Classical Electrochemistry Research Articles

Electrochemistry Beyond Solutions: Modeling Particle Self-Crowding of Nanoparticle Suspensions.

Nanoparticle suspensions hold promise to transform functionality of next-generation electrochemical systems including batteries, capacitors, wastewater treatment, and sensors, challenging the limits of existing electrochemical models. Classical solution-based electrochemistry assumes that charge is transported and transferred by point-like carriers. Herein, we examine the electrochemistry of a model aqueous suspension of nondissolvable electroactive nanoparticles over a wide concentration range using a rotating disk electrode. Past a concentration and rotation rate threshold, the electrochemistry deviates from solution theory with a maximum attainable current due to particle "self-crowding" where reacted particles on the electrode surface reduce the area accessible for charge transfer by unreacted particles. The observed response is rationalized with an analytical model considering the physical adsorption/desorption kinetics and interfacial transport of nondissolvable finite-size charge carriers. Experimental validation shows the model to be applicable across a range of electrode sizes and thus suitable for engineering electrochemical systems employing nondissolvable nanoparticle suspensions.

Modeling of charging dynamics in electrochemical systems with a graphene electrode

A classical electrochemistry problem related to the polarization of a graphene electrode immersed in an aqueous solution and subjected to a small external ac voltage is revisited. The Poisson-Nernst-Planck equations with proper boundary conditions are linearized and normalized, leading to an analytical formula for the impedance of the electrochemical system containing a graphene-metal electrode pair. Electrochemical impedance spectroscopy is utilized to compare the impedance behavior of the graphene-metal electrode pair with the standard metal-metal electrode pair for a range of ion concentrations in the electrolyte. Also studied is the electrochemical capacitive spectroscopy to provide a detailed analysis related to the effects of the quantum capacitance of graphene on the total capacitive properties of the system.

Interfaces and interphases in batteries

Lithium-ion battery (LIB) is the most popular electrochemical device ever invented in the history of mankind. It is also the first-ever battery that operates on dual-intercalation chemistries, and the very first battery that relies on interphases on both electrodes to ensure reversibility of the cell chemistries. Although it was the commercial success of LIBs that highlighted the importance of interphases, its occurrence far predated the birth of LIBs, and its existence goes far beyond the scope of lithium-based battery chemistries.This perspective intends to shed light on the evolution of our knowledge about interfaces and interphases in batteries. As two intimately intertwined components in electrochemical devices, interface has been thoroughly described in classical electrochemistry, while interphase still presents many unanswered questions to us. The efforts of understanding and eventually tailor-designing the latter will hold the key to enable the next generation battery chemistries.

Synthesis and Spectro-Electrochemical Properties of New Metallophthalocyanines Having High Electron Transfer Capability

It is important to synthesis and examine the redox properties of phthalocyanines and related macrocycles in order to reveal their possible applications. In this paper, new Zn2+, Co2+ and Mn2+ phthalocyanine complexes containing substituted 1,2,4-triazole groups on peripheral positions have been prepared and characterized by classical methods and electrochemistry in detail. The use of triethylamine and acetone combination in the synthesis of nitrile structures 3a and 3b, the starting compounds for phthalocyanines, both increased yield of products and shortened reaction time compared to classical synthesis of nitrile structures. The electron transfer capability of new metallophthalocyanines (ZnPcs, CoPcs and MnPcs) was investigated in detail via cyclic voltammetry (CV), square wave voltammetry (SWV) and in situ UV–vis spectroelectrochemistry. For ZnPcs, these experiments demonstrated that the complexes exhibited three well-defined reductions and two oxidations waves based on the Pc ring electroinactive nature of the Zn metal coordinated to the macrocycle. For CoPcs showed three reductions and one oxidation based on both the Pc ring and electroactive nature of Co center. Furthermore, MnPcs displayed three well-defined reductions and two oxidations waves based on either the Pc ring or electroactive Mn center.

Electrosorption at metal surfaces from first principles

Electrosorption of solvated species at metal electrodes is a most fundamental class of processes in interfacial electrochemistry. Here, we use its sensitive dependence on the electric double layer to assess the performance of ab initio thermodynamics approaches increasingly used for the first-principles description of electrocatalysis. We show analytically that computational hydrogen electrode calculations at zero net-charge can be understood as a first-order approximation to a fully grand canonical approach. Notably, higher-order terms in the applied potential caused by the charging of the double layer include contributions from adsorbate-induced changes in the work function and in the interfacial capacitance. These contributions are essential to yield prominent electrochemical phenomena such as non-Nernstian shifts of electrosorption peaks and non-integer electrosorption valencies. We illustrate this by calculating peak shifts for H on Pt electrodes and electrosorption valencies of halide ions on Ag electrodes, obtaining qualitative agreement with experimental data already when considering only second order terms. The results demonstrate the agreement between classical electrochemistry concepts and a first-principles fully grand canonical description of electrified interfaces and shed new light on the widespread computational hydrogen electrode approach.

