Water-in-salt electrolytes for high voltage aqueous electrochemical energy storage devices

If were not by their low electrochemical stability, aqueous electrolytes would be the preferred alternative to be used in electrochemical energy storage devices. Their abundance and nontoxicity are key factors for such application, especially in large scale. The development of highly concentrated aqueous electrolytes, so-called water-in-salt electrolytes, has expanded the electrochemical window of aqueous electrolyte up to 3.0 V (whereas salt-in-water electrolytes normally shows up to 1.6 V), showing that water can be an alternative after all. Many devices, ranging from metal-ion batteries to electrochemical capacitors, have been reported recently, making use of such wider electrochemical stability and enhancing devices energy density. Different salts have also been proposed not only to gain in costs but also to improve physicochemical properties.     

An overview of deep eutectic solvents: Alternative for organic electrolytes,aqueous systems & ionic liquids for electrochemical energy storage

As the demand for sustainable energy sources continues to rise, the need for efficient and reliable energy storage systems becomes crucial. In order to effectively store and distribute renewable energy, new and innovative solutions must be explored. This review examines the deep eutectic solvents(DESs) as a green,safe, and affordable solution for the electrochemical energy storage and conversion field, offering tremendous opportunities and a promising future. DESs are a class of environment-frie...     

A review of understanding electrocatalytic reactions in energy conversion and energy storage systems via scanning electrochemical microscopy

To address climate change and promote environmental sustainability, electrochemical energy conversion and storage systems emerge as promising alternative to fossil fuels, catering to the escalating demand for energy. Achieving optimal energy efficiency and cost competitiveness in these systems requires the strategic design of electrocatalysts, coupled with a thorough comprehension of the underlying mechanisms and degradation behavior occurring during the electrocatalysis processes. Scanning elec...     

Redox polymers in electrochemical systems: From methods of mediation to energy storage

Redox polymers have been an expanding research area over the last 30 years. The design of redox polymers for mediated bioelectrocatalysis revolutionized glucose biosensors in the early 1990s. These concepts were then applied to biofuel cells in the 2000s, but it was not until recently that researchers further translated these concepts to the fields of electrosynthesis, supercapacitors, and redox flow batteries. This review will give a short background to the early work in the field but will primarily discuss the recent applications of the electrosynthesis, supercapacitors, and redox flow batteries.     

The potentials of additive manufacturing for mass production of electrochemical energy systems

Additive manufacturing has established itself as a popular and powerful tool in electrochemistry research and development. In this short review, we focus on the latest results in both 3D printing and electrochemistry communities that could potentially benefit manufacturing in the electrochemical industry. We provide insights from recent and relevant research works and conclude that the likely scenario in the industry is the deployment of a combination of subtractive and additive technologies in order to manufacture high quality and cost-effective electrochemical reactors within reasonable timeframes.     

Underpotential deposit electrocatalysis of fast redox reactions for electrochemical energy storage systems

The electrocatalysis of the Fe^3+/2+ redox reaction at various electrode/electrolyte solution interfaces in the presence/absence of underpotential deposits of various metals has been investigated by the AC impedance method. Exchange current densities and double layer capacity data were obtained. On this basis, changes in the active surface area of the electrode and catalytic effects of the investigated metals were identified. Received: 27 May 1997 / Accepted: 29 July 1997     

Hydrogen-accumulating materials in electrochemical systems

Intermetallic compounds capable of absorbing large amounts of hydrogen attract attention due to their applied significance in the production of chemical power sources. A variety of such compounds have been studied. The present paper gives some examples of hydrogen-absorbing intermetallides and describes their preparation, as well as touches upon some problems of hydride-forming alloys. The survey covers results obtained over the past decade.     

Free energy correlation of rate constants for electron transfer between organic systems in aqueous solutions

Recent experimental data concerning the rate constants for electron transfer reactions of organic systems in aqueous solutions and their equilibrium constants is examined for possible correlation. The data is correlated quite well by the Marcus theory, if a reorganization parameter, λ, of 18 kcal/mole is used. Assuming that the only contribution to λ is the free energy of rearrangement of the water molecules, an effective radius of 5A?for the reacting entities is estimated. For the zero free energy change reaction, i.e., electron exchange between a radical ion and its parent molecule, a rate constant of about 5 × 10⁷ M^?1 s^?1 is predicted.     

Microbe-based electrochemical sensing systems

The combination of micro-organisms with electrochemical sensors can result in new sensing systems with extended analytical capabilities. The most common approaches for this combination are microbial electrodes and microbiological assays which utilize electrochemical detection.     

