Reversible Charge Transfer Reaction Research Articles

Molecular-Level Pore Tuning in 2D Conductive Metal-Organic Frameworks for Advanced Supercapacitor Performance.

Two-dimensional (2D) electrically conductive metal-organic frameworks (MOFs) have emerged as viable candidates for active electrode materials in supercapacitors due to their high electrical conductivity, high specific surface area, and intrinsic redox-active sites. Despite their promising electrochemical performance, their pseudocapacitive behavior via fast and reversible charge transfer reactions remains yet to be fully exploited. Here, we investigate the electrochemical energy storage mechanism of Cu3(HHTATP)2 (HHTATP = 2,3,6,7,10,11-hexahydroxy-1,5,9-triaminotriphenylene), a 2D conductive MOF featuring characteristic redox-active pendant aromatic amines. Cu3(HHTATP)2 exhibited pseudocapacitive charge storage with an average gravimetric capacitance of 340 ± 15 F g-1 at a discharge rate of 0.2 A g-1 and maintained a capacitance retention over 90% after 7000 galvanostatic cycles at 5 A g-1. The polar pendant amines not only enhanced capacitance via additional amine/imine redox activity but also reduced interfacial charge transfer resistance through modified electrode-electrolyte interactions. These results highlight the potential of molecular-level pore environment tuning as a strategic approach in materials design for energy storage applications.

Inkjet-Printed LSM-YSZ Thin Films for Enhanced Oxygen Electrodes in Solid Oxide Fuel Cells.

In the present work, symmetrical oxide ion conducting solid oxide single cells with inkjet-printed composite LSM-YSZ electrodes, onto commercially available YSZ dense substrates using GDC as buffer interlayer, were fabricated and characterized. Stable inkjet-printable LSM-YSZ nanoparticle inks were developed based on water solvent, after processing with high intensity ball milling. The deposition of LSM-YSZ electrodes was performed by inkjet printing, as well as a conventional additive manufacturing technique, screen printing, in order to compare the electrochemical performance of the produced cells for the reversible charge transfer reaction (O2 + 4 e- ↔ 2 O2-). The physicochemical properties of the LSM-YSZ nanoparticle ink was investigated to determine ink printability. The electrochemical performance of fabricated inkjet-printed and screen printed symmetrical cells (LSM-YSZ | GDC | YSZ | GDC | LSM-YSZ) exposed under a synthetic air atmosphere was evaluated in a single chamber cell reactor, employing the AC impedance spectroscopy and linear scan voltammetry techniques, at the temperature range of 700-850 °C. The inkjet-printed electrodes exhibited highly homogeneous and porous morphologies with the corresponding cell achieving current densities almost five times higher, up to 1 A/cm2 at 2 V cell potential and 850 °C, than those of the equivalent screen-printed one. To the best of our knowledge, this is the first successful implementation of water-based inks of LSM-YSZ electrodes in the fabrication of inkjet-printed solid oxide cells.

Bilateral growth of monoclinic WO3 and 2D Ti3C2Tx on 3D free-standing hollow graphene foam for all-solid-state supercapacitor

