Electrocaloric heat pumps use materials that change their temperature when an electric field is applied, thereby generating heat or cold. Optimum heat transfer requires complete wetting of the surface of the electrocaloric components by the working medium. Since these surfaces are initially hydrophobic, i.e. not wettable, the Fraunhofer FEP has developed superhydrophilic metal oxide thin films using magnetron sputtering as part of the Fraunhofer ElKaWe lighthouse project to overcome this challenge.
In contrast to titanium dioxide, which only remains hydrophilic when permanently exposed to UV light, the thin films developed offer permanent hydrophilicity, which is also based on their mesoporous microstructure. Pores with diameters between 2 and 50 nm promote capillary effects on the nanometer scale and thus improve the spread of liquids on the surface. The development of the hydrophilic metal oxide layers was carried out on a laboratory scale on the institute's own UNIVERSA batch system for coating 3D substrates. The permanent superhydrophilicity achieved by the coatings makes them particularly suitable for use in solid-state cooling devices such as electrocaloric heat pumps, but also for other applications.
