The article is devoted to the study of selenium (VI) reduction processes in sulfuric acid solutions when titanium electrodes are polarized by alternating current of industrial frequency (50 Hz). It was found that selenate ion reduction occurs on the surface of titanium electrodes in the cathode half-cycle of alternating current (practically at the cathode) by reaction: ${\mathrm{SeO}}_4^{2-}$+ 6e + 8H⁺ → Se + 4H₂O. In addition, the recovery is carried out by titanium (III) ions: 6Ti³+ ${\mathrm{SeO}}_4^{2-}$+ 8H⁺ → Se + 6Ti⁴⁺ + 4H₂O. It has been established that titanium (III) ions are products of dissolution of titanium during polarization by alternating current, so they can be formed by reaction: 2Ti + 6H⁺ → 2Ti³⁺ + 3H₂. Reduction in selenate ions during polarization by alternating current can also occur due to the cementation reaction with titanium: 3Ti + 2${\mathrm{SeO}}_4^{2-}$ + 16H⁺ → 2Se + 8H₂O + 3Ti⁴⁺. It was shown for the first time that the selenate ion is reduced to form a dispersed selenium powder with a high current efficiency. Depending on the conditions, both amorphous and crystalline selenium modifications are produced.

It is known that catalytic processes are widely applied in the field of organic chemistry; however they also play a significant role in inorganic chemistry. Nonetheless, numerous unresolved issues persist in the technology of inorganic substances and the extraction of metals and nonmetals in their elemental states. This publication aims to consolidate the results of our pioneering research utilizing the redox Ti (IV)–Ti (III) system, which demonstrates a catalytic action on the cathodic reduction of selenium (VI), copper (II), platinum (IV), palladium (IV), bismuth, arsenic (V) ions, uranium (VI), as well as manganese dioxide suspension. It has been demonstrated that in the presence of the redox Ti (IV)–Ti (III) system, hard-to-reduce selenate ions can be reduced at room temperature. The catalytic action of the redox Ti (IV)–Ti (III) system has been reliably demonstrated, and the reaction mechanism has been established. In the electrochemical production of metal powders (Cu, Pt, Pd, Bi) at cathode current densities exceeding the limiting value, a portion of the current is irreversibly lost to the discharge of hydrogen ions. Consequently, the current efficiency (CE) for powder production does not exceed 80 %. We have established that in the presence of titanium (IV) ions, due to their catalytic action, the CE increases by more than 15 %. It has also been shown that during the cathodic polarization of hexavalent uranium its reduction to uranium (IV) in the presence of the catalyst increases by more than 50 %. The reduction of hard-to-reduce arsenate ions in the presence of titanium (IV) ions proceeds with high CE to the active trivalent state, and further reduction can proceed electrochemically. The cathodic reduction of a manganese dioxide suspension was investigated. In the presence of a catalyst — titanium (IV) ions, manganese in this dioxide is reduced to the divalent state with a current efficiency exceeding 90 %.

Among the technologies designed to save energy, flow-through batteries deserve special attention. Their principle of operation is based on the use of systems of variably valent ions. The aim of the work is to create a chemical current source based on the use of the "red – ox" Fe(II)/Fe(III) system and to determine the patterns of formation of electromotive force (EMF) and short-circuit current (SCC) in acidic solutions depending on the concentration of ions. The experiments are carried out by measuring the EMF formed between graphite electrodes and SCC. A special installation has been assembled, consisting of an electrolyzer with separated electrode spaces, an ammeter, a voltmeter and graphite electrodes. Acidified solutions of iron (II) and iron (III) sulfates served as the electrolyte. In an electrolyzer, the electrode spaces of which are separated by an anionite membrane, when one space is filled with iron (II) sulfate and the other with iron (III) sulfate, an EMF occurs between graphite electrodes. When making contact between graphite electrodes, iron (II) oxidation occurs in the first electrode space, and iron (III) reduction occurs in the second. A chemical current source is being formed. At a concentration of iron (III) equal to 20 g/l, a change in the concentration of iron (II) in the range of 1-40 g / l contributes to a shift in the potential of the graphite electrode to negative values. At a concentration of Fe(III) equal to 1 g/l, the potential value is 509 mV, and at 40 g / l – 475 mV. At a constant concentration of iron (II), the addition of Fe(III) leads to a shift in the EMF value to the right. It was found that as a result of these changes, an increase in EMF and SCC is observed.