Article

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: 4.38). 07/2009; 25(14):8217-25. DOI: 10.1021/la900406d
Source: PubMed

ABSTRACT 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.

0 Bookmarks
 · 
66 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Hydrophilic silica (SiO2) nanoparticles (average size = 7 nm), which act as inorganic acids at low pH (<2), were added together with a PEO–PPO–PEO triblock copolymer dispersant to a random disulfonated poly(arylene ether sulfone) copolymer in the potassium salt (SO3−K+) form in order to control permeation and rejection characteristics of the homopolymer. The dispersants (shell) absorbed on the surface of SiO2 nanoparticles (core) formed a distinctive core–shell structure. The PEO units located at the outside of the dispersant formed complexes with SO3−K+ groups of BPS-20 via ion–dipole interactions. These interactions induced a compatible binary system following the Flory–Fox equation associated with glass transition temperature (Tg) depression and prevented extraction of the water-soluble dispersant even under aqueous conditions. The ion–dipole interaction, combined with hydrogen bonding between SiO2 and the dispersant, caused SiO2 nanoparticles to be well distributed within the BPS-20 matrix up to a limit of 1 wt.% of SiO2 and minimized the formation of non-selective cavities within the matrix's hydrophilic water channels. The resulting BPS-20_SiO2 nanocomposites showed improved salt rejection and reduced ionic conductivity. These trends are analogous to those of disulfonated copolymer systems, with polar groups creating hydrogen bonding or acid–base complexation with SO3−K+ groups in BPS copolymers. Well dispersed SiO2 nanoparticles in highly water-permeable desalination membranes are expected to result in an increase in salt rejection but very little change in water permeability. The addition of nanoparticles to desalination membranes may offset the permeability-selectivity tradeoff observed in polymer membranes. Above 1 wt.%, SiO2 nanoparticles increased both the interchain distance between polymer chains and the water uptake. However, the increased hydrophilicity due to high SiO2 content did not yield improved water permeation of the nanocomposite membranes. The SiO2 nanoparticles acted as barriers, hindering water passage (restrictive diffusion) and lowering water permeability. Meanwhile, acidic hydroxyl groups (OH2+) on the SiO2 surface in the sulfonate matrix led to improved ionic conductivity, but NaCl rejection capability decreased because the concentration of SO3−K+ was diluted by highly absorbed water molecules, resulting in weakened Donnan exclusion. The mechanical properties and chlorine resistance of all BPS-20_SiO2 nanocomposites were comparable to those of BPS-20.
    Journal of Membrane Science 03/2012; s 392–393:157–166. · 4.91 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Novel, cost-effective, high-performance, and environment-friendly electrode binders, comprising polyvinyl alcohol chemical hydrogel (PCH) and chitosan chemical hydrogel (CCH), are reported for direct borohydride fuel cells (DBFCs). PCH and CCH binders-based electrodes have been fabricated using a novel, simple, cost-effective, time-effective, and environmentally benign technique. Morphologies and electrochemical performance in DBFCs of the chemical hydrogel binder-based electrodes have been compared with those of Nafion® binder-based electrodes. Relationships between the performance of binders in DBFCs with structural features of the polymers and the polymer-based chemical hydrogels are discussed. The CCH binder exhibited better performance than a Nafion® binder whereas the PCH binder exhibited comparable performance to Nafion® in DBFCs operating at elevated cell temperatures. The better performance of CCH binder at higher operating cell temperatures has been ascribed to the hydrophilic nature and water retention characteristics of chitosan. DBFCs employing CCH binder-based electrodes and a Nafion®-117 membrane as an electrolyte exhibited a maximum peak power density of about 589mWcm−2 at 70°C.
    Journal of Power Sources 07/2011; 196(14):5817-5822. · 5.21 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Hydrocarbon ionomers have not been successfully employed in the cathode of polymer electrolyte fuel cell (PEFC)s due to their low oxygen permeabilities. In this work, we propose a partially fluorinated aromatic polyether with sulfonic acid groups (s-PFPE) as an ionomer for the cathode catalyst layer. Compared to sulfonated poly(ether ether ketone) (s-PEEK), it exhibited more than 1.5 times higher oxygen permeability at RH 40% and 1.3 times higher at RH 100%. The catalyst layer based on s-PFPE showed higher power performance than that based on s-PEEK owing to enhanced oxygen transport and fast proton conduction through the s-PFPE ionomer phase covering the catalyst layer. We demonstrate that the introduction of the perfluorinated moieties to the hydrocarbon backbone is an effective strategy for the use of hydrocarbon ionomer in the cathode of PEMFCs.
    Electrochimica Acta 04/2014; 125:314–319. · 4.09 Impact Factor