Design of an electrochemical cell for in situ XAS studies

In situ X-ray absorption spectroscopy (XAS) studies have been carried out on the electrochemical insertion of Co metal particles in polypyrrole. This has become possible due to the development of an electrochemical cell to allow XAS studies in fluorescence geometry under steady-state conditions. The experimental set-up allows the in situ monitoring of the structural and electronic changes of the selected atom in a matrix. The project of the electrochemical cell is presented with the results obtained at different stages of the electrochemical process. XANES and EXAFS results showed that the initial stage of the cobalt insertion in polypyrrole took place in an ionic form, like [-[(C4H2N)3CH3(CH2)11OSO3−]6Co2+] with posterior reduction to a metallic form. The quantitative analysis of the first shell shows that, at −0.60 V, the cobalt atoms are surrounded by 6 (±0.5) atoms located at 2.12 (±0.05) Å with a large Debye-Waller factor (σ2) value of 0.0368 (±0.0074). At −0.80 V, two distances of R = 1.99 (±0.01) and R = 2.50 (±0.01) Å show the coexistence of cobalt in the oxidized and reduced (Co0) forms. The Co-Co distance corresponds to that of bulk cobalt. At −1.20 V, the obtained values of N = 12 (±0.5) and R = 2.56 (±0.01) Å and a Debye-Waller factor of 0.0176 (±0.0004) suggest the formation of metallic cobalt in a quite disordered form.