Search

Iron is unstable as an oxygen evolution electrode in alkaline media. Thus, relatively expensive nickel-based electrodes are used in industrial alkaline water electrolysis. We show that an iron substrate can be rendered stable and electrocatalytically active for the oxygen evolution reaction by nano-scale surface modification with nickel. The electrocatalytic activity of such a surface-modified iron electrode is comparable to the recently-reported nickel-based catalysts. The electrocatalytic activity is due to a 50-nanometer layer of a high-surface area α-nickel hydroxide on the iron electrode. The nickel modification renders the iron electrode electricallyconductive, prevents dielectric breakdown, and thus endows anodic stability. The electrocatalytic activity is unchanged even after 1000 hours of continuous operation. The temperature of preparation is critical, as excessive dehydration of the hydroxide layer results in nickel ferrite formation and a drastic reduction in electrocatalytic activity. We report significant insight into the surface chemical composition and structure of the catalyst layer by X-ray Absorption Spectroscopy, Photoelectron Spectroscopy, and Transmission Electron Microscopy. Electrochemical kinetics analysis suggests that surface hydroxo-intermediates react with the hydroxide ions from the solution to evolve oxygen. Thus, the surface-modified iron substrates present an opportunity for improving the performance and reducing the cost of alkaline water electrolysis systems. [ABSTRACT FROM AUTHOR]

We have investigated Cr solubility and secondary phase formation in metallorganic chemical vapor deposition (MOCVD) grown (Cr, Zn)O films on Si(100). Simultaneous deposition of 0.15 M Cr(TMHD) and 0.025 M Zn(TMHD) precursors in an oxidizing environment with a flow ratio of 1:10 resulted in secondary phase formation rather than uniform Cr doping. Based on several surface and microstructural techniques, we have identified nanocrystalline ZnCr2O4 and disordered Cr2O3 as the secondary Cr-containing phases. Analysis suggests that ZnCr2O4 crystallites are dispersed throughout the film, and that disordered Cr2O3 layer may form at the interface. These results are consistent with the tendency of Cr to exhibit octahedral, rather than tetrahedral coordination with O. [ABSTRACT FROM AUTHOR]