Vol 59, No 1 (2023)

Based on the analysis of publication activity, trends in the development of the main sections of solid state ionics have been formulated by using expertly curated abstract & citation database of peer-reviewed scientific literature Scopus. Promising areas of research related to in situ and operando experiments, artificial intelligence (machine learning), and the design of new devices using superionic materials are indicated.

The literature on the self-discharge of supercapacitors is reviewed, the advantages of electrochemical supercapacitors over batteries are formulated. The principal disadvantage of the electrochemical supercapacitors is their rapid self-discharge. A study of self-discharge of electrochemical supercapacitors was conducted; methods of the self-discharge studying, the effect of functional carbon groups on the self-discharge, the self-discharge mechanisms and mathematical modeling of the self-discharge are described. The development of new supercapacitor devices destined to minimize the self-discharge is described, including additives to the electrolyte, solid-state supercapacitors, electrochemical supercapacitors with ion-exchange membranes, the using of pure electrolytes, methods of the electrode chemical modification to slow down self-discharge. A study of self-discharge of electrochemical supercapacitors with electrodes based on activated carbon cloth CH 900 (the Kuraray Co. production) and 1 M MgSO4 aqueous electrolyte is conducted. The rate of self-discharge after ~70 min after its start is found to be proportional to the charging voltage. The voltage dependence of the self-discharge rate at 2000 min after its start goes through a minimum. This minimum is explained, firstly, by a significant contribution to the capacity from the Faradaic redox-reaction pseudo-capacity involving the functional groups; secondly, the very presence of these groups increases the self-discharge rate. It is the former factor that dominates in the low-voltage region; the second one, in the high voltage region.

The electrostatic properties of multicharged colloids (the so-called DLVO complexes) at the interface of two media with different permittivities are discussed. It is shown that being quasi-neutral in the electrolyte volume, the DLVO colloids turn out to be partly charged near the z = 0 boundary that separates these media. The problem of the interaction of an individual colloid, which has a solid inoculating core R0≫a0, (a0 is the interatomic distance) and the charge Q=Ze≫e (e is elementary charge), with the metal/electrolyte interface is considered in detail. The problem has various applications in the diagnosis of DLVO complexes and the practice of dealing with solutions capable of maintaining the electrophoretic motion of colloidal assembles.

The hexagonal solid solution La2W1 + xO6 + 3x (x ~ 0.11) and the orthorhombic low-temperature phase β-La2WO6 (La2W1 + xO6 + 3x (x = 0)) are synthesized by the methods of preliminary mechanical activation of oxides followed by high-temperature synthesis at 1400°С, 4 h. In addition, by using the method of crystallization from solution, a single crystal of the La2W1 + xO6 + 3x (x ~ 0.22) composition isostructural to La2W1 + xO6 + 3x (x ~ 0.11) is grown. Both ceramics and the single crystal are studied by the methods of Raman spectroscopy, thermal analysis, and thermogravimetry. Their conductivity is studied by impedance spectroscopy in dry and humid air. The hexagonal single crystal La2W1 + xO6 + 3x (x ~ 0.22) demonstrates strong luminescence in the IR region, in contrast to the hexagonal ceramics La2W1 + xO6 + 3x (x ~ 0.11) and the β-La2WO6 ceramics with the orthorhombic structure. The polycrystalline La2W1 + xO6 + 3x (x ~ 0.11) ceramics is found to be more stable under redox conditions as compared with the single crystal. The conductivity of the hexagonal single crystal La2W1 + xO6 + 3x (x ~ 0.22) is of the oxygen-ionic nature and lower than the conductivity of ceramics La2W1 + xO6 + 3x (x ~ 0.11) due to its perfect structure. The contribution of the protonic component of conductivity is absent for both the hexagonal solid solution La2W1 + xO6 + 3x (x ~ 0.11) and the single crystal La2W1 + xO6 + 3x (x ~ 0.22), their conductivity being of the purely ionic nature with the close values of activation energy (0.89 and 1.08 eV, respectively). The synthesized β-La2WO6 ceramics demonstrates a small contribution of the protonic conductivity in humid air equal to ~1 × 10–6 S/cm at 600°С, which is close to the conductivity of the earlier studied strontium-doped solid solution La1.96Sr0.04WO6 – δ based on β-La2WO6.