Influence of halide anions on the behavior of pyridine adsorbed on Au(111) electrode

The effect of halide anions on pyridine-d₅ adsorbed on Au(111) electrode has been studied in neutral solutions containing F⁻, Cl⁻, and Br⁻ by IRAS and differential capacity measurement. In the NaF solution, N-bonded pyridine increases up to 0.1 V, and a new adsorbed state due to the N-bonded type grows at positive potentials. In the NaCl solution, the N-bonded type grows at all of adsorbed potential except for the appearance of the new adsorbed state at 0.2 V. In the NaBr containing solution, the new adsorbed state is not observed. In the NaCl and NaBr solutions, the total amount of the N-bonded pyridine is suppressed at positive potentials. We propose that the new band is attributed to an ordered layer of the N-bonded pyridine on the Au(111) electrode, and that the formation of the ordered layer is inhibited by the adsorption of Cl⁻ and Br⁻.     

Influence of halides on the dissolution and passivation behavior of AZ91D magnesium alloy in aqueous solutions

The electrochemical behavior of AZ91D in various aqueous sodium halide solutions was investigated using open-circuit potential (E_oc), potentiodynamic polarization and ac impedance (EIS) techniques. Generally, the results reveal that during immersion a protective layer of a salt film is formed on the alloy surface whose passivation performance depends on the halide nature, its concentration and temperature. E_oc shifts positively with time until attaining a steady (E_st) value, which becomes less noble with increasing concentration or temperature of the test solution. At any given conditions, self-passivation was found to be favored in the order F⁻ > I⁻ > Br⁻ > Cl⁻. This sequence is consistent with that for surface film resistance (R_T) and its relative thickness (1/C_T). Nevertheless, in F⁻ medium each of the above parameters increases with [F⁻] up to a critical value of 0.3 M then decreases. Increasing concentration above 0.3 M induces large change in the microstructure of the outermost layer of the fluorinated extremely protective film and depassivation behavior predominates. In Br⁻ and I⁻ solutions, as well as the lower Cl⁻ concentrations (≤0.01 M), AZ91D exhibits pseudo-passive state over the polarization range from the corrosion potential (E_corr) to the knee point (E_pt) in the anodic scan, at which passivity breakdown occurs with rapid increase in the anodic current and hydrogen gas reaction. At Cl⁻ concentrations >0.01 M the negative difference effect (NDE) occurs under cathodic polarization where E_pt lies negative to E_corr. Addition of F⁻ to the Cl⁻ solution can induce large changes in the behavior of AZ91D. Equal concentration addition (1:1) produces the highest propensity of the surface to form passivating layer that can afford better protection.     

Characteristics of thin-film nanofiltration membranes at various pH-values

Salt rejection and ion selectivity of NF-255 and NF-45 nanofiltration (NF) membranes were investigated. The rejection of two cations (Na⁺, Ca²⁺) and two anions (Cl⁻, SO_4²⁻) which are common in natural and in industrial wastewater, were studied as a function of pH at permanent pressure and temperature. The ion rejection of NF membranes were investigated in single salt solutions like NaCl, CaCl₂, Na₂SO₄, CaSO₄, and in multicomponent systems that contained all the previous ions. We found that, there is a minimum rejection of the Na⁺ and Cl⁻ ions between pH 4-5 in NF-255 and between pH 7-8 in NF-45. The rejection of calcium ions were increased in each case at lower pH in both membranes. However the pH value where the ion rejection behaviour of membranes changed, were different: pH 4 in NF-255 and pH 8 in NF-45. In NF-45 the chloride ion has negative rejection which depends on the quality of ions and the pH. We found that below pH values of 4 the selectivity of mono- and multivalent cations considerable increased in NF-255. This phenomena may be used for separation of calcium ions from sodium ions from weakly acidic (hydrochloric and sulfuric acid) solution, e.g. regeneration solution of sodium form softening ion exchangers.     

