The charging/discharging cyclic process in a hydrogen–bromine battery is studied. Porous titanium felt with IrO2–TiO2-mixed-oxide coating in contact with aqueous HBr/Br2 solution is used as positive electrode (the cathode). A hydrogen gas-diffusion electrode with Pt–C catalytic layer served as negative electrode. The hydrogen ion is transferred between the electrodes through a GP-IEM 103 perfluorinated sulfocation-exchange membrane. The morphology, phase, and chemical composition of the cathode material are characterized using scanning electron microscopy with X-ray spectral microanalysis, Raman spectroscopy, and X-ray photoelectron spectroscopy. The condition for switching between the charging and discharging stages within each cycle (the voltage upper limit) is so chosen as to minimize the amount of bromide and polybromide anions relative to the molecular bromine formed at the end of the charging stage (oxidation of Br–), instead of the traditionally used approach which includes only partial conversion of bromide to bromine, in order to increase the stability of the latter in the form of polybromide complexes. Charge–diacharge tests of the hydrogen–bromine battery are carried out in the galvanostatic mode at three current densities: 25, 50, and 75 mA/cm2. Comparison of the charge and average voltage values in the course of the electrical energy generation (the discharge stage) and storage (the charge stage) shows that the highest efficiency of the cycle is achieved at the current density of 50 mA/cm2. This value of the charging/discharging current density also corresponds to the maximal utilization of the electrolyte redox-capacity. The stability of the mixed-oxide cathode material used in contact with bromine compounds in acidic environment is found to exceed significantly that of the carbon paper. The principal reason of the decrease of the battery capacity from cycle to cycle is the molecular bromine absorption by elements of the system contacting the catholyte: components of the membrane–electrode assembly, pipelines, and elements of the pump that ensures the circulation.

Chronoamperometry and steady-state voltammetry data for a specially designed working electrode composed of a Pt disk covered mechanically with various perfluorinated cation-exchange membranes in contact with an external 2 M sulfuric acid solution with addition of various NaBr concentrations have been employed to estimate crossover parameters of bromide ions in relation to redox-flow battery applications. This technically simple but efficient approach has allowed us to determine the values of the diffusion coefficient of the electroactive Br-co-ion inside each membrane and of its equilibrium distribution coefficient between the membrane and the outer solution via an express experimental procedure and subsequent simple calculations. These crossover parameters of bromide co-ions have been found for Nafion NR211, Nafion XL, Nafion NR212, Nafion N115, Nafion N117 as well as GP-IEM-103, GP-IEM-105 membranes. Correlation of the steady-state diffusion-limited current due to the bromide oxidation both with its concentration in the outer solution and with the membrane thickness has been analyzed. It has been established that the transport characteristics of the bromide anion are close to each other for all homogeneous membranes under study in contact with a mixed X M NaBr +2 M H2SO4 solution (the value of X varies between 0.125 and 0.75): their values belong to the range from 2.6 10-6 cm2 s-1 to 3.4 10-6 cm2 s-1 for its diffusion coefficient inside membrane and to the range from 0.13 to 0.18 for its distribution coefficient at the membrane/solution boundary. Compared to the homogeneous membranes, the Br-anion diffusion inside the heterogenous (Nafion XL) membrane is slower and there is a tendency to its accumulation to a larger amount. Comparison of these results for Nafion NR212 in contact with the NaBr+H2SO4 solution with those previously obtained for the same membrane in contact with the HBr + H2SO4 solution has allowed us to conclude that the applied approximate treatment of experimental data based on the theory of molecular-diffusion transport of this co-ion inside the membrane (without taking into account the migration contribution to the bromide flux owing to the suppression of the electric field by highly mobile H+ cations) remains applicable for systems where the NaBr concentration inside the external solution does not exceed 0. 75 M.

