A Reactive Methanol Filter with a Layer of Nanometer-sized Pt50-Sn50 Catalyst Particles Directly Deposited onto the Proton Exchange Membrane Surface

A thin layer of nanometer-sized Pt50-Sn50 catalyst particles deposited onto the proton exchange membrane (PEM) surface that served as methanol filter was prepared by the impregnation-reduction (IR) method to mitigate the methanol crossover and improve the utilization efficiency of methanol fuel. The mitigation of methanol crossover and performance of MEA containing this Pt50-Sn50 layer had been measured and compared to those of normal-MEA which had no treatment on PEM. This paper investigated and presented possible mechanism of the suppression of methanol crossover of the proposed MEA structure. SEM, X-ray, EDS and EPMA analysis were used to characterize microstructures, phases, chemical composition and distributions of the obtained electrocatalyst layers. Methanol crossover rate in a DMFC was determined by measuring the CO2 concentration at the cathode exhaust in real time. The result demonstrated that the MEA with a layer of nanometer-sized Pt50-Sn50 catalyst particles suppressed methanol crossover by up to 17% more than that of the normal-MEA, and improved MEA performance by 8% at 80℃. However, at 60℃ the MEA performance dropped by 8% although the mitigation of methanol crossover was also observed. The Pt50-Sn50 layer in PEM acted both as a methanol filter and an electrode. The dual-role contributed to the suppression of methanol crossover and improvement of performance. Indeed, the reduction of conductivity of PEM with the existence of a Pt50-Sn50 layer in PEM surface has negatively impacted the output cell performance, especially at 60℃.