Correlating Oxygen Evolution Catalysts Activity and Electronic Structure by a High-Throughput Investigation of Ni _1-y-z Fe _y Cr _z O _x

High-throughput characterization by soft X-ray absorption spectroscopy (XAS) and electrochemical characterization is used to establish a correlation between electronic structure and catalytic activity of oxygen evolution reaction (OER) catalysts. As a model system a quasi-ternary materials library of Ni _1-y-zFe _y Cr _z O _x was synthesized by combinatorial reactive magnetron sputtering, characterized by XAS, and an automated scanning droplet cell. The presence of Cr was found to increase the OER activity in the investigated compositional range. The electronic structure of Ni ^II and Cr ^III remains unchanged over the investigated composition spread. At the Fe L-edge a linear combination of two spectra was observed. These spectra were assigned to Fe ^III in O _h symmetry and Fe ^III in T _d symmetry. The ratio of Fe ^III O _h to Fe ^III T _d increases with the amount of Cr and a correlation between the presence of the Fe ^III O _h and a high OER activity is found.