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

Abstract

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.

Tunable Photocatalytic HER Activity of Single-Layered TiO2 Nanosheets with Transition-Metal Doping and Biaxial Strain

“…However, thermodynamics favors the presence of the relatively inactive basal plane and impedes the formation of highly energetic and atomically undercoordinated edge sites, limiting the number of active sites at the surface . As a most promising candidate in photocatalysis, titanium dioxide nanosheets have been applied into water splitting because of a large band gap and proper band alignment relative to the water redox potential . In 1996, Sasaki et al had successfully exfoliated single-layered titanium dioxide nanosheets (LNS-TiO 2 ) by means of soft chemical procedures. , Because of its ultrathin thickness for electron transferring and large surface area, LNS-TiO 2 nanosheets possess high photocatalytic degradation efficiency .…”

“…In addition, Rh dopant in LNS-TiO 2 nanosheets can effectively act as cocatalysts for the water splitting reaction . Besides, LNS-TiO 2 nanosheets had been investigated experimentally , and theoretically , in a photocatalyst.…”

Theoretical calculation of a TiO2-based photocatalyst in the field of water splitting: A review

“…In previous studies, the energy barrier to be overcome during the reaction was one of the main factors affecting the reaction [157]. As the OER is the most important process [158], many researchers have conducted many theoretical reports on the OER mechanism in the last 10 years [159,160]. As shown in Figure 5(a), Hu et al [158] used a first-principles method to study the photocatalytic OER at the water/TiO 2 (110) interface.…”

A Cocatalyst that Stabilizes a Hydride Intermediate during Photocatalytic Hydrogen Evolution over a Rhodium‐Doped TiO2 Nanosheet

“…For example, the GaN–ZnO solid solution exhibits relatively high activity for water splitting under visible light irradiation, and loading with Rh x Cr y O [Rh(core)/CrO x (shell)] cocatalysts significantly improves the water splitting rate . Therefore, it is believed that the roles of the cocatalyst are to introduce reaction sites, to decrease the overpotential, and to promote charge separation ,…”