Two-Dimensional TiO₂ Nanosheets for Photo and Electro-Chemical Oxidation of Water: Predictions of Optimal Dopant Species from First-Principles

Due to a high surface area to volume ratio, two-dimensional nanosheets have gained interest for photo and/or electro-catalytic water splitting. In particular, experimental Rh doping of lepidocrocite TiO₂ nanosheets has significantly increased catalytic activity. We use first-principles density functional theory to consider the oxygen evolution reaction (OER) on both pristine and transition metal doped systems. While the undoped TiO₂ nanosheets exhibit several limitations and require high overpotentials during the water splitting reaction, selected dopants modify the binding strength of reaction intermediates and can reduce rate limiting thermodynamic barriers and theoretical required overpotentials. We present an activity volcano for these nanosheets, with the full spectrum of 3d, 4d, and 5d transition metals as candidate dopants. Subsequent photocatalytic measurements of OER activity with selected dopants are carried out to validate the predictions, and the trends are found to be consistent. These results help describe how surface dopants affect reaction mechanisms and provide general design principles for high performance catalysts during the water splitting reaction. (Graph Presented).