Understanding the behaviour of a niobium oxide cathode in a molten chloride bath using different DC voltammetric techniques.

Abstract

The electro-deoxidation of metal oxides has been presented as an alternative to the pyro- and electro-metallurgical techniques generally used to create metals and alloys. However, previous research has concentrated on employing chronoamperometric techniques to analyse cathodic reactions, ignoring important information on reduction processes. In this work, we examine electro-deoxidation using several DC voltammetric techniques, including constant potential chronoamperometry, sampled-current voltammetry, linear sweep voltammetry, and constant current chronopotentiometry. Niobium pentoxide was taken as the model cathode material. As a result, the following reduction mechanism is proposed: (1) Nb (V) oxidation state, represented by the compounds Nb2O5, CaNbO6, and Ca2Nb2O7, reduced to Nb (IV) in the compounds NbO2 and CaNbO3; (2) Nb (IV) reduced to Nb (III) in the form of CaNb2O4; (3) CaNb2O4 reduced quickly to NbO, which is the only form of Nb(II); the latter is reduced to Nb(0) by the end of the electro-deoxidation process. The results show that NbO partially dissolves in the electrolyte and suggest the creation of two distinct soluble niobium complexes, depending on the oxygen level of the electrolyte.