Salt rejection in nanofiltration for single and binary salt mixtures in view of sulphate removal

Three commercial membranes (NF70, NF90 and TFC-SR) were firstly characterized in terms of pure water flux and the rejection of uncharged (alcohols and sugars) compounds. Subsequently, the rejection of monovalent (sodium and chloride) and divalent (calcium and sulphate) ions in single (NaCl, CaCl, and Na₂SO₄) and binary (NaCI/Na₂,SO₄ CaCl₂/CaSO₄, NaCI/CaCl₂, and Na₂SO₄/CaSO₄) salt mixtures was studied. According to the pure water permeability the TFC-SR membrane is a loosely packed NF membrane (12.3 L.m ⁻².h⁻¹.bar⁻¹), while both NF70 and NF90 are tightly packed (2.6 and 3.6 Lm⁻².h⁻¹.bar-). According to the uncharged solute rejection, the MWCO_NF70 = 60, MWCO_NF90= 200 and MWCO_TFC-SR > 500. NF70 and NF90 were equally efficient in rejecting 1-2, 1-1 and 2-1 salts (>90%), while TFC-SR showed typical negatively charged surface behaviour, i.e., R (1-2) salt > R (11) salt > R (2-1). Sulphate rejection decreased in the presence of sodium chloride more significantly than in the presence of calcium chloride due to the more efficient retention of the bivalent calcium.     

Impact of pH on the removal of fluoride, nitrate and boron by nanofiltration/reverse osmosis

The objective of this study was to evaluate the impact of pH on boron, fluoride, and nitrate retention by comparing modelled speciation predictions with retention using six different nanofiltration (NF) and reverse osmosis (RO) membranes (BW30, ESPA4, NF90, TFC-S, UTC-60, and UTC-80A). Retention was explained with regard to speciation, membrane properties, and ion properties such as charge, hydrated size, and Gibbs energy of hydration. Flux was independent of pH, indicating that pH did not alter pore size and hence permeability for all membranes except UTC-60. Membrane charge (zeta potential) was strongly dependent on pH, as expected. Boron and fluoride retention depended on membrane type, pH, which correlated closely to contaminant speciation, and was due both to size and charge exclusion. While retention at low and neutral pH was a challenge for boron, high boron retention was achieved (> 70% above pH 11). Fluoride retention was generally > 70% above pH 7. Nitrate retention depended on membrane, and was mostly pH independent (as was the speciation). The presence of a background electrolyte matrix (20 mM NaCl and 1 mM NaHCO₃) reduced nitrate and boron retention (at high pH) due to charge shielding, and enhanced the retention of fluoride in single feed solutions, suggesting preferential transport of Cl⁻ compared to F⁻ with Na⁺.     

Separation performance of a nanofiltration membrane influenced by species and concentration of ions

Nanofiltration (NF), which has been largely developed over the past decade, is a promising technology for the treatment of organic and inorganic pollutants in surface and ground waters. The ESNA 1 membrane from the Nitto Denko Corporation of Japan is made of aromatic polyamide, which provides salt rejection from 50% to 90%. In this paper permeation experiments of aqueous solutions of five chlorides (NH₄Cl, NaCl, KCl, MgCl₂ and CaCl₂), three nitrates (NaNO₃, Mg(NO₃)₂ and Ca(NO₃)₂), and three sulfates (NH₄)₂SO₄, Na₂SO₄ and MgSO₄) were carried out. The effects of species and concentration of salts on the separation performance of the ESNA 1 membrane were investigated. The experimental results showed that the rejection to most salts by the ESNA 1 membrane decreased with the growth of the concentration. Then, the reflection coefficient and solute permeability of ESNA 1 membrane were calculated by the Spiegler-Kedem equation from experimental data. The reflection coefficients of the ESNA 1 membrane to salts are all above 0.95. The salt permeabilities, except for magnesium and calcium salts, increased with the growth of concentration. The sequence of rejection to anions by the ESNA 1 membrane is R(SO²⁻₄) > R(Cl⁻) > R(NO⁻₃) at the same concentration which ranges from 10 mol/m³ to 100 mol/m³. The sequence of rejection to anions by the ESNA 1 membrane can be written as follows: R(Na⁺) > R(K⁺) > R(Mg²⁺) > R(Ca²⁺) at 10 mol/m³ concentration and R(Mg²⁺) > R(Ca²⁺) > R(Na⁺) > R(K⁺) at 100 mol/m³ concentration.     

