Vol 60, No 2 (2024)

This review considers the literature on electrochemical supercapacitors (ECSC) operating at extreme temperatures from –80°C to +220°C, which is very important for practice. The influence of the following methods and factors on the efficiency of the ECSC at extreme temperatures is considered: the use of ionic liquids as an electrolyte: the use of a modified gel electrolyte, a combined electrolyte, aqueous electrolytes with a low freezing point; the use of acetonitrile as an electrolyte solvent; the use of clay as a solid electrolyte; application of solid-state EСSC; application of electrodes with an optimized porous structure; the use of graphene and pseudocapacitive electrodes; the use of solar cells; use of combined techniques to create supercapacitors for extreme temperatures. Undoubtedly. This review will be of great interest both for fundamental electrochemistry and for practice.

The electrochemical properties of [Co(Ph2PCH2P(Ph)2PPPPP(Ph)2CH2PPh2)]BF4 complex have been studied by the method of cyclic voltammetry. The electrochemical methylation of this complex have been cunducted in the presence of iodomethane which has led to the formation of phosphonium salt—ethylene bis(methyldiphenylphosphonium) diiodide as final product. It was found, that this reaction proceeds with the breakage of the P–P bonds in polyphosphorus ligand and with the formation of new P–C bonds.

At electrochemical deposition of alloys various phenomena are observed that lead to changes in the kinetics and thermodynamics of these processes. So, as a result of changing the nature of the electrode surface, the exchange current densities of each of the components and the transfer coefficients change. Further, during the formation of solid solutions, the equilibrium potentials of the components change due to the non-zero enthalpy of mixing and entropy of mixing. At deposition of eutectic-type alloys (that is, a mixture of grains of individual components), each of the metals is not deposited on the entire surface of the electrode, but only on its own surface. In the latter case, there is a change in the diffusion pattern of the components compared to the deposition of individual metals: it remains unchanged in the outer part of the diffusion layer but near the surface there is a condensation of the diffusion fields of the components, similar to how it is observed during diffusion to the matrix of microelectrodes or to individual nuclei of a new phase. This also leads to a change in the diffusion part of the overpotential at deposition of components. The diffusion of ions of a discharging negative component of an alloy representing a mechanical mixture of metal grains A and B to the grain surface of this component in the model of a partially blocked electrode is considered. It is shown that at a constant potential, the local current density of the component is increased as a result of diffusion acceleration. The magnitude of the relative increase in current and the corresponding magnitude of apparent depolarization is found as compared between the deposition of an individual metal and the codeposition of the same component into an alloy.