• Hollow graphene foam was successfully prepared by TA-CVD method. • m -WO 3 /Ti 3 C 2 T X /HGF-7 electrode was fabricated by UPED and drop-casting methods. • The electrode exhibited a specific capacitance of 573F g −1 with 93.3% cycling stability. • An ASC device showed 27.2 Wh kg −1 energy density at power density of 752 W kg −1 . • The ASC device endured superior cycling stability of 93% over 10,000 GCD cycles. The free-standing three dimensional (3D) hollow graphene foam (HGF) decorated nanostructured pseudocapacitive materials could offer a large active surface area and a extreme conductive porous 3D network for fast reversible charge transfer reactions in the supercapacitor. Herein, the 3D HGF was prepared by a template assisted-chemical vapor deposition (TA-CVD) method and the monoclinic WO 3 ( m- WO 3 ) interconnected nanoparticles as well as 2D Ti 3 C 2 T x sheets were bilaterally loaded on the inner and outer sides of HGF by a simple unipolar electrodeposition (UPED) method and a drop casting method, respectively. The obtained 3D free-standing m- WO 3 /Ti 3 C 2 T X /HGF electrode exhibited an excellent specific capacitance of 573F g −1 at 5 mV s −1 with outstanding rate performance and 93.3% cycling stability over 5000 cycles, which can be attributed to the metal-like conductivity and reversible redox reactions of hydrophilic 2D Ti 3 C 2 T x . The asymmetric solid-state supercapacitor (ASC) illustrated a 2-fold wider potential of 1.4 V in an acidic electrolyte when compared with the MXene-based symmetric supercapacitor. It displayed an excellent specific capacitance of 145.2F g −1 (111.3 mF cm −2 ) at 5 mV s −1 , an ultra-high energy density of 27.2 Wh kg −1 (20.83 μWh cm −2 ) at a power density of 752 W kg −1 along with 93% cycling stability over 10,000 cycles. Therefore, such a m- WO 3 /Ti 3 C 2 T x /HGF electrode should be promising for the fabrication of advanced supercapacitors.

Bilateral Growth of Monoclinic Tungsten Oxide and 2D Ti3C2Tx-MXene on 3D Free-Standing Multilayer Hollow Graphene Foam for Flexible All-Solid-State Pseudocapacitor

To overcome the subordinate electrochemical performance of the pseudocapacitor, it is essential to design two-dimensional (2D) electroactive nanostructured material with enormous electroactive sites on the highly conductive current collector for enriching the rates of reversible charge transfer reactions. Herein, a scalable strategy was employed to prepare the electrodes by depositing pseudocapacitive materials on a three-dimensional (3D) free-standing highly conductive hollow multilayered graphene foam (HGF) synthesized through a template assisted-chemical vapor deposition (TA-CVD) method for the first time. The stable nanostructured monoclinic tungsten oxide (m-WO3) nanoparticles and 2D transition metal carbide (Ti3C2Tx-Mxene) sheets were bilaterally loaded on inner and outer sides of 3D HGF by a unipolar electrodeposition (UPED) method and a drop casting method, respectively. This free-standing electrode exhibited exceptional specific capacitance (Cs) of 487 F/g (439 mF/cm2) at 2 mA/cm2, outstanding rate performance and extraordinary cycling stability of 92.9 % over 5000 cycles owing to its significant metallic conductivity and reversible redox reactions of hydrophilic 2D Ti3C2Tx-Mxene. To assemble asymmetric pseudocapacitor, a MWCNT/RuO2 electrode with tiny RuO2 was also synthesized through a simple and inexpensive layer-by-layer (LBL) method. The obtained flexible asymmetric solid-state pseudocapacitor (FASC) illustrated 2-fold wider potential of 1.4 V in an acidic electrolyte when compared with Mxene based symmetric supercapacitor. This FASC displayed excellent Cs of 152.2 F/g at 5 mV/s, high energy density of 18 Wh/kg at 497 W/kg and an outstanding capacity retention of 93.3 % over 10000 GCD cycles with superb coulombic efficiencies of 99 ~ 100 %. In addition, the extraordinary demonstration performance of this FASC device by driving light emitting diodes (LEDs) and digital stopwatch signified its real-world applicability in electronic gadgets.

Chronoamperometry for reversible charge transfers at cylindrical wire electrodes: Theory for DO ≠ DR, and a highly accurate computation of the current

Abstract Semi-analytical modelling of transient experiments at cylindrical wire or fiber electrodes is hindered by the unavailability of numerical procedures for calculating special functions arising in the models. A theory is developed, of the chronoamperometric Faradaic current for a reversible charge transfer reaction at a cylindrical electrode. Arbitrary potential steps and unequal diffusion coefficients (δ = DO/DR ≠ 1) are assumed. Two procedures (written in C++) are designed, for computing a special function occurring in the theory. One procedure is computationally inexpensive, but has a low accuracy (relative error moduli close to 2% in the worst case, when −0.5 ≤ log (δ) ≤ 0.5). The second is more expensive, but highly accurate (relative error moduli close to 4 × 10−14 in the worst case, when −3 ≤ log (δ) ≤ 3). Numerical experiments demonstrate that the effect of δ ≠ 1 on the current is not negligible, even for δ not much different from unity. Therefore, the theory presented should be taken into account in experimental investigations. The code for the procedures is freely available.

