Enhanced Performance of Ionomer Binder with Shorter Side‐Chains, Higher Dispersibility, and Lower Equivalent Weight

Abstract

Interaction between the ionomer binder and catalyst nanoparticles in catalyst ink is well known to play an important role in the performance of proton exchange membrane fuel cells (PEMFCs) because it determines the final micro‐morphology of the catalyst layer. Herein, we investigated the 3M series of perfluorinated sulfonic acid (PFSA) ionomer binders, which have higher polymeric main‐chain mobilities, increased solubilities, shorter side‐chains, and lower equivalent weights than the Nafion 1100 series of ionomers. The molecular mobility was determined by 19F nuclear magnetic resonance (NMR), and the differences in the structure of the catalyst layer surfaces were identified using field‐emission scanning electron microscopy (FE‐SEM) and Hg intrusion porosimetry (MIP). The 3M binder with high dispersibility exhibits more developed and connected secondary pore catalyst layer structures and fewer clustered agglomerates; thus, it shows higher performance in a single cell, particularly under conditions of low relative humidity (RH). A comparative study of the electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) results of the 3M and Nafion series of ionomer binders is also included. These insights help us elucidate the reason for the difference in performance by different ionomers and provide the foundation for improving the fuel cell performance of Nafion‐type ionomers.

Differences in the Electrochemical Performance of Pt-Based Catalysts Used for Polymer Electrolyte Membrane Fuel Cells in Liquid Half- and Full-Cells

“…This was attributed to the increased oxygen permeability, leading to enhanced mass transfer. Kim et al 399 proposed an SSC ionomer developed by 3 M (3 M ionomer) in an MEA to examine its effect on the performance. Optimization of the 3 M ionomer content showed that the optimal content was 25 wt %.…”

Component Optimization for Catalyst Layers in Proton Exchange Membrane Fuel Cells

“…[26] Figure 4 The molecular structure, the ionomer morphology in catalyst ink dispersions, and field emission scanning electron microscope (FESEM) surface images of the catalyst layer in the MEA: (a) Nafion 1100; (b) 3M 725 ionomers. [27] Reprinted with permission from Ref. [27].…”

“…It has been commonly accepted that short side-chain ionomers are preferable to be the binders. [27][28][29][30][31][32][33] It has been greatly agreed that the proton conductivity can be improved with the increase of relative humidity. [34] Since the SSC ionomers usually have lower equivalent weight (EW) and better water absorption capability, their proton conductivities are higher than those of LSC ionomers, especially under low humidity conditions, resulting in a substantial performance improvement.…”

“…Consequently, SSC ionomers are expected to show a relatively weaker clustering trend and thus form smaller agglomerated structures (Figure 4). [27] More homogeneous catalyst and ionomer agglomerates improve the platinum utilization, increase the proportion of micropores, and reduce the oxygen transportation resistance. [27,29] Besides, some researches have revealed that MEA prepared with SSC ionomers possess higher durability than those prepared with LSC ionomers.…”

“…[27] More homogeneous catalyst and ionomer agglomerates improve the platinum utilization, increase the proportion of micropores, and reduce the oxygen transportation resistance. [27,29] Besides, some researches have revealed that MEA prepared with SSC ionomers possess higher durability than those prepared with LSC ionomers. [29] However, compared with the LSC ionomers, the chemical stability of the SSC ionomers is required to be further improved.…”