The aim of the work was to elucidate the nature of charge-selective properties of macroporous composite inorganic membranes modified with nanoparticles of hydrated zirconium dioxide. The membranes have been investigated using methods of standard contact porosimetry, potentiometry, electron microscopy and small-angle X-ray scattering. The ion exchanger has been found to deposit inside pores of ceramics. Differential curves of pore volume distribution have been resolved using Lorentz functions; each maximum has been related to structure elements of the matrix and ion exchanger by means of calculations according to homogeneous and heterogeneous geometrical models. It was found that the voids, the radius of which is 4 to 8 nm, are responsible for charge selectivity of the composite membranes. These pores are formed due to blocking of macropores of ceramics with aggregates of nanoparticles of the ion exchanger; the radius of these aggregates is 20 to 24 nm. The membranes were applied to desalination of the solution containing NaCl. The removal degree of the salt from the solution reached 95% and 9% for the composite and unmodified membranes, respectively.

In the electrodes of a proton-exchange membrane fuel cell, the hydrophilic-hydrophobic properties of the catalyst layers (CL), which contain a carbon substrate (CS), an ionomer in the form of Nafion resin, and a platinum catalyst, are investigated with standard contact porosimetry. Regularities in the influence of ionomer on the hydrophilic-hydrophobic properties of ten different CS, including Vulcan XC-72 carbon black, are investigated. The following plots are obtained: pore distribution curves with respect to radii, water desorption isotherms, moisture content distribution curves with respect to capillary pressure and to the free energy of binding water to material, and the wetting angle of water for the samples under investigation as a function of pore radius. It is established that both a hydrophobic effect and a hydrophilic effect occur in CL as a result of ionomer application to the CS under investigation. It is concluded that these different effects are determined by the orientation of the sulfonate groups (inside and outside) in the resin particles. This orientation depends on the extent of the binding of sulfonate groups to the CS surface by adsorption. CS surface properties are determined by the type and concentration of surface groups. Thus, the phenomenon of ionogenic-group inversion is established. When platinum is applied to CS, the CL become partially hydrophilic.

Carbon-free LiFe_0.5Mn_0.5PO₄ and carbon-coated LiFe_0.5Mn_0.5PO₄/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 LiFe_0.5Mn_0.5PO₄/C is twice as high as that of LiFe_0.5Mn_0.5PO₄ 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 LiFe_0.5Mn_0.5PO₄/C. Mathematical modeling of the discharge profiles of LiFe_0.5Mn_0.5PO₄/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.

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.

The electrochemical properties of the highly porous reduced graphene oxide/titanium dioxide (rGO/TiO₂) nanocomposite were studied to estimate the possibility of using it as a supercapacitor electrode. Granular aerogel rGO/TiO₂ was used as an initial material for the first time of manufacturing the electrode. For the aerogel synthesis, industrial TiO₂ Hombikat UV100 with a high specific surface area and anatase structure was used, and the aerogel was carried out with hydrazine vapor. Porous structure and hydrophilic–hydrophobic properties of the nanocomposite were studied with a method of standard contact porosimetry. This is important for a supercapacitor containing an aqueous electrolyte. It was found that the hydrophilic specific surface area of the nanocomposite was approximately half of the total surface area. As a result of electrochemical hydrogenation in the region of zero potential according to the scale of a standard hydrogen electrode, a reversible Faraday reaction with high recharge rate (exchange currents) was observed. The characteristic charging time of the indicated Faraday reaction does not exceed several tens of seconds, which makes it possible to consider the use of this pseudocapacitance in the systems of fast energy storage such as hybrid supercapacitors. Sufficiently high limiting pseudo-capacitance (about 1200 C/g TiO₂) of the reaction was obtained.