Reversible Electrode Reaction Research Articles

An Ultrastable Low-Temperature Na Metal Battery Enabled by Synergy between Weakly Solvating Solvents.

The low ionic conductivity and high desolvation barrier are the main challenges for organic electrolytes in rechargeable metal batteries, especially at low temperatures. The general strategy is to couple strong-solvation and weak-solvation solvents to give balanced physicochemical properties. However, the two challenges described above cannot be overcome at the same time. Herein, we combine two different kinds of weakly solvating solvents with a very low desolvation energy. Interestingly, the synergy between the weak-solvation solvents can break the locally ordered structure at a low temperature to enable higher ionic conductivity compared to those with individual solvents. Thus, facile desolvation and high ionic conductivity are achieved simultaneously, significantly improving the reversibility of electrode reactions at low temperatures. The Na metal anode can be stably cycled at 2 mA cm-2 at -40 °C for 1000 h. The Na||Na3V2(PO4)3 cell shows the reversible capacity of 64 mAh g-1 at 0.3 C after 300 cycles at -40 °C, and the capacity retention is 86%. This strategy is applicable to other sets of weak-solvation solvents, providing guidance for the development of electrolytes for low-temperature rechargeable metal batteries.

Steady-state currents of planar interdigitated electrode arrays in shallow cells

Analytical equations for the steady-state current at shallow electrochemical cells with embedded interdigitated electrode (IDE) arrays were found by solving the diffusion equation in steady state using conformal transformations. These equations consider the cases where the IDE is used with an external counter electrode (four-electrode configuration) and where one of its arrays is used as internal counter electrode (three- and two-electrode configuration). Since the expressions for the current depend on Jacobian elliptic functions, we found approximations which depend only on trigonometric and hyperbolic functions which can ease the calculations at the expense of an error below 5%. Additionally, we provide expressions for steady-state voltammograms for the case of Nernstian (reversible) electrode reactions. The obtained theoretical results agree with theoretical and simulation results from the literature and with our own experiments. These results can be useful as criteria for designing electrochemical cells based on IDEs, and as benchmarks for assessing their performance, especially for polymer- or paper-based microfluidics.

High-Performance Sodium-Ion Batteries Enabled by 3D Nanoflowers Comprised of Ternary Sn-Based Dichalcogenides Embedded in Nitrogen and Sulfur Dual-Doped Carbon.

To make sodium-ion batteries a realistic option for everyday energy storage, a practicable method is to enhance the kinetics of Na+ reactions through the development of structurally stable electrode materials. This study utilizes ternary Sn-based dichalcogenide (SnS1.5 Se0.5 ) in the design of electrode material to tackle several issues that adversely hinder the performance and longevity of sodium-ion batteries. First, the incorporation of Se into the SnS structure enhances its electrical conductivity and stability. Second, the ternary composition restricts the formation of intermediates during the desodiation/sodiation process, resulting in better electrode reaction reversibility. Finally, SnS1.5 Se0.5 lowers the diffusion barrier of Na, thereby facilitating rapid and efficient ion transport within the electrode material. Moreover, nitrogen and sulfur dual-doped carbon (NS-C) is used to enhance surface chemistry and ionic/electrical conductivity of SnS1.5 Se0.5 , leading to a pseudocapacitive storage effect that presents a promising potential for high-performance energy storage devices. The study has successfully developed a SnS1.5 Se0.5 /NS-C anode, exhibiting remarkable rate capability and cycle stability, retaining a capacity of 647 mAh g-1 even after 10000 cycles at 5 A g-1 in half-cell tests. In full-cell tests, Na3 V2 (PO4 )3 //SnS1.5 Se0.5 /NS-C delivers a high energy density of 176.6 Wh kg-1 . In addition, the Na+ storage mechanism of SnS1.5 Se0.5 /NS-C is explored through ex situ tests and DFT calculations. The findings suggest that the ternary Sn-based dichalcogenides can considerably enhance the performance of the anode, enabling efficient large-scale storage of sodium. These findings hold great promise for the advancement of high-performance energy storage devices for practical applications.

