Èlektrohimiâ

A high-entropy composition (Mg_0.2Zn_0.2Ni_0.2Co_0.2Mn_0.2)Nb₂O₆ with a columbite structure and its Ti-substituted composition (5%) were synthesized. The synthesis was carried out using a modified method of combustion solutions followed by high-temperature sintering. X-ray analysis and scanning electron microscopy were used for characterization of the ceramics. According to diffuse reflectance spectra, the band gap of direct electronic transitions was calculated (E_g^dir ≈ 2.98–3.05 eV). Solid solutions are characterized predominantly by electronic conductivity. Substitution of niobium cations with titanium leads to an increase in conductivity by 1.2 orders of magnitude in the temperature range 160–750°C.

Operation of a single cell of redox-flow hydrogen-halogenate current generator which converts the energy of the oxidation reaction of gaseous hydrogen by sodium chlorate in aqueous sulfuric-acid solution into electric energy with the use of a membrane-electrode assembly of the composition: (–) H₂, Pt–C // PEM // NaClO₃, C (+) has been studied. A combined load operation regime (which includes stages of potentio- and galvanostatic control) has been applied, in order to take into account specific features of the chlorate electroreduction half-reaction, i. e. its redox-mediator autocatalytic mechanism (EC-autocat). For aqueous electrolytes containing various sulfuric acid contents, the system parameters determining the power and efficiency of the hydrogen-chlorate current generator have been established: faradaic and energy efficiencies, average discharge power and time to reach the steady-state mode. It has been found that the hydrogen-chlorate cell under study functions most efficiently for the 5 M sulfuric-acid electrolyte: such a cell has reached the constant-current mode to generate the 0.25 A/cm² current density within one and a half minutes; it has been able to convert the chemical energy into the electric one with the 55% efficiency at the average specific discharge power of 0.23 W/cm².