Bimetallic Pt,Ir-containing coatings formed by MOCVD for medical applications.

Biocompatible PtxIr(1-x) layers combining high mechanical strength of the iridium component and outstanding corrosion resistance of the platinum component providing reversible charge transfer reactions in the living tissue are one of the important materials required for implantable medical electrodes. The modern trend to complicate the shape and reduce the electrode dimensions includes the challenge to develop precise methods to obtain such bimetallic coatings with enhanced surface area and advanced electrochemical characteristics. Herein, PtxIr(1-x) coatings were firstly obtained on cathode and anode pole tips of endocardial electrodes for pacemakers using chemical vapor deposition technique. To deposit PtxIr(1-x) coatings with a wide range of metal ratios (x = 0.5-0.9) the combination of acetylacetonate-based volatile precursors with compatible thermal characteristics was used for the first time. The expected metal ratio in the coatings was regulated by a partial pressure of the precursor vapors in the reaction zone and was in the good agreement with its real value measured by various methods, including energy-dispersive and wavelength dispersive spectroscopy, X-ray photoelectron spectroscopy. According to the X-ray powder diffraction analysis, PtxIr(1-x) coatings consisted of fcc-PtxIr(1-x) solid solution phases. The microscopy data confirmed the formation of PtxIr1-x coatings with the enhanced surface areas. The effect of electrochemical activation on the surface composition and morphology of the samples was studied. The electrochemical characteristics of samples were estimated from cyclic voltammetry and electrochemical impedance spectroscopy data. The charge storage capacity (CSC) values of activated samples were in the range of 19-108 mCcm-2 (phosphate buffer saline solution, 100 mV/s).

Electroreduction of Nitrobenzene: Nominal Simulation of Voltammogram

For the electrochemical reduction of nitrobenzene in aqueous cationic micellar solution of cetyltrimethylammonium bromide [CTAB] at platinum electrode using cyclic voltammetry, a reversible/quasi reversible charge transfer reaction pertaining to one electron couple of ArNO2/ArNO2.- was indicated (1). Digital simulation was used to evaluate electrochemical kinetic parameters for the mono-electron transfer step (1). An ECE mechanism, Scheme-1 and Figures 1 and 2 and Table-1, is suggested for the previously reported voltammograms (2) featuring nitrobenzene reduction on a coated platinum electrode partially covered by a thin film of dioctadecyldimethylammonium chloride [DODAC]. Table-1: Diffusion coefficients for nitrobenzene (2) Diffusion coefficient (cm2/s) 6.11×10-5 1.09×10-4 Bare Pt DODAC covered Pt, this work References (1) Tariq, M.; Haque, I. U., Science International (Lahore), 2016, 28, 361 (2) Haque, I. U.; Tariq, M., Journal of the Chemical Society of Pakistan, 2011, 33, 529 Figure 1

Mass transport at electrodes of arbitrary geometry. Reversible charge transfer reactions in square wave voltammetry

The basis for mass transport of the electroactive species in different diffusion fields is examined, pointing out important insights in relation to the value of the surface concentrations for the case of fast electrode processes. Moreover, a general analytical solution for the transient current is given for several geometries, when an arbitrary sequence of potentials pulses is applied to macroelectrodes (planar), spheres, cylinders, discs and bands. The results are particularized for Square Wave Voltammetry. Explicit solutions for the net current and the forward and backward components are given. The effects of frequency, pulse amplitude and electrode size or shape on the peak current are studied. Moreover, the conditions for the attainment of the steady state response are analyzed in the different geometries as well as the characteristics of this response.