Reversible Switch in Charge Storage Enabled by Selective Ion Transport in Solid Electrolyte Interphase.

Solid-electrolyte interphases (SEIs) in advanced rechargeable batteries ensure reversible electrode reactions at extreme potentials beyond the thermodynamic stability limits of electrolytes by insulating electrons while allowing the transport of working ions. Such selective ion transport occurs naturally in biological cell membranes as a ubiquitous prerequisite of many life processes and a foundation of biodiversity. In addition, cell membranes can selectively open and close the ion channels in response to external stimuli (e.g., electrical, chemical, mechanical, and thermal), giving rise to "gating" mechanisms that help manage intracellular reactions. We wondered whether the chemistry and structure of SEIs can mimic those of cell membranes, such that ion gating can be replicated. That is, can SEIs realize a reversible switching between two electrochemical behaviors, i.e., the ion intercalation chemistry of batteries and the ion adsorption of capacitors? Herein, we report such SEIs that result in thermally activated selective ion transport. The function of open/close gate switches is governed by the chemical and structural dynamics of SEIs under different thermal conditions, with precise behaviors as conducting and insulating interphases that enable battery and capacitive processes within a finite temperature window. Such an ion gating function is synergistically contributed by Arrhenius-activated ion transport and SEI dissolution/regrowth. Following the understanding of this new mechanism, we then develop an electrochemical method to heal the SEI layer in situ. The knowledge acquired in this work reveals the possibility of hitherto unknown biomimetic properties of SEIs, which will guide us to leverage such complexities to design better SEIs for future battery chemistries.

Redox Reactions of Ag(I)/Ag and Ferrocenium/Ferrocene in 1-Butyl-1-methylpyrrolidinium Bis(fluorosulfonyl)amide Ionic Liquid

The electrode reactions of Ag(I)/Ag and ferrocenium/ferrocene (Fc+/Fc) were investigated in an ionic liquid, 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)amide (BMPFSA). The potential of Ag(I)/Ag depended on the logarithm of the concentration of Ag(I), as predicted by the Nernst equation, indicating the Ag(I)/Ag can be used as a reference electrode reaction in BMPFSA. The reversible electrode reaction of Fc+/Fc was observed in BMPFSA by cyclic voltammetry. The donor number of BMPFSA was estimated to be 13 from the difference in the formal potentials of Ag(I)/Ag and Fc+/Fc, indicating the coordination ability of FSA– was slightly stronger than that of bis(trifluoromethylsulfonyl)amide (TFSA–). The diffusion coefficients (D) of Fc and Fc+ were (5.7 ± 0.7) and (3.3 ± 0.2) × 10–7 cm2 s–1, respectively. The ratio of D of Fc+ against that of Fc was smaller than those in TFSA–-type ionic liquids, reflecting the higher charge density of FSA–. The standard rate constant (k 0) of Fc+/Fc was estimated to be (5.4 ± 1.1) × 10–3 cm s–1. The apparent activation energy for k 0 was close to the activation energy for D, suggesting the electrode reaction of Fc+/Fc can be regarded as the outer sphere electron transfer reaction with a very small reorganization energy.

Voltammetric Kinetic Studies of Electrode Reactions: Guidelines for Detailed Understanding of Their Fundamentals.

Theoretical and practical foundations of basic electrochemical concepts of heterogeneous charge transfer reactions that underline electrochemical processes are presented for their detailed study by undergraduate and postgraduate students. Several simple methods for calculating key variables, such as the half-wave potential, limiting current, and those implied in the kinetics of the process, are explained, discussed, and put in practice through simulations making use of an Excel document. The current-potential response of electron transfer processes of any kinetics (i.e., any degree of reversibility) are deduced and compared for electrodes of different size, geometry, and dynamics, namely: static macroelectrodes in chronoamperometry and normal pulse voltammetry, and static ultramicroelectrodes and rotating disc electrodes in steady state voltammetry. In all cases, a universal, normalized current-potential response is obtained in the case of reversible (fast) electrode reactions, whereas this is not possible for nonreversible processes. For this last situation, different widely used protocols for the determination of the kinetic parameters (the mass-transport corrected Tafel analysis and the Koutecký-Levich plot) are deduced, proposing learning activities that highlight the foundations and limitations of such protocols, as well as the influence of the mass transport conditions. Discussions on the implementation of this framework and on the benefits and difficulties found are also presented.

