Interplay Between Element-Specific Distortions and Electrocatalytic Oxygen Evolution for Cobalt-Iron Hydroxides

Abstract

A microscopic understanding of how Fe-doping of Co(OH)2 improves electrocatalytic oxygen evolution remains elusive. We study two Co1-xFex(OH)2 series that differ in fabrication protocol and find composition poorly alone correlates to catalyst performance. Structural descriptors extracted using X-ray diffraction, X-ray absorption spectroscopy, and Raman spectroscopy reveal element-specific distortions in Co1-xFex(OH)2. These structural descriptors are composition-dependent within individual sample series but inconsistent across fabrication protocols, revealing fabrication-dependence in catalyst microstructure. Correlations between structural parameters from different techniques show that Fe-O resists bond length changes, forcing distortion of Co environments. We find the difference in O-M-O bond angles between Co and Fe sites to correlate to the electrocatalytic behavior across both sample series. This unifying descriptor supports activation of a lattice-oxygen mechanism by decreasing O-O distance and will assist ongoing efforts to design next-generation catalysts. The fabrication dependence of microscopic catalyst structure should be considered in theoretical and high-throughput analyses of electrocatalyst materials.