An optical hydrogen sensor based on a Pd-capped Mg thin film wedge

We report the proof of concept of a thin film device with a one-to-one relationship between the H₂ partial pressure and the lateral progression of a visible optical change along a thin film multilayer 70 mm long. The device basically consists of a sensing Mg layer with a thickness gradient. It exploits the thickness dependence of the hydrogenation thermodynamics of Pd-capped Mg thin films. The optical change of the Mg layer during the metal–hydride transition can be detected both in reflection and in transmission. This optical sensor allows a continuous measurement of hydrogen partial pressure in the range between 200 and 4000 Pa.