Anna V. Popova

Charge-transfer kinetics in the Nb(V)/Nb(IV) couple in alkali-metal molten chlorides

Charge-transfer standard rate constants ks for Nb(V)/Nb(IV) redox couple in KCl-NbCl5 and CsCl-NbCl5 chloride melts at glassy carbon and platinum electrodes are determined. The Nb(V) electro-chemical reduction process in the NaCl-KCl (equimolar mixture)-NbCl5 melt was shown being reversible even at high polarization scan rate (v = 2.0 V s−1); hence, the determination of ks appeared impossible. Values of ks in KCl-NbCl5 melts are higher than those in CsCl-NbCl5 melts. Quantum-chemical calculations done in nM+[NbCl6]—model systems by the Discrete Fourier Transformation method showed that the calculated ratio of charge-transfer activation energies in the K+-Cs+ series corresponds to changes in the experimental charge-transfer rate constants. The charge-transfer standard rate constants increase with the increasing of temperature and with the passing from glassy carbon electrode to platinum one.