Commercialization applications of proton exchange membrane fuel cells (PEMFCs) are throttled by the durability issues of the electrodes prepared by using catalyst inks. Probing into a desirable catalyst/ionomer interface by adjusting the catalyst inks is an effective way for obtaining high-durability electrodes. The present study investigated quantitatively the catalyst/ionomer interfaces based on the viscosity (η) property of the isopropyl alcohol (IPA) and dipropylene glycol (DPG) nonaqueous mixture solvent for the first time. Accelerated stress test (AST) showed that η as one of the characteristic parameters of the solvent had a threshold effect on the durability of electrodes. The electrodes in the half-cell and single cell all exhibited the highest durability using IPA:DPG = 2:6 (η = 27.00 cP) as the dispersion solvent in this work, embodied by its ECSA loss rate, and the cell potential loss was minimum after AST. The ECSA loss mechanism showed that a fine catalyst/ionomer interface structure was created for the highest durability electrode by regulating the η values of the solvent, and the carbon corrosion loss (le) and Pt particle dissolution loss (ld) were weakened. Based on the molecular dynamics (MD) simulation and 19F NMR spectra results, the solvent ratio (various η and similar ε and δ) affected the dispersion states of the ionomer. For the catalyst inks with the highest durability (IPA:DPG = 2:6), the Nafion backbone and side chain presented a higher mobility behavior in the solvent and tended to show the structure of extension separation and the respective aggregation of hydrophilic/hydrophobic phases. Meanwhile, Pt slab models suggested that the side chain of Nafion more easily adhered to the Pt interface zone, while the backbone was pushed toward the carbon support interface zone as more DPG molecules distributed on the Pt surface, which reduced the dissolution of Pt particles and the corrosion of the carbon support. These catalyst/ionomer interface structures tailored by regulating the solvent η values provide insights into improving the electrode durability.
Keywords: catalyst/ionomer interfaces; durability of PEMFC electrode; ionomer mobility; molecular dynamics simulation; solvent viscosity.