The electrochemical behavior of manganese silicide-germanides with different ratios of germanium and silicon is studied using the methods of voltammetry and impedance spectroscopy in 0.5 M aqueous sodium sulfate solution. It is shown that the oxidation stability of materials decreases with an increase in the ratio of germanium, which, unlike silicon, is incapable of forming a layer of stable oxides on the material surface.
Using the method of polysulfone chloromethylation followed by quaternization, an anion-exchange membrane is synthesized for water electrolyzers with alkaline electrolyte. The characteristics of this membrane such as porosity, electrical conductivity, and gas-tightness are determined. A comparative analysis of characteristics of this membrane as compared with a porous diaphragm (analog of ZifronPerl) is carried out. The results of tests of the membrane within an alkaline electrolyzer battery are compared with the results for the porous diaphragm based on unmodified polysulfone with a hydrophilic filler (TiO2) and synthesized by phase inversion. The possible mechanism of the degradation of the main chain in quaternized polysulfone is presented. The ways are proposed for the further development of the technology of anion-exchange membranes based on polysulfone.
The reduction of permanganate on a rotating disk electrode is accompanied by an inhibition of depositing birnessite. The addition of potassium ferrate(VI) leads to an increase of inhibition. The obtaining of electrode material based on Fe-doped birnessite under alkaline conditions is demonstrated in experiment with deposition at inhibition potentials. This birnessite is single phase and highly disordered. The Fe content varies from 0 to 10 mol % in respect to Mn with increasing ferrate(VI) content in deposition solution. Recharging potentials of birnessite are shifted which is manifested by cyclic voltammetry. Doping allows to increase the rate of oxygen evolution reaction. The specific currents increase with the iron content in birnessite. The Tafel slope is 53 mV/dec and by 2.5 times lower for birnessite containing 10 mol % Fe.
An hydrophobized gas-diffusion electrode with a tin catalyst deposited onto acetylene black A437E is tested with the aim of elucidation of its potential in intensifying the CO2 electroreduction to formate in acidic and alkaline aqueous solutions. Porous electrodes with the fluoroplastic content of 40 wt %, a thickness of 0.5 mm, porosity of 60 vol %, and the tin content ≈0.7 mg/cm2 of the total electrode surface are studied. It is shown that this type of electrodes can be used in electroreduction of CO2 at a current density of up to 900 mA/cm2, a temperature of 25–55°C with the current efficiency from 74 to 96% with respect to formate. The 4 h electrolysis at a current density of 190 mA/cm2 produces a solution with the potassium formate concentration of 1.58 M. This is accompanied by the increase in the capacitance of the electric double layer from 7 to 17 mF/cm2 and the decrease in the current efficiency from 96 to 58%.
The express-method proposed recently for experimental determination of diffusion coefficients of electroactive ions inside a membrane and their distribution coefficients at the membrane/solution boundary (Russ. J. Electrochem., 2022, 58, 1103) is based on the comparison of the measured non-stationary current for the electrode/membrane/electrolyte solution system upon the applying of a potential step with the theoretical expressions for the current–time dependence. Application of this method for the study of bromide-anion transport across the membrane was performed in the previous work under the condition of the membrane permselectivity where the amplitude of the electric field inside the membrane was suppressed owing to a high concentration of non-electroactive counterions. Then, the coion (bromide anion) transport occurred by the diffusional mechanism, for which the solution was available in an analytical form. The present study considers for the first time a non-stationary electrodiffusional transmembrane transport of two singly charged ions (e.g., background cation М+ as the counterion and electroactive anion X– as the coion) having identical diffusion coefficients where the current passage induced a transient electric field in this space, resulting in a deviation from predictions for the diffusional mechanism. It is found that within the short time interval after the applying of the potential step from the membrane equilibrium state to the limiting current regime (where the thickness of the non-stationary diffusion layer is significantly smaller than that of the membrane) the non-stationary distributions of the ion concentrations and of the electric field strength as a function of two variables (the spatial and temporal ones, x and t) can be expressed via a function of one variable, Z(z), where z = x/(4Dt)1/2. The form of the expression, depending on the ratio of the surface concentration of component X to the fixed charge density inside the membrane (Xm/Cf) has been found by numerical integration. The limiting current varies with time according to the Cottrell formula (I ~ t–1/2); the dependence of the dimensionless current amplitude, i, on the Xm/Cf ratio is found by numerical calculation; an approximate analytical formula has also been proposed. In particular, the passing current is shown to be close to the diffusion-limited one for a low coion concentration at the membrane/electrolyte solution boundary as compared with the concentration of immobile charged groups inside the membrane (Xm/Cf ( ll ) 1), whereas the migration contribution to the ionic fluxes doubles the limiting current when the opposite condition (Xm/Cf ( gg ) 1) is fulfilled.