Effect of electrons involved in charge transfer reactions in ECE processes under linear sweep voltametry: A theoretical model

Electrochemical methods have been found to be more efficient but of all the methods, which are vogue for treatment of effluent generated from various industries containing toxic substances like heavy metals, cyanide, organic compounds etc. Mathematical models play an important role in investigating the whole environmental management problems through statistical empirical modeling to more sophisticated statistical computer simulations. The mathematical model of mass transport for LSV under hydrodynamic conditions at tubular electrodes for ECE processes in which an irreversible chemical reaction is coupled between two reversible charge transfer reactions is considered. The resulting boundary value problem is converted into system of two integral equations, which is solved numerically. The effect of electrons (n2/n1) involved in two charge transfer reactions on cv-voltammograms are investigated and shown graphically.

Extension of the Adaptive Huber Method for Solving Integral Equations Occurring in Electroanalysis, onto Kernel Function Representing Fractional Diffusion

AbstractElectroanalytical transient experiments performed under conditions of anomalous diffusion have recently attracted some attention. In order to enable automatic simulation of such experiments in the framework of the formalism of integral equations, the adaptive Huber method, recently elaborated by the present author, is extended onto integral transformation kernel function K(t,τ)=(t−τ)α/2−1 (where 0<α≤1), representing fractional diffusion. The extended method is tested on a model integral equation describing cyclic voltammetry for a reversible charge transfer reaction. The performance of the method is found similar to the case of ordinary diffusion.

Preparation of Mg-Yb alloy film by electrolysis in the molten LiCl-KCl-YbCl 3 system at low temperature

The electrochemical behavior of Yb 3+ and electrodeposition of Mg-Yb alloy film at solid magnesium cathode in the molten LiCl-KCl-YbCl 3 (2 wt.%) system at 773 K was investigated. Transient electrochemical techniques, such as cyclic voltammetry, chronopotentiometry and chronoamperometry were used in order to explore the deposition mechanism of Yb. The reduction process of Yb 3+ is stepwise reactions which are single-electron and double-electron reversible charge transfer reactions. The speed control step was a diffusion-controlled step which is caused by concentration polarization. The microstructures of Mg-Yb alloy film were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and EPMA area analysis. A very thin Mg 2Yb alloy film (∼200 nm) was formed by potentiostatic electrolysis at −1.85 V (vs. Ag/AgCl) for 12 h. A much thicker Mg 2Yb alloy film (∼450 μm) was obtained at −2.50 V (vs. Ag/AgCl) for 2.5 h. The corrosion resistance of magnesium can be enhanced by electrochemical formation of Mg-Yb alloy film on its surface.

Theoretical study of irreversible electrode reactions with Henry adsorption using symmetrical cyclic reciprocal derivative chronopotentiometry

Cyclic reciprocal derivative chronopotentiometry (CRDCP) with successive symmetrical programmed currents applied has been extended to describe irreversible electrode reactions where Henry adsorption occurs at the electrode/solution interface. The numerical simulated (d t/d E)– E curves are sensitive to electrode reactions coupled with adsorption processes. Effects of parameters on (d t/d E)– E curves presented in this work involve adsorption constants ( K Ox and K Red) and kinetic parameters ( k s 0 and α). Characteristic parameters of (d t/d E)– E curves depend on the adsorption strength markedly and afford effective criteria to determine different cases. The characteristic behavior of (d t/d E)– E curves with successive currents applied give distinct descriptions between two limiting cases – the “surface nature” and “diffusion character”. Comparisons are made with reversible charge transfer reaction with Henry adsorption and uncomplicated, irreversible electrode reaction.

