Self-assembling multi-layer Pd nanoparticles onto Nafion™ membrane to reduce methanol crossover

Methanol crossover through the proton exchange membranes (PEMs, e.g., Nafion™ membrane) is one of the major obstacles that currently prevent the widespread commercial applications of direct methanol fuel cell (DMFC). In this paper, multi-layer self-assembly Nafion™ membranes (MLSA Nafion™ membranes) were prepared by alternately assembling charged Pd particles and Nafion ionmers onto Nafion™ membranes. The Pd particles, size of about 1.8 nm in average, are charged by PDDA ionomers with zeta potential of 30 mV (pH value of 8.5). The Pd loading of the first-layer MLSA Nafion™ membranes was 0.63 μg cm−2, and the surface coverage of the Pd nanoparticles on the Nafion™ membrane was estimated as 22%. After 5-double-layer Pd particles/Nafion ionomers assembling, the Pd loading reached to 2.86 μg cm−2. The methanol crossover current of the original Nafion™ membranes and 1-double-layer, 2-double-layer, 3-double-layer, 4-double-layer, 5-double-layer MLSA Nafion™ membranes were 0.0495, 3.87E−3, 1.38E−3, 7.32E−4, 5.16E−4 and 4.25E−4 A cm−2, respectively, corresponding conductivities of 0.112, 0.110, 0.105, 0.094, 0.087 and 0.081 S cm−2. This satisfactory performance has given the MLSA Nafion™ membranes a promised prospect of using as proton exchange membrane in direct methanol fuel cells.