Wine Reduction Potentials: Are These Measured Values Really Reduction Potentials?

During its production wine can react with substantial amounts of aerial oxygen. Some oxidation can be beneficial, especially in red wine, but if allowed to occur in excess it is highly detrimental, making oxygen management an important aspect of wine making. The use of reduction potentials at platinum electrodes to measure the redox state of wines extends back over 80 years. The premise is that reductants in wine produce oxidized derivatives and the balance between the two determines the reduction potential, as in classical electrochemistry. As the detailed mechanism of wine oxidation becomes better understood, it is apparent that redox couples in wine do not function in this way. It is proposed that the observed potentials are mixed potentials largely due to ethanol oxidation coupled with oxygen reduction. Under low oxygen conditions, further redox couples can contribute to the mixed potential, both directly and via adsorption effects at the platinum electrode.

A three dimensional multiphysics model of a solid oxide electrochemical cell: A tool for understanding degradation

Mitigating degradation is essential for extending the lifetime of solid oxide electrochemical cells (SOCs). The conditions leading to degradation, e.g. overpotentials, gas partial pressures, thermal gradients are hard, if not impossible, to retrieve experimentally. Thus, to deconvolute the response from cell testing, modeling can be applied to understand the degradation phenomena in greater detail. Modeling of SOCs is well developed. For computational efficiency, the electrodes are often represented with a mathematical abstraction of zero thickness layer. In this work, further attention is given to the local conditions in the through-thickness of the electrodes, by rigidly integrating classical electrochemistry into a three dimensional multiphysics model of an SOC. Hereby, local conditions (e.g. overpotential) vary through the electrode, and with the coupling to the different transport phenomena occurring (mass, current, momentum and species), this becomes available in three dimensions, throughout a cell. To investigate the validity of the model, a high number of experiments are conducted at different operating conditions, i.e. in both fuel cell and electrolysis mode of operation with H2/H2O as feedstock varying parameters such as temperature, gas flows and gas compositions.

Thin-Film Electrochemistry of Single Prussian Blue Nanoparticles Revealed by Surface Plasmon Resonance Microscopy.

Electrochemical behaviors of Prussian blue (PB) have been intensively studied for decades because it not only serves as a model electro-active nanomaterial in fundamental electrochemistry but also a promising metal-ion storage electrode material for developing rechargeable batteries. Traditional electrochemical studies are mostly based on bulk materials, leading to an averaged property of billions of PB nanoparticles. In the present work, we employed surface plasmon resonance microscopy (SPRM) to resolve the optical cyclic voltammograms of single PB nanoparticles during electrochemical cycling. It was found that the electrochemical behavior of single PB nanoparticles nicely followed a classical thin-film electrochemistry theory. While kinetic controlled electron transfer was observed at slower scan rates, intraparticle diffusion of K+ ions began to take effect when the scan rate was higher than 60 mV/s. We further found that the electrochemical activity among individual PB nanoparticles was very heterogeneous and such a phenomenon has not been previously observed in the bulk measurements. The present work not only demonstrates the thin-film electrochemical feature of single electro-active nanomaterials for the first time, it also validates the applicability of SPRM technique to investigate a variety of metal ion-storage battery materials, with implications in both fundamental nanoelectrochemistry and electro-active materials for sensing and battery applications.

