Hydrophobic Quaternized Poly(fluorene) Ionomers for Emerging Fuel Cells

Abstract

Quaternized polymers as electrode ionomeric binders enable fuel cell operation under high-pH or anhydrous conditions. Herein we report quaternized poly­(fluorene) ionomers with controlled hydrophobicity (contact angle of electrodes with the ionomers 109–164°) by changing the length of tethered fluoroalkyl chains. The anion-exchange membrane fuel cell employing the hydrophobic ionomer exhibits improved durability (voltage loss 0.41 mV h–1) through better water management. The high-temperature proton-exchange-membrane fuel cell using the ionomer shows superior H2/air performance (1.7 A cm–2 at 0.4 V). The finding in this study highlights the benefits of hydrophobic ionomers for emerging fuel cell applications.

Quaternized Polynorbornene Random Copolymers for Fuel Cell Devices

“…We used a quaternized poly(fluorene) ionomer for the catalyst binder. 19 The preparation of the XL-SEBS membrane and MEA fabrication is described in a previous report. 20 The QPN-based MEA was prepared as follows.…”

“…While quaternized polymers are extensively studied for AEMFCs, studies utilizing quaternized polymers in HT-PEMFCs are relatively limited. 19,29,30 The performance of quaternized VAPNBs in AEMFCs is highly dependent on the IEC of the membranes. The un-cross-linked 2.2 mequiv/g tetrablock copolymer mentioned above exhibited a maximum power density of 0.54 W/cm 2 , while a high IEC (3.5 mequiv/g) cross-linked membrane reached a maximum power density of 3.2 W/cm 2 .…”

“…Both anion exchange membrane fuel cells (AEMFC) and high-temperature proton exchange membrane fuel cells (HT-PEMFC) can utilize quaternized polymers as the membrane or ionomer in the fuel cell device. While quaternized polymers are extensively studied for AEMFCs, studies utilizing quaternized polymers in HT-PEMFCs are relatively limited. ,, The performance of quaternized VAPNBs in AEMFCs is highly dependent on the IEC of the membranes. The un-cross-linked 2.2 mequiv/g tetrablock copolymer mentioned above exhibited a maximum power density of 0.54 W/cm 2 , while a high IEC (3.5 mequiv/g) cross-linked membrane reached a maximum power density of 3.2 W/cm 2 . , These previous studies have shed light on understanding the impact of IEC and polymer architecture, especially block copolymer structure, of VAPNBs on their AEMFC performance.…”

“…Over the last several years, considerable progress has been made in identifying polymer backbones that offer increased stability for quaternized polymers. Polymer backbones consisting of aryl ether linkages have shown to degrade quickly under basic conditions, − and quaternized polymers with the best known alkaline stability are those consisting of an all-C–C bond aliphatic or aromatic backbones. − Quaternized polymers including Diels–Alder poly­(phenylene), poly­(aryl piperidinium), , poly­(fluorene), ,, and polystyrene block copolymers have high alkaline stability and demonstrate promising device performance.…”

Phenyl‐Free Polynorbornenes for Potential Anion Exchange Ionomers for Fuel Cells and Electrolyzers

“…To further improve the recoverable performance, we developed fluorinated FLN ionomers that have hydrophobic fluoroalkyl side chains with similar conductivity to the nonfluorinated system (Table 1). [ 40 ] The MEA using a fluorinated FLN ionomer exhibited much‐improved stability (pink symbol). Figure 5b shows the 200‐hr test of the polynorbornene‐based MEA at 80 °C and a constant current density of 1 A cm −2 .…”