a horizontal positioning of the spectroelectrochemical cell [21, 22, 28, 31] in which
the entire optical path is pre-adjusted. The cell and the detector are placed on a
movable platform in order to set a required angle of incidence of the incoming
radiation. A similar set-up was designed by Lipkowski at the University of Guelph,
Canada [18]. A modified version of the spectroelectrochemical cell, machined at the
University of Oldenburg, Germany is shown in Fig. 2.8b.
2.3 Experimental Considerations Prior to In Situ
Spectroelectrochemical Experiments
Application of IRRAS to the electrochemical interface allows the determination of
the impact of electrical potentials on the structure of molecules in films adsorbed on
electrode surfaces [32–39]. Determination of the structure and molecular scale order
in films adsorbed on electrodes brings new requirements to IRRAS experiments.
Neither the reactivity nor the stability of adsorbed molecules may be affected by ions
present in the electrolyte solution. Therefore, the composition of the electrolyte
solution has to be carefully chosen. Aqueous, buffered electrolyte solutions are
usually used in electrochemical studies. Metal surfaces such as Au, Pt, Ag, Al or
Cu are available as electrodes and mirrors for IR radiation [5]. A large number of
anions (e.g. Cl
À , Br
À
, I
À
, SO 4
2À ) adsorbs on metal surfaces (e.g. Au, Pt), thus their
use in in situ spectroelectrochemical experiments should be limited. Some ions
present in the electrolyte solution (e.g. ClO 4
À or PO 4
3À ) or organic buffers, e.g.
[tris (hydroxymethyl) aminomethane] (TRIS) absorb the IR radiation. The frequency
of the absorption of the IR light by the ions of the electrolyte may overlap with the
frequency of the absorption of the IR light by species adsorbed on the electrode
surface. In consequence, the IR absorption signal from the sample cannot be
distinguished from the strong background absorption of the electrolyte ions.
To combine electrochemical and spectroscopic experimental requirements the
following issues shall be taken into consideration:
(i) Selection of the mirror (electrode) materials and a possible modification of its
surface;
(ii) Selection of the optical window material suitable for a particular sample;
(iii) Sample composition.
2.3.1 Selection of the Mirror (Electrode) Material
Use of flat, polished metallic surfaces is required in IRRAS. These materials are
often used as electrodes [3, 5, 10, 11, 26, 40, 41]. Such metallic electrodes are not
always suitable for electrochemical studies. To increase the applicability of in situ
IRRAS a modification of metallic surfaces may be done [17, 37, 42–44]. Figure 2.9
2.3 Experimental Considerations Prior to In Situ Spectroelectrochemical Experiments
21
the entire optical path is pre-adjusted. The cell and the detector are placed on a
movable platform in order to set a required angle of incidence of the incoming
radiation. A similar set-up was designed by Lipkowski at the University of Guelph,
Canada [18]. A modified version of the spectroelectrochemical cell, machined at the
University of Oldenburg, Germany is shown in Fig. 2.8b.
2.3 Experimental Considerations Prior to In Situ
Spectroelectrochemical Experiments
Application of IRRAS to the electrochemical interface allows the determination of
the impact of electrical potentials on the structure of molecules in films adsorbed on
electrode surfaces [32–39]. Determination of the structure and molecular scale order
in films adsorbed on electrodes brings new requirements to IRRAS experiments.
Neither the reactivity nor the stability of adsorbed molecules may be affected by ions
present in the electrolyte solution. Therefore, the composition of the electrolyte
solution has to be carefully chosen. Aqueous, buffered electrolyte solutions are
usually used in electrochemical studies. Metal surfaces such as Au, Pt, Ag, Al or
Cu are available as electrodes and mirrors for IR radiation [5]. A large number of
anions (e.g. Cl
À , Br
À
, I
À
, SO 4
2À ) adsorbs on metal surfaces (e.g. Au, Pt), thus their
use in in situ spectroelectrochemical experiments should be limited. Some ions
present in the electrolyte solution (e.g. ClO 4
À or PO 4
3À ) or organic buffers, e.g.
[tris (hydroxymethyl) aminomethane] (TRIS) absorb the IR radiation. The frequency
of the absorption of the IR light by the ions of the electrolyte may overlap with the
frequency of the absorption of the IR light by species adsorbed on the electrode
surface. In consequence, the IR absorption signal from the sample cannot be
distinguished from the strong background absorption of the electrolyte ions.
To combine electrochemical and spectroscopic experimental requirements the
following issues shall be taken into consideration:
(i) Selection of the mirror (electrode) materials and a possible modification of its
surface;
(ii) Selection of the optical window material suitable for a particular sample;
(iii) Sample composition.
2.3.1 Selection of the Mirror (Electrode) Material
Use of flat, polished metallic surfaces is required in IRRAS. These materials are
often used as electrodes [3, 5, 10, 11, 26, 40, 41]. Such metallic electrodes are not
always suitable for electrochemical studies. To increase the applicability of in situ
IRRAS a modification of metallic surfaces may be done [17, 37, 42–44]. Figure 2.9
2.3 Experimental Considerations Prior to In Situ Spectroelectrochemical Experiments
21