Passive DMFC system using a proton conductive hydrocarbon membrane

A passive direct methanol fuel cell (DMFC) system was fabricated based on a sulfonated polyimide–silica nanocomposite (SPI–SiO2-1) membrane with high proton conductivity, low methanol (MeOH) permeability, and thin thickness compared to Nafion 117 as a reference sample. The electrochemical performance of the passive systems were highly affected by both MeOH permeation through the membranes and MeOH fuel concentration. Electrochemical performance was improved as the MeOH concentration increased up to 3 M. For high concentrations greater than 5 M MeOH, highly-permeated MeOH led to a severe poisoning on the Pt catalyst surface, which resulted in a rapid reduction in the activation polarization region. SPI–SiO2-1 acted as a better MeOH barrier than Nafion1 117. The maximum power density of a passive DMFC based on SPI–SiO2-1 was 140% greater than Nafion1 117, indicating that SPI–SiO2-1 may be an alternative proton exchange membrane for passive DMFC operated under high MeOH concentrations with high energy density.

The following conclusions were drawn from the study: (1) A passive DMFC system was successfully fabricated with MEAs based on SPI–SiO2-1 nanocomposite membranes with higher proton conductivity, better methanol barrier property, and thinner membranes than Nafion1 117. The passive system was electrochemically evaluated with different MeOH concentrations. The passive DMFC system exhibited better electrochemical performance than a system using Nafion1 117 under all MeOH concentrations. The maximum cell performance (maximum power density ¼ 7.3 mW cmÀ2 at 0.26 V) was observed at 3 M MeOH. Increasing MeOH concentration caused a significant difference of I–V polarization in passive DMFC systems based on SPI–SiO2-1 and Nafion1 117. Differing from Nafion1 117 exhibiting much reduced electrochemical performances under harsh 5 M MeOH condition, SPI– SiO2-1 may be considered as a potential PEM for high-performance passive DMFC system operated with a long fuel-exchange cycle. (2) In the DMFC system assembly, compact adhesion between each component was necessary for improved electrochemical performance. The change of the location of joining screws provided reduced contact resistance between the MEA and current collectors, leading to enhanced I–V performance.