Influence of the Nafion agglomerate morphology on the water-uptake behavior and fuel cell performance in the proton exchange membrane fuel cells

Abstract

In the preparation of catalyst ink for proton exchange membrane fuel cell, the dispersing solvent has significant influence on the physicochemical and electrochemical properties of catalyst layer (CL), primarily due to the variation of the Nafion ionomer mobility. In this work, based on the Nafion mobility, the effect of solvent on water uptake (WU) behavior in the CL was investigated with respect to different solvents. To vary main- and side-chain mobilities of the Nafion ionomers, we consider different solvents such as glycerol, propylene glycol (PG), isopropyl alcohol (IPA), and N-methyl-2-pyrrolidinone (NMP). Experimental results demonstrated that the NMP CL showed the highest WU at 90% relative humidity, presenting 1.23, 1.27, and 1.28 times higher than that of the glycerol, PG, and IPA CL, respectively. Furthermore, the microstructure and phase images of the CLs revealed that the main-chain mobility governs the clustering behaviors among the Nafion agglomerates, whereas the side-chain mobility determines the ion-clustering behavior within the Nafion agglomerate. From the electrochemical performances, it was observed that the main- and side-chain mobility are related to the electrochemically active area and the proton-conduction pathway, respectively.