Elucidation of the effects of competitive adsorption of Cland Br ions on the initial stages of Pt surface oxidation by means of electrochemical nanogravimetry

At anodically polarized Pt electrodes in aqueous H₂SO₄ solution, Cl⁻ and Br⁻ ions are adsorbed competitively with the oxygen species that is deposited between 0.8 and 1.1 V, RHE, forming the initial stage of anodic oxide-film generation at Pt anodes. The Cl⁻ adsorption leads to selective and progressive blocking of the first 50% of coverage by O species at the Pt surface with increasing Cl⁻ concentration (commencing at 10⁻⁷ M) while relatively little effect is seen on the place-exchanged Pt/O→O/Pt lattice that is formed beyond 1.10 V, except at Cl⁻ concentrations greater than 10⁻¹ M, where evolution of Cl₂ commences and hence interferes. The states of co-adsorbed Cl and O-containing species, and their relative surface coverages, determine the nature of the electrocatalytic surface on which anodic Cl₂ evolution takes place. How this selective blocking behavior arises has not previously been well understood. In the present paper, complementary applications of the electrochemical quartz crystal nanobalance (EQCN) technique with cyclic voltammetry are brought to bear on this matter and provide new results at high levels of sensitivity and reproducibility which help to elucidate the competitive and selective chemisorption effects of Cl⁻ at Pt anodes. The results obtained with Cl⁻ ions exhibit some peculiarities which comparative experiments on Br⁻ adsorption help to rationalize.     

Electrode reactions of nickel(II) at mercury electrodes in aqueous solutions of pyridine at high ionic strengths

At high ionic strength the ion pair (NiPy²⁺₄, nX^?) or complex (NiPy₄X₂), n = 0, 1, 2; X^? = Cl^?, Br^?, SCN^?, N^?₃, F^?, NO^?₃, ClO^?₄; is adsorbed at the surface of mercury electrode. Under specified conditions in chloride, bromide, and thiocyanates solutions the electroreduction is preceded by a crystallization of a complex on the electrode surface. The inductive role of specifically coadsorbed Cl^? ions is discussed.     

The mechanism of electrode process in the system silver/silver cyanide complexes

The electrode's surface inhomogeneity was taken into account studying the mechanism of process. The effect of CN⁻ adsorption and partial surface coverage was investigated by electrochemical fast Fourier transform (FFT) impedance spectroscopy (0.03-3900 Hz). The isopotential solutions (E₀=−0.350 V) as well as solutions containing constant silver cyanide complex concentration (0.05 M) and different free cyanide ion concentrations (from 0.01 to 1.0 M) were studied. The exchange current density, re-calculated for only active area, gives electrochemical reaction order (R_CN=1.8 for α=0.5, and R_CN=2 for α=0.6) which is independent from CN⁻ concentration and from the composition of complexes prevailing in the bulk of electrolyte. The value of R_CN close to 2, obtained in a series of isopotential solutions confirms that in all cases the complex ions Ag(CN)₂⁻ take direct part in the charge transfer step.     

Uranyl Halide Species Sorbed on Ion Exchangers

Uranyl ions were sorbed on a cation and anion exchanger from fluoride, chloride, and bromide solutions. The visible and IR spectra of the sorbed species were recorded. The species identified were UO₂F^?₃, UO₂Cl⁺, UO₂Cl^?₃ and UO₂Cl^2?₄, UO₂Br⁺ and UO₂Br^2?₄. Analysis of the spectra obtained made possible the determination of the coordination number and the symmetry of the species, i.e., the cationic species have the coordination number six, while the anionic species have the coordination number four.     

Room temperature living cationic polymerization of styrene with HX-styrenic monomer adduct/FeCl3 systems in the presence of tetrabutylammonium halide and tetraalkylphosphonium bromide salts

