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

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 concen-trated on employing chronoamperometric techniques to analyse cathodic reactions, ignoring important infor-mation on reduction processes. In this work, we examine electro-deoxidation using several DC voltammetric techniques, including constant potential chronoamperometry, sampled-current voltammetry, linear sweep vol-tammetry, 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.