With the increasing amount of energy harvested from the intermittent renewable sources (e.g. wind and solar) grows the need of reliable system capable of storing the energy during the overproduction and releasing it in times of deficit. Promising solution is the concept of hydrogen economy. Proton exchange membrane water electrolyzers (PEMWE), the backbone of this concept, are ideal systems for conversion of overproduced electricity to hydrogen. Stored high-purity hydrogen could subsequently be used not only for stabilizing the electrical grid during windless nights but also for variety of fuel cell powered devices from consumer electronics to vehicles.

Wider commercialization of PEMWE technology is however hindered by high prices of noble metals which are necessary for catalyzing the redox reactions within the cell. Namely, platinum for hydrogen evolution reaction (HER), running on cathode and iridium for oxygen evolution reaction (OER) on anode. Possible way of how to lower the loading of Pt and Ir is by using conductive high-surface nanostructures as catalyst supports in conjunction with thin-film catalyst deposition.

We present a unique preparation technique of membrane electrode assembly (MEA), containing just a fraction of commonly used noble metals. Ir and Pt electrocatalysts were magnetron sputtered in very low loadings onto the porous sublayers, forming so-to-say localized three-phase boundary. Ultrasonically sprayed corrosion resistant TiC-based sublayer was used on anode, while nanostructured etched nitrogenated carbon (CN_x) on cathode. This way of preparation allowed us to significantly reduce the amount of noble metals (to thickness of just tens of nanometers) while obtaining performance comparable to that of average state-of-the-art catalysts. Complex characterization of prepared supported catalysts included in-cell performance and durability tests, electrochemical impedance spectroscopy (EIS) as well as scanning electron microscopy (SEM) imaging and X-ray photoelectron spectroscopy (XPS) analysis.

Our research proves that magnetron sputtering is a suitable method for thin-film deposition of electrocatalysts. Tested set-up of thin-film supported anode and cathode catalysts with combined loading of just 120 ug.cm^-2 yielded remarkable values of specific current. Described approach of thin-film low-loading catalyst deposition might be relevant when noble metal reduction is the topmost priority.

Acknowledgement:

Authors acknowledge financial support from the Czech Science Foundation (grant No. 18-06989Y), from the Charles University Grant Agency (grant No. 1016217) and from Specific Academic Research Project of Charles University (project No. 260446).