Operando identification of active sites in Co-Cr oxyhydroxide oxygen evolution electrocatalysts

Identifying the active sites and their dynamic changes is of critical significance for designing efficient oxygen evolution reaction (OER) catalysts, but remains challenging owing to the complexity in structure and reaction process. Herein, using various operando characterizations, we identify the origin of a 12-time enhancement of OER activity over pure cobalt oxyhydroxide achieved by confining high-valance chromium into its lattice. Operando X-ray absorption spectroscopy reveals in-situ generation of high-valence Cr state with shortened Cr O bond relative to original state, indicating potential-dependent formation of OER intermediates on Cr sites. Operando electrochemical impedance and infrared spectroscopy provide direct spectroscopic evidence of OOH* on Cr site. Combined with theoretical calculations, the confined Cr is identified as the active site with improved bonding strength with O*, exhibiting a lower overpotential than that on Co site. This study elucidates the dynamic behaviour of active sites and provides guiding for improving OER catalysts via introducing high-valance metals. Layered cobalt oxyhydroxide showed a 12-fold OER activity enhancement after confining chromium. Various operando characterizations revealed the potential-relevant electronic and structural dynamics of Co and Cr under realistic working conditions, identifying that high-valence Cr is the active site with moderate bond strength with reaction intermediates. • The origin of a 12-time OER activity enhancement is identified by various operando characterizations. • Operando electrochemical impedance and X-ray absorption spectroscopy reveal the dynamic evolutions of the Co and Cr sites. • Operando infrared spectroscopy provide direct spectroscopic evidence of OOH* intermediates on Cr site. • High-valence Cr is identified as the active site with moderate bond strength with reaction intermediates.