Living cationic polymerization of styrene was achieved with a series of initiating systems consisting of a HX-styrenic monomer adduct (X = Br, Cl) and ferric chloride (FeCl₃) in conjunction with added salts such as tetrabutylammonium halides (nBu₄N⁺Y⁻; Y⁻ = Br⁻, Cl⁻, I⁻) or tetraalkylphosphonium bromides [nR′₄PBr; R′ = CH₃CH₂-, CH₃(CH₂)₂CH₂-, CH₃(CH₂)₆CH₂-] or tetraphenylphosphonium bromide [(C₆H₅)₄PBr] in dichloromethane (CH₂Cl₂) and in toluene. Comparison of the molecular weight distributions (MWDs) of the polystyrenes prepared at different temperatures (e.g., −25 °C, 0 °C and 25 °C) showed that the polymerization is better controlled at ambient temperature (25 °C). The polymerization was almost instantaneous (completed within 1 min) and quantitative (yield ∼100%) in CH₂Cl₂. In CH₂Cl₂, polystyrenes with moderately narrow (M_w/M_n ∼ 1.33-1.40) and broad (M_w/M_n ∼ 1.5-2.4) MWDs were obtained respectively with and without nBu₄N⁺Y⁻. However, in toluene, the MWDs of the polystyrenes obtained respectively with and without nBu₄N⁺Y⁻/nR′₄P⁺Br⁻ were moderately narrow (M_w/M_n = 1.33-1.5) and extremely narrow (M_w/M_n = 1.05-1.17). Livingness of this polymerization in CH₂Cl₂ was confirmed via monomer-addition experiment as well as from the study of molecular weights of obtained polystyrenes prepared simply by varying monomer to initiator ratio. A possible mechanistic pathway for this polymerization was suggested based on the results of the ¹H NMR spectroscopic analysis of the model reactions as well as the end group analysis of the obtained polymer.     

Variations in the crystalline deposits formed upon electrochemical oxidation of the anions, [Ir(CO)2X2] (X = Cl, Br, and I)

The electrochemical properties of the ions [Ir(CO)₂X₂]⁻ (X = Cl, Br, and I) have been studied in dichloromethane solutions using cyclic voltammetry, chronoamperometry, electrochemical quartz crystal microbalance (EQCM), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and infrared spectroscopy. For the chloro and bromo salts, the anion [Ir(CO)₂X₂]⁻ is oxidized initially to form [Ir(CO)₂X₂]⁺. The standard rate constants for the two-electron oxidations of [Ir(CO)₂X₂]⁻ are 7.8(±0.6) × 10⁻³ and 9.2(±0.9) × 10⁻⁴ cm s⁻¹ for the redox couples, [Ir(CO)₂Cl₂]^−/+ and [Ir(CO)₂Br₂]^−/+, respectively. The processes following electrolysis lead to the formation of two types of crystalline deposits on the electrode surface: needles and plates. The relative amounts of these solid phases that form depend mainly on the concentration of iridium complex in solution and on the time window of experiment. The strong intermetallic Ir-Ir interaction is responsible for the formation of the one-dimensional iridium complex chain. The crystal structures of the needle phases formed from [Ir(CO)₂Cl₂]⁻ and [Ir(CO)₂Br₂]⁻ are the same and belong to the space group Cmcm (no. 63). The stoichiometry of the one-dimensional crystals depends on the constitution of the supporting electrolyte: (TAA)_0.6[Ir(CO)₂Cl₂] and (TAA)_0.7[Ir(CO)₂Br₂] (TAA is tetra(alkyl)ammonium cation) salts are formed on the electrode surface. The formation of large three-dimensional crystal is responsible for the accumulation of electroactive materials on the electrode surface. The irreversible oxidation of [Ir(CO)₂I₂]⁻ leads only to the formation of large, plate-like crystals on the electrode surface, no needles are formed.     

Ab initio studies of complexation of anions to neutral species

The complexation of simple anions (F⁻ and Cl⁻) to different neutral species, anion-coordinating agents, has been studied using electronic structure calculations. The obtained changes in the equilibrium constants for salt dissolution reactions in different typical electrolyte systems are reported. In addition the lithium ion affinities of the obtained anionic complexes have been calculated. Using the present results we discuss strategies for future usage of anion complexing agents and make recommendations of salt and agent combinations for better lithium battery electrolyte performance.     

The Effects of Halide Anions on the Partitioning Behavior of Pertechnetate in Polyethylene Glycolbased Aqueous Biphasic Systems

Abstract

The pertechnetate anion quantitatively partitions to the upper polyethylene glycol (PEG)-rich phase in aqueous biphasic systems (ABS) formed by the addition of aqueous high-molecular-weight PEG solutions to aqueous water-structuring salt solutions. Most metal cations partition to the salt-rich phase in these systems. Other matrix ions, such as those that might be present in real-world waste streams, affect the distribution ratios observed for TcO₄ ^?, however, the effects are not well understood. The halide ions F^?, Cl^?, Br^?, I^? represent a wide range of water-structuring to chaotropic ions. The heavier halide ions have distribution ratios above one and are observed to follow the order D_I > D_Br > D_Cl. These ions depress D_Tc. Fluoride saltsout PEG and thus partitions primarily to the salt-rich phase and fluoride increases D_Tc. These trends can be correlated with the ions' Gibbs free energies of hydration (ΔG_hyd), a measure of their interactions with water. Based upon these results, it is possible to predict which ions will depress, elevate, or not affect D_Tc for a given PEG-ABS based upon the matrix ion's Δ G_hyd.     

