Highly Active Surface Structure in Nanosized Spinel Cobalt-Based Oxides for Electrocatalytic Water Splitting

Abstract

Spinel cobalt-based oxides are a promising family of materials for water splitting to replace currently used noble-metal catalysts. Identifying the highly active facet and the corresponding coordinated structure of surface redox centers is pivotal for the rational design of low-cost and efficient nanosized catalysts. Using high-resolution transmission electron microscopy and advanced X-ray techniques, as well as ab initio modeling, we found that the activity of Co3+ ions exhibits the surface dependence owing to the variability of its electronic configurations. Our calculation shows that the Co3+ site in {100} facet of nanosized Li2Co2O4 exhibits an impressive intrinsic activity with low overpotential, far lower than that of the {110} and {111} facets. The unique, well-defined CoO5 square-pyramidal structure in this nonpolar surface stabilizes the unusual intermediate-spin states of the Co3+ ion. Specially, we unraveled that oxygen ion anticipates the redox process via the strong hybridization Co 3d–O 2p s...