Determining the vanadium content and the average degree of oxidation of vanadium ions in an electrolyte is a highly important task, both in the production and operation of vanadium flow batteries and in scientific research aimed at improving the performance characteristics of electrolytes throughout their entire life cycle. This article proposes a solution to this issue using the coulometric analysis of electrolyte samples circulating through a cell with a membrane-electrode unit consisting of a gas diffusion hydrogen electrode, a proton exchange membrane, and a liquid flow electrode. The coulometric analysis involves the oxidation of the sample to the highest degree of vanadium oxidation with further reduction to an oxidation state of +4. The parameters of the procedure (polarization modes and completion conditions) were chosen in order to minimize the relative error in determining the concentration of vanadium up to 5% and the average degree of oxidation up to 2% based on model composition electrolytes with different concentrations and degrees of vanadium oxidation, including sulfuric acid, as well as mixed acid (H2SO4 + HCl) compositions

In the context of chlorate’s application as a cathodic reagent of power sources, the mechanism of its electroreduction has been studied in electrochemical cells under diffusion-limited current conditions with operando spectrophotometric analysis. Prior to electrolysis, the electrolyte is represented as an aqueous mixed NaClO3 + H2SO4 solution (both components being non-electroactive within the potential range under study), without addition of any external electroactive catalyst. In the course of potentiostatic electrolysis, both the cathodic current and the ClO2 concentration demonstrate a temporal evolution clearly pointing to an autocatalytic mechanism of the process (regions of quasi-exponential growth and of rapid diminution, separated by a narrow maximum). It has been substantiated that its kinetic mechanism includes only one electrochemical step (chlorine dioxide reduction), coupled with two chemical steps inside the solution phase: comproportionation of chlorate anion and chlorous acid, as well as chlorous acid disproportionation via two parallel routes. The corresponding set of kinetic equations for the concentrations of Cl-containing solute components (ClO3−, ClO2, HClO2, and Cl−) has been solved numerically in a dimensionless form. Optimal values of the kinetic parameters have been determined via a fitting procedure with the use of non-stationary experimental data for the ClO2 concentration and for the current, taking into account the available information from the literature on the parameters of the chlorous acid disproportionation process. Predictions of the proposed kinetic mechanism agree quantitatively with these experimental data for both quantities within the whole time range, including the three characteristic regions: rapid increase, vicinity of the maximum, and rapid decrease.

The first covalently linked dimer has been prepared for cyclazine systems by regioselective oxidative homocoupling of 1,2-dicarbomethoxy-3-phenylcycl[3.2.2]azine. The regioselectivity of this reaction at 4-position, having been confirmed by X-ray diffraction analysis and NMR spectroscopy, has been also reliably predicted within the model of average local ionization energy on the molecular surface of the starting monomer at the BP86/def2-TZVP level of theory. Due to the planar it-it interaction of the cycl[3.2.2]azine subunits, the dimer is a green fluorophore (tem = 527 nm, toluene), characterized by a bathochromic shift of the main bands in the UV-vis and fluorescence spectra relative to the monomer by 41 and 71 nm, respectively. Furthermore, the dimer demonstrates an increased fluorescence quantum yield relative to the monomer (55 % vs. 35 % in toluene), and according to the data of X-ray diffraction analysis, DFT calculations and variable temperature 1D and 2D 1H NMR spectroscopy, is characterized by hindered rotation of the S1-state-involved cycl[3.2.2]azine cores along the C4-C4 ' bond axis. Such prerequisites determine good application potential of the 4-4 ' coupled cycl[3.2.2]azine derivatives as turn-on fluorescent, i.e. fluorogenic probes for advanced bioimaging in living systems. Finally, unlike the monomer, the dimer shows reversibility of both one- and two-electron reduction and oxidation processes, and therefore can become the basis of both n- and p-type semiconductors.

Here, we analyzed the performance of a hydrogen/bromate fuel cell (HBFC) operating in batch recirculation mode. We adjusted the catholyte composition and operating conditions to ensure stable cell discharging and prevent the formation of liquid bromine. To achieve this, we analyzed the evolution of bromate catholytes with different acid content using thermodynamic calculations, which considered equilibria between bromine compounds and material balance for protons. We used the results of these calculations and data on catholyte chemical stability to select compositions appropriate for HBFC testing. To obtain data on catholyte evolution, we employed novel spectrophotometric and electrochemical in situ/operando techniques. Our study revealed that the composition of the catholyte and its average oxidation state, as well as the interplay between chemical and electrochemical reactions, significantly impact the power output of the HBFC. The main practical finding of our study is that under optimized conditions, the HBFC demonstrated both high energy density and reasonable performance. For instance, with a catholyte composition of 1 M LiBrO3 3 and 0.3 M H2SO4, 2 SO 4 , energy density is 116 Wh L- 1 (theoretical 1270 Wh L- 1 for 5.5 M LiBrO3) 3 ) the cell operated with 98.7% capacity utilization and power of 194 mW cm- 2 at 250 mA cm-- 2 .

