In this paper, different preparation routes and designs for pH sensing metal/metal oxide electrodes are evaluated. Crystallographic changes in the oxide film are responsible for the pH‐sensing capability of tungsten oxide. As the present oxide structure is directly limiting the measuring range, as‐received tungsten oxide powders were heat treated to produce polymorphs of WO3, in an attempt to extend the measuring range. Furthermore, electrochemical oxide covered electrodes ranging from micro‐ down to nano‐dimensions have been implemented. Optional coating with Nafion, serving as a membrane material, allows shifting the measuring range even to strongly alkaline conditions.
In this work, differently prepared palladium films are tested toward their hydrogen sensing properties in aqueous electrolytes. The Pd thin films were either electroless deposited, electrochemically deposited, or prepared by physical vapor deposition. The outcome of each fabrication process and characteristics of the Pd films were determined by means of SEM and cyclic voltammetry. Electrochemical impedance spectroscopy was performed in order to calibrate the prepared hydrogen sensors. The Pd films react on different hydrogen concentrations in the electrolyte by changing their electrical resistivity. Elemental hydrogen can diffuse into the Pd film leading to a lattice expansion and a phase transition. A second hydrogen sensing mechanism due to a change in charge transfer resistance can be observed.
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