The self-discharge of an electric double-layer capacitor with composite activated carbon electrodes and aqueous electrolyte (1 M MgSO4) was studied in detail. Under a long-term potentiostatic charge (stabilization), a decrease in the discharge capacity was observed in the region of voltages exceeding 0.8 V. The self-discharge process consists of two phases. In the initial phase, the cell voltage drop is due to the charge redistribution inside electrodes. During the main phase, the charge transfer between the electrodes determines the voltage drop. The optimal stabilization time of the self-discharge was found to be 50 min at 1.4 V. Hydrophilization of the negative electrode occurred during long-term polarization due to the formation of epoxy functional groups.

Comprehensive characterization of basic MK-40 and Ralex CMH heterogeneous cation-exchange membranes and composite membranes with polyaniline based on them is performed including the determination of specific electrical conductivity and diffusion permeability; measurement of current–voltage curves in solutions of sodium, calcium, and magnesium chlorides and hydrochloric acid and curves of distribution of water with respect to the bond energies and effective pore radii as well as assessment of the transport structural parameters of a microheterogeneous model. The time of synthesis of polyaniline on the surface of cation-exchange membranes for obtaining samples with an anisotropic structure and asymmetric electric transport properties is determined by successive diffusion of a solution of an oxidizing agent and a monomer through the membrane into water. It is shown based on the analysis of the electric transport properties, structural characteristics, and model transport structural parameters of the membranes in solutions of singly and doubly charged ions that the obtained materials are promising for use in the processes of electrodialysis desalination of multicomponent solutions.

This study aimed to investigate the mechanical behaviour and microstructure of an environmentally friendly fibre-reinforce alkali-activated composites. The composites were obtained from alkali-activated granulated blast furnace slag reinforced with chopped secondary carbon fibres (SCFs) coming from the aircraft industry carbon fiber reinforced plastics waste. Three types of surfactants and two concentrations of SCFs were investigated. The compressive and bending strengths were measured to evaluate the mechanical behaviour of specimens. Moreover, the polycondensation products, pore structure, and microscopic morphology of the composites were analyzed using X-ray diffraction (XRD), method of standard contact porosimetry (MSCP), and scanning electron microscopy (SEM). It was found that tetraethylammonium bromide and a superplasticizer agent Glenium-51® increase compressive strength for reference granulated blast furnace slag-based alkali-activated matrix approximately by 60 % and lead to lower open porosity from 16 to 5 %. The experimental results showed that the incorporation of 0.7 vol. % SCFs had an optimal influence on mechanical behaviour and microstructure of composite. Based on the test results, it can be clearly said that using of Glenium-51® is improving the compressive strength of slag based alkali-activated composites reinforced SCFs.

The free solvent transport number in an MF-4SK perfluorinated membrane in solutions of alkaline metal chlorides and hydrochloric acid is for the first time calculated within the framework of a capillary model based on the data of standard contact porosimetry and membrane conductometry. The reasons for the change in the structural characteristics and specific conductivity upon varying the nature of the counterion are discussed. The portion of through mesopores in MF-4SK homogeneous and MK-40 heterogeneous sulfonated cation-exchange membranes is estimated using the experimental data on the water transport numbers in solutions of electrolytes of different natures.

Composite aerogels based on reduced graphene oxide (rGO) and polytetrafluoroethylene (PTFE) have been synthesized at different component ratios. It has been found by the sessile droplet method that the external surface is highly hydrophobic with water contact angles of 166–170°. The porous structure of aerogel granules has been studied by the standard contact porosimetry method (SCPM). The porosimetric curves obtained with the use of octane and water intersect in the region of small pores, thereby indicating that the specific surface area of the aerogel with respect to water is much larger than that with respect to octane, in spite of the fact that octane is known to wet all materials almost ideally. This phenomenon, which we have classified as superhydrophilicity, is explained by swelling of the sample in water in the region of mesopores due to the hydration of the –CO and –COH surface groups, which have been identified by IR spectroscopy. Thus, the granules of the rGO–PTFE composite aerogel, which have a highly hydrophobic outside surface, have a superhydrophilic inside surface in the area of small pores, which is a unique phenomenon. It has also been found that the degree of superhydrophilicity decreases with an increase in the fraction of PTFE in the aerogels. The reasons for the high hydrophobicity of the external surface of aerogel particles have been considered.

A study of the self-discharge of supercapacitor (SC) with electrodes based on the activated carbon (AC) cloth CH 900 of the Kuraray Company with an aqueous electrolyte of 1 M MgSO4 was conducted. The elemental composition of the positive and negative electrodes after electrochemical treatment up to 1.6 V began to radically differ from each other. A very high concentration of hydrogen and oxygen appeared on the positive electrode, which is explained by the formation of functional surface groups (FSG). It was found that the logarithm of the self-discharge rate after 70 min is proportional to the charging voltage. Self-discharge rate dependences on the charge voltage after 1000 and 2000 min have its minimums. These minimums is explained by the action of two oppositely directed mechanisms. First, the pseudocapacity of Faraday redox reactions of FSG makes a significant contribution to the capacity, and second, the very presence of these groups increases the self-discharge rate. At low voltages, the first factor dominates, and at high voltages, the second factor. Based on impedance measurements for small self-discharge times, an equivalent electric circuit of the SC cell has been developed. It is shown that the resistance of the leakage current decreases with voltage increasing, which corresponds with measurements of the self-discharge rate. It is also shown that the self-discharge rate of the SC after 2000 charge-discharge cycles is lower than that corresponding to the initial state of the cell, which is explained by the presence of the FSG.

