Constant Potential Conditions Research Articles

Structural, electronic and magnetic properties of Mn doped ZnO nanoplates synthesized by electrodeposition method

The electronic, crystallographic and magnetic properties of ZnO thin films doped with manganese (Mn) agent were studied at various Mn concentrations. The samples were prepared electrochemically, under constant electric potential conditions. All Zn1−xMnxO (x = 1, 3, 5, 7 and 10%) samples exhibit typical wurtzite crystal structure with strong (002) orientation. The grains of samples are well-shaped and highly oriented nanoplates observed from SEM measurements. There is a strong correlation between the magnetic properties and electronic structure for all samples. The XPS analysis data revealed that Mn atoms are in oxidized state rather than metallic state. In addition, electron donation from Mn to Zn has changed the electronic structure of host lattice. The magnetic properties of samples are investigated by sweeping temperature and magnetic field. It is revealed that the antiferromagnetic interactions increases with Mn content in ZnO host lattice which is addressed by the formation of Mn-O-Mn bonding from the XPS data.

Constant Potential, Electrochemically Active Boundary Conditions for Electrochemical Simulation

In this manuscript, we present a model for simulating active electrochemical systems using a classical molecular dynamics framework. We describe a computationally efficient method of enforcing the electrostatic properties of constant potential boundary conditions and demonstrate how this method can be adapted to support stochastic interfacial charge-transfer processes. We highlight the utility of this model by simulating the nonequilibrium dynamics of a model battery system. We demonstrate the ability of this model to support the formation of a stable double structure, consistent with expectations from macroscopic equilibrium. We also illustrate how this model can be used to provide microscopic physical insight into the results of standard potential-jump experiments.

Efficient Three-Component One-Pot Synthesis of 4H-Pyrans

Clean, practical, and efficient electrochemical synthesis of pharmaceutically relevant 4H-pyran derivatives by one-pot three-component combination of an aryl aldehyde, malononitrile, and a dicarbonyl compoundis developed. The synthesis is performed in ethanol with lithium perchlorate as a supporting electrolyte in an undivided cell on a platinum electrode under constant potential electrolysis conditions.

Analysis of Lithium Insertion/Desorption Reaction at Interfaces between Graphite Electrodes and Electrolyte Solution Using Density Functional + Implicit Solvation Theory

The charge transfer reaction at the electrode/solution interface is regarded as a major component that limits the current densities of Li-ion batteries. A combination of density functional theory for the electronic structure calculations of an electrode and a reacting component with implicit solvation theory for an electrolyte solution is used for the lithium insertion/desorption reaction (R). At the interfaces between tilted-graphite electrodes and a 1 M LiPF6 ethylene carbonate solution, the energy landscapes of reaction R are revealed under constant electron chemical potential conditions. Across the transition state where the Li forms a half solvation shell, the reacting Li inside the electrode changes to a full solvation structure in the solution accompanied by electron transfer. On graphite with two tilt angles, the activation energies at the equilibrium potentials of reaction R are approximately 0.6 eV, which is consistent with the electrochemical impedance spectroscopy measurements. However, opposi...

Post-Functionalization of P3HT Via Anodic Oxidation with High Current Efficiency

Recently, post-functionalization has attracted attention as a useful strategy to obtain functional polymers. We have already reported the anodic chlorination of poly(3-hexylthiophene) (P3HT) in the presence of chloride ions under a constant potential condition, and found that introduction of a chlorine atom to the 4-position of the thiophene rings could tune the optoelectronic properties of P3HT. However, the current efficiency of this reaction was low because of the competitive oxidation between P3HT and the chloride ions used as a chlorine source.1 In this study, we improved the current efficiency of the anodic chlorination of P3HT by using boron trifluoride-diethyl ether complex (BFEE). BFEE is well-known to decrease oxidation potentials of aromatic compounds due to the π-complex formation between BF3 and aromatic rings.2 BFEE used as a solvent and an electrolyte in voltammetric studies successfully decreased the oxidation potential of P3HT, and increased the oxidation potential of chloride ions. These interesting effects of BFEE also worked in the macroscale electrolysis of P3HT, giving higher current efficiency compared to the conventional methods.References S. Hayashi, S. Inagi, K. Hosaka, T. Fuchigami, Synth. Met., 2009, 159, 1792.S. Jin, G. Xue, Macromolecules, 1997, 30, 5753. Figure 1

