Abstract
For future fuel cell operations under high temperature and low- or non-humidified conditions, high-performance polymer electrolyte membranes possessing high proton conductivity at low relative humidity as well as suitable gas barrier property and sufficient membrane stability are strongly desired. In this study, novel nanofiber framework (NfF)-based composite membranes composed of phytic acid (Phy)-doped polybenzimidazole nanofibers (PBINf) and Nafion matrix electrolyte were fabricated through the compression process of the nanofibers. The NfF composite membrane prepared from the pressed Phy-PBINf showed higher proton conductivity and lower activation energy than the conventional NfF composite and recast-Nafion membranes, especially at low relative humidity. It is considered that the compression process increased the nanofiber contents in the composite membrane, resulting in the construction of the continuously formed effective proton conductive pathway consisting of the densely accumulated phosphoric acid and sulfonic acid groups at the interface of the nanofibers and the Nafion matrix. Since the NfF also improved the mechanical strength and gas barrier property through the compression process, the NfF composite polymer electrolyte membranes have the potential to be applied to future fuel cells operated under low- or non-humidified conditions.
Highlights
The polymer electrolyte fuel cell (PEFC) that offers electrical power generation with high efficiency and zero carbon dioxide emission is a crucial technology for resolving global energy and environmental issues [1,2,3]
In our recent studies [25,27], we developed polymer electrolyte composite membranes based on acid-doped polymer nanofibers as a framework that we named “nanofiber framework (NfF)” for the proton conduction pathway
The Nafion dispersion was poured onto the NfF (Phy-polybenzimidazole nanofiber (PBINf)), and the solvent was slowly evaporated to provide a dense membrane
Summary
The polymer electrolyte fuel cell (PEFC) that offers electrical power generation with high efficiency and zero carbon dioxide emission is a crucial technology for resolving global energy and environmental issues [1,2,3]. PEMs that can be utilized under high temperatures (above 100 ◦C) and non-humidified conditions will reduce the usage and cost of the precious metal catalyst due to improved catalytic activity at high temperatures and reduce the cost and complexity of the PEFC system by eliminating the humidifiers [6,7]. It is hard for the conventional PEMs to attempt under such severe conditions because conventional PEMs, mostly based on sulfonated polymers, require sufficient water to dissociate protons from the acid groups and conduct protons effectively. High gas barrier property and improved membrane stability are other issues on PEMs, especially at high temperatures
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