Nanoscaffold effects on the performance of air-cathodes for microbial fuel cells : Sustainable Fe/N-carbon electrocatalysts for the oxygen reduction reaction under neutral pH conditions

Nanostructured electrocatalysts for microbial fuel cell air-cathodes were obtained via use of conductive carbon blacks for the synthesis of high performing 3D conductive networks. We used two commercially available nanocarbons, Black Pearls 2000 and multiwalled carbon nanotubes, as conductive scaffolds for the synthesis of nanocomposite electrodes by combining: a hydrothermally carbonized resin, a sacrificial polymeric template, a nitrogenated organic precursor and iron centers. The resulting materials are micro-mesoporous, possess high specific surface area and display N-sites (N/C of 3–5 at%) and Fe-centers (Fe/C < 1.5 at.%) at the carbon surface as evidenced from characterization methods. Voltammetry studies of oxygen reduction reaction activity were carried out at neutral pH, which is relevant to microbial fuel cell applications, and activity trends are discussed in light of catalyst morphology and composition. Tests of the electrocatalyst using microbial fuel cell devices indicate that optimization of the nanocarbon scaffold for the Pt-free carbon-based electrocatalysts results in maximum power densities that are 25% better than those of Pt/C cathodes, at a fraction of the materials costs. Therefore, the proposed Fe/N-carbon catalysts are promising and sustainable high-performance cathodic materials for microbial fuel cells

Molecular dynamics of glycerol and glycerol-trehalose bioprotectant solutions nanoconfined in porous silicon

Glycerol and trehalose-glycerol binary solutions are glass-forming liquids with remarkable bioprotectant properties. Incoherent quasielastic neutron scattering (QENS) is used to reveal the different effects of nanoconfinement and addition of trehalose on the molecular dynamics in the normal liquid and supercooled liquid phases, on a nanosecond timescale. Confinement has been realized in straight channels of diameter D=8 nm formed by porous silicon. It leads to a faster and more inhomogeneous relaxation dynamics deep in the liquid phase. This confinement effect remains at lower temperature where it affects the glassy dynamics. The glass transitions of the confined systems are shifted to low temperature with respect to the bulk ones. Adding trehalose tends to slow down the overall glassy dynamics and increases the non-exponential character of the structural relaxation. Unprecedented results are obtained for the binary bioprotectant solution, which exhibits an extremely non-Debye relaxation dynamics as a result of the combination of the effects of confinement and mixing of two constituents

Humidity effect on baseline conductance and H₂S sensitivity of cadmium germanium oxynitride thick film gas sensors

International audienceCadmium germanium oxynitrides are excellent sensing materials for the detection of H2S. The effect of humidity on both the baseline conductance and the sensitivity to H2S of thick-film gas sensors was investigated. The devices were subjected to dry and moist (varying relative humidity (RH)) air. Results showed that, unlike most semiconductor gas detectors, the presence of moisture has no significant effect on conductivity nor on the sensitivity to H2S of cadmium germanium oxynitride sensors. Hypotheses on surface processes accounting for such insensitivity are given. It appears likely that the surface states involved in responses to changes in RH are different from those involved in the detection of other gases

Manufacturing of transparent ZnS ceramics by powders sintering

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Hot-pressed ZnS infrared ceramics: correlating precursor synthesis method to sinterability and transparency

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Utilization of (Cd,Zn)_2-xGeO_4-x-3yN_2y oxynitride as sensitive material for H₂S gas sensor

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