Electrochemical behaviour of 2,8-dihydroxyadenine at a glassy carbon electrode

The electrochemical behaviour of 2,8-dihydroxyadenine (2,8-DHA)– the main adenine oxidation product– has been investigated over a wide pH range at a glassy carbon electrode (GCE) using cyclic, differential pulse and square wave voltammetry. The oxidation of 2,8-DHA is a quasi-reversible process, pH dependent and occurs with the formation of a main oxidation product, P 2,8-DHA, that strongly adsorbs on the electrode surface. The reduction of 2,8-DHA also occurs and is a reversible process in the absence of molecular oxygen. In electrolytes with pH between 4 and 9 two consecutive reversible charge transfer reactions were identified. However, it was observed that O 2 interfered with the reductive electron transfer process of 2,8-DHA and that, in the presence of oxygen, the reduction of 2,8-DHA occurs at less negative potentials than in the absence of oxygen.

Further Applications of Cyclic Voltammetry with Spherical Electrodes

In this work we show analytical and easily manageable explicit equations corresponding to the application of any multipulse potential sequence to planar, spherical and cylindrical electrodes. We apply these expressions to study reversible charge transfer electrode processes in cyclic voltammetry with spherical electrodes, by considering that both members of the redox pair are initially present in solution, and showing that a conventional symmetrical sweep can be used under these conditions. These expressions allow study in depth fundamental aspects of cyclic voltammetry with spherical electrodes. Thus, in the cyclic voltammograms obtained for simple reversible processes with conventional spherical electrodes at different sweep rates, characteristic common points of non zero current (isopoints) appear from which unknown thermodynamic parameters of these systems can be easily determined. From these equations it can be predicted and demonstrated that there are important analogies of the I/E behavior between a simple reversible charge transfer reaction and a first-order catalytic process when any single or multipulse voltammetric transient techniques are applied.

Filter functions in pulse techniques: application to the study of a slow charge transfer reaction

A first class filter function is a mode of pulse voltammetry that removes completely the current response for a reversible charge transfer reaction without modifying the corresponding signal for a slow charge transfer reaction. Therefore, the application of these modes permits study without interferences of the response for an irreversible electron transfer in those cases where reversible processes are also present. In the double potential step technique, the mode defined by the linear combination c 1 I 1 + c 2 I 2, with I k ( k = 1,2) being the current response for the potential step k at the end of the corresponding pulse and where E 2 is set on the anodic diffusion current plateau, can be easily modulated as a first class filter function if the ratio of the coefficients c 1/ c 2 and the pulse durations are chosen appropriately. This polarization mode has interesting features that allow us to determine the kinetic parameters of the slow charge transfer reaction and, in addition, the curves obtained are well defined peak-shaped waves displaying zero baselines with the analytical advantages that this represents.

Electrochemical determination of 8-oxoguanine in the presence of uric acid

The electrochemical oxidation of 8-oxoguanine (8-oxoG) in the presence of uric acid (UA) was studied by differential pulse voltammetry over a wide pH range (1–12). The results showed that both compounds follow a pH-dependent oxidation mechanism that involves two electrons and two protons corresponding to reversible charge transfer reactions. The difference between the peak potential for the oxidation of each analyte was found to be always less than 100 mV over the whole pH range, the separation being greater in the pH interval 4–7. In mixtures of both analytes, pH 6 was shown to be the best for 8-oxoG determination in the presence of uric acid, since the peak current is higher and a greater peak separation is achieved.

PolyOne expects loss for fourth quarter 2002, takes steps to reduce costs

Semi-analytical modelling of transient experiments at cylindrical wire or fiber electrodes is hindered by the unavailability of numerical procedures for calculating special functions arising in the models. A theory is developed, of the chronoamperometric Faradaic current for a reversible charge transfer reaction at a cylindrical electrode. Arbitrary potential steps and unequal diffusion coefficients (δ = DO/DR ≠ 1) are assumed. Two procedures (written in C++) are designed, for computing a special function occurring in the theory. One procedure is computationally inexpensive, but has a low accuracy (relative error moduli close to 2% in the worst case, when −0.5 ≤ log (δ) ≤ 0.5). The second is more expensive, but highly accurate (relative error moduli close to 4 × 10−14 in the worst case, when −3 ≤ log (δ) ≤ 3). Numerical experiments demonstrate that the effect of δ ≠ 1 on the current is not negligible, even for δ not much different from unity. Therefore, the theory presented should be taken into account in experimental investigations. The code for the procedures is freely available.