An enormous amount of energy is wasted annually in the form of low-grade heat with a temperature below 100 degrees C. Recently, studies on heat harvesting have focused on semiconductor-based devices, but nowadays, electrochemical devices based on a thermally regenerative cycle (TREC) are growing in importance due to their superior thermoelectric power. Among them, TRECs based on flow batteries (TREC-FB) are especially attractive since they offer more flexibility for heat harvesting and an opportunity for continuous heat-to-power (HTP) conversion. However, this technology struggles due to the high cost of the flow batteries they are based on, particularly the costly electrolyte solutions. We offer a novel approach for continuous heat harvesting based on the emerging technology of the neutralization flow battery (NFB) with low-cost and highly soluble electrolytes, which consists of two hydrogen electrodes immersed in acid and base solutions. Since values of both electrodes' temperature coefficient differ, NFB can be used for heat harvesting: the cell temperature coefficient varies in the range of 0.64-1.1 mV K 1. Here, we present both intermittent and continuous TREC based on NFB, with a focus on the latter due to its convenience. Our study on continuous heat harvesting shows that for a temperature difference between the heat source and heat sink of 25 degrees C, one can achieve power of 10-24 mu W cm 2, and efficiency of 1.4-2.9 % even without any recuperation. Alternatively, increasing the temperature difference to 55 degrees C results in a 6-fold increase in power at 1.6-3.5 % efficiency. We found that due to the low freezing point of the electrolytes, one can obtain even higher HTP performance if the heat sink temperature is about 0 degrees C. Additionally, we examined NFB performance under various temperatures and proposed low-grade heat harnessing using intermittent NFB heating/cooling to enhance its cycling performance. We believe that the proposed approaches facilitate further development of high-performance TREC-FB and thereby extend the possibilities for heat harvesting.

A comparative study of the electrochemical behavior of various forms of the antitumor antibiotic doxorubicin (DOX) - free and encapsulated in micelle-like nanoparticles of the biocompatible amphiphilic copolymer N-vinylpyrrolidone (VP) — methacrylic acid — triethylene glycol dimethacrylate (TEGDM) — in aqueous neutral buffer solutions on a glassy carbon electrode was carried out. The hydrodynamic radii of the Rh copolymer and DOX polymer nanostructures were determined using the dynamic light scattering method. It was demonstrated using cyclic and square wave voltammetry the presence of two main redox transitions for both forms of DOX at pH 7.24: irreversible oxidation/reduction in the potential range from 0.2 to 0.6 V and reversible reduction/reoxidation — from −0.4 to −0.7 V (saturated Ag/AgCl reference electrode), and their redox potentials were determined. The difference in the potentials of the corresponding peaks of both redox transitions does not exceed several tens (20–30) mV, while the oxidation of the encapsulated form is easier than the free one, and reduction is somewhat more difficult. Analysis of the dependence of the reduction current of both forms of DOX on the rate of potential sweep shows that electron transfer to a molecule of free DOX is largely determined by the rate of accumulation of the reagent in the adsorption layer, and the encapsulated form is characterized by mixed adsorption-diffusion control. Based on voltammetric data and the results of quantum chemical modeling, it was concluded that a hydrogen bond is formed between the oxygen-containing groups of the monomer units of the copolymer and the H-atoms OH and NH2 groups of DOX. The bond energies in the structures considered are calculated and it is shown that their values are close to classical ones if the carbonyl group of the lactam ring of VP in the encapsulating polymer is an electron donor, and the hydrogens OH and NH2 groups of DOX are acceptors. At the same time, the bonds formed with the participation of the oxygen atom of the ester group of the TEGDM unit are extremely weak.