New Organic Molecules for Energy Storage Applications

A range of structurally variable redox active molecules that are suitable for electrical energy storage were investigated for their potential applications in redox flow batteries. The molecules were selected based on their electron acceptor and/or donor properties, their solubility in aqueous and non-aqueous solvents, their lifetimes in reduced and oxidized states, their formal potentials, their abilities to coexist together in the catholyte and anolyte cell compartments, their resistance to degradation reactions with molecular oxygen and water, their behavior in the presence of acids and bases, and their ease of synthesis. The molecules included a number of redox active quinones and flavins, vitamins (B2, E and K1) and modified forms of the vitamins, aromatic esters, 1,4-phenylenediamines and benzidines. The performance of the molecules were evaluated using a combination of voltammetry, electrolysis under constant potential conditions and in situ spectroelectrochemical analysis (UV-vis and electron paramagnetic resonance). It was found that systems with high redox potentials, although allowing for large voltages (3 – 5 V), suffered from relatively short lifetimes in their charged states due to undesirable reactions with trace impurities including molecular oxygen and trace water (in non-aqueous solutions). Therefore, an optimal potential difference range for the redox couples was found to be between 1 – 2 V, which decreased the likelihood of decomposition reactions of the redox active components and often allowed seemingly indefinite lifetimes. Two systems that provided excellent characteristics were, (i) a modified form of vitamin K1 (as the electron acceptor) and a modified form of vitamin E (as the electron donor), and, (ii) a substituted anthraquinone (as the electron acceptor) and o-tolidine (as the electron donor). Figure 1

Recent Progress in the Theoretical Investigation of Electrocatalytic Reduction of CO2

AbstractThe worldwide combustion of fossils produces anthropogenic CO2, which has deleterious effects on global climate patterns. An ideal solution is to develop high‐performance CO2 capture and utilization technologies that can convert CO2 into commercial products by means of electrocatalytic reduction with renewable energy. The design of electrocatalysts can be facilitated by accurate computational simulations based on density functional theory (DFT). Herein, commonly used models, from the computational hydrogen electrode model with constant charge assumption, to the explicit and implicit solvation model under constant potential condition, are reviewed. Thereafter, the applications of recent data‐driven methods, such as neutral network and machine learning, are introduced. Also, based on DFT calculations, four composition based classes of electrodes are further discussed, including (1) bulk metals and alloys, (2) nanoparticles, (3) metal‐nonmetal compounds and (4) carbon‐based materials. In this Review, several theoretical investigations which have been realized in practice are highlighted in particular, such as metal‐hydride nanocluster and carbon nitride supported copper complex for high‐efficiency CO2 reduction. It shows that the theoretical study can not only explain experimental phenomena but also predict improved candidates.

Electrostatic interactions between charged dielectric particles in an electrolyte solution: constant potential boundary conditions.

The problem of electrostatic interactions between colloidal particles in an electrolyte solution has been solved within the Debye-Hückel approximation using the boundary condition of constant potential. The model has been validated in two independent ways - by considering the limiting cases obtained from DLVO theory and comparison with the available experimental data. The presented methodology provides the final part of a complete theory of pairwise electrostatic interactions between spherical colloidal particles; one that embraces all possible chemical scenarios within the boundary conditions of constant potential and constant charge.

Synthesis of Nanoparticle Copolymer Brushes via Surface-Initiated seATRP

Synthesis of densely grafted (co)polymer brushes, including poly(tert-butyl acrylate) (PtBA), poly(tert-butyl acrylate)-b-poly(styrene) (PtBA-b-PS), and poly(tert-butyl acrylate)-b-poly(butyl acrylate) (PtBA-b-PBA), from 15.8 nm silica nanoparticles (NPs) via a surface-initiated simplified electrochemically mediated atom transfer radical polymerization (SI-seATRP) under constant potential electrolysis conditions is reported for the first time. The rate of polymerization was enhanced by applying more negative potentials, which resulted in an increase in grafting density, up to 0.93 nm–2. Furthermore, temporal control over the polymerization was achieved by adjustment of the applied potential. The polymers showed narrow molecular weight distributions (Đ = 1.20–1.32), and polymer-grafted nanoparticles had excellent size uniformity. Dispersions in suitable solvents were stable without any nanoparticle aggregation. Microstructures observed in thin films of densely block copolymer tethered silica NPs suggested ...