Investigating the Oxygen Reduction Reaction in Lithium-Oxygen Cells

The rechargeable Lithium (Li)-Oxygen (O2) battery has great potential as a high energy battery system due to its high theoretical specific energy of 3505 Wh Kg-1, which is significantly higher than current Li-ion cells.1,2 However, to succeed as a practical replacement for Li-ion cells, Li-O2 cells must overcome known problems such as (i) poor cycle life, (ii) high charge and discharge overpotentials (iii) low coulombic efficiency and (iv) low power capability.3 In recent studies, the poor cycle life and high overpotentials could be traced to the oxidative instability of the electrolyte in conjunction with electrode passivation by lithium peroxide (Li2O2).4-6 Early theoretical predictions for the Oxygen Reduction Reaction (ORR) at the cathode, envisioned a Li2O2 covered surface after the initial cycle and further ORR occurring on the deposited Li2O2, while also predicting large overpotentials in accordance with the experimental observations.7,8 However, the issue of electron transfer across poorly conducting Li2O2 had to be explained using mechanisms such as d-band bending and poloron hopping.7,9 The use of classical electrochemical techniques, such as Rotating Disk Electrode (RDE) and Rotating Ring-Disk Electrode (RRDE) to study the kinetics and catalytic activity of various surfaces has been common for aqueous ORR.10-12 However, application of such techniques to the Li-O2 ORR has been challenging due to surface changes during peroxide deposition, previously reported anomalous Tafel behavior, and extreme sensitivity to experimental conditions.13,14 To date, no clear mechanistic understanding or explanation of the ORR has been established, via theoretical simulations or electrochemical experiments. Here, we intend to establish such a mechanistic understanding of the ORR by combining information from theoretical simulations and classical electrochemistry. We report first principles, Density Functional Theory (DFT) modeling of the Li-O2 ORR on carbon, noble metals and their alloys under vacuum and in solvents, along with the correlation between intermediate species binding energies and favored reaction pathways from amongst 1e-, 2e- and 4e- mechanisms. Further, classical electrochemical techniques were utilized to experimentally study (and support) the reaction kinetics and mechanisms via RDE and RRDE experiments, which are difficult to explain through theoretical simulations alone. It is the authors’ hope that such use of theoretical simulations and classical electrochemistry in tandem, will serve as a guide towards future experimental studies; especially those directed towards the screening of potential catalytic surfaces for efficient ORR. Bruce et al., Nature Materials, 11, 2011, 19-29.Christensen et al., J. Electrochem. Soc., 159(2), R1 – R30, (2012).Y-C Lu, H.A. Gasteiger, E. Crumlin, R. McGuire, Jr., Y. Shao-Horn; J. Electrochem. Soc., 157 (9), A1016-A1025 (2010).S.A. Freunberger, Y. Chen, Z. Peng, J.M. Griffin, L.J. Hardwick, F. Barde, P. Novak, P.G. Bruce, J. Am. Chem. Soc., 133(2011), 8040–8047.S.A. Freunberger, Y. Chen, N.E. Drewett, L.J. Hardwick, F. Barde, P.G. Bruce, Angew. Chem. Int. Ed., 50(2011), 8609 –8613.Y. Chen, S.A. Freunberger, Z. Peng, F. Bardé, P.G. Bruce, J. Am. Chem. Soc., 134(2012), 7952−7957.Hummelshøj, J.S; Blomqvist,J; Datta,S.; Vegge, T.; Rossmeisl,J.; Thygesen, K.S.; Luntz,A.C.; Jacobsen,K.W.; Nørskov,J.K.; J.Chem.Phys., 132(2010), 071101.Viswanathan, V.; Nørskov, J.K; Speidel, A.; Scheffler, R.; Gowda, S.; Luntz, A.C; J. Phys. Chem. Lett., 4(2013),556−560.J. M. Garcia-Lastra, J. S. G. Myrdal, R. Christensen, K. S. Thygesen, T. Vegge; J. Phys. Chem. C, 117(2013), 5568−5577.J. Prakash, D.A. Tryk, E.B. Yeager; J. Electrochem. Soc., 146(1999), 4145-4151.W.E. Mustain, K.Kepler, J. Prakash; Electrochim.Acta,52(2007), 2102–2108.W.E. Mustain, J. Prakash; J. Pow. Soc., 170(2007), 28–37.C.O. Laoire, S. Mukerjee, K.M. Abraham, E.J. Plichta, M.A. Hendrickson, J. Phys. Chem. C 114(2010) 9178–9186.W. Torres, N. Mozhzhukhina, A.Y. Tesio, E.J. Calvo, J. Electrochem. Soc., 161 (14) A2204-A2209 (2014).

Three-electrode analytical and preparative electrochemistry in micro-volume hanging droplets

Three-electrode micro-cells equipped with a conventional reference electrode (SCE) were easily constructed based on micro-volume droplets suspended by capillary forces to the fritted glass of the SCE bridge. Working and counter electrodes were simply inserted through the droplet surface, allowing classical electrochemistry to be readily performed in minute samples.

Effect of cation species on surface-induced phase transition observed for platinum complex anions in platinum electrodeposition using nanoporous silicon.