Comparative study on photocatalytic degradation and sensor properties of Chonemorpha fragrans leaf extract assisted MgxZn1−xO (0 ≤ x ≤ 1) nanoparticles

• Mg x Zn 1-x O (x = 0, 0.25, 0.5, 0.75 and 1) NPs were synthesized by Chonemorpha fragrans leaf extract assisted solution combustion method. • The photocatalytic degradation of Fast Blue (FB) and Malachite Green (MG) dyes were tested for all the samples. • MG dyes has higher (90%) degradation compared with FB (87% degradation) dye due to rise in the hydroxyl ions. • The low charge transfer resistance and high capacitance value of Mg x Zn 1-x O electrode were studied for all the samples. • The Nyquist plot is in the order MgO ˃ Zn 0.25 Mg 0.75 O ˃ Zn 0.50 Mg 0.50 O ˃ Zn 0.75 Mg 0.25 O ˃ ZnO. Chonemorpha fragrans leaf extract assisted solution combustion method was carried out for synthesizing Mg x Zn 1−x O (x = 0, 0.25, 0.5, 0.75 and 1) nanoparticles. The obtained samples were characterized using powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, and diffuse reflection spectroscopy techniques. The powder X-ray diffraction patterns of Mg x Zn 1−x O (x = 0 and 1) show pure hexagonal and cubic phases respectively and x = 0.25, 0.5, and 0.75 shows mixed phases. The Rietveld refinement study was done to refine structural parameters of × = 0, 0.5, and 1. A scanning electron microscope shows the high agglomeration with increasing ‘x’ content. Based on the Williamson-Hall plot, the average size of crystallites was found to be between 25 and 40 nm. Transmission electron microscope results also revealed the formation of nanoparticles. The energy bandgap was calculated from diffuse reflectance spectra using the Kubelka Munk relation and found to vary from 3.2 to 5.28 eV. The photocatalytic degradation of Fast Blue and Malachite Green dyes for all the Mg x Zn 1−x O nanoparticles catalysts was tested under the irradiation of UV light. Mg x Zn 1−x O nanoparticles showed enhanced degradation with increasing ‘x’ contents for Fast Blue (87%) and Malachite Green (90%) dyes under UV light. This enhanced degradation is due to variation in the bandgap of Mg x Zn 1−x O. Mg x Zn 1−x O electrodes exhibit a reversible electrode reaction based on their low charge transfer resistance and high capacitance value. Based on our results, the synthesized nanoparticles are promising candidates for wastewater treatment and lead sensor applications.

Electrode reaction of N-hydroxyphthalimide in sulfuric acid-acetonitrile mixed solution as a catalytic mediator for alcohol oxidation

• Highly reversible electrode reaction of NHPI. • 1M sulfuric acide-acetonitrile mixture as eletrolyte. • Catalytic oxidation of alchol as well as in aprotic. • The second eletron oxidation reaction is more complex. The reactivity of the electro-oxidation products of N -hydroxyphthalimide (NHPI) with an aromatic alcohol, 4-methoxybenzyl alcohol (MBA) in a sulfuric acid-acetonitrile mixed solution was investigated. Phthalimide N -oxyl radical (PINO · ), which is produced by one-electron oxidation of NHPI, reacted with MBA in the mixed solution as well as in aprotic solvent. Further oxidation products of PINO · also reacted with MBA but the results showed complex-shaped voltamograms.

