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(Color online) Sketch of the experiment. Hydrogen is dissociated and dissolved in the Pd-cap layer. A “passivating” surface hydride is formed and the hydrogenation stops. Hydrogen uptake is still possible after applying a current via the indicated electrodes.
(Color online) Photographs in optical transmission of a typical electrocatalysis experiment. The region of higher hydrogen content (lower H content) in is recognizable by its higher (lower) transmission. The top image represents the state of the Mg film after exposing to hydrogen for . Due to slow kinetics, only a surface layer is hydrided, which is not visible in transmission. The white bar (highlighted by a red line) is an artificial scratch on the surface. The second image shows the evolving front after applying . The front moves toward the positive side. After the fourth image the polarity is changed and simultaneously a new front evolves, which moves in reversed direction.
(Color online) Electrocatalytically enhanced hydrogenation of a Mg-wedge sample with a thickness gradient. The subsequent photographs show the development and movement of the front, which starts at a hole in the film (white spot). The sketch illustrates the sample setup and the main directions of the front moving. Two effects have to be considered: heating and electromigration.
(Color online) Optically derived hydrogen content along the indicated line scan (see image) as a function of time during the electrically enhanced hydrogen uptake. The hydrogenation takes place at constant voltage in hydrogen. The top figures show the macroscopic appearance of the film and a microscopy image of the front.
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