The nanocomposite of a resorcinol–formaldehyde xerogel and carbon nanotubes after carbonation was obtained in the form of a composite carbon nanopaper (CCNP) with the thickness of 100–300 microns, the density from 0.1 to 0.5 g/cm3 and the electronic conductivity of more than 10 S/cm. The microporous structure of the nanopaper is formed by carbonized resorcinol–formaldehyde xerogel, and the mesoporous structure is formed by the nanotube framework. Previously, the characteristics of nanopaper electrodes in an aqueous electrolyte of 1M H2SO4 were measured, where the maximum capacitance was 155 F/g (56 F/cm3). To work with an organic electrolyte, a method for activating CCNP with potassium hydroxide has been developed. In this paper the characteristics of electrodes made of activated nanopaper (a-CCNP) in an organic electrolyte 1 M 1,1-Dimethylpyrrolidinium tetrafluoroborate (DMPBF4)/acetonitrile solution were measured. The capacitance in this electrolyte has been reached 70 F/g (27 F/cm3). According to measurements on a laboratory assembly of a symmetrical supercapacitor (SC) with electrodes made of CCNP, the characteristics are calculated when the SC operates in the mode of short pulse switching with an efficiency of EF = 95%. In an aqueous electrolyte of 1 M H2SO4 (U0 = 1.0 V), the volumetric energy density was E0.95,SC = 0.9 W h/L and the volumetric power density was P0.95,SC = 2.1 kW/L. In 1 M DMPBF4/acetonitrile electrolyte (U0 = 2.7 V), the design characteristics of the capacitor were: volumetric energy density E0.95,SC = 3.8 W h/L and volumetric power density P0.95,SC = 2.0 kW/L. The specific characteristics of power SCs are compared with electrodes made of activated CCNP and of other carbon materials. In mass production, nanocomposite electrodes are estimated to be cheaper than activated carbon microfibers and significantly cheaper than graphene electrodes.
Transition metals, one of the many modifiers used in enzyme-free sensors, have received impressive attention among the various modification materials for urea electrochemical sensors with low cost. Textiles represent a flexible material for collecting sweat samples for non-invasive urea detection. In our study, we developed a nonwoven fabric-based modified carbon paste electrode using Ag-doped NiO (Ag/NiO) as a sensitive non-enzymatic electrochemical urea sensor. A variety of techniques were used to characterize synthesized Ag/NiO, including scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), electrochemical impedance spectroscopy (EIS), diffuse reflectance spectroscopy (DRS), and X-ray diffraction (XRD). The electrochemical properties of the Ag/NiO nanocomposite modified carbon paste on a textile electrode were studied using electrochemical impedance spectroscopy, cyclic voltammetry, and amperometry. The electrode was able to oxidize urea in alkaline solutions with high sensitivity, a wide linear range (2.5 × 10–3 to 5 mM), a low detection limit (8 µM), long-term stability, and good selectivity. Finally, urea concentrations in human sweat samples and plasma were determined by the sensor.
Catalysts of the hydrogen peroxide cathodic synthesis are obtained from multiwalled carbon nanotubes pre-oxidized with nitric acid, follow by hydrogen reduction in the 300–500°C temperature range. Evaluation of physico-chemical properties of the catalysts showed the synthesis method used to be able controlling changes in the surface oxygen groups’ composition without any change in the multiwalled carbon nanotubes’ structure and morphology. Investigation of catalytic activity in the cathodic process for hydrogen peroxide production demonstrated the sample prepared by hydrogen reduction at 300°C with oxygen content of 5.2 at % (according to XPS data) to have the highest efficiency. The sample produced the hydrogen peroxide with the rate of 0.34 mol/(g h) and Faradaic efficiency of 78%. Increase in the reduction temperature above 300°C resulted in a decrease in the rate of Н2О2 accumulation without severe changes in Faradaic efficiency.
Phytic acid (PA) benzotriazole composite conversion films with different concentrations of BTA were prepared by an impregnation method, and their wettability, microstructure, and corrosion resistance were studied. The results showed that when the BTA content was 1.6 wt %, the maximum water contact angle of the conversion film reached 137.5°, and the corrosion current density reached a minimum of 1.610 × 10–7 A/cm2. The salt spray and corrosive liquid environments experimental results also showed that the synergistic effect of PA and BTA was the best when the BTA concentration was 1.6 wt %. Hydrogen bonds are formed between PA chelates and BTA chelates enhancing the density of the conversion film leading to the improvement of corrosion resistance of conversion film on a copper surface with the introduction of BTA.
With the development of energy storage, potassium ion batteries (PIBs) have gradually become a suitable substitute for lithium-ion batteries. Where the layered transition metal oxides cathode materials of potassium ion batteries have attracted much attention due to their high theoretical capacity, unique two-dimensional potassium ion diffusion channels, simple preparation and low cost. In this work, we designed a K0.5MnO2@MWCNT@Super P (KMP) composite electrode with P3-type layered structure as the cathode in PIBs through coprecipitation—high temperature sintering method. The SEM results show that the prepared KMP composite electrodes are secondary particles formed by three-dimensional network structures and particles through point–line contact and point–point contact. As a result, the composite electrode with a 7 : 2 : 1 weight ratio of K0.5MnO2, conductive carbon (Super-P: MWCNT = 1 : 1) and PVDF delivers a high initial discharge capacity of 112.7 mA h g–1 at a current density of 20 mA g–1 and 72.1 mA h g–1 at 100 mA g–1. And, it has a capacity retention of 44% at 100 mA g–1 after 50 cycles. The results show that the unique three-dimensional network structure not only improves the conductivity of K0.5MnO2 material, but also effectively alleviates the volume change caused by K+ in the charging and discharging process. This study provides a new way to develop layered cathode materials for high energy density potassium ion batteries.
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