Suppressing Methanol Crossover with Nanometer-Sized Pt3Sn Particles Self-Assembled on a Nafion Membrane Surface

• Published in: International journal of electrochemical science 2013-06, Vol.8 (6), p.8236-8251
• Main Authors: Lin, Chien-Heng, Wan, Chieh-Hao, Wu, Weite
• Format: Article
• Language: English
• Subjects: methanol crossover; nano-particles; Platinum-Tin alloy; proton conductivity; self-assembly layer
• ISSN: 1452-3981; 1452-3981
• DOI: 10.1016/S1452-3981(23)12883-5

In this paper, 5 and 10 poly(allylamine hydrochloride) (PAH)/poly(styrene sulfonic acid sodium salt) (PSS) bi-layers with dispersed Pt3Sn alloy nano-particles are self-assembled onto both sides of the Nafion-117 membrane to suppress methanol crossover. The Pt3Sn alloy in PAH/PSS bi-layers are synthesized by the reduction of Pt and Sn ions in PSS with NaBH4. The UV-visible spectroscopy was used to monitor the PAH/PSS self-assembly bi-layers. The methanol crossover in membrane electrode assembly (MEA) was determined by measuring the CO2 concentration at cathode exhaust using a CO2 sensor. The results confirm that the Pt and Sn deposited in PAH/PSS bi-layers exist in a Pt-Sn alloy phase with atomic ratio of 3:1 (Pt:Sn). The layer thicknesses of 5 and 10 PAH/PSS bi-layers containing Pt-Sn alloy are 150nm and 300nm, respectively. The MEA, with 5 PAH/PSS bi-layers containing Pt-Sn alloy nano-particles (average particle size is 17 nm) catalyst, suppress methanol crossover by 50% and slightly improve the output current by 6% (@0.40V). This is because the presence of Pt-Sn alloy and PAH/PSS bi-layers itself functions like a catalytic active layer and methanol barrier that react and block the crossed-over methanol. These dual roles contribute to the suppression of methanol crossover and performance improvement. However, the thickness effect is evident for the 10 PAH/PSS bi-layers sample and results in the decrease of cell performance by 19%, while suppressing methanol crossover by 50%.