The influence of the porous structure on the electrochemical characteristics of supercapacitors with nanocomposite paper electrodes based on carbon nanotubes and resorcinol–formaldehyde xerogel is studied. The porous structure and hydrophilic–hydrophobic properties of electrodes based on the carbon paper were studied by the method of standard contact porosimetry in the range of pore radii from ~1 to 105 nm. The specific surface area ranged from 780 to 960 m2/g. The samples contained both hydrophilic and hydrophobic pores. Cyclic capacitance–voltage curves and impedance spectra in 1 M H2SO4 solution showed practically solely the charging of the electrical double layer without a noticeable effect of the pseudocapacitance from Faraday reactions. When the voltage sweep rate was changed by a factor of 100, the values of the equilibrium specific capacitance changed insignificantly (by a factor of 1.25 to 1.36), which indicates the optimality of the porous structure and the dominant contribution of the electrical double layer capacitance to the total capacitance of the supercapacitor. The dependences of the specific volumetric capacitance of the electrode on the logarithm of the voltage sweep rate have a falling linear character for all studied electrodes. A proportionality between the specific capacitance and the electrode specific surface area is demonstrated. This is due to the high porosity of the electrodes (~80 vol %) and the regularity of their porous structure. In addition, according to estimates, from 87 to 89% of the surface was hydrophilic, i.e., can be attributed to functioning pores; only 13 to 11%, to hydrophobic pores. A very high value of the supercapacitor specific power (45.8 kW/kg) was achieved. This shows that the nanocomposite paper is promising for supercapacitors.

The effects that conditions of pyrrole electropolymerization on Norit RXS activated carbon (AC) have on the physicochemical and porometric properties and biocompatibility of resulting composite materials are studied. Using the method of standard contact porosimetry, we show that polypyrrole deposited onto AC samples subjected to preliminary conditioning in a pyrrole solution has almost no effect on the distribution of their pore volume with respect to the pore radius, but it does influence their hydrophilic properties; i.e., a longer duration of conditioning makes the surface of composite samples more hydrophilic. The fact that our polypyrrole/AC composites display electrochemical activity, while the initial AC does not, is observed for the first time. This phenomenon is evidence in favor of the formation of electrochemically active complexes on the surface of synthesized composites, and the hypothetical composition of the complexes can be presented as [surface compounds]/[intermediate products of pyrrole electropolymerization]. The considerable influence that microquantities of polypyrrole present on the AC surface (at around 0.13%) have on its electrochemical, hydrophilic/hydrophobic, and adsorption properties suggests that the aforementioned complexes on the surface of composites display electrocatalytic behavior. In addition, the influence of electropolymerization conditions on the activity of composites toward blood cells is revealed.

A composite aerogel with superhydrophobic external surface has been synthesized from reduced graphene oxide and polytetrafluoroethylene taken in a weight ratio of 1 : 1. The porous structure of the aerogel has been studied by the standard contact porosimetry method (SCPM). The porosimetric curves measured with respect to octane and water intersect in the region of small pores, thereby leading to the fact that the specific surface area of the aerogel in water is much larger than that in octane, although octane is known to wet any material almost ideally. This phenomenon, which is referred to as “superhydrophilicity,” is explained by the fact that, in the region of mesopores, a sample swells in water due to the hydration of surface –CO and –COH groups, which have been identified with the help of IR and Raman spectroscopies. Thus, the outside surface of the aerogel granules is superhydrophobic, while their interior is superhydrophilic in the region of small pores. As follows from the SCPM data, the total porosity and specific surface area of the aerogel are substantially larger than those of Vulcan XC-72 carbon black, which is a standard carrier for Pt catalysts used in fuel cells based on proton-exchange membranes. Oxygen electroreduction at the aerogel, containing Pt deposited in an amount of 28 µg/cm 2 , has been studied by the method of rotating disk electrode (RDE) in an aqueous 0.5 M H 2 SO 4 solution, and the results obtained have been compared with the data on standard commercial Pt (20%)/Vulcan XC-72 catalyst. It has been shown that the limiting diffusion RDE currents for Pt supported on the hydrophobic–hydrophilic aerogel are markedly higher than those for the standard catalyst because of the easier access of oxygen to the reaction zone as compared with hydrophilic Vulcan XC-72 carbon black carrier.

