Wettability of Nafion and Nafion/Vulcan Carbon Composite Films

摘要

The wettability of the Pt/carbon/Nafion catalyst layer in proton exchangenmembrane fuel cells is critical to their performance and durability, especially the cathode, asnwater is needed for the transport of protons to the active sites and is also involved in deleteriousnPt nanoparticle dissolution and carbon corrosion. Therefore, the focus of this work has been onnthe first-time use of the water droplet impacting method to determine the wettability of 100%nNafion films, as a benchmark, and then of Vulcan carbon (VC)/Nafion composite films, bothndeposited by spin-coating in the Pt-free state. Pure Nafion films, shown by SEM analysis tonhave a nanochanneled structure, are initially hydrophobic but become hydrophilic as the water droplet spreads, likely due tonreorientation of the sulfonic acid groups toward water. The wettability of VC/Nafion composite films depends significantly onnthe VC/Nafion mass ratios, even though Nafion is believed to be preferentially oriented (sulfonate groups toward VC) in allncases. At low VC contents, a significant water droplet contact angle hysteresis is seen, similar to pure Nafion films, while at highernVC contents (>30%), the films become hydrophobic, also exhibiting superhydrophobicity, with surface roughness playing ansignificant role. At >80% VC, the surfaces become wettable again as there is insufficient Nafion loading present to fully cover thencarbon surface, allowing the calculation of the Nafion:carbon ratio required for a full coverage of carbon by Nafion.