A comparative study of the electrochemical behavior of various forms of the antitumor antibiotic doxorubicin (DOX), both free and encapsulated in micelle-like nanoparticles of the biocompatible amphiphilic copolymer of N-vinylpyrrolidone (VP) and methacrylic acid, viz., triethylene glycol dimethacrylate (TEGDM), is carried out in aqueous neutral buffers on a glassy carbon electrode. The hydrodynamic radii Rh of the copolymer and the DOX polymeric nanostructures are determined using dynamic light scattering. Using cyclic and square wave voltammetry, for both forms of DOX at pH 7.24, the two main redox transitions are revealed namely, the irreversible oxidation/rereduction in the potential interval from 0.2 to 0.6 V and the reversible reduction/reoxidation in the interval from –0.4 to –0.7 V (vs. saturated Ag/AgCl), and their redox potentials are determined. For both redox transitions, the potential difference between the corresponding peaks does not exceed several tens (20–30) mV; and, moreover, the oxidation of the encapsulated form proceeds easier as compared with the free form, whereas its reduction is somewhat more difficult. The analysis of the dependence of the reduction current of both DOX forms on the potential scan rate shows that the electron transfer to a free DOX molecule is largely determined by the rate of reagent accumulation in the adsorption layer, whereas the electron transfer to the encapsulated form is characterized by the mixed adsorption-diffusion control. Based on voltammetric data and the results of quantum chemical modeling, it is concluded that a hydrogen bond is formed between the oxygen-containing groups of copolymer’s monomeric units and the H atoms in OH and NH2 groups of DOX. The bond energy in these structures is calculated and shown to be close to the classical values, assuming that the carbonyl group in the VP lactam ring in the encapsulating polymer is the electron donor, and the hydrogen atoms in OH and NH2 groups of DOX are the electron acceptors. At the same time, the bonds involving oxygen of the ester group in the TEGDM unit are extremely weak.

In this work, we aimed to reveal two main contributors to the capacity fade of a vanadium redox flow battery (VRFB). These contributors are the oxidative imbalance caused by the hydrogen evolution reaction (HER) competing with V3+ reduction during charging, and crossover, particularly the net transfer of vanadium ions from negolyte to posolyte. To investigate this, we performed VRFB cycling under various operation conditions with sequential monitoring of the electrolytes composition. We discovered that shortly after cycling starts, the crossover makes the negolyte capacity-limiting. This leads to high polarization of the negative electrode inducing HER and increasing average oxidation state (AOS) of the electrolyte. Our examination shows that the magnitude of the oxidative imbalance correlates with that of the crossover, both being dependent on the state-of-charge (SoC). Therefore, by changing operation conditions, we can slightly influence the crossover, while dramatically affect the oxidative imbalance. We also found that the resulting magnitude of the capacity fade is a trade-off between these two side-processes. This necessitates careful optimization of the battery and electrolyte composition, along with its cycling regime. From the data obtained, we conclude that the only proper approach to achieve lower capacity fade is by ensuring that the negolyte is capacity-limiting over long-term cycling. We hope that the data on the capacity fade mechanisms presented here will facilitate development of more stable and cost-effective VRFBs.

Hybrid flow chemical power source (Pt–C)H2|Nafion|VO2+(C) in which the membrane–electrode assembly combines gas-diffusion anode of hydrogen–air fuel cell and cathode of vanadium redox flow battery is studied. Concept of such a hydrogen–vanadium flow battery had been proposed earlier (2013) as an alternative to the vanadium redox flow battery, also designed for large-scale electrical energy storage but its practical implementation has so far been limited to single cells having the active area within several tens of cm2. The goal of this work is the establishing of the factors limiting the discharge power density of such hybrid. hydrogen–vanadium flow battery cells which is inferior to both hydrogen–air fuel cell and vanadium redox flow batteries, even though the hydrogen–vanadium flow battery cell represents a combination of their more reversible half-cells. The object of the study is a cell with a 2 × 2 cm membrane–electrode assembly equipped with Luggin capillary on the vanadium electrolyte side. Measurements of the current–voltage characteristics of the entire cell, as well as the polarization characteristics of its half-cells, are performed using a six-electrode scheme of the cell connection with varied vanadium electrolyte circulation rate and different cathode materials (carbon felts, 4.6 or 2.5 mm thick, as well as carbon paper). The contribution of the hydrogen gas diffusion electrode to the total dc resistance of the hydrogen–vanadium flow battery cell is shown being twice that of the flow-through vanadium cathode. A record high discharge power density has been achieved: 0.75 W cm–2, for the cell based on the commercially available material, Sigracell GFD 2.5 EA-TA carbon felt as the cathode material, without its special surface modification.

