Paper Number
PO47 

Session
Poster Session

Title
MEEPT: A flowable redox-active organic with a charged state that remains flowable at concentrations of at least 0.5 M

Presentation Date and Time
October 23, 2019 (Wednesday) 6:30

Track / Room
Poster Session / Ballroom C on 4th floor

Authors (Click on name to view author profile)

  1. Wang, Yilin (University of Illinois at Urbana Champaign, Mechanical Science and Engineering)
  2. Suduwella, Malsha T. (University of Kentucky, Department of Chemistry)
  3. Yu, Zhou (Argonne National Laboratory)
  4. Cheng, Lei (Argonne National Laboratory)
  5. Zhang, Lu (Argonne National Laboratory)
  6. Odom, Susan A. (University of Kentucky, Department of Chemistry)
  7. Ewoldt, Randy H. (University of Illinois at Urbana-Champaign, Department of Mechanical Science and Engineering)

Author and Affiliation Lines (in printed abstract book)
Yilin Wang1, Malsha T. Suduwella2, Zhou Yu3, Lei Cheng3, Lu Zhang3, Susan A. Odom2, and Randy H. Ewoldt1
1Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801; 2Department of Chemistry, University of Kentucky, Lexington, KY; 3Argonne National Laboratory, Lemont, IL

Speaker / Presenter 
Wang, Yilin

Text of Abstract
We report viscous flow properties of N-[2-(2-methoxyethoxy)ethyl]phenothiazine (MEEPT), a new redox active molecule (ROM), with molecular weight 388.2 g mol-1, that has been evaluated as an active charge-storage material in redox flow batteries for electrochemical energy storage systems. To study a broad spectrum of concentrations without requiring significant amounts of sample, we employed a microfluidic viscometer (Rheosense mVROC). Using this technique, we measured the viscosity of both the pure liquid state and variably concentrated solutions of neutral (MEEPT) state, and measured variably concentrated solutions of the charged cation state (MEEPT-BF4) – a solid material – both in the non-aqueous solvent acetonitrile at concentrations up to 0.5 M. Experiments confirm that the pure MEEPT substance is flowable, but with a large Newtonian viscosity (412 mPa s-1 at room temperature), a value approximately 1,000x larger than acetonitrile. By contrast, MEEPT / acetonitrile solutions have significantly lower viscosities. At concentrations up to 0.5 M, the viscosity increased by less than a factor of two compared to the solvent. It is notable that higher-order concentration effects are generally negligible and there is no sharp increase in viscosity up to 0.5 M for all ROM systems, including acetonitrile solutions containing both uncharged and charged forms of this ROM, as well as solutions containing supporting salts at concentrations of 0.5 M - in this case LiTFSI or TEABF4. Here the viscosity versus concentration exhibited a nearly linear trend, which was used to determine intrinsic viscosity and molecular hydrodynamic diameter. The hydrodynamic diameter ranges from 9.4 – 11.6 Å, with the diameter of the neutral ROM being smaller than the charged form. Inclusion of supporting salt does not significantly change the hydrodynamic diameter. Further, for all compositions studied here, we observed the Newtonian constant viscosity over shear rate 5000 to 30000 s-1.