(393bb) Application of Novel Spectroscopy Methods in Electrochemical Studies

Application of novel spectroscopy methods in
electrochemical studies

Aria Kahyarian, Damilola A. Daramola, and Gerardine G. Botte

Center for
Electrochemical Engineering Research

Department of
Chemical and Biomolecular Engineering

Ohio University

Athens, OH 45701

In the past few decades, there has been a growing
interest in minimizing the dimensions of engineered devices. Electrochemical
systems are not exempted from this general trend. Specifically in
electrochemical engineering, theoretical framework, principles and equations
for design, understanding and diagnostics of electrochemical devices had been
developed at the continuum scale. Although these principles have been accepted
and used, their validation has been cumbersome due to difficulties associated
with measuring properties.

This study is focused on the characterization of
electrochemical reactions at the molecular level. In other words, is there any
way to validate or modify known electrochemical principals at the macro scale
and to extend that to the nano scale systems? This understanding is necessary
for the appropriate design of electrochemical devices like super capacitors,
micro fluidic and nano fluidic cells, and also, electrochemical reaction
kinetics and surface behavior of electrodes.

Recently developed cavity ring down spectroscopy
(CRDS) is considered as a very precise and powerful method due to its
outstanding measurement limit in the order of ppm and ppb. CRDS was first
introduced in 1988 ¹ and it has become a well-established method in
gas phase concentration measurement after just a few years.^2,3 Unique characteristics of this method over conventional
spectroscopy methods include its independence on light source intensity
fluctuations, which allows the use of lasers, and the long exposure lengths
between the light and the substrate, which is due to the use of optical cavity.

Although CRDS has shown outstanding detection limits
in gas phase, its accuracy is limited in liquid phase in
liquid phase due to light absorption being orders of magnitude higher in the
liquid phase. This fact limits the exposure length and consequently the
detection limits. Despite this limitation, this method is still able to measure
concentrations in the order of micro and nano moles with a repetition rate of
up to MHz and spatial resolution of a few hundred nanometers.^4,5,6,7

The main goal of this project is the fundamental
study of electrochemical principles at the nano scale. Additionally, new
methods based on CRDS will be introduced as an alternative way to study
electrochemical reaction kinetics during this study. As an example, capillary-based
microelectrochemical cells are now well established and showed the importance
of the ability to probe electrochemical activity of surfaces on the micro
scale. However, this method exhibits complications like the limiting effect of resolution
of the potentiostat on the size of tip diameter. These complications are due to
natural behavior of electrochemical systems in such dimensions such as high absolute
impedance caused by micrometer area of working electrode.⁸ Using new
methods based on CRDS in order to direct measurement of concentration profile
in such a device can be an alternative solution to avoid such limitations.

References

[1] Anthony O'Keefe and David A. G. Deacon,? Cavity
ring-down optical spectrometer for absorption measurements using pulsed laser
sources?, Rev. Sci. Instrum. Vol. 59, p 2544-2551, 1988

[2] Giel Berden, Rudy Peeters, and Gerard
Meijer, ?Cavity ring-down spectroscopy: Experimental schemes and applications?,
Reviews
in Physical Chemistry, Vol. 19, No. 4, p 565-607, 2000

[3] J. J. Scherer, J. B. Paul, A. O'Keefe, and R. J.
Saykally, ?Cavity Ringdown Laser Absorption Spectroscopy: History, Development,
and Application to Pulsed Molecular Beams?, Chem. Rev. Vol. 97, p 25-51, 1997

[4] Kate L. Snyder and Richard N. Zare, ?Cavity
Ring-Down Spectroscopy as a Detector for

Liquid Chromatography?, Anal.
Chem., Vol. 75, p 3086-3091, 2003

[5] Shucheng
Xu, Guohe Sha, and Jinchun Xie,? Cavity ring-down spectroscopy in the
liquid phase?, Rev. Sci. Instrum.Vol.
73, p 255-258, 2002

[6] Helen Waechter, Jessica Litman, Adrienne H.
Cheung, Jack A. Barnes and Hans-Peter Loock,? Chemical Sensing Using Fiber
Cavity Ring-Down Spectroscopy?, Sensors,Vol. 10,
1716-1742, 2010

[7] Alexander J. Hallock, Elena S. F. Berman, and
Richard N. Zare,? Direct Monitoring of Absorption in Solution by Cavity
Ring-Down Spectroscopy?, Anal. Chem., Vol. 74, p 1741-1743, 2002

[8] N. Birbilis, B.N. Padgett, R.G. Buchheit,?
Limitations in microelectrochemical capillary cell testing and transformation
of electrochemical transients for acquisition of microcell impedance data?,
Electrochimica
Acta, Vol. 50, p 3536?3544 , 2005