Nonconformal Particles of Hyperbranched Sulfonated Phenylated Poly(phenylene) Ionomers as Proton-Conducting Pathways in Proton Exchange Membrane Fuel Cell Catalyst Layers

Abstract

Characteristic poor electrochemical kinetics, high ionic resistance, and high mass transport resistance within the catalyst layer (CL) are chief among parameters that cause poor performance of proton exchange membrane fuel cells (PEMFCs) utilizing hydrocarbon-based proton-conducting ionomers. Herein, the design and addition of nondimensionally swellable, nonconformal, hyperbranched sulfo-phenylated poly-(phenylene) ionomer particles (HB-sPPT-H + ) are reported to introduce a direct pathway for proton conduction in hydrocarbon ionomer-based CLs, resulting in an eight times reduction in ionic resistance of the CL, a 71% increase in catalyst mass activity, and a >90% increase in power at 0.6 V (H 2 /air) compared to state-of-the-art hydrocarbon ionomer-based CLs. The benefits of incorporating HB-sPPT-H + ionomer particles are also shown when employed in perfluorosulfonic acid (PFSA) ionomer-based PEMFCs. These results dispel a commonly held conception that hydrocarbon ionomers possess limitations of gas permeability and electrochemical activity and open up previously unexplored avenues of ionomer development for nonfluorous, wholly hydrocarbon PEMFCs.

Anion Exchange Ionomers: Design Considerations and Recent Advances ‐ An Electrochemical Perspective

“…Finally, water uptake can also have an impact on stability as reduction in ionomer swelling can reduce adhesion to the catalyst layer, as summarized in a review by Holdcroft and co‐workers. [ 4 ]…”

“…[ 63 ] As suggested by Mardle et al., standardization of this procedure could provide a quick ex situ way to screen ionomers for adhesiveness. [ 4 ]…”

“…[ 154,155 ] Therefore, the optimization of the ink composition and ionomer should also take into account the choice of deposition method, particularly as CCM might overcome the necessity of an AEI in KOH‐fed AEM water electrolyzers. [ 4 ]…”

“…For a more focused discussion of AEM electrolyzers, we direct the reader to a recent review by Holdcroft and co‐workers. [ 4 ] As this review will show, some of their conclusions in the context of electrolyzers are also applicable to fuel cells, mainly the importance of developing ex situ techniques, to be able to study in isolation: i) the binding ability of the ionomer with the catalyst, ii) the role of AEI morphology and distribution on the device performance, and iii) specific ionomer–catalyst interactions.…”

Molecular-Level Control over Oxygen Transport and Catalyst–Ionomer Interaction by Designing Cis–Trans Isomeric Ionomers

“…The interaction between ionomer and catalyst will directly affect the distribution of ionomer–catalyst clusters and the microstructure of CLs, ultimately playing a crucial role in fuel cell performance. − Dynamic light scattering (DLS) was performed to estimate the hydrodynamic sizes of the particle clusters in the catalyst inks. , Figure a and Figure b show the particle size distribution of anode (the catalyst is Pt–Ru/C) and cathode (the catalyst is Pt/C) inks, respectively. The anode ink shows a bimodal distribution characteristic in the cis- and trans-ionomers coated systems, while there is only unimodal size distribution for the cathode catalyst ink.…”