Stray current control by a new approach based on current monitoring on a potential probe

ABSTRACTTo control stray current interference due to DC transit systems, cathodic protection at the so-called constant potential condition is used. Pipeline potential is continuously measured by means of a fixed reference electrode, and the measured value is used to control dynamically the feeder in order to match the protection condition. An accurate analysis of this technique reveals that during interference what is maintained constant is the IR drop in soil rather than the true potential of the structure. A new approach was investigated: the innovation consists of the use of the current, rather than the potential, to control the feeder on the basis of an effective range of the current the probe should receive. Laboratory tests confirmed the feasibility of such an approach. Modelling and test results are presented and discussed.

Heteroaggregation of oppositely charged particles in the presence of multivalent ions.

Time-resolved dynamic light scattering is used to measure absolute heteroaggregation rate coefficients and the corresponding stability ratios for heteroaggregation between amidine and sulfate latex particles. These measurements are complemented by the respective quantities for the homoaggregation of the two systems and electrophoresis. Based on the latter measurements, the stability ratios are calculated using Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. In monovalent salt solutions, the two types of particles investigated are oppositely charged. In the presence of multivalent ions, however, one particle type reverses its charge, while the charge of the other particle type is hardly affected. In this region, the heteroaggregation stability ratio goes through a pronounced maximum when plotted versus concentration. This region of slow aggregation is wider than the one observed in the corresponding homoaggregation process. One also finds that the onset of this region sensitively depends on the boundary conditions used to calculate the double layer force. The present results are more in line with constant potential boundary conditions.

Simulation of local ion transport in lamellar block copolymer electrolytes based on electron micrographs

ABSTRACTA method is presented to relate local morphology and ionic conductivity in a solid, lamellar block copolymer electrolyte for lithium batteries, by simulating conductivity through transmission electron micrographs. The electrolyte consists of polystyrene‐block‐poly(ethylene oxide) mixed with lithium bis(trifluoromethanesulfonyl) imide salt (SEO/LiTFSI), where the polystyrene phase is structural phase and the poly(ethylene oxide)/LiTFSI phase is ionically conductive. The electric potential distribution is simulated in binarized micrographs by solving the Laplace equation with constant potential boundary conditions. A morphology factor, f, is reported for each image by calculating the effective conductivity relative to a homogenous conductor. Images from two samples are examined, one annealed with large lamellar grains and one unannealed with small grains. The average value of f is 0.45 ± 0.04 for the annealed sample, and 0.37 ± 0.03 for the unannealed sample, both close to the value predicted by effective medium theory, 1/2. Simulated conductivities are compared to published experimental conductivities. The value of fUnannealed/fAnnealed is 0.82 for simulations and 6.2 for experiments. Simulation results correspond well to predictions by effective medium theory but do not explain the experimental measurements. Observation of nanoscale morphology over length scales greater than the size of the micrographs (∼1 μm) may be required to explain the experimental results. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 266–274

Electrochemical Catalyst-Support Effects and Their Stabilizing Role for IrOx Nanoparticle Catalysts during the Oxygen Evolution Reaction.

Redox-active support materials can help reduce the noble-metal loading of a solid chemical catalyst while offering electronic catalyst-support interactions beneficial for catalyst durability. This is well known in heterogeneous gas-phase catalysis but much less discussed for electrocatalysis at electrified liquid-solid interfaces. Here, we demonstrate experimental evidence for electronic catalyst-support interactions in electrochemical environments and study their role and contribution to the corrosion stability of catalyst/support couples. Electrochemically oxidized Ir oxide nanoparticles, supported on high surface area carbons and oxides, were selected as model catalyst/support systems for the electrocatalytic oxygen evolution reaction (OER). First, the electronic, chemical, and structural state of the catalyst/support couple was compared using XANES, EXAFS, TEM, and depth-resolved XPS. While carbon-supported oxidized Ir particle showed exclusively the redox state (+4), the Ir/IrOx/ATO system exhibited evidence of metal/metal-oxide support interactions (MMOSI) that stabilized the metal particles on antimony-doped tin oxide (ATO) in sustained lower Ir oxidation states (Ir(3.2+)). At the same time, the growth of higher valent Ir oxide layers that compromise catalyst stability was suppressed. Then the electrochemical stability and the charge-transfer kinetics of the electrocatalysts were evaluated under constant current and constant potential conditions, where the analysis of the metal dissolution confirmed that the ATO support mitigates Ir(z+) dissolution thanks to a stronger MMOSI effect. Our findings raise the possibility that MMOSI effects in electrochemistry-largely neglected in the past-may be more important for a detailed understanding of the durability of oxide-supported nanoparticle OER catalysts than previously thought.

