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内容記述 |
This work shows a strategy to reveal the key structural factor of local hydration number (llocal) for improving the chemical stability of hydrocarbon-based polymer electrolyte membranes (PEMs), which is the major problem for their applications in energy conversion devices such as fuel cells and electrolyzers. llocal is defined as the number of water molecules surrounding ion-conducting ionic groups in nanometer scaled ion-channels, determined by partial scattering function analysis. In a series of radiation-grafted PEMs, consisting of poly(styrene sulfonic acid) grafted onto poly(ethylene-co-tetrafluoroethylene) (ETFE-g-PSSA) with ion exchange capacities (IECs) ranging from 0.8 to 2.5 mmol/g, we clarify that ion-channel structures of the PEM in a length scale of a few nanometers are subjected to morphological transition from spherical to bicontinous structure at an approximate IEC of 1.7 mmol/g. Namely, the spherical and bicontinous structures in these PEMs are the origin of low and high llocal (~ 6.5 and >10), leading to high and low chemical stabilities, respectively. Therefore, it is one of the inevitable strategies that to suppress the hydration level down to llocal ~ 6.5, for high chemical stability of these grafted PEMs as well as high conductivity. |
