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Science. 2012 May 18;336(6083):889-93. doi: 10.1126/science.1219468.

Water-mediated proton hopping on an iron oxide surface.

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Interdisciplinary Nanoscience Center and Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C, Denmark.


The diffusion of hydrogen atoms across solid oxide surfaces is often assumed to be accelerated by the presence of water molecules. Here we present a high-resolution, high-speed scanning tunneling microscopy (STM) study of the diffusion of H atoms on an FeO thin film. STM movies directly reveal a water-mediated hydrogen diffusion mechanism on the oxide surface at temperatures between 100 and 300 kelvin. Density functional theory calculations and isotope-exchange experiments confirm the STM observations, and a proton-transfer mechanism that proceeds via an H(3)O(+)-like transition state is revealed. This mechanism differs from that observed previously for rutile TiO(2)(110), where water dissociation is a key step in proton diffusion.

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