Ensemble Site Requirements for Oxidative Adsorption of Methanol and Ethanol on Pt Membrane Electrode Assemblies

The ensemble site requirements for the oxidative adsorption of methanol and ethanol on platinum based membrane electrode assemblies in operating liquid feed fuel cells were measured by CO stripping voltammetry. At 30 °C and 0.2 V vs reference hydrogen electrode (RHE), the CO_ads coverage from directly dosed CO (CO_CO), methanol (CO_MeOH), and ethanol (CO_EtOH) are 94%, 49%, and 39%, respectively. At 50 °C the CO_MeOH and CO_EtOH approach equality. The ratio of CO_EtOH/CO_MeOH was simulated with assumed ensemble site requirements of 3 and 2 for ethanol and methanol respectively. Experimental and simulated ratios of 0.79 and 0.78 suggest that high surface area fuel cell Pt catalysts at 30 °C have adsorption properties similar to that of a Pt (100) surface. Potential dependent infrared spectroscopy of CO_MeOH and CO_EtOH from flash evaporated aqueous alcohols delivered to a 50 °C fuel cell show lower CO_EtOH relative to CO_MeOH with Stark tuning rates below 10 cm^–1/V

Ensemble Site Requirements for Oxidative Adsorption of Methanol and Ethanol on Pt Membrane Electrode Assemblies

The ensemble site requirements for the oxidative adsorption of methanol and ethanol on platinum based membrane electrode assemblies in operating liquid feed fuel cells were measured by CO stripping voltammetry. At 30 °C and 0.2 V vs reference hydrogen electrode (RHE), the CO_ads coverage from directly dosed CO (CO_CO), methanol (CO_MeOH), and ethanol (CO_EtOH) are 94%, 49%, and 39%, respectively. At 50 °C the CO_MeOH and CO_EtOH approach equality. The ratio of CO_EtOH/CO_MeOH was simulated with assumed ensemble site requirements of 3 and 2 for ethanol and methanol respectively. Experimental and simulated ratios of 0.79 and 0.78 suggest that high surface area fuel cell Pt catalysts at 30 °C have adsorption properties similar to that of a Pt (100) surface. Potential dependent infrared spectroscopy of CO_MeOH and CO_EtOH from flash evaporated aqueous alcohols delivered to a 50 °C fuel cell show lower CO_EtOH relative to CO_MeOH with Stark tuning rates below 10 cm^–1/V

Influence of Anions on Proton-Conducting Membranes Based on Neutralized Nafion 117, Triethylammonium Methanesulfonate, and Triethylammonium Perfluorobutanesulfonate. 2. Electrical Properties

The electrical properties of a Nafion proton exchange membrane change dramatically when neutralized and then doped with a proton-conducting ionic liquid (PCIL). Broadband electric spectroscopy elucidates the molecular relaxation and polarization phenomena of neutralized Nafion (nN117) doped with triethylammonium methanesulfonate (TMS) and triethylammonium perfluorobutanesulfonate (TPFBu) ionic liquids. These data, coupled with those of part 1 suggest proton conduction mechanisms for both the pure PCILs and in PCIL-doped nN117. At 130 °C, the PCILs have conductivities of σ_TMS = 1.4 × 10^–2S/cm and σ_TPFBu = 9 × 10^–3S/cm, while correspondingly doped nN117 have conductivities of σ_NTMS = 6.1 × 10^–3 S/cm and σ_NTPFBu = 1.8 × 10^–3S/cm. The pure PCILs show three interfacial polarizations associated with proton transfer mechanisms above the melting point. PCIL-doped nN117 also has three interfacial polarizations that depend on the nanostructure characteristics of the PCIL sorbed within the nN117 polar domains. Below the PCIL melting point, doped nN117 has two dielectric relaxations, α and β, associated with dipolar relaxations involving both the sorbed PCILs and the ionomer matrix. The data indicate a long-range charge transfer process that occurs through proton exchange between cationic clusters. Segmental motion of the polymer chains and the molecular dimensions of the ionic liquid nanoaggregates mediate this charge transfer

Thermal Processing as a Means to Prepare Durable, Submicron Thickness Ionomer Films for Study by Transmission Infrared Spectroscopy

A high temperature solution processing method was adapted to prepare durable, freestanding, submicrometer thickness films for transmission infrared spectroscopy studies of ionomer membrane. The materials retain structural integrity following cleaning and ion-exchange steps in boiling solutions, similar to a commercial fuel cell membrane. Unlike commercial membrane, which typically has thicknesses of >25 μm, the structural properties of the submicrometer thickness materials can be probed in mid-infrared spectral measurements with the use of transmission sampling. Relative to the infrared attenuated total reflection (ATR) technique, transmission measurements can sample ionomer membrane materials more uniformly and suffer less distortion from optical effects. Spectra are reported for thermally processed Nafion and related perfluoroalkyl ionomer materials containing phosphonate and phosphinate moieties substituted for the sulfonate end group on the side chain. Band assignments for complex or unexpected features are aided by density functional theory (DFT) calculations