In-situ X-ray diffraction study of the electrochemical reaction on lead electrodes in sulphate electrolytes

University of Vienna, Faculty of Chemistry, Währinger Straße 42, A-1090 Wien, Austria
Materials Chemistry and Physics (Impact Factor: 2.26). 04/2009; 114:983-989. DOI: 10.1016/j.matchemphys.2008.11.006


The anodic oxidation of pure lead in two acidic sulphate electrolytes with identical ionic strength (pH similar to 0 and pH similar to -0.1) was studied by in situ grazing incidence X-ray diffraction method (GIXD). Crystalline products such as lead sulphate (anglesite, PbSO(4), orthorhombic), alpha- and beta-lead dioxide (alpha-PbO(2), orthorhombic, and beta-PbO(2), tetragonal), and tribasic lead sulphate hydrate with the stoichiometric composition 3PbO center dot PbSO(4)center dot H(2)O (triclinic) were detected at defined potentials. A method for the semi-quantitative determination of the thickness of the deposited layer from diffraction data is described. After the in situ measurement, the washed and dried working electrodes were additionally characterized ex situ by GIXD measurements at different angles of incidence. The phase litharge (lead oxide, t-PbO, tetragonal) and lead sulphate were observed at the surface of the lead substrate. The quantitative evaluation of the diffraction intensity of this measurement series enables the modelling of a qualitative depth profile of the layer generated during the electrochemical treatment. The anglesite phase is located in the uppermost layer, while the litharge phase was detected closer to the lead substrate.

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    ABSTRACT: This paper describes the quantitative measurement, by in situ synchrotron X-ray diffraction (S-XRD) and subsequent Rietveld-based quantitative phase analysis and thickness calculations, of the evolution of the PbO2 and PbSO4 surface layers formed on a pure lead anode under simulated copper electrowinning conditions in a 1.6 M H2SO4 electrolyte at 318 K. This is the first report of a truly in situ S-XRD study of the surface layer evolution on a Pb substrate under cycles of galvanostatic and power interruption conditions, of key interest to the mining, solvent extraction and lead acid battery communities. The design of a novel reflection geometry electrochemical flow cell is also described. The in situ S-XRD results show that -PbO2 forms immediately on the anode under galvanostatic conditions, and undergoes continued growth until power interruption where it transforms to PbSO4. The kinetics of the -PbO2 to PbSO4 conversion decrease as the number of cycles increases, whilst the amount of residual PbO2 increases with the number of cycles due to incomplete conversion to PbSO4. Conversely, complete transformation of PbSO4 to -PbO2 was observed in each cycle. The results of layer thickness calculations demonstrate a significant volume change upon PbSO4 to -PbO2 transformation.
    Journal of Synchrotron Radiation 03/2015; 22(Pt 2):366-375. DOI:10.1107/S1600577514027659 · 2.74 Impact Factor