Engineering Band Edge Positions of Nickel Oxyhydroxide through Facet Selection

A promising material for catalysis should have appropriate band edge positions. Unfortunately, the band edge positions are unknown for nickel oxyhydroxide (NiOOH), one of the best water oxidation catalysts. We present here first-principles calculations of band edge positions for surfaces of pure NiOOH. Specifically, the band edge positions of NiOOH (001), (100), and (01̅5) were calculated using density functional theory (DFT) + U, PBE0, and G₀W₀ methods by using slab models for the surfaces with a vacuum region and periodic boundary conditions. The band edge positions were determined by calculating the band gap center using DFT + U and by accounting for the band gap using G₀W₀. This approach was validated with other methods. Our results show that due to the polarity of NiOOH, the valence band position is especially sensitive to surface orientation: facets with O–H bonds parallel to the normal of the surface have the highest valence band edge. The following relation between valence band edges is obtained: E_VBM(001) > E_VBM(01̅5) > E_VBM(100). As a result, the (100) surface should be the most active, while the other surfaces may be less efficient in enabling the oxygen evolution reaction. Our results suggest that chemical activity of polar materials can be controlled through facet selection.