Surface microstructures and oxygen evolution properties of cobalt oxide deposited on Ir(111) and Pt(111) single crystal substrates

We investigated the structural and activity changes of cobalt oxide (CoO _x ) thin films on Ir and Pt substrates during the oxygen evolution reaction (OER). After repeated OER measurements, CoO _x on Ir showed remarkable activity enhancement due to the formation of CoO _x -Ir interfacial active sites. In contrast, the activity of CoO_x/Pt decreased.

Abstract

We investigated the oxygen evolution reaction (OER) activity changes of cobalt oxide (CoO _x ) thin films on Ir(111) and Pt(111) substrates by repeated OER measurements in 0.1 M KOH. Atomic force microscopy and X-ray photoelectron spectroscopy analysis of the as-prepared CoO _x /Ir(111) and CoO _x /Pt(111) showed similar surface morphologies of the CoO _x thin films and almost the same OER overpotentials, which were estimated to be around 430 mV. However, after three OER measurements, the overpotential of CoO _x /Ir(111) decreased by 70 mV, whereas that of CoO _x /Pt(111) increased slightly. Structural analysis showed that CoO _x /Ir(111) revealed the island-like nanostructures of CoO _x dispersed on Ir(111) surface, accompanied by the generation of CoOOH. In contrast, for CoO _x /Pt(111), the Pt(111) substrate remains covered by the CoO _x thin film. The results suggest that the interaface at CoO _x (CoOOH) nano-islands and Ir(111) substrate are responsible for reducing the OER overpotential.

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