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

Abstract

Novel charge‐transfer (CT) complex hybrid films for high temperature polymer electrolyte fuel cell (PEFC) application based on sulfonated polyimide (SPI) with hydrophobic unit (4,4 (sulfonylbis(4,1‐phenylene)bis(oxy)dianyline (BAPPS)) are synthesized and characterized. In this study, property changes of the polymer electrolytes prepared by a unique CT complex postmodification process are evaluated. The effect of the CT complex formation in the obtained films on the properties of the polymer films is evaluated, because the CT complex can work as a binder between SPIs. Water uptake of the CT complex hybrid films shows a lower value than that of the original SPI film. The CT complex hybrid films also exhibit comparable proton conductivity to Nafion 115 under high‐temperature operational conditions (100–120 °C). These results suggest that the CT complex hybrid films developed are promising alternatives for high temperature PEFC application.

Aliphatic SPI charge‐transfer complex hybrid films for high temperature polymer electrolyte membrane fuel cells

“…The maximum absorbance of the aliphatic SPI CT hybrid films was observed at 500–525 nm. This result confirms previous work in which the characteristic absorbance peak was assigned to a CT band formed between NDI and 2,6‐DHN in the solid state . This indicates that aliphatic SPI and 2,6‐DHN can form CT complexes in these films.…”

“…This indicates that aliphatic SPI has low efficiency in forming a CT complex, and that some of the donor molecules did not contribute to formation of the CT complex. The aromatic SPI CT complex hybrid films reported previously also showed the similar behavior …”

“…After drying, the 2,6‐DHN‐free AS‐1 film was yellow [Figure (a)]. However, as with previously studied SPI CT films, the aliphatic SPI CT complex hybrid films were largely dark brown [Figure (a)] and did not undergo phase separation. This drastic color change from yellow to dark brown is typical evidence of CT complex formation.…”

“…The next loss at around 180 °C is attributed to evaporation of DMSO residue in the films. The loss at around 210 °C corresponds to the decomposition temperature of the sulfonic acid group, whilst the main chain starts to decompose at about 250 °C. Compared with AS‐1, the other films experienced lower mass loss, indicating that only polymer decomposition affected the weight loss of the films in this temperature range, and that 2,6‐DHN did not affect weight loss.…”

“…DSC was measured from 50 to 300 °C, under nitrogen atmosphere [Figure (b)]. In a previous study, aromatic SPI CT films did not show any glass transition temperature ( T g ) below 300 °C. Unlike aromatic SPI, some aliphatic SPI CT films containing higher amounts of the donor molecule (i.e., AS‐3 and AS‐4) displayed a T g of around 140–160 °C.…”