Evaluation of proton conductivity of sulfonated polyimide/dihydroxy naphthalene charge-transfer complex hybrid membranes

Abstract

Sulfonated polyimide (SPI)/dihydroxynaphthalene (DHN) charge‐transfer (CT) complex hybrid films were investigated as possible alternative for polymer electrolyte membranes in polymer electrolyte fuel cells. SPI/DHN CT complex hybrid films include CT complexes, which might work as electronic conductors, and sulfonic acid units, which could work as proton conductors. Therefore, the origin of the conductivity of SPI/DHN complex hybrid films was evaluated by four‐probe impedance measurements in the through‐plane direction of the films. The obtained conductivity of the CT complex hybrid films increased with the increase of ion exchange capacity of the CT films and the decrease of CT complex concentration in the films. These results indicated that proton transfer dominantly occurred in the CT complex hybrid films. Proton conductivity of the CT complex hybrid films consisting of 2,6‐ or 1,5‐DHN showed the similar values, although the molecular geometries of the CT complex were different. The activation energy values for proton conductivity in the CT films were approximately the same as that of Nafion 212. Water uptake (WU) results were also conducted and suggest that CT complex formation could control the degree of WU of the films and prevent dissolution of SPI. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 2991–2997

Development of Charge-Transfer Complex Hybrid Films as Polymer Electrolyte Membrane for High Temperature PEFC Operation

“…For example at 100 °C, 9‐a, 9‐c, and 9‐f CT complex hybrid films exhibited proton conductivities of 141, 136, and 124 mS cm −1 , respectively. This behavior was similar to SPI homopolymer . The IEC of 9‐a (3.08) was close to that of SPI homopolymer (3.47).…”

“…In the previous study, CT complex hybrid films composed of SPI homopolymer showed comparable proton conductivity to Nafion . In this study, the nonproton conductive unit BAPPS was introduced to SPI.…”

“…In the previous study, CT complex hybrid fi lms composed of SPI homopolymer showed comparable proton conductivity to Nafi on. [ 24 ] In this study, the nonproton conductive unit BAPPS was introduced to SPI. Introduction of BAPPS to SPI might lead to a signifi cant drop in proton conductivity, although BAPPS contributed to an improvement of mechanical strength and suppression of water solubility for practical PEFC application.…”

“…[ 22 ] In order to develop promising PEMs, we have proposed a new advanced processing method to functionalize and modify the polymeric materials by using charge-transfer (CT) interaction which is commonly used in supermolecular chemistry. [21][22][23][24] This method can be categorized one of the reinforcement methods for polymeric materials by addition of additives such as nanofi llers. [ 22 ] However, the positions of the additives can be easily controlled at a molecular level using CT interaction.…”

“…We have applied the CT complex method to develop CT complex hybrid fi lms composed of SPI homopolymer and 2,6-dihydroxynaphtharene (2,6-DHN) as an additive and could confi rm the effect of the CT complex in the fi lms. [21][22][23][24] The CT complex in the prepared fi lms composed of SPI homopolymer worked as a molecular glue to bind between the SPI main chains. As a result, the mechanical strength and water solubility of the CT complex fi lms have been improved.…”