Spectroelectrochemical studies of some species in fused PbCl2 + KCl at 440°C

The electrochemical reduction of Pb(II), Ag(I). Ni(II), In(III)_and Rh(III), and the oxidation of O(?II), I(?I) and S(?II) have been investigated in a PbCl₂+KCl melt with 23% mol KCl at 440°C, by potentiometry, linear potential sweep and cyclic voltammetry, and potential step chronoamperometry. The potential of the Pb/Pb(II) electrode was found to change linearly with the melt composition. The Ag/Ag(I) system has a Nerstian behaviour and was used as a reference electrode. All species showed a one step oxidation or reduction process, leading to Ni(0), In(I), Rh(0), CO₂ and I₂, except that the sulphide oxidizes in two steps. Absorption of light by Co(II), Ni(II), and Rh(III) was measured with a new device using fibre optics, which allowed us to record the spectrum of Ni(II) and Rh(III) inside the electrolytic cell, during oxidation at controlled potential of a nickel wire, or reduction of Rh(III).