Reversible and Quasireversible Electron Transfer under Conditions of Differential Square-Wave Voltammetry

A theoretical analysis of reversible and quasireversible electrode reactions of a dissolved redox couple under conditions of the novel technique of differential square-wave voltammetry (DSWV) is presented. The technique is recently introduced as a hybrid form between differential pulse voltammetry (DPV) and square-wave voltammetry (SWV) as the two most advanced and competitive pulse-form voltammetric techniques for a purpose of unifying their advantages and further advancing both techniques in terms of analytical performances, mechanistic analysis, and electrode kinetics. The potential modulation of DSWV consists of potential steps and pulses providing a plethora of voltammetric curves, which enable in-depth characterization of the electrode reaction with a minimal set of measurements. Based on numerical simulations, a set of criteria for characterization and differentiation between reversible and quasireversible electrode reactions are established.

A Homogeneous Polymer Network Organogel Prepared in Concentrated Lithium-ion Battery Electrolytes Using a Nonflammable Fluorinated Solvent

Abstract We report an organogel electrolyte for lithium (Li)-ion batteries based on tetra-arm poly(ethylene glycol) (TetraPEG) network and highly concentrated electrolyte using nonflammable solvent, tris (2,2,2-trifluoroethyl) phosphate. The gel electrolyte was obtained via a Michael addition reaction between maleimide (MA)-terminated and thiol (SH)-terminated TetraPEGs, which was characterized via chemical reaction kinetics. The resulting TetraPEG gels with an ideal polymer network exhibited comparable ionic conductivity to the corresponding liquid electrolytes and reversible electrode reaction for graphite negative electrode.

Simulation of two electrode reactions coupled by the chemical reaction.

A model of an ECE mechanism consisting of two reversible electrode reactions coupled by the kinetically controlled, second order, reversible chemical reaction is developed for the staircase cyclic voltammetry on the rotating disk electrode. The relationship between the limiting current of the second wave and the rate constant of chemical reaction is investigated. The concentration of electroinactive component of the forward reaction influences the half-wave potential of the first wave and the limiting current of the second wave. The responses of the mechanisms with reversible and irreversible chemical reactions are compared.

Square-Scheme Electrochemistry in Battery Electrodes

ConspectusSustainable development cannot be achieved without substantial technological advancements. For instance, flexible electricity management requires smart power sourcing with advanced energy storage/conversion technologies. Remedies for abrupt power spikes/drops observed in renewable energy sources such as solar and wind require rapid load-leveling using high-power energy storage systems when they are integrated into a microgrid. Electrochemical energy storage devices efficiently convert electrical and chemical energy, which can potentially function as distributed power sources. Among these, lithium-ion batteries are a present de facto standard with their relatively high energy density and energy efficiencies that are based on topochemical intercalation chemistry, whereby guest lithium ions are (de)intercalated reversibly with simultaneous redox reactions and minimal structural changes. However, their energy density, power density, life-cycle cost, calendar life, and safety remain unsatisfactory for widespread use. When the storage capacity is maximized, as a result of which a labile deep charge/discharge state is generated, to develop batteries with high energy density, subsequent irreversible phase transformations or chemical reactions occur in many cases. The combination of the reversible electrode reactions and the subsequent irreversible phase transformations sometimes causes a charge/discharge curve characterized by a large voltage hysteresis with 100% Coulombic efficiency. Because a large voltage hysteresis significantly degrades the energy efficiency, unveiling the reaction mechanism is of primary importance in mitigating energy loss.In this Account, we comprehensively discuss the distinct and reversible charge/discharge reactions, generalized by the term “square scheme”, which includes both thermodynamic and kinetic processes. The difficulties encountered in analyzing the square scheme are that both energy efficient and inefficient processes coexist and compete with each other, where the latter involves the time-dependent phenomenon. Here, we provide the theoretical models and analytical expressions for kinetic square-scheme electrodes under several electrochemical conditions, including galvanostatic charge/discharge, the galvanostatic intermittent titration technique (GITT), the potentiostatic intermittent titration technique (PITT), and constant-current/constant-voltage (CC–CV) charge/discharge. The validity of the analytical models was confirmed for two typical square-scheme electrodes: Na1–xTi0.5Co0.5O2 and Na2–xMn3O7. Na1–xTi0.5Co0.5O2, which is a sodium-ion battery cathode material, undergoes phase transitions between high-spin and low-spin states after transition-metal oxidation/reduction, while Na2–xMn3O7, which is a large-capacity oxygen-redox cathode material, exhibits O–O bond formation after oxide-ion oxidation and O–O bond cleavage after peroxide reduction, both of which trigger large voltage hysteresis. This Account emphasizes the importance of the quantitative analyses of the square scheme in which a large amount of voltage hysteresis can occur within any electrode material with a large capacity or high voltage that undergoes irreversible chemical reactions upon deep charging or discharging. Such parasitic energy-consuming transformations slowly proceed over a number of hours or days and should be carefully avoided to realize energy-efficient and stable battery systems.

