Powder X-ray Diffraction As a Tool for In Situ Characterization of Electrochemical Systems

Objective

Understanding and characterization of electro­chemical systems conventionally studied through indirect electrical response of the system. The capabilities and accuracy of these methods have been on a continuous growth for decades, however, this type of diagnosis has a natural ambiguity and uncertainty due to inability of distinguishing the active species involved in electron transfer reac­tions. One of the alternative approaches to enhance diagnosis of electron transfer reactions is adopting in-situ characterization techniques to electro­chemical systems in order to observe chemical species along with electrical response of the cell.

The use of X-ray diffraction (XRD) along with electrochemical systems in both in-situ and ex-situ forms is well established now. However, in-situ application of X-ray diffraction technique has been limited to the use of Synchrotron facilities. Although, this combination has proven useful in providing extensive and complementary information, the cost and limited resources puts this method out of reach for many research groups. On the other hand, powder X-ray diffraction systems are widely available at a relatively low cost for many researchers.  Therefore, the possibility of using powder XRD systems along with electrochemical systems seems to be a very attractive opportunity. Although this method has been used for in-situ investigation of battery systems, there have been minimal studies in using in-situ XRD for other electrochemical systems including the cells with liquid electrolytes. This lack of development is mainly due to distorted and unclear X-ray patterns, which caused by scattering and absorption of X-ray by liquid in the cell, in addition with, the difference in height for various layers of the cell. In this project the possibility of using a typical powder XRD system in-situwith electrochemical systems as well as the extent to which useful qualitative data can be extracted from the XRD pattern will be investigate. This objective follows the design of a three electrode, flow cell compatible with XRD requirements.

Methodology

A coin cell assembly with nickel/Mylar microfilm (100 nm nickel on 3.5 micrometer Mylar), polypropylene membrane and platinum counter electrode with 1 molar KOH electrolyte will be used. This setup is designed to demonstrate typical requirements of an electrochemical cell. The working electrode which also acts as the X-ray window is selected based on previous studies of Rhodes et.al.^1,2

Results

Figure shows the XRD pattern of the cell assembly which represents the characteristic X-ray patterns of all the layers in the cell assembly suggesting that solid chemicals can be detected in different layers. More results for mentioned objectives will be presented in the meeting.

 References

1. K. Rhodes, R. Meisner, Y. Kim, N. Dudney, and C. Daniel, Journal of The Electrochemical Society, 158, A890 (2011) http://jes.ecsdl.org/cgi/doi/10.1149/1.3596376.

2. K. Rhodes et al., The Review of scientific instruments, 82, 075107 (2011) http://www.ncbi.nlm.nih.gov/pubmed/21806227.