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The inhibition of the electrochemical oxygen reduction reaction (ORR) by zinc corrosion products plays an important role in the corrosion protection of galvanized steel. Hence, the electrocatalytic mechanism of the ORR on electrodeposited zinc hydroxide-based model corrosion products was investigated by in situ and operando attenuated total reflection infrared (ATR-IR) spectroscopy, supplemented by density functional theory (DFT) calculations. Model corrosion products containing flake-like crystalline Zn5(NO3)2(OH)8 were cathodically electrodeposited on germanium(100) electrodes from a zinc nitrate precursor electrolyte. Substantial amounts of the films are non-crystalline, and their surfaces predominantly consist of zinc oxide and hydroxide species, as evidenced by x-ray photoelectron spectroscopy. ATR-IR spectra show a peak at 1180 cm−1 during cathodic currents in O2-saturated NaClO4 solution. This peak is assigned to a surface-bound superoxide, the only ORR intermediate detected. Absorbance from the intermediate increases with increasing cathodic current, indicating an increase in surface concentration of superoxide intermediates at larger ORR current densities. The zinc hydroxide ages in the experiments, most likely by a transformation into zinc oxide, consistent with the observed decrease in absorbance over time of the OH bending mode of zinc hydroxide at 1380 cm−1. This aging is a time-dependent chemical process, implying that pure chemical aging is important in actual corrosion products as well. DFT calculations of adsorbed superoxide yield a Zn–O bond length similar to the bond length in Zn–O, thus enhancing superoxide interaction with undercoordinated tetrahedral Zn2+ sites on the surface. Thus, such active sites catalyze the first reduction step in the ORR. [ABSTRACT FROM AUTHOR]

The charge-dependent structure of interfacial water at the n-Ge(100)-aqueous perchlorate interface was studied by controlling the electrode potential. Specifically, a joint attenuated total reflection infrared spectroscopy and electrochemical experiment was used in 0.1M NaClO4 at pH ≈ 1–10. The germanium surface transformation to an H-terminated surface followed the thermodynamic Nernstian pH dependence and was observed throughout the entire pH range. A singular value decomposition-based spectra deconvolution technique coupled to a sigmoidal transition model for the potential dependence of the main components in the spectra shows the surface transformation to be a two-stage process. The first stage was observed together with the first appearance of Ge–H stretching modes in the spectra and is attributed to the formation of a mixed surface termination. This transition was reversible. The second stage occurs at potentials ≈0.1–0.3 V negative of the first one, shows a hysteresis in potential, and is attributed to the formation of a surface with maximum Ge–H coverage. During the surface transformation, the surface becomes hydrophobic, and an effective desolvation layer, a “hydrophobic gap,” developed with a thickness ≈1–3 Å. The largest thickness was observed near neutral pH. Interfacial water IR spectra show a loss of strongly hydrogen-bound water molecules compared to bulk water after the surface transformation, and the appearance of “free,” non-hydrogen bound OH groups, throughout the entire pH range. Near neutral pH at negative electrode potentials, large changes at wavenumbers below 1000 cm−1 were observed. Librational modes of water contribute to the observed changes, indicating large changes in the water structure. [ABSTRACT FROM AUTHOR]

Lead halide perovskites are materials with excellent optoelectronic and photovoltaic properties. However, some hurdles remain prior to commercialization of these materials, such as chemical stability, phase stability, sensitivity to moisture, and potential issues due to the toxicity of lead. Here, we report a new type of lead-free perovskite related compound, Cs 2 PdBr 6 . This compound is solution processable, exhibits long-lived photoluminescence, and an optical band gap of 1.6 eV. Density functional theory calculations indicate that this compound has dispersive electronic bands, with electron and hole effective masses of 0.53 and 0.85 m e , respectively. In addition, Cs 2 PdBr 6 is resistant to water, in contrast to lead-halide perovskites, indicating excellent prospects for long-term stability. These combined properties demonstrate that Cs 2 PdBr 6 is a promising novel compound for optoelectronic applications.

The electrochemical oxygen reduction reaction (ORR) on a n-Ge(100) surface in 0.1 M HClO4 was investigated in situ and operando using a combination of attenuated total reflection infrared (ATR-IR) spectroscopy and density functional (DFT) calculations. The vibrational modes of the detected intermediates were assigned based on DFT calculations of solvated model clusters such as Ge-bound superoxides and peroxides. ATR-IR shows the Ge-bound superoxide with a transition dipole moment oriented at (28 ± 10)° with respect to the surface normal. At slightly negative potentials, the surface-bound peroxide is identified by an OOH bending mode as a further intermediate, oriented at a similar angle. At strongly negative potentials, a surface-bound perchlorate is found. The findings indicate a multistep mechanism of the ORR. The reaction is furthermore coupled with the hydrogen evolution reaction (HER).