It was reported that the size reduction of CoO particles to nanometer range induces photocatalytic activity so that water molecules can be dissociated into H2 and O2 gases at room temperature even without externally applied potential. This photocatalytic activity of the CoO nanocrystals was suggested to be as a result of the up-shift of band edges by the size reduction, which in turn moves the band gap region to cover both water reduction and oxidation potential levels. Nevertheless, fundamental reason behind the band edge shift has not been understood. In this study, we find optimal morphology of CoO nanocrystal in a water environment by using first-principles density-functional theory (DFT) calculations. The band edge positions of the facets are estimated by the explicit solvation calculation and then compared to the experimentally observed values. We hereby discuss why CoO surfaces have different band edge positions in water based on the degree of band bending at the interface of each CoO slab/water. Finally, the role of each facet on the CoO nanocrystal in the hydrogen/oxygen evolution reaction was identified by estimating the relative activity of each facet for the hydrogen/oxygen evolution reaction.

Nanocrystalline CoO photocatalyst: Role of facets in overall water splitting

253rd National Meeting (2017)

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