Discovery of High-Entropy Oxide Electrocatalysts: From Thin-Film Material Libraries to Particles.

Discovery of new high-entropy electrocatalysts requires testing of hundreds to thousands of possible compositions, which can be addressed most efficiently by high-throughput experimentation on thin-film material libraries. Since the conditions for high-throughput measurements ("screening") differ from more standardized methods, it is frequently a concern whether the findings from screening can be transferred to the commonly used particulate catalysts. We demonstrate the successful transfer of results from thin-film material libraries to particles of Cantor alloy oxide (Co-Cr-Fe-Mn-Ni) 3 O 4 . The chemical compositions of the libraries, all single-phase spinels, cover a wide compositional range of (Cr 8.1-28.0 Mn 11.6-28.4 Fe 10.6-39.0 Co 11.4-36.7 Ni 13.5-31.4 ) 37.7±0.6 O 62.3±0.6 , with composition-dependent lattice constant values ranging from 0.826 to 0.851 nm. Electrochemical screening of the libraries for the oxygen evolution reaction (OER) identifies (Cr 24.6±1.4 Mn 15.7±2.0 Fe 16.9±1.8 Co 26.1±1.9 Ni 16.6±1.7 ) 37.8±0.8 O 62.2±1.2 as the most active composition, exhibiting an overpotential of 0.36 V at a current density of 1 mA cm -2 . This "hit" in the library was subsequently synthesized in the form of particles with the same composition and crystal structure using an aerosol-based synthesis strategy. The similar OER activity of the most active thin-film composition and the derived catalyst particles validates the proposed approach of accelerated discovery of novel catalysts by screening of thin-film libraries.