ABSTRACT
For further commercializing proton-exchange membrane fuel cells, it is crucial to attain long-term durability while achieving high performance. In this study, a strategy for modifying commercial Nafion membranes by introducing ultrathin multiwalled carbon nanotubes (MWCNTs)/CeO2 layers on both sides of the membrane was developed to construct a mechanically and chemically reinforced membrane electrode assembly. The dispersion properties of the MWCNTs were greatly improved through chemical modification with acid treatment, and the mixed solution of MWCNTs/CeO2 was uniformly prepared through a high-energy ball-milling process. By employing a spray-coating technique, the ultrathin MWCNTs/CeO2 layers were introduced onto the membrane surfaces without any agglomeration problem because the solvent rapidly evaporated during the layer-by-layer stacking process. These ultrathin and highly dispersed MWCNTs/CeO2 layers effectively reinforced the mechanical properties and chemical durability of the membrane while minimizing the performance drop despite their non-ion-conducting properties. The characteristics of the MWCNTs/CeO2 layers and the reinforced Nafion membrane were investigated using various in situ and ex situ measurement techniques; in addition, electrochemical measurements for fuel cells were conducted.
ABSTRACT
The catalyst layer's high durability is essential in commercializing polymer electrolyte membrane fuel cells (PEMFCs), particularly for vehicle applications, because their frequent on/off operation can induce carbon corrosion, which affects surface properties and morphological characteristics of the carbon and results in aggregation and detachment of Pt nanoparticles on the carbon surface. Herein, to address the carbon corrosion problem while delivering a high-performance PEMFC, polydimethylsiloxane (PDMS) with high gas permeability, chemical stability, and hydrophobicity was employed to protect the catalyst layer from carbon corrosion and improve the mass transport. Because the catalyst slurry using alcohol-based solvents showed low compatibility with nonpolar solvents of the PDMS solution, a parallel two-nozzle system with separated solution reservoirs was developed by modifying a conventional three-dimensional printing machine. To determine the optimal PDMS amount in the cathode catalyst layer, PDMS solution concentration was varied by quantitatively controlling the PDMS amount coated on the electrode layer. Finally, the PEMFC with the PDMS-modified cathode of 0.1 mgPDMS cm-2 loading showed enhanced durability due to increased electrochemical surface and maximum power density by 37.2 and 21.7%, respectively, after the accelerated stress test. Furthermore, an improvement in the initial performance from enhanced water management was observed compared to those of PEMFCs with a conventional electrode.