Calculation of adiabatic free energy surfaces in the case of electrochemical tunneling microscopy of redox systems

A method of adiabatic (infinitely slow) switching-on of interaction of the reactant with the electrode and the tip of a tunneling microscope at a bias voltage other than zero is used to derive expressions for the average number of electrons in the valence orbital of the reactant, the current passing through the valence orbital of the reactant at fixed values of coordinates of the slow subsystem of the solvent, and the electronic contribution to an expression that describes the adiabatic free energy surface (AFES) of the electrode-reactant-tip of the tunneling microscope system. The derived expressions are the same that had already been obtained in a Kuznetsov-Schmickler work, by a not-quite-correct method, though. Relationships that link the AFES corresponding to the opposite signs of the bias voltage are deduced. Examples of calculations of AFES and a current for a number of characteristic sets of parameters of the system are presented.Translated from Elektrokhimiya, Vol. 41, No. 3, 2005, pp. 259–272.Original Russian Text Copyright © 2005 by Medvedev.     

Electron free energy levels in oxidic solutions: relating oxidation potentials in aqueous and non-aqueous systems

We provide background to the problem of describing the state of redox couples in different types of solvent media ranging from acidic aqueous solutions to high temperature molten silicates, pointing out the essential similarity between these solvent media in Lewis acid–base terms. We review the adaptation of the Gurney proton energy level diagram approach to the case of electron transfer processes. Using data from various spectroscopic and analytical chemistry sources, we review the construction of electron free energy level diagrams for redox couples in aqueous and non-aqueous systems using, as a common reference, the potential of the oxygen gas (1 atm)/oxide ion couple in the solution of interest. We emphasize the anomalous effect of “oxide ion activity” (mean ionic activity of alkali oxide) on the state of equilibrium and interpret this in terms of oxide ion transfers that accompany electron transfers. After showing the essential agreement between recent direct electrochemical assessments of the energy levels and those deduced in our original analysis of oxidic melts of different glass formers, we provide an interpretation of the apparent “oxide ion transfer” in terms of the differential medium polarization by the two redox species involved in the equilibrium. We anticipate the extension of these ideas to redox chemistry in the currently burgeoning field of “ionic liquids” in its recent ambient temperature liquid incarnation. Dedicated to the 85th birthday of John O’M. Bockris.

---

An extension of the Pitzer equation for the excess Gibbs energy of aqueous electrolyte systems to aqueous polyelectrolyte solutions

Pitzer's equation for the excess Gibbs energy of aqueous solutions of low-molecular electrolytes is extended to aqueous solutions of polyelectrolytes. The model retains the original form of Pitzer's model (combining a long-range term, based on the Debye–Hückel equation, with a short-range term similar to the virial equation where the second osmotic virial coefficient depends on the ionic strength). The extension consists of two parts: at first, it is assumed that a constant fraction of the monomer units of the polyelectrolyte is dissociated, i.e., that fraction does not depend on the concentration of the polyelectrolyte, and at second, a modified expression for the ionic strength (wherein each charged monomer group is taken into account individually) is introduced. This modification is to account for the presence of charged polyelectrolyte chains, which cannot be regarded as punctual charges. The resulting equation was used to correlate osmotic coefficient data of aqueous solutions of a single polyelectrolyte as well as of binary mixtures of a single polyelectrolyte and a salt with low-molecular weight. It was additionally applied to correlate liquid–liquid equilibrium data of some aqueous two-phase systems that might form when a polyelectrolyte and another hydrophilic but neutral polymer are simultaneously dissolved in water. A good agreement between the experimental data and the correlation result is observed for all investigated systems.     

Natural convection effects in electrochemical systems

1. Download : Download high-res image (77KB)
2. Download : Download full-size image

     

Mass-transfer problems in the electrochemical systems

The problems concerning quantitative analysis of mass-transfer processes in the electrochemical systems (ECS) are briefly reviewed. The interrelation between the mass-transfer problems in the electrochemical and heat systems is considered. Various approaches to the numerical determination of distributions of concentrations of ions of all types and electrochemical potential in the ECS are considered. The methods of allowance for the migration transfer and choosing the boundary conditions for the transfer equations and other problems are considered. Some actual lines of development of the theory of mass-transfer in the ECS are pointed out.     

Architected porous metals in electrochemical energy storage

Porous metallic structures are regularly used in electrochemical energy storage (EES) devices as supports, current collectors, or active electrode materials. Bulk metal porosification, dealloying, welding, or chemical synthesis routes involving crystal growth or self-assembly, for example, can sometimes provide limited control of porous length scale, ordering, periodicity, reproducibility, porosity, and surface area. Additive manufacturing has shown the potential to revolutionize the fabrication of architected metals, allowing complex geometries not usually possible by traditional methods, by enabling complete design freedom of a porous metal based on the required physical or chemical property to be exploited. We discuss properties of porous metal structures in EES devices and provide some opinions on how architected metals may alleviate issues with electrochemically active porous metal current collectors, and provide opportunities for optimum design based on electrochemical characteristics required by batteries, supercapacitors or other electrochemical devices.