An appropriate reference and counter electrode in an all-solid-state battery using NASICON-structured solid electrolyte

Anti-NASICON-structured Fe2(MoO4)3 (FMO) thin films are formed on NASICON-structured LATP solid-state electrolyte by pulsed laser deposition, and their electrochemical properties are investigated. The FMO thin films operate at 3.0 V flat voltage vs. Li/Li+ within the potential window of LATP. The apparent diffusion coefficient of the FMO thin film on LATP is almost consistent with that measured in a conventional organic liquid electrolyte (0.5–1.2 × 10-12 cm2 s−1) and stable and fast charge–discharge reactions are realized. These results indicate that FMO/LATP is appropriate as a reference and counter electrode for all-solid-state batteries using NASICON-structured LATP. Combining crystalline electrode-solid electrolytes with a similar framework structure at relatively low temperatures will play an important role in realizing reversible electrode reactions. An all-solid-state battery, FMO/LATP/LiCoO2, is developed to apply the FMO as a reference and counter electrode, and the SSB operates at 1.0 V without visible capacity fading.

Effect of Plasma-Assisted Electrochemical Treatment of Boron-Doped Diamond on the Kinetic Characteristics of Reversible Electrode Reactions

Effect of Plasma-Assisted Electrochemical Treatment of Boron-Doped Diamond on the Kinetic Characteristics of Reversible Electrode Reactions

Square‐wave Voltammetry and Electrochemical Faradaic Spectroscopy of a Reversible Electrode Reaction: Determination of the Concentration Fraction of the Redox Couple

AbstractA comparative study conducted with square‐wave voltammetry (SWV) and electrochemical faradaic spectroscopy (EFS) is presented for a reversible electrode reaction of dissolved redox couple in the presence of both Ox and Red components. In agreement with previous studies, the net peak current ΔΨp of the theoretical SW voltammograms is positioned at the formal potential E0′ and does not depend on the concentration ratio c(Ox)/c(Red). However the forward‐to‐backward peak current ratio is sensitive to the redox state. For very low SW amplitudes, theoretical data imply superior features of EFS over SWV. Theoretical and experimental calibration lines are in good agreement within the interval 0.2≤x(Ox)≤0.8.

Spectroelectrochemistry for the study of reversible electrode reactions with complex stoichiometries

The value of spectroelectrochemistry (SPEC) for the elucidation of electrode reactions with complex stoichiometries (aO +ne-⇄bR) is investigated theoretically. The analytical equations presented enable the modelling of the absorbance response in both normal- and parallel-beam modes and any potential-controlled technique. As a proof of concept, the SPEC signals of the 1:2 and 2:1 stoichiometries in chronoamperometry and cyclic voltammetry are studied and compared with the 1:1 case, demonstrating how SPEC can assist the simultaneous and unambiguous determination of the stoichiometric coefficients of the redox species.

Sub- and super-Nernstian Tafel slopes can result from reversible electron transfer coupled to either preceding or following chemical reaction

A general scheme for an electrochemically reversible one-electron electrode reaction containing both preceding and following coupled chemical kinetics is analysed in the light of simulation in the context of linear sweep voltammetry at a macro-electrode. In particular, we explore the influence of the coupled chemistry on the observed Tafel slope at potentials where it is influenced minimally by mass transport effect. In the absence of coupled chemistry, an apparent transfer coefficient of unity is observed, as expected for a simple electrochemically reversible one-electron process. However, the presence of a preceding chemical reaction serves to lower the apparent transfer coefficient markedly below unity; the coupled kinetics create the illusion of electrochemical irreversibility. In contrast, a following chemical reaction can give an apparent transfer coefficient in excess of unity creating a ‘super-Nernstian’ response. Thus, a full range of Tafel slopes, both below and above unity, characterize an intrinsically reversible reaction in the presence of coupled kinetics. • Simulation of electrochemically reversible processes with coupled chemistry. • Effects of following and preceding chemistry on Tafel slope is analysed. • Preceding chemical reaction decreases the apparent transfer coefficient. • Following chemical reaction increases the apparent transfer coefficient.

