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