Impact of Ionomer Dispersion on PEM Fuel Cell Performance

Abstract

Conventional polymer electrolyte membrane (PEM) fuel cell electrodes using aqueous ionomer dispersion suffer from high manufacturing costs and rapid performance degradation. We have investigated an innovative method of designing fuel cell electrodes to reduce manufacturing costs and extend the lifetime. Our approach to obtaining good fuel cell performance is to; 1) understand ionomer particle morphology in dispersion; 2) investigate the electrode morphology, catalyst, and ionomer binder distributions in the electrodes; 3) evaluate the electrode performance using various electrodes prepared from different dispersing agents. First, laser diffraction particle size analysis was used to understand the various solvents’ impacts on catalyst ink structure. It can be seen that nPA/H 2 O and ethylene glycol (EG) solvent systems provide better ink structure, implied by much smaller agglomeration sizes. IPA/H 2 O and pentanediol based solvent systems exhibit large agglomerations in the ink, which may account for their poor quality. The laser diffraction particle size will be correlated with electrode structure and fuel cell performance later. Low magnification transmission electron microscopy element mapping was then used to characterize the ionomer distribution in these cathode layers. The best ionomer distribution was found in the EG based sample, with ionomer aggregates <50 nm. The porosity and pore size distribution of the electrode layers were also obtained from transmission electron microscopy image analysis. The EG-based electrode shows the lowest porosity (i.e., 13%). It also contains the smallest pore sizes and the highest number of pores. The effect of the dispersing agents on initial fuel cell performance was investigated. In this experiment, four ionomer dispersions were used and compared with nPA/H 2 O and IPA/H 2 O. All MEAs had a Pt loading of ~0.20 mg Pt /cm 2 . The IPA/H 2 O baseline shows very low performance especially in the mass transport region, which is probably attributed to its poor coating quality. The ionomer dispersions have shown significant influence on the fuel cell performance, with a general ranking as: nPA/H 2 O > ethylene glycol > butanediol > pentanediol). The ethylene glycol based sample displays the best performance of all the non-aqueous samples, and its performance is very comparable to the nPA/H 2 O baseline.

Key findings

• ▸nPA/H2O and ethylene glycol solvent systems provide better ink structure, implied by smaller agglomeration sizes.
• ▸IPA/H2O and pentanediol based solvent systems exhibit large agglomerations in the ink, leading to poor electrode quality.
• ▸Laser diffraction particle size analysis was used to understand the impacts of solvents on catalyst ink structure.

Keywords

Identifiers

DOI

10.1149/ma2018-02/44/1515

Journal

ECS Meeting Abstracts

Year

2018