Mixed bimetallic oxides offer great opportunities for a systematic tuning of electrocatalytic activity and stability. Here, we demonstrate the power of this strategy using well-defined thermally prepared Ir-Ni mixed oxide thin film catalysts for the electrochemical oxygen evolution reaction (OER) under highly corrosive conditions such as in acidic proton exchange membrane (PEM) electrolyzers and photoelectrochemical cells (PEC). Variation of the Ir to Ni ratio resulted in a volcano type OER activity curve with an unprecedented 20-fold improvement in Ir mass-based activity over pure Ir oxide. In situ spectroscopic probing of metal dissolution indicated that, against common views, activity and stability are not directly anticorrelated. To uncover activity and stability controlling parameters, the Ir-Ni mixed thin oxide film catalysts were characterized by a wide array of spectroscopic, microscopic, scattering, and electrochemical techniques in conjunction with DFT theoretical computations. By means of an intuitive model for the formation of the catalytically active state of the bimetallic Ir-Ni oxide surface, we identify the coverage of reactive surface hydroxyl groups as a suitable descriptor for the OER activity and relate it to controllable synthetic parameters. Overall, our study highlights a novel, highly active oxygen evolution catalyst; moreover, it provides novel important insights into the structure and performance of bimetallic oxide OER electrocatalysts in corrosive acidic environments.
A facile strategy to synthesize water‐soluble fluorescent gold nanoclusters (Au NCs) stabilized with the bidentate ligand dihydrolipoic acid (DHLA) is reported. The DHLA‐capped Au NCs are characterized by UV–vis absorption spectroscopy, fluorescence spectroscopy, transmission electron microscopy, and X‐ray photoelectron spectroscopy. The Au NCs possess many attractive features including ultrasmall size, bright near‐infrared luminescence, high colloidal stability, and good biocompatibility, making them promising imaging agents for biomedical and cellular imaging applications. Moreover, their long fluorescence lifetime (>100 ns) makes them attractive as labels in fluorescence lifetime imaging (FLIM) applications. As an example, the internalization of Au NCs by live HeLa cells is visualized using the FLIM technique.
We present highly efficient electroluminescent devices using size-separated silicon nanocrystals (ncSi) as light emitting material. The emission color can be tuned from the deep red down to the yellow-orange spectral region by using very monodisperse size-separated nanoparticles. High external quantum efficiencies up to 1.1% as well as low turn-on voltages are obtained for red emitters. In addition, we demonstrate that size-separation of ncSi leads to drastically improved lifetimes of the devices and much less sensitivity of the emission wavelength to the applied drive voltage.
A long-term mountain station series of tropospheric 14C data for the period 1959 to 1984 is presented. This series is considered representative of the higher altitude14C level over central Europe. Even tree-ring 14C levels from a rural ground level site in southern Germany are consistently lower (by Δ14Cdepression = −15‰ if compared with the mountain station summer average in atmospheric CO2). The rural tree-ring series is considered to represent the additional continental Suess effect at ground level without local contamination. This Suess effect decreases gradually with the distance from the ground (ie, source) level. We therefore estimate the additional continental Suess effect in the vegetation period to be Δ14Cdepression = −5‰ for the mountain station and −20‰) for a rural ground level site, respectively. Based on this assumption, yearly mean tropospheric 14C levels corrected for fossil fuel contamination and representative of the Northern Hemisphere are provided for use in global carbon cycle models.
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