A series of Co1+xFe2–xO4 (0≤x≤2) spinel nanowires was synthesized by nanocasting using SBA‐15 silica as hard template, which was characterized by X‐ray powder diffraction, X‐ray photoelectron spectroscopy, and transmission electron microscopy. The Co1+xFe2–xO4 spinels were applied in the aerobic oxidation of aqueous 2‐propanol solutions to systematically study the influence of exposed Co and Fe cations on the catalytic properties. The activity of the catalysts was found to depend strongly on the Co content, showing an exponential increase of the reaction rate with increasing Co content. Ensembles of Co3+cus (coordinatively unsaturated) sites were identified as the active sites for selective 2‐propanol oxidation, which are assumed to consist of more than six Co ions. In addition, gas‐phase oxidation with and without water vapor co‐feeding was performed to achieve a comparison with liquid‐phase oxidation kinetics. An apparent activation energy of 94 kJ mol−1 was determined for 2‐propanol oxidation over Co3O4 in the liquid phase, which is in good agreement with the gas‐phase oxidation in the presence of water vapor. In contrast to gas‐phase conditions, the catalysts showed high stability and reusability in the aqueous phase with constant conversion in three consecutive runs.

The three-dimensional (3D) distribution of individual atoms on the surface of catalyst nanoparticles plays a vital role in their activity and stability. Optimising the performance of electrocatalysts requires atomic-scale information, but it is difficult to obtain. Here, we use atom probe tomography to elucidate the 3D structure of 10 nm sized Co2FeO4 and CoFe2O4 nanoparticles during oxygen evolution reaction (OER). We reveal nanoscale spinodal decomposition in pristine Co2FeO4. The interfaces of Co-rich and Fe-rich nanodomains of Co2FeO4 become trapping sites for hydroxyl groups, contributing to a higher OER activity compared to that of CoFe2O4. However, the activity of Co2FeO4 drops considerably due to concurrent irreversible transformation towards CoIVO2 and pronounced Fe dissolution. In contrast, there is negligible elemental redistribution for CoFe2O4 after OER, except for surface structural transformation towards (FeIII, CoIII)2O3. Overall, our study provides a unique 3D compositional distribution of mixed Co-Fe spinel oxides, which gives atomic-scale insights into active sites and the deactivation of electrocatalysts during OER.

No abstract

No abstract

We report on a laboratory study of the atmospheric corrosion of NaC1-treated zinc in air containing different concentrations of carbon dioxide (<1, 100, 350, 1000, and 40,000 ppm). Each sample was exposed individually to synthetic atmospheres with careful control of CO2 concentration and flow conditions. The relative humidity was 95%. The protective properties of carbonate-containing corrosion products were investigated in 225 ppb SO2. Mass gain and metal loss results are reported. The corrosion products were analyzed quantitatively and qualitatively by a combination of X-ray diffraction, scanning electron microscopy, gravimetry, and quantitative analysis for carbonate. The corrosion of zinc in the presence of NaCl resulted in heavy pitting of the metal. Carbon dioxide slowed down the corrosion rate by a factor of three to six. This is explained by the neutralization of the surface electrolyte resulting in the precipitation of chloride in the form of insoluble Zn5(OH)5C12H2O. In the presence of NaCl large amounts of hydroxy carbonates formed. There is no indication that hydroxy carbonates are protective in a SO2 environment. InfroductionThe frequent occurrence of hydroxy carbonates in the corrosion products on zinc in the environment implies that CO2 plays an important role in the atmospheric corrosion of zinc. Several authors maintain that zinc hydroxy carbonates have protective properties.1-3 In a previous paper4 we showed that the hydroxy carbonates formed on zinc are not protective in humid air containing S0.The deposition of chloride is known to be one of the main factors that influence zinc corrosion in the atmosphere.5'6 In this study we investigate the interaction of CO2 and NaCl in the atmospheric corrosion of zinc. NaCltreated samples are exposed in air with different CO2 concentrations. In addition, we investigate the possible protective properties of zinc hydroxycarbonate in the presence of NaCl in 503 environment.We found that CO2 slows down zinc corrosion in the presence of NaCI. However, there is no indication that zinc hydroxycarbonates are protective.