Use of in situ polymerized phenol-formaldehyde resin to modify a Nafion® membrane for the direct methanol fuel cell

Commercial Nafion®-115 (trademark registered to DuPont) membranes were modified by in situ polymerized phenol formaldehyde resin (PFR) to suppress methanol crossover, and SO3− groups were introduced to PFR by post-sulfonatation. A series of membranes with different sulfonated phenol formaldehyde resin (sPFR) loadings have been fabricated and investigated. SEM-EDX characterization shows that the PFR was well dispersed throughout the Nafion® membrane. The composite membranes have a similar or slightly lower proton conductivity compared with a native Nafion® membrane, but show a significant reduction in methanol crossover (the methanol permeability of sPFR/Nafion® composite membrane with 2.3 wt.% sPFR loading was 1.5 × 10−6 cm2 s−1, compared with the 2.5 × 10−6 cm2 s−1 for the native Nafion® membrane). In direct methanol fuel cell (DMFC) evaluation, the membrane electrode assembly (MEA) using a composite membrane with a 2.3 wt.% sPFR loading shows a higher performance than that of a native Nafion® membrane with 1 M methanol feed, and at higher methanol concentrations (5 M), the composite membrane achieved a 114 mW cm−2 maximum power density, while the maximum power density of the native Nafion® was only 78 mW cm−2.