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)₃O₄. The chemical compositions of the libraries, all single-phase spinels, cover a wide compositional range of (Cr_8.1-28.0Mn_11.6-28.4Fe_10.6-39.0Co_11.4-36.7Ni_13.5-31.4)_37.7±0.6O_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±1.4Mn_15.7±2.0Fe_16.9±1.8Co_26.1±1.9Ni_16.6±1.7)_37.8±0.8O_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.