Extended UNIQUAC model for correlation and prediction of vapor-liquid-liquid-solid equilibria in aqueous salt systems containing non-electrolytes. Part B. Alcohol (ethanol, propanols, butanols)-water-salt systems

The Extended UNIQUAC model for electrolyte solutions is an excess Gibbs energy function consisting of a Debye-Hückel term and a term corresponding to the UNIQUAC equation. For vapor-liquid equilibrium calculations, the fugacities of gas-phase components are calculated with the Soave-Redlich-Kwong equation of state. The model only requires binary, temperature-dependent interaction parameters. It has previously been used to describe the excess Gibbs energy for aqueous electrolyte mixtures and aqueous electrolyte systems containing methanol. It has been found to be an adequate model for representing solid-liquid-vapor equilibrium and thermal property data for strongly non-ideal systems. In this work, the model is extended to aqueous salt systems containing higher alcohols. The calculations are based on an extensive database consisting of salt solubility data, vapor liquid equilibrium data, and liquid-liquid equilibrium data for solvent mixtures and for mixed solvent-electrolyte systems.The application of this model to represent the vapor-liquid-liquid-solid equilibria in aqueous systems containing various non-electrolytes (ethanol, 1-propanol, 2-propanol, 1-butanol, 2- butanol, 2-methyl 1-propanol, 2-methyl 2-propanol) and various ions (Na⁺, K⁺, NH₄⁺, Cl⁻, NO₃⁻, SO₄²⁻, SO₃²⁻, HSO₃⁻, CO₃²⁻, and HCO₃⁻) shows the capability of the model to accurately represent the phase behavior of these kinds of systems.     

Evaluation and origins of the difference between double-layer capacitance behaviour at Au-metal and oxidized Au surfaces

In studies of processes at oxidized compared with unoxidized electrode surfaces by transient methods corrections for double-layer charging are usually required and have often been made by extrapolation of double-layer capacitance (C_dl) data for the metallic surface, e.g. at Au or Pt, into the potential region of oxide-film formation. Voltammetry and impedance spectroscopy provide direct information on C_dl values determined at unoxidized, i.e. metallic, Au surfaces compared with those of anodic oxide films generated potentiostatically to various extents that are stable in time, and characterized by reductive linear-sweep voltammetry. C_dl is derived from constant-phase element (CPE) values and the CPE parameter, ?, which is near unity for most conditions. At oxidized Au surfaces C_dl depends on potential for various extents of oxide formation; it increases from 15 (±1) μF cm⁻² at 1.75 V (RHE) to 25 (±1) μF cm⁻² at 1.45 V (RHE) and is independent of added Cl⁻ or Br⁻ for concentrations 0-10⁻³ M of both anions, while, at unoxidized Au electrodes in the absence of halide anions, C_dl has a maximum value of 60 (±2) μF cm⁻² at 0.80 V (RHE) and is now dependent on concentration of added Cl⁻ or Br⁻ ion. These major differences of C_dl for the oxidized and unoxidized Au surfaces indicate that double-layer charging corrections cannot be made simply by extrapolation of C_dl data for unoxidized Au metal surfaces into the potential region for oxide formation.     

CO2 attraction by specifically adsorbed anions and subsequent accelerated electrochemical reduction

The electrochemical reduction of CO₂ was studied on a copper mesh electrode in aqueous solutions containing 3 M solutions of KCl, KBr and KI as the electrolytes in a two and three phase configurations. Electrochemical experiments were carried out in a laboratory-made, divided H-type cell. The working electrode was a copper mesh, while the counter and reference electrodes were Pt wire and Ag/AgCl electrode, respectively. Results of our work suggest a reaction mechanism for the electrochemical reduction of CO₂ in the two phase configuration where the presence of Cu-X as the catalytic layer facilitates the electron transfer from the electrode to CO₂. Electron-transfer to CO₂ may occur via the X_ad⁻(Br⁻, Cl⁻, I⁻)-C bond, which is formed by the electron flow from the specifically adsorbed halide anion to the vacant orbital of CO₂. The stronger the adsorption of the halide anion to the electrode, the more strongly CO₂ is restrained, resulting in higher CO₂ reduction current. Furthermore, it is suggested that specifically adsorbed halide anions could suppress the adsorption of protons, leading to a higher hydrogen overvoltage. These effects may synergistically mitigate the overpotential necessary for CO₂ reduction, and thus increase the rate of electrochemical CO₂ reduction.     

