Evolution of the Bromate Electrolyte Composition in the Course of Its Electroreduction inside a Membrane-Electrode Assembly with a Proton-Exchange Membrane.

The passage of cathodic current through the acidized aqueous bromate solution (catholyte) leads to a negative shift of the average oxidation degree of Br atoms. It means a distribution of Br-containing species in various oxidation states between -1 and +5, which are mutually transformed via numerous protonation/deprotonation, chemical, and redox/electrochemical steps. This process is also accompanied by the change in the proton (H) concentration, both due to the participation of H ions in these steps and due to the H flux through the cation-exchange membrane separating the cathodic and anodic compartments.

A Hydrogen-Bromate Flow Battery as a Rechargeable Chemical Power Source.

The hydrogen-bromate flow battery represents one of the promising variants for hybrid power sources. Its membrane-electrode assembly (MEA) combines a hydrogen gas diffusion anode and a porous flow-through cathode where bromate reduction takes place from its acidized aqueous solution: BrO3− + 6 H+ + 6 e− = Br− + 3 H2O (*). The process of electric current generation occurs on the basis of the overall reaction: 3 H2 + BrO3− = Br− + 3 H2O (**), which has been studied in previous publications.

Current Distribution in the Discharge Unit of a 10-Cell Vanadium Redox Flow Battery: Comparison of the Computational Model with Experiment.

Shunting currents are among the main problems of all-vanadium redox flow battery stacks since, in addition to capacity losses, they cause negative effects associated with the local destruction of electrodes and bipolar plates. The values of both the shunting currents and their destructive effects on materials can be reduced at the battery development stage by adjusting the resistance of the electrolyte supply channels. The solution to this problem can be found using a calculation model for current distribution based on the current balance in the nodes as well as voltage drops and electromotive force in internal circuits according to Kirchhoff's laws.

Electrochemical Measurement of Interfacial Distribution and Diffusion Coefficients of Electroactive Species for Ion-Exchange Membranes: Application to Br/Br Redox Couple.

A novel method has been proposed for rapid determination of principal transmembrane transport parameters for solute electroactive co-ions/molecules, in relation to the crossover problem in power sources. It is based on direct measurements of current for the electrode, separated from solution by an ion-exchange membrane, under voltammetric and chronoamperometric regimes. An electroactive reagent is initially distributed within the membrane/solution space under equilibrium.

Analysis of the Composition of Bromide Anion Oxidation Products in Aqueous Solutions with Different pH via Rotating Ring-Disk Electrode Method.

We measured the ring collection coefficient of bromide anion oxidation products in a neutral and slightly alkaline medium on a rotating ring-disk electrode (glassy carbon disk, platinum ring) varying the following parameters: disk electrode rotation velocity, sodium bromide concentration, pH of the medium (in the range of 6−12), anode current on the disk, and the electroreduction potential of the bromide anion oxidation products on the ring. The data obtained are presented via dependences of the cathode ring current on the disk current ratio vs. the ring electrode potential.

Hydrogen-Chlorate Electric Power Source: Feasibility of the Device, Discharge Characteristics and Modes of Operation.

A power source based on the current-generating reaction of aqueous chlorate-to-chloride reduction by molecular hydrogen would provide as much as 1150 Wh per 1 L of reagent storage (for a combination of 700 atm compressed hydrogen and saturated aqueous solution of lithium chlorate) at room temperature, but direct electroreduction of chlorate only proceeds with unacceptably high overvoltages, even for the most catalytically active electrodes. In the present study, we experimentally demonstrated that this process can be performed via redox-mediator catalysis by intermediate products of chlorate reduction, owing to their participation in homogeneous com- and disproportionation reactions. A series of current-voltage and discharge characteristics were measured for hydrogen-chlorate membrane-electrode assembly (MEA) cells at various concentrations of chlorate and sulfuric acid under operando spectrophotometric monitoring of the electrolyte composition during the discharge.

Electrolyte Flow Field Variation: A Cell for Testing and Optimization of Membrane Electrode Assembly for Vanadium Redox Flow Batteries.

A great deal of research has been dedicated to improving the performance of vanadium redox flow battery (VRFB). In this work, we propose the design of a cell for testing membrane electrode assembly of VRFB, which enables the optimization of the flow field, conditions of charge-discharge tests, and the nature of components (electrodes, membrane) with minimal time and material expenses. The essence of the proposed cell is that the system of channels distributing the electrolyte is made by cutting shaped holes in the sheets of graphite foil (GF).

Mixed solutions of silver cation and chloride anion in acetonitrile: voltammetric and EQCM study.

Electrochemical behavior of Pt and Au electrodes in acetonitrile solutions at different concentration ratios of Cl(-) and Ag(+) ions was studied by cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM). The composition of the mixed silver chloride solutions, i.e.

Electrochemical and spectral properties of ferrocene (Fc) in ionic liquid: 1-butyl-3-methylimidazolium triflimide, [BMIM][NTf(2)]. Concentration effects.

Several earlier studies of the electrochemical oxidation of ferrocene (Fc) in room-temperature ionic liquids revealed an essentially nonlinear dependence of the oxidation current on the Fc concentration in its relatively dilute solutions, with its formally calculated diffusion coefficient strongly increasing with the concentration. Since no plausible mechanism leading to this very unusual finding had been proposed, our study of Fc solutions in 1-butyl-3-methylimidazolium triflimide, [BMIM][NTf(2)], was performed to verify whether the above observation originated from an incorrect determination of the dissolved Fc concentration. Our observations have demonstrated that reliable control of the Fc concentration in solution is complicated by factors such as the low amount of Fc used to prepare small-volume solutions or the great difficulty to dissolve completely a solid powder in a solvent with an extremely high viscosity.

Metallocene-containing conjugated polymers.

The paper gives a review of publications on polymers with conjugated matrices (PPy, PTh, PAni, hydrocarbon or mixed chains...