PROTECTIVE COATING FOR METALHYDRIDE BASED DEVICES: PTFE (Teflon) coating for hydrogen sensors

A switchable mirror device comprising active layer (4) wherein said active layer changes its optical properties by ~ adding/removal of hydrogen and comprises a Mg-transition metal layer, or an Y or rare earth based layer said active layer being 0 provided on one side with a further protective layer (3) comprising a hydrogen and oxygen permeable and water impermeable layer, > characterized in that said layer is liquid water impermeable and water vapor permeable and has hydrophobic surface properties. A ~ pd catalyst layer (5) may be disposed between the active layer (4) and the protective layer (3).