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Abstract: We report a new method of preparation of a methanol-tolerant Se/Ru cathode catalyst for the direct methanol fuel cell (DMFC) , whereby selenium is deposited on ruthenium nanoparticles by H2-reduction of SeO2 in aqueous solution at room temperature. The obtained Se/Ru(aq) was studied by electrochemical measurements and tested as a cathode catalyst in H2–air and direct methanol fuel cells. The new catalyst formulation (Se/Ru(aq)) is shown to be superior to Se/Ru synthesized from xylenes solvent and to Ru black by RRDE measurements, in terms of both activity and selectivity for complete oxygen reduction to water. Although Ru black is less active, the Tafel slopes and activation energies of Se/Ru catalysts and reduced-Ru black are similar, implying similar ORR mechanisms. In H2–air fuel cell tests, Se/Ru(aq) was more active than Se/Ru(xyl) at all voltages. Compared to Ru black, Se/Ru(aq) was superior at low current densities, but Ru black slightly exceeded the performance of Se/Ru at high current densities. To explain the RRDE and fuel cell observations, the two roles of Se as an inhibitor of Ru oxidation and as a site-blocker are discussed. [Copyright &y& Elsevier]

A series of prototype direct methanol fuel cells (DMFCs) were constructed and operated under identical procedures and conditions except for the surface compositions of the anode electrocatalysts. The cathode electrocatalyst was Pt black (loading 2 mg/cm2, specific surface area: ca. 27 m2/g), the electrolyte membrane was Nafion™ 117, and the anode electrocatalysts were a series of Pt–Ru adatom (Pt–Ruad) nanoparticles (loading 2 mg/cm2, specific surface area: ca. 27 m2/g) prepared by a direct surface reductive deposition of Ruad onto Pt black. The optimum surface coverage of Pt by Ruad was ca. 33% for DMFCs operating at 60 °C. The optimum ranged from ca. 30 to 60% at 90 °C. A DMFC using Pt–Ruad nanoparticles supported on carbon (Vulcan XC-72™) as anode electrocatalyst was operated for 20 days at 8 h each day without loss of activity. These results, combined with those from an in situ cyclic voltammetry study, indicate that no significant Ruad dissolution and/or redistribution occurred during fabrication and operation of the prototype DMFCs. [Copyright &y& Elsevier]

The organometallic precursor Ru4(μ-H)4(CO)12 (1) reacts with dihydrogen (60 atm, room temperature hexane as solvents, 3 h) over either blacked Pt gauze or Pt black powder to deposit Ru adatoms (Ruad) and CO on the Pt surface. The deposition is self-poisoned by adsorbed CO, stopping when a specific coverage of Pt by CO is reached. The results from the electrooxidation of the adsorbed CO, from base voltammograms recorded in aqueous sulfuric acid, from exhaustive anodic stripping of Ruad, and from the potentiodynamic and potentiostatic electrooxidation of MeOH, all show that the deposition self-poisons after ca. 0.05 surface equivalents (moles Ruad vs. moles Pt surface) of Ruad are deposited on blacked Pt gauze. The deposition over Pt black powder self-poisons after depositing ca. 0.10 surface equivalents of Ruad. A direct CH3OH fuel cell using the resulting black Pt–Ruad powder was constructed by hot-pressing the catalyst into a Nafion® membrane. Contrary to expectations, the Pt–Ruad catalyst did not lose significant amounts of surface Ru during either hot pressing the membrane electrode assembly, nor during operation of the fuel cell at 90 °C. [Copyright &y& Elsevier]

Abstract: The synthesis, electrochemical analysis, and hydrogen-air fuel cell testing results for a new type of Se/Ru catalyst called Se/Ru(aq) were described in Part 1. In this second report, we present methanol tolerance studies and direct methanol fuel cell testing for the same catalyst. A “methanol-tolerant” catalyst does not oxidize methanol, nor becomes depolarized by its presence, which is a desirable property for DMFC cathodes used with methanol-permeable membranes or in mixed-reactant designs. In perchloric acid electrolyte, the Se/Ru(aq) catalyst was found to be highly tolerant to 1.0M methanol. More importantly, in fuel-cell testing as a DMFC cathode, Se/Ru(aq) was shown to be highly tolerant to methanol crossing through the membrane (from the anode side) up to a feed concentration of 17M. The results were compared to those obtained using unmodified Ru black and Pt black at the DMFC cathode, in order to gain insight into the catalyst function and to compare the performance to relevant benchmarks. Compared to Pt cathodes, the performance of Se/Ru(aq) is significantly better at high methanol concentrations (e.g., 17M), suggesting their use either in DMFCs with high methanol feed concentrations or in mixed-reactant fuel cells. [Copyright &y& Elsevier]