Abstract

Molecular Studies of Ionic Liquids at Interfaces with Application to Supercapacitors

In order to be self-sufficient with relatively constant energy output, renewable energy sources, such as solar and wind, require that energy be stored during periods of high energy production so that it can be available during periods of low or zero energy production. Among the many choices for energy storage devices, electrical double layer capacitors (EDLCs), also called supercapacitors, are attracting considerable attention.

Supercapacitors store electrical energy via ion electrosorption directly in the EDLs at the electrolyte-electrode interface, suggesting that such liquid-solid interfaces play a dominant role in the underlying energy storage mechanism and the resulting device performance. Because electrical energy in supercapacitors is stored based on physical phenomena rather than chemical reaction (as in batteries), supercapacitors have fast rates of charge/discharge and a virtually limitless number of charge cycles (unlike batteries, which are often limited to 104 or less cycles). Much of the goal of supercapacitor research is aimed at increasing the amount of energy stored (energy density is the strong point in favor of batteries), which in turn focuses attention on the electrolyte, the nature of the electrode, and the electrode-electrolyte interactions.

To date, ionic liquids (ILs) have become emerging candidates for electrolytes used in supercapacitors, due to their exceptionally wide electrochemical window, excellent thermal stability, nonvolatility, and relatively inert nature; meanwhile carbons are the most widely used electrode materials in supercapacitors, due to their high specific surface area, good electrical conductivity, chemical stability in a variety of electrolytes, and relatively low cost. To improve the energy density and the transport properties of the charge carriers in supercapacitors, carbons have been developed in diverse forms such as activated carbons, carbon nanotubes (CNTs), onion-like carbons (OLCs), carbode-derived carbons and graphene. Using molecular modeling combined with molecular experimental probes, such as SAXS, SANS, NMR, and AFM, we report on our investigations into the interfacial phenomena occurring between the IL electrolytes and electrodes of varying geometries to understand the energy storage mechanism of supercapacitors that rely on EDLs established at IL-electrode interfaces.

Biography

Peter T. Cummings is the John R. Hall Professor of Chemical Engineering at Vanderbilt University. He also holds the position of Associate Dean for Research in the Vanderbilt University School of Engineering.

For 20 years (1994-2013), he was associated with Oak Ridge National Laboratory (ORNL) at levels of effort ranging from 40 to 50%. Most recently (2007-2013), he served as the chief scientist (with title Principal Scientist) of the ORNL’s Center for Nanophase Materials Sciences (CNMS); previous to this, he was the founding director of the Nanomaterials Theory Institute, the theory program within the CNMS, and one of the four principal investigators who wrote the proposal to establish the CNMS. His research interests include statistical mechanics, molecular simulation, computational materials science, computational and theoretical nanoscience, and computational biology. He is the author of over 400 refereed journal publications and the recipient of many awards, including the 1998 Alpha Chi Sigma award given annually to the member of the American Institute of Chemical Engineers (AIChE) with the most outstanding research contributions over the previous decade, the 2007 AIChE Nanoscale Science and Engineering Forum Award, the 2010 AIChE Founders Award for Outstanding Contributions to the Field of Chemical Engineering in recognition of his “outstanding contributions through research, service to the Institute, and national leadership on behalf of the profession,” the 2012 Yeram S. Touloukian Award from the American Society of Mechanical Engineers and the 2013 John Prausnitz award, the most prestigious research award – presented every three years – in chemical engineering thermodynamics. He has been elected fellow of the American Physical Society, of the American Association for the Advancement of Science (AAAS), and of the American Institute of Chemical Engineers