Additional Technical Details
Counterion Dynamics Measurements using Quasi-elastic neutron scattering (QENS) were used to measure the correlations between counter-ion dynamics and bulk mechanical relaxations in alkyl ammonium neutralized membranes. These measurements have provided a physical description of how the network structure contributes to the ionic conductivity properties of the membrane.
QENS is a powerful tool to investigate the counter-ion dynamics in alkyl ammonium neutralized PFSI membranes. We have shown explicitly that the mechanical properties via the a-relaxation in these materials is indeed linked to the onset of mobility of the counter-ions on the length-scale related to the characteristic ionomer morphology. To our knowledge, these data are the first direct measure of the dynamics associated with the ion-hopping process in these ion-containing polymers. These data provide important links between electrostatic interactions and dynamics in ionomers and, moreover, show unequivocally that at the α-relaxation temperature a significant destabilization of the electrostatic network may be observed. This results in the activation of a dynamic network facilitated through an ion-hopping process (figure above).
Recent advancements in SANS techniques have been applied to this problem for oriented membranes. Initial studies of the rotationally dependent scattering (above) support a fibillar structure in the stretched state. It is anticipated that a full analysis over several length scales will yield the detailed information about the relative orientation and distribution of the morphological features and aid in developing accurate models of the overall morphology.
- A huge array of emerging technologies, from new portable electronic devices to smart energy vehicles, depend on the successful development and deployment of efficient, light weight, reliable and cost-effective fuel cells. The potential market for these new goods represents billions of dollars to the U.S. economy.
- Our measurements of polyelectrolyte membrane (PEM) materials will help industry better understand, design and optimize this most critical part of low temperature fuel cells. NIST experimental methods, analytical tools and technological infrastructure will help accelerate the characterization, development and deployment of these important new technologies.
- A new NIST collaboration with General Motors (GM), a leading manufacturer of PEM fuel cell systems, will identify and address key measurement challenges in PEMs.
Project Summary (PDF)
Prof. Do Yoon
Seoul National University
NIST Center for Neutron Research