Hydrous cobalt-iridium oxide two-dimensional nanoframes: insights into activity and stability of bimetallic acidic oxygen evolution electrocatalysts.

Acidic oxygen evolution reaction (OER) electrocatalysts that have high activity, extended durability, and lower costs are needed to further the development and wide-scale adoption of proton-exchange membrane electrolyzers. In this work, we report hydrous cobalt-iridium oxide two-dimensional (2D) nanoframes exhibit higher oxygen evolution activity and similar stability compared with commercial IrO2; however, the bimetallic Co-Ir catalyst undergoes a significantly different degradation process compared with the monometallic IrO2 catalyst. The bimetallic Co-Ir 2D nanoframes consist of interconnected Co-Ir alloy domains within an unsupported, carbon-free, porous nanostructure that allows three-dimensional molecular access to the catalytically active surface sites. After electrochemical conditioning within the OER potential range, the predominately bimetallic alloy surface transforms to an oxide/hydroxide surface. Oxygen evolution activities determined using a rotating disk electrode configuration show that the hydrous Co-Ir oxide nanoframes provide 17 times higher OER mass activity and 18 times higher specific activity compared to commercial IrO2. The higher OER activities of the hydrous Co-Ir nanoframes are attributed to the presence of highly active surface iridium hydroxide groups. The accelerated durability testing of IrO2 resulted in lowering of the specific activity and partial dissolution of Ir. In contrast, the durability testing of hydrous Co-Ir oxide nanoframes resulted in the combination of a higher Ir dissolution rate, an increase in the relative contribution of surface iridium hydroxide groups and an increase in specific activity. The understanding of the differences in degradation processes between bimetallic and monometallic catalysts furthers our ability to design high activity and stability acidic OER electrocatalysts.

Application of scanning angle Raman spectroscopy for determining the location of buried polymer interfaces with tens of nanometer precision.

Near-infrared scanning angle (SA) Raman spectroscopy was utilized to determine the interface location in bilayer films (a stack of two polymer layers) of polystyrene (PS) and polycarbonate (PC). Finite-difference-time-domain (FDTD) calculations of the sum square electric field (SSEF) for films with total bilayer thicknesses of 1200-3600 nm were used to construct models for simultaneously measuring the film thickness and the location of the buried interface between the PS and PC layers. Samples with total thicknesses of 1320, 1890, 2300, and 2750 nm and varying PS/PC interface locations were analyzed using SA Raman spectroscopy. Comparing SA Raman spectroscopy and optical profilometry measurements, the average percent difference in the total bilayer thickness was 2.0% for films less than ∼2300 nm thick. The average percent difference in the thickness of the PS layer, which reflects the interface location, was 2.5% when the PS layer was less than ∼1800 nm. SA Raman spectroscopy has been shown to be a viable, non-destructive method capable of determining the total bilayer thickness and buried interface location for bilayer samples consisting of thin polymer films with comparable indices of refraction.

Characterization of silver halide fiber optics and hollow silica waveguides for use in the construction of a mid-infrared attenuated total reflection fourier transform infrared (ATR FT-IR) spectroscopy probe.

Advances in fiber optic materials have allowed for the construction of fibers and waveguides capable of transmitting infrared radiation. An investigation of the transmission characteristics associated with two commonly used types of infrared-transmitting fibers/waveguides for prospective use in a fiber/waveguide-coupled attenuated total internal reflection (ATR) probe was performed. Characterization of silver halide polycrystalline fiber optics and hollow silica waveguides was done on the basis of the transmission of infrared light using a conventional fiber optic coupling accessory and an infrared microscope. Using the fiber optic coupling accessory, the average percent transmission for three silver halide fibers was 18.1 ± 6.1% relative to a benchtop reflection accessory. The average transmission for two hollow waveguides (HWGs) using the coupling accessory was 8.0 ± 0.3%. (Uncertainties in the relative percent transmission represent the standard deviations.) Reduced transmission observed for the HWGs was attributed to the high numerical aperture of the coupling accessory. Characterization of the fibers/waveguides using a zinc selenide lens objective on an infrared microscope indicated 24.1 ± 7.2% of the initial light input into the silver halide fibers was transmitted. Percent transmission obtained for the HWGs was 98.7 ± 0.1%. Increased transmission using the HWGs resulted from the absence or minimization of insertion and scattering losses due to the hollow air core and a better-matched numerical aperture. The effect of bending on the transmission characteristics of the fibers/waveguides was also investigated. Significant deviations in the transmission of infrared light by the solid-core silver halide fibers were observed for various bending angles. Percent transmission greater than 98% was consistently observed for the HWGs at the bending angles. The combined benefits of high percent transmission, reproducible instrument responses, and increased bending tolerance indicated HWGs should be preferred in the construction of a fiber/waveguide-coupled ATR probe.

Identification of a domain in the V0 subunit d that is critical for coupling of the yeast vacuolar proton-translocating ATPase.

Vacuolar proton-translocating ATPase pumps consist of two domains, V(1) and V(o). Subunit d is a component of V(o) located in a central stalk that rotates during catalysis. By generating mutations, we showed that subunit d couples ATP hydrolysis and proton transport. The mutation F94A strongly uncoupled the enzyme, preventing proton transport but not ATPase activity. C-terminal mutations changed coupling as well; ATPase activity was decreased by 59-72%, whereas proton transport was not measurable (E328A) or was moderately reduced (E317A and C329A). Except for W325A, which had low levels of V(1)V(o), mutations allowed wild-type assembly regardless of the fact that subunits E and d were reduced at the membrane. N- and C-terminal deletions of various lengths were inhibitory and gradually destabilized subunit d, limiting V(1)V(o) formation. Both N and C terminus were required for V(o) assembly. The N-terminal truncation 2-19Delta prevented V(1)V(o) formation, although subunit d was available. The C terminus was required for retention of subunits E and d at the membrane. In addition, the C terminus of its bacterial homolog (subunit C from T. thermophilus) stabilized the yeast subunit d mutant 310-345Delta and allowed assembly of the rotor structure with subunits A and B. Structural features conserved between bacterial and eukaryotic subunit d and the significance of domain 3 for vacuolar proton-translocating ATPase function are discussed.