Synthesis of α-d-glucose-based star polymers through simplified electrochemically mediated ATRP

Abstract A glucose-based star-like block copolymer with a hydrophilic α- d -glucose core and amphiphilic block copolymer arms composed of n -butyl acrylate (BA) and oligo (ethylene glycol) acrylate (OEGA) has been synthesized for the first time via a simplified electrochemically mediated ATRP ( se ATRP) under both constant potential electrolysis and constant current electrolysis conditions, utilizing only 30 ppm of catalyst complex (significantly less than previously reported: 5000–50,000 ppm). The rate of the polymerizations was controlled by applying more positive potential values to prevent the possibility of intermolecular coupling of the polymer stars which are being formed and preparation of glucose-based star polymers with narrow molecular weight distributions. The lack of radical coupling reactions was confirmed by GPC analyses of the arm length of synthetized star (co)polymers. The results from 1 H NMR spectral studies support the formation of star-like block (co)polymers. It is expected that these new glucose-based star polymers may find application as biomaterials of an increased hydrophobicity and antifouling coatings.

Pd Nanoparticle Formation during Constant Potential Electrodepositions in Ionic Liquids

Electrodepositions in ionic liquids (ILs) allow for opportunities to improve deposited morphologies, access redox potentials that cannot be achieved in aqueous baths, and utilize less hazardous bath compositions. The driver to utilize ILs for Pd electrodeposition is to minimize hydrogen embrittlement challenges commonly associated with Pd electrodeposition in aqueous electrolytes. Generally, the resulting Pd deposits in ILs are thin films, loosely adhered fine powders or dendritic structures, depending upon the IL selected and the electrochemical parameters used(1, 2). Recently, it has also been shown that electroreduction of Pd in ILs can result in nanoparticles being formed in solution, rather than on an substrate electrode when high overpotentials are used(3). Previously, we showed Pd nanosphere formation can be controlled through potentiostatic pulse deposition in 1-butyl, 3-methylimidazolium chloride [Bmim][Cl] onto Ni electrode substrates(4). The nanosphere size was found to be a function of cycle time. In contrast, using 1-buty, 1-methylpyrrolidinum dicyanamide [Bmpyrr][DCA] under constant potential conditions, thin film Pd layers on nickel electrode substrates were obtained(5). We will present how, upon further investigation, these Pd “thin films” formed from constant potential deposition in [Bmpyrr][DCA] are actually agglomerates of nanoparticles that can be scraped off the Ni substrate and dispersed in solution in an unagglomerated state. These nanoparticles have an average size of 6.3 ± 1.6 nm when deposited at -2.3V vs. Fc/Fc+. Further investigation into the conditions for electrodeposition in ILs where it was thought that thin films were formed will also be discussed to better understand if the resulting deposits were truly thin films and not nanoparticle agglomerations.

Electrochemical studies on the reduction of uranyl ions in nitric acid-hydrazine media

The redox behaviour of uranyl ions (UO22+) in nitric acid and nitric acid-hydrazine media were investigated by the transient electrochemical techniques cyclic voltammetry (CV) and chronopotentiometry (CP), at the working electrodes platinum, gold, titanium and glassy carbon (GC) at 298K. At a very low concentration of 0.05M nitric acid and in the absence of hydrazine, the reduction of uranyl ions was found to be under charge transfer and diffusion control. Nevertheless, as the acidity of the supporting electrolyte increased, the reduction was purely under kinetic control. The diffusion coefficient (Do) values for the reduction of U (VI) at the working electrodes platinum, gold GC as well as Ti were determined. The current efficiency and conversion efficiency for the reduction of uranyl ions were found to be better under constant potential conditions than that at constant current conditions.

