Electrochemical EXAFS

Figure 15. Preliminary (water activation) A r curves derived from in situ electrochemical EXAFS experiments for CoTMPP pyrolized at (left) 600°C, (center) 700°C, (right) 800°C. The anodic potential (vs. RHE) for the CoTMPP cathodes are (A) 0.50 V, (B) 0.60 V, (C) 0.70 V, and (D) 0.90 V.

N. Alonso-Vante, M. Fieber-Erdmann, H. Rossner, E. Holub-Krappe, C. Giorgetti, A. Tadjeddine, E. Dartyge, A. Fontaine, R. Frahm, The catalytic centre of transition metal chalcogenides vis-a-vis the oxygen reduction reaction An in situ electrochemical EXAFS study. J. de Physique IV France 1997, 7, C2-887-C2-889. 

Alonso-Vante N, Fieber-Erdmann M, Rossner H, Holub-Krappe E, Giorgetti C, Tadjeddine A, Dartyge E, Fontaine A, Frahm R (1997) The catalytic centre of transition metal chalcogenides vis-4-vis the oxygen reduction reaction an in situ electrochemical EXAFS study. J Phys IV 7(2 Part 2) 887-889... 

Figure 15.11. Interaction of molecular oxygen in acid medium at the Chevrel phase cluster-electrolyte interface [6]. (Reprinted from Journal de Physique, vol. 7, C2, The Catalytic Centre of Transition Metal Chalcogenides vis- -vis the Oxygen Reduction Reaction An In situ Electrochemical EXAFS Study, Alonso-Vante, N. et al. 31997, with permission from EDP Sciences.)...

Mazurek M, Benker N, Roth C, Buhrmester T, Fuess H. 2006. Electrochemical impedance and X-ray absorption spectroscopy (EXAFS) as in situ methods to study PEMFC anode. Fuel Cells 6 16-20. 

In this chapter, I will try to present an introduction to these various techniques with emphasis on EXAFS and X-ray standing waves and their application to the study of electrochemical interfaces. Each technique will be treated from theoretical and experimental points of view, and selected examples from the literature will be employed to illustrate their application to the study of electrochemical interfaces. 

In order to simplify the discussion, the EXAFS studies on electrochemical systems reported to date will be divided into the categories listed below ... 

Antonio et al100 have performed an in situ EXAFS spectro-electrochemical study of heteropolytungstate anions. 

In addition to surface EXAFS and X-ray standing waves, X-ray diffraction can be employed in the study of electrochemical interfaces. Although an extensive treatment of X-ray diffraction techniques is beyond the scope of this chapter, some brief statements are appropriate. 

The coordination of transition metal ions in acidic chloroaluminate melts has not been firmly established. However, in the case of AICb-EtMelmCI. the E0 values of simple redox systems that are electrochemically accessible in both acidic and basic melt, e.g., Hg(II)/Hg [51], Sb(III)/Sb [52], and Sn(II)/Sn [53] exhibit a large positive potential shift on going from basic melt, where metal ions are known to exist as discrete anionic chloride complexes, to acidic melt. Similar results were observed for Cu(I) in AlCh-NaCl [48]. This dramatic decrease in electrochemical stability isprima facie evidence that metal ions in acidic melt are probably only weakly solvated by anionic species such as AICI4 and AECI-. Additional evidence for this is derived from the results of EXAFS measurements of simple metal ions such Co(II), Mn(II), and Ni(II) in acidic AlCh-EtMelmCl, which indicate that each of these ions is coordinated by three bidentate AICI4 ions to give octahedrally-coordinated species such as [ M (AIC14) 2 ] [54]. Most transition metal chloride compounds are virtually... 

Loglio, F. Innocenti, M. D Acapito, F. Felici, R. Pezzatini, G. Salvietti, E. Foresti, M. L. 2005. Cadmium selenide electrodeposited by ECALE electrochemical characterization and preliminary results by EXAFS. J. Electroanal. Chem. 575 161-167. 

The electrochemical cell for the EXAFS experiments (Figure 1) was machined from a teflon cylinder (6 cm diameter x 6 cm high) and was provided with contacts for all electrodes as well as teflon fittings for the injection of electrolyte. The electrode was placed flat on the top of the cell and covered with a thin Tefzel (E. 

Figure 1. Electrochemical cell for in situ surface EXAFS at chemically modified electrodes.

Synchotron based techniques, such as surface X-ray scattering (SXS) and X-ray absorption spectroscopy (XAS), have found increased use in characterization of electrocatalysts during electrochemical reactions.37 These techniques, which can be used for characterization of surface structures, require intricate cell designs that can provide realistic electrochemical conditions while acquiring spectra. Several examples of the use of XAS and EXAFS in non-precious metal cathode catalysts can be found in the literature.38 2... 

We have already discussed ion association in Section 6.2. In that section we referred to evidence for the existence of ion clusters from static techniques such as IR, Raman, EXAFS and X-ray diffraction. In this section we examine ion association from the point of view of dynamics, concentrating in particular on electrochemical measurements which reveal the presence of ion clusters. Because ion association is so intimately connected to the transport of matter and charge through polymer electrolytes, it seems appropriate to consider these two topics in the same section. 

---