The first examples of planar binuclear phthalocyanines sharing a common carbazole unit were obtained using indirect and direct mixed cyclization approaches. The synthetic route to the starting 9-benzylcarbazole-2,3,6,7-tetranitrile was reconsidered and literature conditions were successfully optimized. In addition to the binuclear complex, a low-symmetry A3B phthalocyanine with free cyano groups was isolated and identified. Accurate assignment of absorption bands in the UV-Vis spectra was performed using magnetic circular dichroism and simplified TD-DFT calculations. The target binuclear complexes demonstrate the ability of singlet oxygen generation, with Phi(Delta) values reaching 0.15 for the tert-butyl-substituted compound. The products of photodegradation were studied using mass spectrometry and UV-Vis spectroscopy. Electrochemical and spectroelectrochemical studies showed a gradual oxidation of the macrocycle, accompanied by the interruption of an extended binuclear p-system.

Quantum chemical approach has been applied for modeling the change in the conformation of the polypyrrole (PPy) chain both in its neutral and positively charged (doped) states due to its interaction with incorporated counterions. Polymer has been modeled by oligopyrrole molecule of 9-15 monomer units. It is shown that it is energetically favorable to reorient the pyrrole rings closest to the anion from trans to cis position. This reorientation leads to the formation of meanders which include 3-5 pyrrole rings per loop. Reduction in the loop size decreases the energy of interaction with the ion while an increase in the loop size reduces the number of attached ionic species accompanied by a slight change in their interaction energy with the PPy chain. The observed effect of polymer chain structuring in the presence of anions is proposed as a possible reason explaining the experimentally recorded broadening of the electroactivity potential region and the conductive state of the polypyrrole film on the electrode surface as a result of multiple repetitions of charge/discharge cycles of the polymer chain. Vibrational spectra of oligopyrrole complexes have been calculated, and prospects for experimental detection of predicted conformational states by IR spectroscopy are assessed.

A series of 5,7-disubstituted 1,4-diazepinoporphyrazinato magnesium(II) and nickel(II) complexes, including two novel compounds, were obtained by metal-templated macrocyclization. A combination of X-ray diffraction, 1H NMR, UV-vis, and electrochemical analyses allowed us to study their tendency towards H-type dimerization and trace the influence of structural and solvation factors on dimer stability. Based on the physicochemical and theoretical DFT calculation data, it was found that the main binding forces between 6H-1,4-diazepinoporphyrazine decks in the dimers were efficient π-π donor-acceptor interactions induced by the interdeck C-H⋯N hydrogen bonds. Furthermore, the metal-ligand (Pz2- → M2+) electronic interactions have a key influence on the π-π stacking of the porphyrazine cores. It was shown that the displacement of the metal ion out of the macrocycle plane induced by coordinating agents can trigger the dissociation of the dimer, since the resulting enhancement of the donor-acceptor electronic interaction between the metal ion and the π-system of the ligand leads to a subsequent weakening of the π-π stacking of the porphyrazine cores. The TD-DFT calculations predicted the non-degeneracy of the HOMO-1 → LUMO and HOMO → LUMO+1 transitions in the 6H-1,4-diazepinoporphyrazine H-dimers, which explains the Q-band splitting in their UV-vis spectra.

A covalently-bonded structure (triad PP-PDI-PP) based on pyropheophorbide dye (PP, chlorin e6 derivative) and an organic non-fullerene acceptor, perylenediimide derivative (PDI), has been obtained. The triad has a pronounced absorption in the red region of the spectrum. Compared to the native dye, the obtained triad shows partial fluorescence quenching, and its singlet oxygen generation efficiency upon red light irradiation decreases by five times. At the same time, this triad, solubilized in water by polyvinylpyrrolidone, generates superoxide anion-radical three times more efficiently than the native dye. The demonstrated results show the promising potential of such perylene-dye structures as type I photosensitizers for photodynamic therapy.