Ion size effects on the osmotic pressure and electrocapillarity in a nanoslit: Symmetric and asymmetric ion sizes.

We analyze the effect of asymmetric finite ion size in nanoconfinement in the view of osmotic pressure and electrocapillarity. When the confinement width becomes comparable with the Debye length, the overlapped electric double layer is significantly deformed by the steric effects. We derive the osmotic pressure from the modified Poisson-Boltzmann equation in a nanoslit to examine the deviation from the ideal osmotic pressure and the repulsive force on the wall considering the asymmetry of ion sizes. Then the electrocapillarity due to the steric effect is investigated under constant potential condition with the flat interface assumption. Later, the deformation by the electrocapillarity is also considered in the first order approximation.

Efficient fluorescence quenching in electrochemically exfoliated graphene decorated with gold nanoparticles

High surface area graphene sheets were obtained by electrochemical exfoliation of graphite in an acid medium under constant potential conditions. Filtration and centrifugation processes played an important role in order to obtain stable dispersions in water. Scanning electron microscopy and transmission electron microscopy imaging revealed highly exfoliated crystalline samples of ∼5 μm. Raman, Fourier transform infrared and x-ray photoelectron spectroscopy further confirmed the high quality of the exfoliated material. The electrochemically exfoliated graphene (EEG) was decorated with gold nanoparticles (AuNPs) using sodium cholate as a buffer layer. This approach allowed for a non-covalent functionalization without altering the desirable electronic properties of the EEG. The AuNP-EEG samples were characterized with various techniques including absorbance and fluorescence spectroscopy. These samples displayed a fluorescence signal using an excitation wavelength of 290 nm. The calculated quantum yield (Φ) for these samples was 40.04%, a high efficiency compared to previous studies using solution processable graphene.

Evaluation of molecular dynamics simulation methods for ionic liquid electric double layers.

We investigate how systematically increasing the accuracy of various molecular dynamics modeling techniques influences the structure and capacitance of ionic liquid electric double layers (EDLs). The techniques probed concern long-range electrostatic interactions, electrode charging (constant charge versus constant potential conditions), and electrolyte polarizability. Our simulations are performed on a quasi-two-dimensional, or slab-like, model capacitor, which is composed of a polarizable ionic liquid electrolyte, [EMIM][BF4], interfaced between two graphite electrodes. To ensure an accurate representation of EDL differential capacitance, we derive new fluctuation formulas that resolve the differential capacitance as a function of electrode charge or electrode potential. The magnitude of differential capacitance shows sensitivity to different long-range electrostatic summation techniques, while the shape of differential capacitance is affected by charging technique and the polarizability of the electrolyte. For long-range summation techniques, errors in magnitude can be mitigated by employing two-dimensional or corrected three dimensional electrostatic summations, which led to electric fields that conform to those of a classical electrostatic parallel plate capacitor. With respect to charging, the changes in shape are a result of ions in the Stern layer (i.e., ions at the electrode surface) having a higher electrostatic affinity to constant potential electrodes than to constant charge electrodes. For electrolyte polarizability, shape changes originate from induced dipoles that soften the interaction of Stern layer ions with the electrode. The softening is traced to ion correlations vertical to the electrode surface that induce dipoles that oppose double layer formation. In general, our analysis indicates an accuracy dependent differential capacitance profile that transitions from the characteristic camel shape with coarser representations to a more diffuse profile with finer representations.

Electrochemical transformation of DDT into new 2-(Bis(4-chlorophenyl)methylene) and 2-(Bis(4-chlorophenyl)methyl)phenanthro[9,10-d][1,3]dioxoles

Concomitant cathodic reduction of 9,10-phenanthrenequinone and 1,1,1-trichloro-2,2-bis(4-chlorophenyl) ethane (DDT), under constant potential conditions, led to new and interesting [1,3]dioxoles through two possible and simultaneous reaction pathways: (1) an electron-transfer from the quinone dianion to DDT molecules, and (2) electrogeneration of a carbene from DDT and further reaction with the 9,10-phenanthrenequinone dianion. Mechanism proposals are discussed.