Electrochemical characteristics of LSCF-SDC composite cathode for intermediate temperature SOFC

A kind of composite cathode, La_0.58Sr_0.4Co_0.2Fe_0.8O_3−δ-Ce_0.8Sm_0.2O_2−δ (LSCF-SDC), was presented in this paper. The electrochemical performance of the cathode on the electrolyte of SDC and YSZ coated with a thin SDC (YSZ/SDC) layer was studied by electrochemical impedance spectroscopy (EIS) and cathodic polarization techniques for their potential utilization in the intermediate temperature solid oxide fuel cell (IT-SOFC). Also studied was the relationship between the electro-catalytic characteristics and the electrode microstructure. Results showed that the LSCF-SDC composite electrode performed better on the SDC electrolyte than on the electrolyte of YSZ/SDC. The polarization resistance, R_p, of the cathode on the SDC electrolyte was 0.23 Ω cm² at 700 °C and 0.067 Ω cm² at 750 °C, much lower than the corresponding R_p of the same cathode on the YSZ/SDC electrolyte. At 750 °C, the cathodic overpotential of the composite cathode on the SDC electrolyte was 99.7 mV at the current density of 1.0 A cm⁻².     

Role of Cl in breakdown of Cu-Ag alloys passivity in aqueous carbonate solutions

The electrochemical behaviour of two Cu-Ag alloys was studied in 0.1 M Na₂CO₃ solution containing different concentrations of Cl⁻ ions using linear polarization and current/time transients under the effect of different variables of Cl⁻ ions concentration, scan rate and applied anodic potentials. In Cl⁻ free solutions, the anodic voltammogram consists of two potential regions I and II. The potential region I exhibits three anodic peaks A₁, A₂ and A₃ that correspond to the formation of Cu₂O, Cu(OH)₂ and CuO, respectively. The potential region II exhibited four anodic peaks A₄, A₅, A₆ and A₇ due to the formation of AgO⁻, Ag₂O, Ag₂CO₃ and Ag₂O₂. In the presence of Cl⁻ ions, the anodic voltammograms depends considerable on the concentration of Cl⁻ ions. Increasing the amounts of Cl⁻ ions up the 0.02 M (alloy I) or 0.006 M (alloy II) the heights of all the anodic peaks were decreased and their peak potentials were shifted to less negative values. The existence of pitting was confirmed by SEM micrograph. The pitting potential E_pit was shifted towards more active potential values as the concentration of Cl⁻ ions in the solution was increased. When the scan rate is high, initiation of the pitting can be noticed only at more positive potentials, corresponding to a sufficiently short pit incubation time. The potentiostatic current/time transients show that the incubation time decreases with increasing the applied anodic potential and the Cl⁻ ion concentration and the pitting corrosion can be described in terms of instantaneous three-dimensional growth under diffusion control.     

Study by EQCM on the voltammetric electrogeneration of poly(neutral red). The effect of the pH and the nature of cations and anions on the electrochemistry of the films

Generation of poly(neutral red) films has been studied by means of the simultaneous measurements of current-potential and mass-potential curves during cyclic voltammetry (CV) experiments. It has been proved that the presence of molecular oxygen in the solution increases the amount of polymer deposited on the electrode. Otherwise, using the mass/charge ratio it is possible to obtain quantitative information about the electrodeposition by different procedures. It is observed that this ratio decreases when the amount of polymer electrogenerated increases, except when the polymer is not reduced and oxidised after its electrogeneration. The study of poly(neutral red) by CV and quartz crystal microbalance in solutions without monomer allows to discern between the role of different charged species which are present in the solution: salt cations (Cs⁺, Na⁺ and K⁺), salt anions (NO₃⁻, Cl⁻, I⁻ and Br⁻) and hydrated protons that can compensate electrical charge within the film during electrochemical processes.