Editorial pubs.acs.org/JPCL
Optical Interrogation of Complex Interfaces
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of SOFCs is an ongoing subject of great interest, also represented in recent Letters published in JPC Letters.1 We look forward to future developments that further improve the experimental methods needed to characterize complex interfaces, many of which are likely to be published in the pages of this journal.
any important chemical processes occur at the interface between two phases, whether gas/liquid, gas/solid, liquid/liquid, or liquid/solid. The challenge to experimental interrogation of these interfaces is that, in many circumstances, the bulk phases themselves contain the same molecules in far greater abundance, masking the signals from their interfacial counterparts. Ideal probes of these interfaces would be interface-specific, noninvasive, provide quantitative data on the interfacial composition, determine the spatial arrangement and orientation of these components, and do so in a timedependent and spatially resolved manner. In this issue, two Perspectives describe recent advances in the optical detection of complex interfaces that meet many of these criteria remarkably well. The Perspective by Verreault, Hua, and Allen focuses attention on phase-sensitive vibrational sumfrequency generation (VSFG) spectroscopy (Verreault, D.; Hua, W.; Allen, H. C. From Conventional to Phase-Sensitive Vibrational Sum Frequency Generation Spectroscopy: Probing Water Organization at Aqueous Interfaces. J. Phys. Chem. Lett. 2012, 3, 3012−3028). Here, the nonlinear SFG signal is selectively produced only at the interface, where the centrosymmetric bulk phase is broken. Allen describes the challenges with obtaining the absolute orientation of molecules at these interfaces and the clever solution in which the interference with the signal from a well-characterized second interface is used to deduce these absolute orientations. Application of this phase-sensitive scheme to the aqueous−air interface adds further insight to an amazingly complicated set of competing effects that accompany bringing water molecules and molecular ions to the interface. In the second Perspective, Pomfret, Walker, and Owrutsky describe the use of thermal imaging and vibrational Raman spectroscopy to provide diagnostics of the chemical species formed inside of working solid oxide fuel cells, with 100 μm spatial resolution and on time scales sufficiently short to track the chemical fouling of these fuel cells in real time (Pomfret, M. B.; Walker, R. A.; Owrutsky, J. C. High-Temperature Chemistry in Solid Oxide Fuel Cells: In Situ Optical Studies. J. Phys. Chem. Lett. 2012, 3, 3053−3064). In this case, the methods are not interface-specific; however, the surface area of the SOFCs is intrinsically large, making it possible to track both surfacebound and gas-phase species with good sensitivity. The chemistry inside of these SOFCs is a complicated mixture of pyrolysis of gas-phase fuels and electrochemical reactions at the gas−solid interfaces of the electrodes. Not surprisingly, carbon deposition is a major source of deterioration of the fuel cells. The multifaceted data obtained by the combination of imaging, vibrational spectroscopy, and electrochemical methods is making real progress in characterizing the unique chemistry associated with the wide range of fuels and operating conditions of importance in these fuel cells. The continued development of experimental methods such as these will provide muchneeded constraints on modeling the complicated chemical pathways and the competition between thermodynamics and kinetics that controls these fuel cell properties. Such modeling © 2012 American Chemical Society
Timothy S. Zwier, Senior Editor
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Purdue University, West Lafayette, Indiana, United States
AUTHOR INFORMATION
Notes
Views expressed in this Editorial are those of the author and not necessarily the views of the ACS.
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REFERENCES
(1) Ammal, C. S.; Heyden, A. Combined DFT and Microkinetic Modeling Study of Hydrogen Oxidation at the Ni/YSZ Anode of Solid Oxide Fuel Cells. J. Phys. Chem. Lett. 2012, 3, 2767−2772.
Published: October 18, 2012 3070
dx.doi.org/10.1021/jz301522e | J. Phys. Chem. Lett. 2012, 3, 3070−3070
