Chemically Tuned Anode with Tailored Aqueous Hydrocarbon Binder for Direct Methanol Fuel Cells

School of Chemical Engineering, Hanyang University, Seoul 133-791, Korea.
Langmuir (Impact Factor: 4.46). 07/2009; 25(14):8217-25. DOI: 10.1021/la900406d
Source: PubMed


An anode for direct methanol fuel cells was chemically tuned by tailoring an aqueous hydrocarbon catalyst (SPI-BT) binder instead of using a conventional perfluorinated sulfonic acid ionomer (PFSI). SPI-BT designed in triethylamine salt form showed lower proton conductivity than PFSI, but it was stable in the catalyst ink forming the aqueous colloids. The aqueous colloidal particle size of SPI-BT was much smaller than that of PFSI. The small SPI-BT colloidal particles contributed to forming small catalyst agglomerates and simultaneously reducing their pore volume. Consequently, the high filling level of binders in the pores, where Pt-Ru catalysts are mainly located on the wall and physically interconnected, resulted in increased electrochemical active surface area of the anode, leading to high catalyst utilization. In addition, the chemical affinity between the SPI-BT binder and the membrane material derived from their similar chemical structure induced a stable interface on the membrane-electrode assembly (MEA) and showed low electric resistance. Upon adding SPI-BT, the synergistic effect of high catalyst utilization, improved mass transfer behavior to Pt-Ru catalyst, and low interfacial resistance of MEA became greater than the influence of reduced proton conductivity in the electrochemical performance of single cells. The electrochemical performance of MEAs with SPI-BT anode was enhanced to almost the same degree or somewhat higher than that with PFSI at 90 degrees C.

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    • "However, when a hydrocarbon membrane is assembled with catalyst layers (CLs) based on a perfluorinated ionomer, a problem of interfacial delamination between the membrane and the CL is often encountered [4] [5]. To address this problem, hydrocarbon ionomers having chemical structures similar to those of the membrane have been introduced as proton conducting polymer electrolytes into CL [6] [7] [8] [9] [10]. However, due to the low oxygen permeability of the hydrocarbon ionomers, the corresponding CL showed a relatively low power performance; compared to Nafion, a typical example of perfluorinated ionomer, hydrocarbon ionomers have gas permeability two orders of magnitude lower [11]. "
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    ABSTRACT: A novel and simple thermal imidization method is used to prepare the sulfonated polyimide/Nafion multilayer (NF-SPI-NF) membrane from sulfonated polyimide (SPI) and Nafion-containing solution (Na+ form). The NF-SPI-NF membrane is prepared by immersing a sulfonated poly(amic acid) (SPAA) membrane into the Nafion-containing solution followed by thermal imidization via solvent evaporation. This Nafion is firmly adhered to either side of the SPI membrane via thermal imidization. The prepared membranes are characterized by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and proton conductivity. The membranes are immersed in Fenton's reagent at room temperature to test their oxidative stability and the durability of a single proton exchange membrane fuel cell (PEMFC) system. Analytical results show a marked improvement in NF-SPI-NF membrane stability by adding Nafion layer comparing with that of native SPI membrane. The performance of PEMFC with the NF-SPI-NF membrane is similar to that of PEMFC with the commercially available Nafion 212 at 70°C.
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