In an earlier work [K. Fukami et al., J. Chem. Phys. 138, 094702 (2013)], we reported a transition phenomenon observed for platinum complex anions in our platinum electrodeposition experiment using nanoporous silicon. The pore wall surface of the silicon electrode was made hydrophobic by covering it with organic molecules. The anions are only weakly hydrated due to their large size and excluded from the bulk aqueous solution to the hydrophobic surface. When the anion concentration in the bulk was gradually increased, at a threshold the deposition behavior exhibited a sudden change, leading to drastic acceleration of the electrochemical deposition. It was shown that this change originates from a surface-induced phase transition: The space within a nanopore is abruptly filled with the second phase in which the anion concentration is orders of magnitude higher than that in the bulk. Here we examine how the platinum electrodeposition behavior is affected by the cation species coexisting with the anions. We compare the experimental results obtained using three different cation species: K(+), (CH3)4N(+), and (C2H5)4N(+). One of the cation species coexists with platinum complex anions [PtCl4](2-). It is shown that the threshold concentration, beyond which the electrochemical deposition within nanopores is drastically accelerated, is considerably dependent on the cation species. The threshold concentration becomes lower as the cation size increases. Our theoretical analysis suggests that not only the anions but also the cations are remarkably enriched in the second phase. The remarkable enrichment of the anions alone would give rise to the energetic instability due to electrostatic repulsive interactions among the anions. We argue that the result obtained cannot be elucidated by the prevailing view based on classical electrochemistry. It is necessitated to consult a statistical-mechanical theory of confined aqueous solutions using a molecular model for water.

Influence of Edge Effects on Local Corrosion Rate of Magnesium Alloy/Mild Steel Galvanic Couple

The effect of the insulator-mixed-material edge on the galvanic corrosion rate of magnesium alloy (AE44)-mild steel (MS) couple is experimentally studied using scanning vibrating electrode technique (SVET), profilometry, and classical electrochemistry. The local and average corrosion rates estimated from the experimental depth of anodic attack profile of AE44-MS couple are validated by 2D and 3D corrosion numerical models. Our study demonstrates experimentally and theoretically that the presence of the insulator edge increases the local current density, which enhances the corrosion rate. The extent of the local corrosion rate enhancement and its effect on the overall corrosion rate of the mixed material is discussed and depends on the mixed material's geometry and the edge type.

Study of the Influence of the Rare Earth Elements (Ce3+ and Ce4+) Concentration on the Siloxanes Coating Applied on the Copper Surface

This work studied the influence of the rare earth (Ce3+ and Ce4+) elements concentration in polysiloxane films deposited on copper by dip-coating process, and evaluated their resistance in a 3.5 wt.% NaCl medium. Classical electrochemistry techniques were used as open circuit potential, polarization curves and electrochemical impedance spectroscopy. The results revealed that by adding low concentration of Ce4+ ions, the coating prevents the electrolyte uptake any longer retarding the substrate degradation consequently.

Electroless Oxidation of Diamond Surfaces: Relevance of Concepts Developed for Classical SC Electrochemistry

"Electroless" oxidation has been widely studied on III-V and II-VI semiconductor (SC) interfaces. These works showed that using oxidizing agents with standard potentials close to the valence band (VB) position of the material, the reduction of the oxidizing specie (Ox+) by holes injection in the valence band and the oxidation of the SC can take place simultaneously on the same surface. In the present work, we study the relevance of these concepts in the oxidation of a non conventional wide gap SC: Boron Doped Diamond (BDD). Therefore, we used two different oxidizing agents (Ce4+ and Fe(CN)63-) and studied the possibility to produce "C-O" moieties on diamond electrodes in an "electroless" way.

Electroless Oxidation of Diamond Surfaces: Relevance of Concepts Developed for Classical SC Electrochemistry

not Available.

The electrochemical potential and ionic activity coefficients. A possible correction for Debye–Hückel and Maxwell–Boltzmann equations for dilute electrolyte equilibria

When the electrical contribution in the electrochemical potential of ionic species is reduced with a factor two from its traditional value, the ionic activity coefficients are closer to unity and need to account only for the short-range interactions at high concentrations. Such a change is needed to remove inconsistencies in the models and to comply with basic electrostatic principles. This will have serious implications, in many applications. For example, it will cause changes in many of the fundamental models that are used to explain measured data in the dilute range for the various disciplines that embrace classical electrochemistry. Examples are Debye–Hückel and Gouy–Chapman theories; Maxwell–Boltzmann distribution; Nernst theory; Donnan equilibrium, etc. These theories impact a wide range of observable phenomena such as activity coefficients of electrolytes, diffuse double layer capacitance, electrode potentials, membrane potentials, streaming potentials, electro-osmosis, flotation, sedimentation, corrosion, charged micellar behaviour, space-charge semiconductor behaviour, and electrical phenomena in biological tissue, e.g. membranes; cells; and nerves, etcetera.

