Temperature Jump Infrared Electrochemical Spectroscopy (TIR-SEC) of Catalytic Intermediates

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In this project funded by the Chemical Structure, Dynamics, and Mechanisms-A (CSDM-A) program of the Chemistry Division, Professor John Asbury of The Pennsylvania State University is using advanced laser techniques to understand how to control complex reactions at the surfaces of catalytic materials. Many sluggish chemical reactions can be accelerated by applying voltage to catalysts - materials that are designed to direct the course of the reactions. In this project, catalysts are developed to accelerate and direct reactions that can reduce carbon dioxide to fuels or that can reduce nitrogen gas to ammonia for fertilizers. Such reactions can play important roles in building sustainable energy and agricultural systems in the future. The reactions occur by transferring multiple electrons and multiple protons to the products that form during the course of the reactions. Each time electrons and protons are added to the product molecules, their chemical properties change. This project is providing insights into how chemical reactions occur at the surfaces of catalysts and what types of sites on their surfaces can most effectively direct each electron and proton transfer step. Students engaged in this research project are gaining valuable experience in state of the art laser techniques, electrochemistry and catalytic materials design. The broader impacts of this work include potential societal benefits from the development of catalysts to more efficiently convert gases such as carbon dioxide and nitrogen to useful products for more sustainable energy and agricultural systems as well as opportunities to train students in the design of advanced spectroscopy and electrochemical instrumentation for catalytic studies under operating conditions. Some of the spectroscopy techniques developed in this research project will be introduced into undergraduate teaching laboratories.The project focuses on time-resolving reaction intermediates involved in multiple electron and proton transfer steps that lead to the conversion of carbon dioxide to alkanes and gaseous nitrogen to ammonia. The reaction intermediates are identified through their mid-infrared vibrational signatures as they form on catalyst surfaces that are deposited onto attenuated total internal reflection mid-infrared waveguides. The catalysts are incorporated into operating electrochemical cells that allow chemical intermediates to be monitored under operating electrochemical potentials. The catalytic reactions are triggered by application of an electrochemical potential and a short laser pulse that are followed by a mid-infrared probe pulse that propagates through the waveguide. The waveguide consists of a silicon prism on which the catalyst and working electrode are deposited, immersed in an electrolyte, and sealed in a vessel to contain gases that are involved in the reactions. The spectroscopic observations of chemical intermediates are correlated with the activity of the electrocatalysts to provide insight about how catalytic intermediates at various stages of the reactions influence the overall activity and selectivity.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.