A cobaltphosphate (Co-Pi) oxygen evolution cocatalyst on a SrTiO3 photoelectrode was investigated by Co and P K-edge X-ray absorption fine structure (XAFS) spectroscopy. Formation of an edge-sharing CoO6 octahedral structure nanocluster in the Co-Pi cocatalyst was verified by the Co K-edge XAFS spectra under the photoelectrochemical reaction. The P K-edge XAFS spectrum for the Co-Pi cocatalyst showed a pre-edge peak derived from the hybridization of Co(3d)O( 2p)P( 3p) valence orbitals. Therefore, it was spectroscopically demonstrated that a phosphate species binds to the Co edge of the CoO6 cluster in the Co-Pi cocatalyst. The phosphate species is likely to stabilize the CoO6 cluster for efficient oxygen evolution activity.
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