system frequency. Through stochastic optimisation, the HOM allows computing the variable operating costs and VRFB investment costs, considering the uncertainties associated to the PS. This stochastic optimisation utilises a new quasi-stationary simulations of the PS operation, which demands lower computing effort. To this aim, this study proposes a novel modelling approach of both the VRFB and the PS operation. Moreover, statistical indexes are proposed as new factor used in sizing the LFC operating reserve. The results show that the developed methodology allows evaluating with precision the stochastic characteristics of the PS. Fil: Martinez, Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Energía Eléctrica. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Energía Eléctrica; Argentina Fil: Molina, Marcelo Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Energía Eléctrica. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Energía Eléctrica; Argentina Fil: Mercado, Pedro Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Energía Eléctrica. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Energía Eléctrica; Argentina

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.

Herein, we present a multigram scale-up route for the preparation of novel polymer composite nanoparticles as potential multifunctional rechargeable material for future, sustainable batteries. The nanoparticles (20 nm) comprise three innocuous yet functional interpenetrated macromolecular networks: polypyrrole, methylcellulose, and lignin. They are uniquely assembled in strands or chains (~200 nm) such as necklace beads and show long-term stability as water dispersion. We find that an aqueous suspension of this hierarchical nanomaterial shows two sets of reversible redox peaks, separated by ~600 mV, originating from the catechol moieties present in the lignin biopolymer. Remarkably, the addition of carbon dioxide increased the capacity of one of the redox processes by 500%. Importantly, the three redox stages occur in the presence of the same nanostructured polymer so being a potentially bifunctional material to be used in advanced electrochemical systems. The new properties are attributed to an intrinsic chemical and electronic coupling at the nanoscale among the different building blocks of the metal-free polymer composite and the structural rearrangement of the interpenetrated polymer network by the incorporation of CO. We have provided both a new electrochemically multifunctional hierarchically structured material and a facile route that could lead to novel sustainable energy applications., J.C.G. acknowledges support from the Spanish Ministry of Economy, Industry, and Competitiveness (MINECO) through a Ramon y Cajal Fellowship (RYC-2015-17722) and the Retos Project (MAT2017-86796-R, AEI/FEDER/UE). D.A.E. and D.A.B acknowledge the Retos Project (MAT2017-84385-R, AEI/FEDER/UE). P.N. acknowledges the postdoctoral contract from the Government of the Comunidad de Madrid (CAM, PEJD-2018-POST/AMB-9248). M.L.M. and J.C.G. acknowledge the PTI-FLOWBAT project (Ref. Nº: 201980E101) from the Spanish Research Council (CSIC). We would also like to thank the Biomaterials Group from the ICTP-CSIC for letting us use the DLS equipment.

Unlike traditional fossil fuel plants, the wind and the sun provide power only when the renewable resource is available. To accommodate large scale use of renewable energy sources for efficient power production and utilization, energy storage systems are necessary. Here, we introduce a scalable energy storage system which operates by performing cycles during which energy generated from renewable resource is first used to produce highly concentrated brine and diluate, followed up mixing these two solutions in order to generate power. In this work, we present theoretical results of the attainable energy density as function of salt type and concentration. A linearized Nernst-Planck model is used to describe water, salt and charge transport. We validate our model with experiments over wide range of sodium chloride concentrations (0.025–3 m) and current densities (−49 to +33 A m −2 ). We find that depending on current density, charge and discharge steps have significantly different thermodynamic efficiency. In addition, we show that at optimal current densities, mechanisms of energy dissipation change with salt concentration. We find the highest thermodynamic efficiency at low concentrate concentrations. When using salt concentrations above 1 m, water and co-ion transport contribute to high energy dissipation due to irreversible mixing.

Despite the considerable initial optimism behind its development and prospective commercialization, the Li/air battery chemistry has now reached a mature stage of development, which has served to highlight the main underlying technological limitations, as well as what can realistically be expected from it. One of the main challenges is the control of the discharge product morphology, that is, Li2O2, onto the positive electrode. In this article, we show how the three‐phase configuration required to ensure cell operation can be induced in a two‐phase system made of mesoporous carbon and an ionic liquid electrolyte [N‐butyl‐N‐methylpyrrolidinium bis(trifluoromethane sulfonyl)imide, Pyr14TFSI] by means of an oxygen‐bubbling device (OBD) and a peristaltic pump. The use of a non‐flammable, non‐volatile electrolyte ensures long‐term, extensive discharging (up to 4.78 mAh cm−2), as well as operation at temperatures higher than room temperature., The authors acknowledge the support of the European Commission FP7 Project “Lithium‐Air Battery with Split Oxygen Harvesting and Redox Processes” (LABOHR) (FP7‐NMP‐2010, grant agreement No. 265971). P.P. acknowledges a FPI‐UCM fellowship (BE45/10).

Here, a pH neutral aqueous organic redox flow battery (AORFB) consisting of three electrolytes channels (i.e., an anolyte channel, a catholyte channel, and a central salt water channel) to achieve integrated energy storage and desalination is reported. Employing a low cost, chemically stable methyl viologen (MV) anolyte, and sodium ferrocyanide catholyte, this desalination AORFB is capable of desalinating simulated seawater (0.56 m NaCl) down to 0.023 m salt concentration at an energy cost of 2.4 W h L−1 of fresh water—competitive with current reverse osmosis technologies. Simultaneously, the cell delivers stored energy at 79.7% efficiency with a cell voltage of 0.85 V. Furthermore, the cell is also capable of higher current operation up to 15 mA cm−2, providing 4.55 mL of fresh water per hour. Combining energy storage and water desalination into such a bifunctional device offers the opportunity to address two growing global issues from one hardware installation.

