Green hydrogen is considered a promising energy carrier for a sustainable future and is produced by electrolysis using renewable energies. The water electrolysis can be divided into different technologies. The most promising process is the alkaline exchange membrane (AEM) electrolysis which combines the advantages of proton exchange membrane (PEM) and alkaline electrolysis (AEL) [1].

In this study, an equiatomic Al₂₀Co₂₀Cr₂₀Fe₂₀Ni₂₀ high entropy alloy (HEA) was developed to use them as low-cost, precious metal-free catalysts for the AEM electrolysis. HEA alloys consist of at least five homogeneously distributed elements in one solid solution phase [2,3]. Therefore, the different powders with high catalytic activity in the hydrogen evolution reaction under alkaline conditions were mechanically alloyed (MA) with different parameters in a planetary ball mill. Afterwards, the milled powder was characterized by particle size, shape, phase, and chemical composition to fulfil the conditions of a HEA.

The MA powder was already used to directly coat the porous transport layers of stainless-steel fleece by plasma spraying. A homogeneous coating could be achieved but did not exhibit a high catalytic activity. For this reason, sputtering targets were produced from the HEA powder via spark plasma sintering.

To achieve sputter targets with a 100 mm diameter, we implemented a special sintering tool design and adjusted sintering parameters. The achieved density values of ̴6.95 g/cm³ and hardness values up to 800 HV0.5 were much higher compared to the mechanical properties of casted or vacuum arc melted samples and fulfilled the requirements for the following physical vapour deposition process [4]. The formation of two distinct, homogeneously distributed cubic crystal structures (FCC, BCC) over the target can be observed (figure 1). Their lattice parameters correspond to the developed HEA composition [5].

Finally, the HEA-coated porous transport layers were characterized electrochemically by measuring the catalytic activity in comparison to the plasma sprayed samples. A high catalytic activity affects the AEM electrolysis and results in a larger production of green hydrogen.