Fundamental Studies on the Dynamics and Energetics of Protic Ionic Liquids, and Some Applications to Fuel Cells
Abstract
The fundamental objective of this research project has been to build up the so-called Protic Ionic Liquid (PIL) branch of the major Ionic Liquids field of physical and applied chemistry. There has been spectacular growth in the study of Ionic Liquids since the time that air- and water-stable versions were discovered in 1992, but it has disproportionally focused on the aprotic members of the overall family of materials. We were attracted to the protic members, meaning those that are formed by simple transfer of protons between molecular species (i.e. from Br¿nsted acid to Br¿nsted base) because of the degree of control on liquid properties that can be exercised by variation of the strength of the proton transfer involved. We aimed to identify and control the distinct properties of ÒionicityÓ and ÒacidityÓ, learning how to make protic ionic liquids that were not only fully dissociated, and therefore capable of record-breaking conductivities, but also to accomplish this while controlling how acidic (in the Br¿nsted sense) the stoichiometric protic salt would be. Thus we aimed to make superacid ionic liquids, by transfer of protons from superacids to very weak molecular bases such that the proton potential in the final product remained in the strongly acidic, even superacidic domain. We aimed to develop: (a) new methods for classifying the strengths of strong and superacids so that we could quantify the outcomes of our experimental preparations, and (b) methods of studying samples we synthesized by companion techniques of NMR and ionic conductivity, without needing to move the sample from one sample holder to another through hostile environments. (and success was reported early in the current grant period) Another objective, only partially met so far, has been to discover how to accomplish the migration of protons in condensed media without requiring the molecular environments that ÓhostÓ the protons in the absence of field, to move with them. This is the problem of ÒdecouplingÓ the proton motion from the environment, and was the subject of one of our most recent papers in which major progress was reported. A newer goal is the understanding of details of the modes of motion of protons in these media, in particular the distinction between ÒvehicularÓ transport in which protons move as a part of a larger entity, e.g. an NH4+ cation, or by assisted hopping or Grotthus type migrations using reorientational or rotational fluctuations of host molecules, or even (at the limit) simple itinerant motions in a proton ÒseaÓ. For this purpose, there is a need to develop sophisticated NMR techniques some of which will be discussed in the body of this report.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Oct 30, 2018
- Source ID
- W911NF1510137
Entities
People
- Charles Angell
Organizations
- Arizona State University
- Army Contracting Command
- United States Army