Nanostructured carbon–coated composite cathode materials LiFe 0.5 Mn 0.5 PO 4 /C (LFMP/C) are prepared by the mechanochemically assisted solid-state synthesis using different reagent mixtures and carbon as reducing and covering agent. The effect of the precursors, gas release during the solid-state reaction, and of the intensity of high-energy ball milling on the porous structure and electrochemistry of LFMP/C is studied using DSC/TG/MS, XRD, SEM, TEM, standard contact porosimetry (MSCP), EIS, CV, and GVC. It is shown that the particle size and porosity of LFMP/C strongly depend on the chosen precursors and intensity of mechanical impact. The higher the intensity, the more effective incorporation of carbon black in the pores formed in LFMP, which leads to improved electronic conductivity and better access of the electrolyte to the surface of the electrode, while smaller particles provide improved Li diffusion in the bulk of LFMP. As a result, the cyclability and high-rate performance of the LFMP/C composites are improved.

The high–temperature reagentless activation of carbonized cellulose cloth is used to manufacture supercapacitor (SC) electrodes with different fast times of activation t. It is established by means of the standard contact porosimetry that an increase in t raises both the degree of electrode hydrophilicity and the specific surface area. Thermogravimetry shows that the mass–temperature curves have two steps in the temperature ranges of 25 to 100 and 500 to 650°C, and a plateau in the range of 200 to 400°C. For symmetric supercapacitors (SCs), the potentiodynamic approach provides the voltage–capacity curves characteristic of double–layer SCs. An increase in t raises the electrode capacity from 130 to 170 F/g in 30% KOH solution, due probably to the growing influence of surface groups. It is found that the self–discharge current grows upon an increase in t. The maximum energy density for pulse SCs can be obtained at a charging voltage of 1.4 V. Life cycle tests are performed for a pulse symmetrical SC based on activated carbon electrodes with t = 60 s. It is shown that such SCs can withstand long–term cycling (at least several thousands of cycles) with no noticeable degradation and a negligible reduction in capacity.

Mosaic membranes for capacitive deionization of water contained cation-exchange and anion-exchange components in matrices based on synthetic fibers. The method of the membrane preparation involved pressing of cation-exchange and anion-exchange membranes into each other - pressed membrane was obtained in this manner. Another way was the subsequent formation of the strips of cation-exchanger and anion-exchanger in the fibrous matrix (striped membrane). The specific energy consumptions were 31.9 and 111.7 Wh mol(-1) for the assembles containing striped and pressed membranes, respectively. Thus, the striped membrane was preferable for obtaining pure drinking water.

Materials based on pyrolyzed electrospun nanofiber polyacrylonitrile were studied by the method of standard contact porosimetry. An influence of oxidation and pyrolysis temperatures on specific surface area. It was shown that an increase of oxidation temperature from 300 to 350°C and of pyrolysis temperature from 900 to 1000°C leads to a decrease of pore specific surface area and to a decrease of a part of micropore specific surface area. Platinated samples showed sufficient values of electrochemically active platinum surface area (12‒35 m2 g $$_{{{\text{Pt}}}}^{{ - 1}}$$ ) and were tested as cathodes for high temperature polymer electrolyte membrane fuel cell. An increase in power density was found when a part of electrode micropore specific surface area was decreasing.

Carbon-free LiFe0.5Mn0.5PO4 and carbon-coated LiFe0.5Mn0.5PO4/C cathode materials were prepared by the mechanochemically assisted solid-state synthesis. The influence of the carbon coating on the porous structure, morphology, conductivity, and electrochemical characteristics of the cathode materials was analyzed using scanning electron microscopy (SEM), standard contact porosimetry (MSCP), electrochemical impedance spectroscopy (EIS), galvanostatic cycling, and galvanostatic intermittent titration technique (GITT). It has been shown that the specific surface area of LiFe0.5Mn0.5PO4/C is twice as high as that of LiFe0.5Mn0.5PO4 despite the very low content of carbon (3%). This was explained by a non-additive contribution of carbon and the active cathode material to the total specific surface area of the composite due to an introduction of carbon in the pores of the cathode material. Among the two key characteristics of a porous structure—specific surface area and volumetric porosity—specific surface area has the greatest impact on electrochemistry of LiFe0.5Mn0.5PO4/C. Mathematical modeling of the discharge profiles of LiFe0.5Mn0.5PO4/C was carried out and compared with the experiment. The cathode heating at high currents was evidenced. The temperatures and coefficients of solid-state diffusion were estimated at different currents. The calculated diffusion coefficient corresponds to the experimental one obtained by GITT at room temperature.

According to standard contact porosimetry data, treatment of electrospun pyropolymer mats based on pyrolyzed polyacrylonitrile and polybenzimidazole (PBI) nanofibers with a mixture of sulfuric and nitric acids causes a drastic increase in the specific surface area of macro- and mesopores and complete disappearance of micropores. Acid treatment is followed by hydrophilization of pores with radiir< 10 nm. Taken altogether, these effects lead to higher performance of the membrane-electrode assembly of a high-temperature polymer electrolyte membrane fuel cell based on PBI membrane with the cathode made of the platinized acid-treated material.

An Erratum to this paper has been published: https://doi.org/10.1134/S1023193522070175