Scanning Electrochemical Microscopy and Ultramicroelectrode Studies of Electrocatalysis at Nanoparticle Ensembles of Microdimensions and at Single Nanoparticles

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In this project funded by the Chemical Measurement and Imaging Program of the Division of Chemistry, Professor Cynthia Zoski of New Mexico State University is studying electrocatalysis at finite nanoparticle ensembles and single nanoparticles on conducting surfaces of ultramicrodimensions where kinetic investigations are carried out under high mass transport conditions. Nanoparticles are an important part of the overall catalyst design in energy devices such as fuel and solar cells. These studies provide wide-ranging knowledge on the relationship between nanoparticle size, distribution, and catalytic activity. These studies also address a key issue in electrocatalysis regarding the nature of intermediates and adsorbed species on a catalyst surface while the electrode reaction occurs, which aid in diagnosis of reaction mechanisms, with relevance to molecular recognition, sensing, and to infectious diseases where biofilm integrity and the relationship to quorum sensing and bacteria micro-colonies are of interest. Broader impacts also include training of post-doctoral fellows and graduate students in multi-disciplinary scientific research in areas of national importance, and developing a new course in advanced electrochemical techniques which targets post-doctoral fellows, graduate and senior undergraduate students from chemistry, chemical engineering, physics, and biology.This project focuses on electrocatalysis at nanoparticle ensembles and single nanoparticles, development of simulations to describe their behavior, fabrication and analysis of ensemble and single nanoparticle electrodes through single nanoparticle collisions at ultramicroelectrodes, and the use of scanning electrochemical microscopy to study the kinetics and nature of the reactivity of electrogenerated oxide films and those adsorbed as a result of an electrocatalytic reaction. The collision approach to nanoparticle electrodes allows control over the number of nanoparticles on a surface, flexibility in selection of the electrode material and nanoparticle type (e.g. metallic, core shell, alloy) and size, and a direct comparison between finite ensemble and single nanoparticle kinetics at the same electrode. The shape of collision transients provides insight into the microscopic details of the nature of nanoparticle interaction with an electrode and the kinetics of electrocatalytic reactions such as oxygen reduction at single nanoparticles. Using transient surface interrogation scanning electrochemical microscopy to study the nature and reactivity of oxide films overcomes the difficulties in traditional electrochemical experiments where the working electrode itself is used to find intermediates and the response is convoluted with the current from the electrolysis and capacitive charge.