1 3
Topics in Current Chemistry (2019) 377:11
surrounding the cell that contains CO 2 and water vapor, which would otherwise render portions of the spectra unusable [55].
The setup for the IRRAS technique used in most studies presented below is
based on the Otto’s configuration in which the solution is squeezed between internal
reflection element (IRE) and the working electrode, as shown in Fig. 2 [55, 56]. The
IR light enters the IRE and strikes the IRE/solution interface at the angle θ. If the
refractive index n 1 of the IRE element is higher than that of the solution (n 2 ), there
exists a critical angle θ c = sin
−1
(n 2 /n 1 ) above which the IR beam totally reflects back
into the IRE. Simultaneously, an evanescent wave is generated and propagates inside
the rarer medium to a depth of a 1–3 µm, carrying information on the absorption
of species in its path. This phenomenon is utilized in internal reflection spectroscopy [33]. In infrared electrochemistry, the electrode is placed within the penetration depth of the evanescent wave, so that the reflected IR radiation also carries the
information on the species at the electrode surface. The incident angle of the IR light
should be accurately adjusted to a few degrees above θ c to obtain the greatest sensitivity [55–58].
The necessary accuracy in the incident angle can only be achieved if the light is
collimated. However, common FTIR spectrometers have the IR beam focused into a
spot in the middle of the internal chamber of the instrument. A hemisphere (or hemicylinder) of a high-refractive index material can be used to collimate the IR beam by
keeping the focal point at the distance d = r/(n 1 − 1) before the curvature of the IRE,
where r and n 1 are the radius and index of refraction of the IRE, respectively [33, 55,
57]. The IR beam travels from the source of the IR spectrometer, reflects of the first
gold mirror so that the instrument’s focal point F is moved to the point F′ in front of
Fig. 2 Schematic representation of the setup for in situ FTIR spectroelectrochemical experiments. The
electrochemical cell built on top of the flat surface of the ATR hemisphere is made of Teflon with bored
holes for gas purging and a three-electrode system consisting of a working electrode (WE), Pt wire-gauze
counter electrode (CE), and a leak-proof Ag/AgCl reference electrode (RE)
Reprinted from the journal
5
Topics in Current Chemistry (2019) 377:11
surrounding the cell that contains CO 2 and water vapor, which would otherwise render portions of the spectra unusable [55].
The setup for the IRRAS technique used in most studies presented below is
based on the Otto’s configuration in which the solution is squeezed between internal
reflection element (IRE) and the working electrode, as shown in Fig. 2 [55, 56]. The
IR light enters the IRE and strikes the IRE/solution interface at the angle θ. If the
refractive index n 1 of the IRE element is higher than that of the solution (n 2 ), there
exists a critical angle θ c = sin
−1
(n 2 /n 1 ) above which the IR beam totally reflects back
into the IRE. Simultaneously, an evanescent wave is generated and propagates inside
the rarer medium to a depth of a 1–3 µm, carrying information on the absorption
of species in its path. This phenomenon is utilized in internal reflection spectroscopy [33]. In infrared electrochemistry, the electrode is placed within the penetration depth of the evanescent wave, so that the reflected IR radiation also carries the
information on the species at the electrode surface. The incident angle of the IR light
should be accurately adjusted to a few degrees above θ c to obtain the greatest sensitivity [55–58].
The necessary accuracy in the incident angle can only be achieved if the light is
collimated. However, common FTIR spectrometers have the IR beam focused into a
spot in the middle of the internal chamber of the instrument. A hemisphere (or hemicylinder) of a high-refractive index material can be used to collimate the IR beam by
keeping the focal point at the distance d = r/(n 1 − 1) before the curvature of the IRE,
where r and n 1 are the radius and index of refraction of the IRE, respectively [33, 55,
57]. The IR beam travels from the source of the IR spectrometer, reflects of the first
gold mirror so that the instrument’s focal point F is moved to the point F′ in front of
Fig. 2 Schematic representation of the setup for in situ FTIR spectroelectrochemical experiments. The
electrochemical cell built on top of the flat surface of the ATR hemisphere is made of Teflon with bored
holes for gas purging and a three-electrode system consisting of a working electrode (WE), Pt wire-gauze
counter electrode (CE), and a leak-proof Ag/AgCl reference electrode (RE)
Reprinted from the journal
5