La10Si6O27:Tb 3+ nanomaterial; its photocatalytic and electrochemical sensor activities on Disperse Orange and Fast Blue dyes

For the first time, Tb3+ ions were successfully doped into La10Si6O27 by using low temperature initiate solution combustion method. The resulting Tb3+ doped lanthanum nanophosphors (LNPs) were characterized by PXRD, FTIR, TEM and UV-DRS techniques. The PXRD patterns of calcined sample show a pure hexagonal oxy apatite phase. The crystallite size was found to be within a range of 25–40 nm and it is matched with TEM results. The energy band gap (Eg) was found to vary from 5.64 eV to 5.77 eV. The photocatalytic degradation of Disperse Orange (DO) and Fast Blue (FB) dyes by La10Si6O27:Tb3+ was tested under the irradiation of UV light. La10Si6O27: Tb3+ NPs showed enhanced degradation for Disperse orange and Fast blue dyes under UV light. La10Si6O27:Tb3+ (5 mol %) electrode exhibited reversible electrode reaction with low charge transfer resistance and high capacitance value. All the above findings confirm that the synthesized LNPs is a potential candidate for waste water treatment and sensor applications.

Non-unity stoichiometric reversible electrode reactions. The effect of coupled kinetics and the oxidation of bromide

We explore via simulation, the cyclic voltammetry of the following mechanism involving a reversible electrode process coupled with a follow up reaction in which the product (B) of the electrode reaction reacts chemically with the reactant, A, to form a species C:2A−2e−⇄BB+A⇌kbkfC Such a mechanism is shown, under certain critical combinations of rate constant and reactant concentration to give rise to two voltammetric peaks despite the assumption of a single redox couple (A/B). This results from the formation of C during the first peak whilst the second peak, seen at more oxidizing potentials, reflects the dissociation of C releasing A. A mechanism of the type investigated may hold during the oxidation of bromide(Br−, A) in solution to form bromine(Br2, B) and tribromide (Br3−,C). Simulations are used to explore the conditions for which two peaks are expected in the bromide oxidation system in aqueous solution and for which the two following limiting cases operate3Br−−2e−⇄Br3− and2Br−−2e−⇄Br2 We report experimental data for the bromide oxidation in aqueous solution. These are interpreted via simulations using independent literature values for the rate and equilibrium constants for tribromide formation.

Cyclic square wave voltammetry of electrode reactions with nonunity stoichiometry

Abstract A general and easy-to-manage analytical theory is presented for the square wave voltammetry (SWV) of reversible electrode reactions with complex stoichiometry, aO + ne− ⇌ bR, at macroelectrodes valid for any value of the stoichiometric and diffusion coefficients of the redox species. A comprehensive study of the SWV in cyclic mode is performed, investigating the effect of all the key variables for different stoichiometries a:b stoichiometries. As reported in literature, these reactions are of interest in the electrochemistry of hydrogen, halides and mercury complexes, among others. The concentration-dependence of the position of the SWV signal along with the peak height, width and symmetry are demonstrated to be sensitive to the reaction stoichiometry, offering rapid and simple diagnostic clues. Then, the quantitative analysis of the peak current, peak potential and half-peak width with the theory here presented allows for the determination of the stochiometric coefficients and number of electrons transferred. Also, the diffusion coefficients of the oxidized and reduced species and/or the formal potential of the redox couple can be extracted. For this, accurate procedures are proposed on the basis of simple explicit equations and working curves, proving the remarkable value of the SWV method.