Combinatorial Synthesis and Screening of a Ternary NiFeCoO_xLibrary for the Oxygen Evolution Reaction

The development of an efficient catalyst for the oxygen evolution reaction (OER) is critical to fulfilling the mission of hydrogen generation by water splitting. Various multicomponent systems have been investigated so far for the OER, although a systematic investigation is lacking and there are discrepancies as to which formulations make the best catalyst. Here, we perform a systematic investigation of a ternary Ni-Fe-Co oxide gradient library for the OER, using a combinatorial approach. This approach allows a much faster investigation of a vast compositional space compared to the traditional step by step approach. Also, it enables a more reliable comparison of the various catalysts as they all experience the same process and measurement conditions. We used the spray pyrolysis technique in combinatorial electrocatalyst screening for the first time for the generation of a gradient library of Ni-Fe-Co oxides. Combinatorial electrochemical screening using a scanning droplet cell (SDC) set up allowed the study of 94 different points in the compositional space of the trimetallic Ni-Fe-Co oxide library, which was used to deduce a composition-activity relationship. At 10 mA cm^-2, the investigated points spanned an overpotential window of 294-320 mV, with the best performing ternary oxides being confined to a compositional space of 4-15% Fe, 4-15% Co, and 80-90% Ni. This study provides a foundation for broad exploration of other mixed-metal oxide combinations.