Due to their properties, the most suitable application for flow batteries currently is a bulk energy storage. This paper investigates the economic feasibility of the technology in terms of monetary profitability in the appropriate business cases, namely employment in energy markets and in isolated island systems with the high share of renewable generation. We calculate the flow batteries life cycle costs and compare them with the potential revenues from participation in the Finnish energy markets and operation in isolated power systems of the Faroe Islands and the island of Graciosa. We find that the flow batteries exploitation in the Finnish market is not profitable - they collect 43-60% of their costs in the most promising application. The island cases represent a more viable option due to the high fuel costs of the thermal plants that the batteries and renewable sources substitute or decrease their share. However, the revenue and subsequent profitability highly depend on the volatile fuel prices.

The oxidation of ferrocene (Fc/Fc+) and reduction of cobaltocenium (Cc+/Cc) under different temperatures has been studied by cyclic voltammetry and double potential step chronoamperometry in deep eutectic solvents (DESs) consisting of methyltriphenylphosphonium bromide salt with tri-ethylene glycol, glycerol or ethylene glycol as hydrogen bond donors. The temperature dependence of the measured physical properties of DESs (such as viscosity and conductivity) is discussed in detail. The kinetics of the redox couples are studied using cyclic voltammetry, and the standard heterogeneous electron transfer rate constant, k0 is found to be of the order of 10−5 to 10−4 cms−1 at different temperatures. The diffusion coefficient, D, of Fc and Cc+ is determined to lie between 8.28 × 10−10 to 6.65 × 10−9 cm2 s−1. These results show that both k0 and D increase with temperature in the studied DESs. In addition, better kinetic parameters for the DES with ethylene glycol as hydrogen bond donor means that this could be evaluated favorably as both solvents and electrolytes for redox flow cells.

© 2015 Elsevier B.V. The cost of a flow battery system can be reduced by increasing its power density and thereby reducing its stack area. If per-pass utilizations are held constant, higher battery power densities can only be achieved using higher flow rates. Here, a 3D computational fluid dynamics model of a flow battery flow field and electrode is used to analyze the implications of increasing flow rates to high power density operating conditions. Interdigitated and serpentine designs, and cell sizes ranging from 10 cm2 to 400 cm2, are simulated. The results quantify the dependence of pressure loss on cell size and design, demonstrating that the details of the passages that distribute flow between individual channels and the inlet and outlet have a major impact on pressure losses in larger cells. Additionally, in-cell flow behavior is analyzed as a function of cell size and design. Flow structures are interrogated to show how and where electrode parameters influence pressure drops, and how regions where transport is slow are correlated with the presence of experimentally observed cell degradation.

Although Vanadium Redox Flow Batteries (VRFB) are suitable for grid-scale applications, their power-related cost must be reduced in order to boost the use of this technology in the market, allowing their widespread commercialization. One effective way to make the VRFB a competitive and viable solution could be through new strategies for improving the electrocatalytic activity of the electrodes with enhanced electrolyte/electrode interface characteristics. Herein, we report the synergistic effect demonstrated by N- and WO3- decorated carbon-based positive electrode, named HTNW electrode, which demonstrates the feasibility of achieving: i) enhanced electrocatalytic activity, achieving large current density and high reversibility towards VO2+/VO2 + couple (promotion of oxygen and electron transfer processes), ii) decrement of the electron-transfer resistance from 76.18 Ω to 13.00 Ω for the pristine electrode and HTNW electrodes, respectively; iii) 51% of the electrolyte utilization ratio at high rates (i.e. 200 mA cm−2) with 70% of energy efficiency; iv) increment of more than 50% of the power–peak in comparison with pristine electrode.

Solar powered redox cells (SPRCs) are promising for large-scale and long-term storage of solar-energy, particularly when coupled with redox flow batteries (RFBs). While efforts have primarily focused on heterostructure engineering, the potential of synergistic morphology and photonic design has not been carefully studied. Here, we investigate the wavelength-dependent effects of light-absorption and charge transfer characteristics on the performance of gold decorated TiO2-based SPRC photoanodes operating with RFB-compatible redox couples. Through an in-depth optical and photoelectrochemical characterization of three complementary TiO2 microstructures, namely nanotubes, honeycombs, and nanoparticles, we elucidate the combined effects of nanometer-scale semiconductor morphology and plasmonic design across the visible spectrum. In particular, thin-walled TiO2 nanotubes exhibit a similar to 50% increase in solar-to-chemical efficiency (STC) compared to thick-walled TiO2 honeycombs thanks to improved charge transfer. Au nanoparticles both increase generation and interfacial charge transfer (above bandgap) and promote hot carrier injection (below bandgap) leading to a further 25% increase in STC. Overall, Au/TiO2 nanotubes achieve a high photocurrent at 0.098 mA/cm2 and an excellent STC of 0.06%, among the highest with respect to the theoretical limit. The incident photon to current efficiency and internal quantum efficiency are also superior to those of bare TiO2 showing maximum values of 54.7% and 67%, respectively. Overall, nanophotonic engineering that synergistically combines morphology optimization and plasmonic sensitization schemes offer new avenues for improving rechargeable solar-energy technologies such as solar redox flow batteries.