High-valent states drive the bond-forming and bond-breaking steps of catalysis, such as the oxygen evolution reaction. The Co4O4 topology has been likened to the cobalt-based oxygen evolving anode, CoPi, and can house a stable, but electronically delocalized, mixed-valent Co(IV) state. However, these states in metal clusters and oxygen-evolving anodes can be difficult to study because they can be obscured by spectroscopically active and complex backgrounds. We use complimentary X-ray spectroscopies to overcome this issue. Together, X-ray absorption and 1s3p resonant inelastic X-ray scattering (Kβ RIXS) of a Co4O4 model of CoPi can effectively map out Co(IV) contributions within a spectroscopically active background. Co K- and L-edge X-ray absorption directly probe the 3d-manifold of effectively localized Co(IV), providing a handle on the covalency of the dπ-based redox active molecular orbital of Co4O4. Kβ RIXS is shown to be highly sensitive to metal cluster oxidation state and oxo-mediated metal-metal coupling in high-valent, delocalized mixed-valent species. Guided by the data, DFT calculations define electronic structure contributions to the formation of high-valent states in Co4O4 and perturbed topologies.

Redox in the Co4O4 topology: Electronic structure contributions to the formation of high-valent states relevant to the oxygen evolution reaction

252nd National Meeting (2016)

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