Influence of surface inhomogeneities of boron doped CVD-diamond electrodes on reversible charge transfer reactions

The electrochemical behaviour of reversible charge transfer reactions on boron doped diamond (BDD) was studied by cyclic voltammetry and electrochemical impedance spectroscopy using rotating disc electrodes under defined convection. Diamond films of 5 μm thickness with doping levels of 200, 3000 and 6000 ppm were prepared by hot filament chemical vapour deposition on niobium substrate. The electrochemical measurements were carried out on BDD electrodes in deaerated 0.5 M Na2SO4 + 5 mM K3[Fe(CN)6]/K4[Fe(CN)6] solution at rotation frequencies 0 < frot < 4000 rpm. Comparative measurements were carried out on an active Pt electrode. The BDD electrodes exhibit distinct irreversibilities indicated by a larger peak potential difference in the cyclic voltammograms, lower diffusion limiting current densities and an additional impedance element at high frequencies. Mechanical polishing with carbon fleece and SiC paper strongly affects the irreversible behaviour of the BDD electrodes. The experimental results are explained by a partial blocking of the diamond surface with reversible charge transfer at active sites. The impedance spectra are analysed quantitatively using a transport impedance model for reversible reactions on partially blocked electrode surfaces.

Filter functions for reversible charge transfer reactions in pulse techniques

A filter function is a mode of pulse voltammetry that removes completely the current response for a reversible charge transfer reaction for all values of potential or gives a constant response (≠0) for all values of E. These modes will be designated as filter functions of the first and second class, respectively. With both kinds of functions it is a key condition to obtain the corresponding effect that the current is sampled at selected values of the pulse durations, i.e. if the times for the potential steps are chosen arbitrarily the filtering effect is not observed. In turn, and because for a slow charge transfer reaction the current response with a first class filter function is not zero (nor constant when a second class filter function is applied), we have that the use of these modes of pulse voltammetry provides a way of obtaining without interferences the signal for an irreversible electron transfer in those cases where reversible processes are also present. Thus, if reversible and irreversible electron transfers with close discharge potentials occur simultaneously the response observed when a first class filter function is applied shows only the contribution due to the irreversible process while with a second class mode this last response is superimposed to the constant output obtained for the reversible process. In this paper the theory for these kinds of filter functions is established, particularly for double and triple pulse potential step techniques, and the characteristics of the responses obtained with some of these modes is discussed. Finally, the characteristics of the response obtained with filter functions at spherical electrodes are also shown.

Excited-State Dynamics of Organic Radical Ions in Liquids and in Low-Temperature Matrices

The excited-state dynamics of the radical cations of perylene (PE•+), tetracene (TE•+), and thianthrene (TH•+), as well as the radical anions of anthraquinone (AQ•-) and tetracenequinone (TQ•-), formed by γ irradiation in low-temperature matrices (PE•+, TH•+, AQ•-, and TQ•-) or by oxidation in sulfuric acid (PE•+, TE•+, and TH•+) have been investigated using ultrafast pump−probe spectroscopy. The longest ground-state recovery time measured was 100 ps. The excited-state lifetime of PE•+ is substantially longer in low-temperature matrices than in H2SO4, where the effects of perdeuteration and of temperature on the ground-state recovery dynamics indicate that internal conversion is not the major decay channel of PE•+*. The data suggest that both PE•+* and TE•+* decay mainly through an intermolecular quenching process, most probably a reversible charge transfer reaction. Contrarily to AQ•-*, TQ•-* exhibits an emission in the visible which, according to theoretical calculations, occurs from an upper excited state.