Phosphonated Ionomers of Intrinsic Microporosity with Partially Ordered Structure for High-Temperature Proton Exchange Membrane Fuel Cells

Abstract

High mass transport resistance within the catalyst layer is one of the major factors restricting the performance and low Pt loadings of proton exchange membrane fuel cells (PEMFCs). To resolve the issue, a novel partially ordered phosphonated ionomer (PIM-P) with both an intrinsic microporous structure and proton-conductive functionality was designed as the catalyst binder to improve the mass transport of electrodes. The rigid and contorted structure of PIM-P limits the free movement of the conformation and the efficient packing of polymer chains, resulting in the formation of a robust gas transmission channel. The phosphonated groups provide sites for stable proton conduction. In particular, by incorporating fluorinated and phosphonated groups strategically on the local side chains, an orderly stacking of molecular chains based on group assembly contributes to the construction of efficient mass transport pathways. The peak power density of the membrane electrode assembly with the PIM-P ionomer is 18−379% greater than that of those with commercial or porous catalyst binders at 160 °C under an H 2 /O 2 condition. This study emphasizes the crucial role of ordered structure in the rapid conduction of polymers with intrinsic microporosity and provides a new idea for increasing mass transport at electrodes from the perspective of structural design instead of complex processes.

Proton‐Conducting Polymers: Key to Next‐Generation Fuel Cells, Electrolyzers, Batteries, Actuators, and Sensors

“…Sun et al presented the synthesis of a novel phosphonated ionomer of intrinsic microporosity (PIMÀ P, Figure 1f). [19] This polymer was designed for better mass transport in electrodes, which was strongly related to fuel cell performance. The proton conductivity of PIMÀ P was 74 mS cm À 1 at 160 °C under humidified conditions.…”

“…[16] Copyright 2020 Springer Nature). (f) Synthetic pathway to phosphonated poly(pentafluorophenylalkane) [19] (Copyright The authors. Published by American Chemical Society (2023)).…”

ACS Central Science Virtual Issue on Advanced Materials and Processes for Building Low-Carbon Energy Systems

“…A high current density up to 15.17 A cm –2 at 2.0 V was even achieved by an AEM electrolyzer using the cross-linked catalyst layer. Zhang, Zheng, and co-workers developed a phosphonated ionomer featuring an intrinsic microporous framework and durable proton-conductive −PO 3 H 2 groups . As a high-performance catalyst binder, the ionomer helps to construct stable mass transport pathways to enhance the electrode performance for high-temperature PEM fuel cells.…”

Polymer of Intrinsic Microporosity as Binders for both Acidic and Alkaline Oxygen Reduction Electrocatalysis

“…[33] More recently, they have been also exploited in electrochemical applications [18,34] as in electrocatalysis. For instance, Sun et al [35] reported a novel ionomer based on the strategical incorporation of fluorinated and phosphonated groups in the PIM's local side chains, resulting in promising performances when added to MEA. Particularly, a lower mass transfer resistance was observed with a peak power density much greater than those of commercially available porous binders.…”