Ultrafast Laser Spectroelectrochemistry

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In this project funded by the Chemical Measurement and Imaging program in the Division of Chemistry, Prof. Dana Dlott of the University of Illinois is developing advanced laser-based instruments that probe molecules on the surfaces of electrodes during electrochemical transformations. Electrochemical systems such as fuel cells and batteries form a significant part of our industrial economy, yet it has proven difficult to understand how these processes work at the fundamental level of individual molecules. A deeper fundamental understanding produces the knowledge needed for major new advances in electrochemical sciences. The investigators build batteries and fuel cells with optical windows, and shine laser beams at the electrodes to watch how the molecules behave in real time. There is a major problem, though; for every molecule at the electrode where the chemistry takes place, there are about one billion spectator molecules not doing anything of interest. To address this problem, the investigators are developing methods that involve pulsing the laser beams and controlling the laser wavelengths by computers. This allows the laser beams to ignore the spectator molecules so the researchers can see how chemistry takes place deep inside electrochemical reactors. The work will have a broad impact on the development of new technologies that will enhance the performance of devices such as fuel cells and batteries. It is having a further broad impact on the training of the next generation of scientists, by involving students at the graduate and undergraduate level in scientific research. The project consists of two related efforts to develop instruments for spectroscopic probing of electrochemistry using a nonlinear coherent infrared (IR) spectroscopy method termed sum-frequency generation (SFG). SFG is one of the most powerful methods to study chemistry at buried interfaces such as electrodes buried under thick electrolyte layers. The first effort seeks to improve the ability to obtain SFG spectra at buried interfaces by overcoming temporal and frequency distortions of fs IR pulses passing through an IR window and an electrolyte. Computer-controlled IR pulse-shaping techniques are used to predistort the IR pulses so they arrive undistorted at the electrodes. The second effort seeks to develop instruments to study ultrafast molecular dynamics at electrodes by ultrafast laser temperature jumping of the electrodes while probing the adsorbed molecules by SFG. In an electrochemical cell, a rather small (50 K) temperature jump can have a significant effect (100 mV) on the electrode potential. The temperature-jump method is a way to rapidly (in nanoseconds) jump electrode potentials far faster than is possible by electrical methods.