Facet-Defined Strain-Free Spinel Oxide for Oxygen Reduction

Abstract

Exposing facet and surface strain are critical factorsaffecting catalytic performance but unraveling the composition-dependent activity on specific facets under strain-controlledenvironment is still challenging due to the synthetic difficulties.Herein, we achieved a (001) facet-defined Co-Mn spinel oxidesurface with different surface compositions using epitaxial growthon Co3O4nanocube template. We adopted composition gradientsynthesis to relieve the strain layer by layer, minimizing the surfacestrain effect on catalytic activity. In this system, experimental andcalculational analyses of model oxygen reduction reaction (ORR)activity reveals a volcano-like trend with Mn/Co ratios because ofan adequate charge transfer from octahedral-Mn to neighboringCo. Co0.5Mn0.5as an optimized Mn/Co ratio exhibits bothoutstanding ORR activity (0.894 V vs RHE in 1 M KOH) and stability (2% activity loss against chronoamperometry). By controllingfacet and strain, this study provides a well-defined platform for investigating composition-structure-activity relationships inelectrocatalytic processes.