Active Reaction Sites for Oxygen Reduction in La0.9Sr0.1,MnO3/YSZ Electrodes

Active reaction sites for 02 reduction in La0.~Sr01MnO3 electrode have been characterized by addressing the origin of the cathodic polarization effects on this electrode material. Cathodic polarization (up to - 1.2 V vs. Pt reference electrode} had several effects on O2 reduction kinetics. First, the O2 reduction rate was favorably increased when the perovskite electrode was cathodically polarized. Second, in situ x-ray photoelectron spectroscopy results indicated that the Mn ions are electrochemically reduced and concomitantly the oxygen stoichiometry decreases. Reduction of Mn ions was further demonstrated in the cyclic voltammogram traced under nitrogen atmosphere. Third, hysteresis in cathodic currents was observed in the cyclic voltammograms of the perovskite/YSZ/Pt system, and the hysteresis phenomena were more prominent at higher O~ pressure. We interpreted these findings to mean that the internal and/or external surface oxide vacancies participate in the O2 reduction reaction. However, it has been explained from the Po2-dependent hysteresis phenomena that, even though those surface sites are active in the O2 reduction~ their activity is less than that of the three-phase boundary sites since additional diffusional processes are required for the former sites. Consequently, the three-phase boundary sites are the major reaction sites at lower O2 pressure, which leads to a small hysteresis. However, at higher 02 pressure, the surface sites also participate in the reaction, resulting in a larger hysteresis.Funding for this work was provided by the R&D Management Center for Energy and Resources (Korea). S. M. Oh gratefully acknowledges the financial support from the Alexander yon Humboldt Foundation

Highly-fluorous pyrazolide-based lithium salt in PVDF-HFP as solid polymer electrolyte

For the first time, the concept of fluorophilicity f(i) is adapted to the development of a novel solid polymer electrolyte (SPE) by computationally evaluating a new class of lithium salts, the perfluoroalkylated pyrazolides. An SPE consisting solely of poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) and different concentrations of highly-fluorous lithium [5-(perfluorobutyl)-3-(trifluoromethyl)-1H-pyrazol-1-yl] trifluoroborate (LiPFAPB14) is reported. Membranes with a salt concentration up to 80 wt.% are prepared and are investigated by 3D laser scanning confocal microscopy, scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) concerning the correlation between the LiPFAPB14 salt concentrations with the miscibility in PVDF-HFP. Membrane performances as SPE are evaluated by impedance spectroscopy revealing ionic conductivities of 1.4 x 10(-4) S cm(-1) at 90 degrees C with 80 wt.% LiPFAPB14

3D laser scanning confocal microscopy of siloxane-based comb and double-comb polymers in PVDF-HFP thin films

Currently, atomic force microscopy is the preferred technique to determine roughness on membrane surfaces. In this paper, a new method to measure surface roughness is presented using a 3D laser scanning confocal microscope for high-resolution topographic analysis and is compared to conventional SEM. For this study, the surfaces of eight samples based on a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) host polymer with different liquid interpenetrating components were analyzed. Polymethylhydrosiloxane, triethylene glycolallylmethyether, (3,3,3-trifluoropropyl) methylcyclotrisiloxane (D-3-C2H4CF3), polysiloxane-comb-propyloxymethoxytriglycol (PSx), poly-siloxane-comb-propyl-3,3,3-trifluoro (PSx-C2H4CF3), poly [bis(2-(2-methoxyethoxy) ethoxy) phosphazene, or poly [bis(trifluoro) ethoxy] phosphazene was chosen as interpenetrating compound to investigate the impact of comb and double-comb-structured polymer backbones, as well as their dipolar or fluorous residues on the PVDF-HFP-miscibility. Different phases of the constituting ingredients were identified via their thermal properties determined by DSC. Additionally, the COSMO-RS method supported the experimental results, and with regard to computed sigma-profiles, new modified structures for polysiloxane and polyphosphazene synthesis were suggested