Multi-metal electrocatalysts provide nearly unlimited catalytic possibilities arising from synergistic element interactions. We propose a polymer/metal precursor spraying technique that can easily be adapted to produce a large variety of compositional different multi-metal catalyst materials. To demonstrate this, 11 catalysts were synthesized, characterized, and investigated for the oxygen evolution reaction (OER). Further investigation of the most active OER catalyst, namely CoNiFeMoCr, revealed a polycrystalline structure, and operando Raman measurements indicate that multiple active sites are participating in the reaction. Moreover, Ni foam-supported CoNiFeMoCr electrodes were developed and applied for water splitting in flow-through electrolysis cells with electrolyte gaps and in zero-gap membrane electrode assembly (MEA) configurations. The proposed alkaline MEA-type electrolyzers reached up to 3 A cm À 2 , and 24 h measurements demonstrated no loss of current density of 1 A cm À 2 .

Discovery of new catalysts is crucial for future growth and development of environmentally friendly energy conversion processes e. g. the production of hydrogen by water electrolysis. We developed an aerosol-based synthesis technique as a comparatively fast and facile method to prepare multi-metal catalysts. 22 different quinary metal compositions were synthesized and investigated with respect to their activity for the oxygen evolution (OER) and the glycerol oxidation (GOR) reactions. The impact of the element composition and the homogeneous distribution of the elements in the particles on catalytic performance were evaluated. The highest activity for OER was found for Co 20 Cu 20 Ni 20 Fe 20 Zn 20 . For GOR, Ag-containing catalysts were the most active, however, in most cases Ag was locally enriched and not homogeneously mixed with the other metals in the particles. Ag-based catalysts outperformed similar compositions containing one or more noble metals. The GOR selectivity of selected catalysts during long-term electrolysis was also investigated and it was shown that varying the catalyst composition via aerosol-based synthesis is a potential way to modulate the GOR selectivity.

Multimetall-Elektrokatalysatoren bieten nahezu unbegrenzte katalytische Möglichkeiten, die sich aus synergistischen Elementwechselwirkungen ergeben. Wir schlagen eine Polymer/Metallsalz-Sprühtechnik vor, die leicht angepasst werden kann, um eine große Vielfalt von Multimetall-Katalysatormaterialien mit unterschiedlicher Zusammensetzung herzustellen. Um dies zu demonstrieren, wurden 11 Katalysatoren synthetisiert, charakterisiert und für die Sauerstoffentwicklungsreaktion (OER) untersucht. Weitere Untersuchungen des aktivsten OER-Katalysators, nämlich CoNiFeMoCr, ergaben eine polykristalline Struktur, und Operando-Raman-Messungen deuten darauf hin, dass mehrere aktive Zentren an der Reaktion beteiligt sind. Darüber hinaus wurden auf Ni-Schaum basierende CoNiFeMoCr-Elektroden entwickelt und für die Wasserspaltung in Durchflusselektrolysezellen mit Elektrolytspalten und in "zero-gap" Membran-Elektroden-Anordnungen (MEA) eingesetzt. Die alkalischen MEA-Elektrolyseure erreichten bis zu 3 A cm À 2 , und 24-Stunden-Messungen zeigten keinen Verlust der Stromdichte von 1 A cm À 2 .