Regensburg 2013 – scientific programme

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DS: Fachverband Dünne Schichten

DS 35: Application of Thin Films

DS 35.9: Talk

Friday, March 15, 2013, 11:30–11:45, H8

The Co2p spin and oxidation state in Co-PI catalysts — •Matthias Richter and Dieter Schmeißer — Brandenburg University of Technology Cottbus, Applied Physics and Sensors, K.-Wachsmann-Allee 17, 03046 Cottbus, Germany

The electronic structure of cobalt based catalysts used for photocatalytic water splitting in solar cells is analyzed using synchrotron radiation photoelectron spectroscopy. The catalyst films are prepared by electrochemical deposition. We employ a X-ray photoelectron spectroscopy study to analyze the Co2p and O1s core levels, absorption edges and valence bands. We discuss our resonant data in terms of the partial density of states of the valence and conduction band. We find a difference in the Co oxidation state as a function of film thickness (deposited charge). From the relative amount of Co, O, K and P we favor the molecular cobaltate cluster-like structure as the structural motif of the Co-PI catalyst. Further, at resonant PES at the Co2p edge we find the Co2p partial DOS to exhibit no sharp features next to the VBM, instead there is a broad emission at around 6eV below E_Fermi. The former are found in LiCoO₂ and other Co-oxide systems with a Co³⁺ ground state. We attribute such sharp features to the low spin (LS) configuration of Co³⁺ and deduce that in the Co catalysts there is no evidence for the corresponding LS contributions. Our data prove the Co²⁺ ground state and demonstrate that it is exclusively in the Co3d⁷ high spin state in the pristine catalyst films.