Investigation of active sites in cobalt spinel oxide Co3O4 via high-energy-resolution X-ray absorption spectroscopy

However, there is still controversy over whether the main active sites are tetrahedral Co2+(Td) or octahedral Co3+(Oh).This study aims to distinguish the true OER active sites in Co3O4 by employing OER-inactive Al element substitution to engineer coordination environments, synthesizing spinel CoAl2O4 as the Co2+(Td)-enriched model for comparative analysis with Co3O4.X-ray diffraction (XRD), transmission electron microscope (TEM) and X-ray absorption fine structure (XAFS) were used to obtain the morphological and atomic structure information of Co3O4 and CoAl2O4.

Moreover, high energy resolution fluorescence-detected X-ray absorption spectroscopy (HERFD-XAS) and electrochemical characterization were used to obtain information about the refined electronic structure and alkaline OER performance of Co3O4 and CoAl2O4. Co3O4 exhibits a lower overpotential of 375 mV compared to 404 mV for CoAl2O4 at a current density of 10 mA/cm2. The HERFD-XAS results indicate that, in contrast to CoAl2O4, Co3O4 shows a pre-edge feature at approximately 7712 eV, which is attributed to non-local electron transitions.