It is necessary for vanadium redox flow battery (VRFB) to become more cost-effective due to long-term stable operation with minimal life-cycle maintenance for its further development. Despite the absence of self-discharge in idle mode, the available capacity of VRFB gradually decreases during the battery cycling. The capacity decrease is attributed to side reactions appearance, which increase the average oxidation state (AOS) of vana-dium electrolyte. This negative effect can be minimized by periodic electrolyte capacity recovery. However, it is crucial to have reliable information on the electrolytes composition to conduct rebalancing efficiently and timely. Various methods for vanadium electrolyte assessment have been previously proposed, however, none of them can be used coupled with industrial VRFBs. In this work, we present an operando coulometric analysis of an electrolyte sample in a VRFB cell and its subsequent return to the bulk solution. The proposed approach out-performs other methods due to sensitivity of the signal to the overall vanadium content and AOS and stable performance under imbalance conditions. The analysis of AOS was verified by three methods - coulomb -counting, ex-situ spectrophotometry, and coulometry. Therefore, this method can be successfully used not only in lab-scale VRFB studies, but can also be coupled with industrial VRFB stacks.

The development of experimental methods for rapid evaluation of electroactive components’ crossover parameters in electrolyte solutions separated by membrane is an actual problem in the development of membrane electrode assemblies of redox flow batteries and other chemical power sources. A novel method has been proposed which is based on direct measurement of the electroactive component diffusion flux density through membrane under chronoamperometric regime after applying a potential step of selected amplitude. To this purpose, the membrane under study is pressed up toward the surface of the working electrode with the use of an originally designed device. By combination of the expressions for the diffusion flux through the membrane under steady-state and non-steady-state conditions, relations are derived that allow determining the diffusion coefficient of the studied component inside the membrane and its distribution constant at the membrane/solution interface by using experimental data of the chronoamperometric measurements. The proposed method is applied to estimate the parameters for bromide-anion transport through sulfonic cation-exchange membrane in contact with sulfuric acid solution added with hydrobromic acid for a set of the latter’s concentrations. For the HBr concentration range from 0.125 to 0.75 M, the values of the diffusion coefficient of the bromide-anion inside membrane and of its distribution constant at the membrane/solution interface are obtained: (3.3 ± 0.2) × 10–6 cm2/s and 0.18 ± 0.2, respectively. They well agree with the results obtained by means of longer and more laborious measurements.

First studies on electrochemical devices converting chemical energy of neutralization into electricity – neutralization (or acid-base) flow batteries (NFB) - are dated 70s, but at the time they did not attract adequate attention due to a moderate performance of first prototypes. A renaissance of NFBs was in the 2010s: researchers proposed various battery designs with unique features. Since available studies overview great diversity of experimental methodology and devices, comparison of NFBs performance is challenging. Therefore, this review focuses on summarizing for the first time the NFB development achievements with special attention to device architecture and their performance metrics. Considering the available data, we highlight two operation modes with distinctive requirements – energy harvesting from acidic and alkaline streams, and stationary energy storage. We hope that this review will provide a clear NFBs state-of-the-art overview, and thereby facilitate further technology improvement.

A new technology of neutralization flow batteries was recently proposed as a promising alternative to conven-tional redox flow batteries due to the low cost of employed electrolytes - acid and base solutions. Despite the advantages of this concept, their performance metrics are still quite modest for industrial applications. To fulfill this gap, in previous work, the authors presented a new two-membrane neutralization flow battery that is meant to overcome issues of reverse electrodialysis cells with bipolar membrane. This concept demonstrates promising results, but the battery discharge performance was limited by alkaline anode where the hydrogen oxidation reaction occurs. In this study we offer the approach to advance the battery performance by implementation of gas diffusion electrodes with gas-fed supply mode. The aforementioned modification allows us to achieve record power (40-87 mW cm-2) and energy (8-48 Wh L-1) densities along with a significant enhancement of the cycling performance.

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. Variations of the composition of the catholyte concentrations of all these components has been analyzed for various initial concentrations of sulfuric acid, cA0 (0.015–0.3 M), and two values of the total concentrations of Br atoms inside the system, ctot (0.1 or 1.0 M of Br atoms), as functions of the average Br-atom oxidation degree, x, under the condition of the thermodynamic equilibrium of the above transformations. It is shown that during the exhaustion of the redox capacity of the catholyte (x pass from 5 to −1), the pH value passes through a maximum. Its height and the corresponding average oxidation state of bromine atoms depend on the initial bromate/acid ratio. The constructed algorithm can be used to select the initial acid content in the bromate catholyte, which is optimal from the point of view of preventing the formation of liquid bromine at the maximum content of electroactive compounds.