Design of ecologically safe and science intensive electrochemical processes

This review discusses the results of and prospects for studies aimed at design of new science intensive, environmentally safe technologies for the synthesis of organophosphorus compounds by halogenation of α-olefins, including modification of rapeseed oil; it also considers methods for the production of some other intermediates for chemical industry. New synthetic applications have been developed, using combined methods of classical organic chemistry and electrochemistry, for processes based on electrochemical generation of catalysts (mediators)—complexes of metals in low oxidation states, halogen complexes, etc. Selective electrochemical procedures are suggested for the synthesis of triphenylphosphine, trialkylphosphates, and nanosized transition metal phosphides from white phosphorus.

In situ monitoring the effects of a magnetic field on the open-circuit corrosion states of iron in acidic and neutral solutions

The effects of a 0.4 T horizontal magnetic field (HMF) on the open-circuit corrosion states of iron in static aqueous solutions are studied by in situ monitoring the responses of two electrochemical parameters to the applied magnetic field, i.e. the open-circuit potential (OCP) and the current under potentiostatic polarization. The applied magnetic field makes the OCP shift in the noble direction. Withdrawing the magnetic field causes a negative shift of the OCP in acidic solutions, but it does not cause any significant change of OCP in neutral solutions. Imposing a magnetic field induces a cathodic current for iron that was previously potentiostatically polarized at the OCP without magnetic field. Withdrawing the magnetic field induces an anodic current for iron that was previously potentiostatically polarized at the OCP with the magnetic field. The magnetic field effect is more significant in the acid solutions than in the salt solutions. The magnetic field effects on the oxygen reduction and on the activation-controlled iron dissolution reaction are found to be insignificant. The magnetic field effect on the hydrogen reduction reaction on iron in acidic solutions is demonstrated. Results show the possibility that a magnetic field would affect the hydrogen evolution by enhancing the electron-transfer process that has been categorized in the classical electrochemistry kinetics to be the rate-determining process. The memory effect of the magnetic field on the electrochemical reaction is identified and discussed.

Adsorption and Electrochemical Activity: An In Situ Electrochemical Scanning Tunneling Microscopy Study of Electrode Reactions and Potential-Induced Adsorption of Porphyrins

The effect of adsorption on molecular properties and reactivity is a central topic in interfacial physical chemistry. At electrochemical interfaces, adsorbed molecules may lose their electrochemical activity. The absence of in situ probes has hindered our understanding of this phenomenon and electrode reactions in general. In this work, classical electrochemistry and electrochemical scanning tunneling microscopy (EC-STM) were combined to provide molecular level insight into electrochemical reactions and the molecular adsorption state at the electrolyte-electrode interface. The metal-free porphyrin 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine (TPyP) adsorbed on Au(111) in 0.1 M H(2)SO(4) solution was chosen as a model system. TPyP is found to irreversibly adsorb on Au(111) over a wide range of potentials, from -0.25 to 0.6 V(SCE). The adsorption state of TPyP has a dramatic effect on its electrochemistry. Preadsorbed, oxidized TPyP displays no well-defined cathodic peaks in cyclic voltammograms in sharp contrast to solution-phase TPyP. Our present work provides direct, molecular level evidence of the electrochemically "invisible" species. Electrochemical activity of absorbed species is recovered by allowing the oxidized molecule sufficient time (tens of minutes) to reduce. The redox state of adsorbed TPyP also affects the nature of the adsorption. Oxidized species can apparently only form monolayers. However, multilayers, stable enough to be imaged by STM, can form when the adsorbed TPyP is in the reduced state. This suggests that by controlling the electrochemistry one can either promote or suppress the formation of multilayers.

Demonstration of the Elusive Concentration-Gradient Paramagnetic Force

Using classical electrochemistry, it is demonstrated that the concentration-gradient paramagnetic force, FnablaC, is a body force proportional to |B|2 acting parallel to the concentration gradient of electrogenerated radicals. FnablaC can balance gravity, holding volumes of solution wherein mass transfer continues to take place by diffusion. In contrast to usual levitation forces, FnablaC does not depend on field gradients and may be present even in homogeneous magnetic fields. Understanding the properties of FnablaC is relevant to magnetic confinement and levitation and is speculated even to propulsion with objects having permanent susceptibility gradients.