Behavior of Channel Water and CF 2 H Side-Chain Terminal Groups in Swollen Nafion Polymer Electrolyte Membranes after Thermal Treatment

• Published in: ACS macro letters 2016-07, Vol.5 (7), p.801-804
• Main Authors: Kim, Hyun Na, Hwang, Ryeo Yun, Han, Oc Hee
• Format: Article
• Language: English
• ISSN: 2161-1653; 2161-1653
• DOI: 10.1021/acsmacrolett.6b00388

Polymer electrolyte membranes (PEMs) are representative systems for the study of the proton conduction mechanism and water dynamics in nanopores/channels. Our H nuclear magnetic resonance data for Nafion PEMs, which are subjected to thermal degradation and then swollen in water, indicate that (1) water is present next to the side chains even after the removal of the SO H groups, (2) longer heat-treatment depletes more SO H groups and produces more CF H groups, (3) the water near the side chains allows for the liquid-like motion of the CF H groups, and (4) the motion correlates well with the content and dynamics of water in the channels. As the thermal degradation progresses, the Nafion membranes lose their ionic and hydrophilic nature due to the conversion of CF SO H groups to CF H groups. In addition, our results demonstrate that increasing channel hydrophobicity leads to increased water dynamics in the channels.