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The diffusion of alkaline chlorides (LiCl, KCl, and CsCl) and water in mesoporous silica samples with pore sizes covering the range from micropores (2 nm) up to mesopores larger than 30 nm have been measured by resorting to a simple diffusional technique in the case of electrolytes and 1H NMR in the case of water. The morphology of the silica samples varies from a microporous structure, an interconnected network of pores, and typical mesoporous materials with ink-bottle pores, with increasing pore size. The release of electrolytes from the silica as a function of time exhibits two differentiated regimes, at short and long times, which correlates quite well with the size of the pores and that of necks of the pores, respectively. The diffusion of water inside the pores follows the same trend with pore size that the diffusion of electrolytes, indicating a coupling between the ions and water diffusional mobilities. The tortuosity effect on the diffusion of all studied electrolytes and water shows a monotonic slight increase with decreasing diameter for pores larger than 5 nm, while the tortuosity factor increases markedly for smaller pores. In microporous and mesoporous silica with pore sizes below 10 nm, the tortuosity factor of Li+ ion is much larger than those for K+ and Cs+ ions, since its diffusion is hindered by a stronger electrostatic interaction with the ionizable silanol groups on the pore wall; and also larger than that for water diffusion which it is retarded by a weaker hydrogen bond interaction with the silanol groups. The differences in tortuosity factors among alkaline chlorides and water become negligible for pore sizes larger than 10 nm. The spin-lattice relaxation time measurements of 1H-water and Li+ ions confirm this behavior. Fil: Martínez Casillas, Diana Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Longinotti, María Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Bruno, Mariano Martín. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina Fil: Vaca Chávez Fornasero, Fabián. Universidad Nacional de Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina Fil: Acosta, Rodolfo Héctor. Universidad Nacional de Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina Fil: Corti, Horacio Roberto. Comisión Nacional de Energía Atómica. Gerencia del Área Investigaciones y Aplicaciones no Nucleares; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Microbial fuel cells (MFCs) can evolve in a viable technology if environmentally sound materials are developed and became available at low cost for these devices. This is especially important not only for the designing of large wastewater treatment systems, but also for the fabrication of low-cost, single-use devices. In this work we synthesized membranes by a simple procedure involving easily-biodegradable and economic materials such as poly (vinyl alcohol) (PVA), chitosan (CS) and the composite PVA:CS. Membranes were chemical and physically characterized and compared to Nafion®. Performance was studied using the membrane as separator in a typical H-Type MFCs showing that PVA:CS membrane outperform Nafion® 4 times (power production) while being 75 times more economic. We found that performance in MFC depends over interactions among several membrane characteristics such as oxygen permeability and ion conductivity. Moreover, we design a paper-based micro-scale MFC, which was used as a toxicity assay using 16 µL samples containing formaldehyde as a model toxicant. The PVA:CS membrane presented here can offer low environmental impact and become a very interesting option for point of need single-use analytical devices, especially in low-income countries where burning is used as disposal method, and toxic fluoride fumes (from Nafion®) can be released to the environment. Fil: Gonzalez Pabon, Maria Jesus. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales; Argentina Fil: Figueredo, Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales; Argentina Fil: Martínez Casillas, Diana Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales; Argentina Fil: Corton, Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales; Argentina

The sonochemical synthesis of PdCu is presented. The electrocatalyst was characterized by X-ray diffraction (XRD) and scanning electronic microscopy (SEM). The XRD result shows evidence of the alloy nanoparticles with 8 nm in average size. SEM image shows regular spherical agglomerates between 50 and 200 nm in size. Its catalytic activity for the oxygen reduction reaction (ORR) was evaluated using cyclic voltammetry (CV) and rotating-disk electrode (RDE) in a 0.5 M H2SO4 electrolyte at 25 °C. Then the PdCu was tested as cathode in a PEMFC. The electrochemical activity and its performance in the PEM fuel cell were compared with the behavior of palladium. The bimetallic catalyst shows in both cases higher activity for the ORR than the Pd alone.

A study of the oxygen reduction reaction on PdCu electrocatalyst synthesized by a NaBH4 reduction of PdCl2 and CuCl in a THF solution was examined in a 0.5 M H2SO4 electrolyte, at 25 °C. The electrochemical techniques used were cyclic voltammetry (CV) and rotating disc electrode (RDE). The electrocatalyst was characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM). The physical characterization showed that the method of synthesis allows the formation of spherical agglomerated nanocrystalline particles about 11 nm in size. The PdCu catalyst exhibited high current densities for the ORR compared to that obtained on nanometric Pd catalyst synthesized by the same method.

In this work the oxygen reduction reaction (ORR) on PdCo particles (~ 11 nm) supported in carbon Vulcan XC-72 is analyzed. In 0.5 M H2SO4/O2 the impedance spectra showed one or two time constants, the first time constant was associated to the reduction of O2 to H2O, while the second, to the reduction from H2O2 to H2O. By using electric circuits, the kinetics parameters of ORR were obtained. The values of charge transfer resistance Rct1 obtained from the impedance spectra were used to determine the kinetic parameters (b, α and i0) of ORR. The impedance spectra of PEMFC fed with H2/air and H2/O2 allows determining the values of Rc; with these, the values of b, α, and i0 were calculated. The values of i0, are related to the kinetics of ORR on PdCo/C, the highest value of i0 belongs to the PEMFC fed with H2/O2.

Electrochemical studies on the catalytic activity of bimetallic PdAg and PdCu compounds for the oxygen reduction reaction (ORR) in acid media are presented. The electrocatalytic activity for the ORR was evaluated using cyclic voltammetry (CV) and rotating-disk electrode (RDE) measurements in a 0.5 M H2SO4 electrolyte at 25 {degree sign}C. These materials were synthesized through PdCl2, AgNO3 and CuCl reductions with NaBH4 in a THF solution. The synthesized powder electrocatalysts were characterized by powder X-ray diffraction (XRD) and data analyzed with the software MDI jade 5.0. The XRD results show evidence of the alloy particles with 3nm as average sizes. The electrochemical current-potential behavior was compared with the Palladium and Platinum. Kinetics results show that the bimetallic catalysts containing Ag and Cu are more active for the ORR than the Pd pure, and less active than the nanometric Pt.

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