Structure-Property Relationship of Oxygen-Doped Two-Dimensional Gallium Selenide for Hydrogen Evolution Reaction Revealed from Density Functional Theory
Document Type
Article
Publication Date
5-1-2022
Abstract
Two-dimensional (2D) gallium selenide (GaSe) is known for its inert surface and wide bandgap, limiting its application as a photocatalytic material for the hydrogen evolution reaction (HER). Partial substitution of Se with O atoms can improve its catalytic efficiency. This work discovered that the surface activity of the substitutional O-doped single-layer GaSe surfaces (GaSe1-xOx, for x <= 22%) and their bandgap sizes are dependent on the detailed atomic configuration of the dopants, as revealed from density functional theory. For GaSe1-xOx at low O contents, where all O atoms are favorably separated by at least one-GaSe-Ga- unit, the surface activity for the HER is insignificantly improved by increasing dopant concentration. By contrast, when more O dopants are available and arranged in adjacent positions (O-Ga-O), the hydrogen adsorption efficiency of GaSe1-xOx increases and their bandgaps are reduced with increasing dopant concentration. These important features are attributed to weakening of the Ga-O covalent interaction in these more localized dopant arrangements, which in turn strengthens the O-H bonds. This weakened Ga-O covalent bond also descends the conduction band minimum toward the Fermi level, resulting in bandgap reduction and thus favoring visible-light absorption. Optimal atomic configurations (all having localized O-dopant arrangements) have been identified, and they exhibit almost thermoneutral hydrogen adsorption free energy Delta G(H) and small bandgaps (2.09-2.21 eV), making them promising materials to perform an efficient HER. Fine-tuning the Ga-O interaction by applying tensile strength T-s parallel to the 2D surface of up to 1% further reduces their bandgaps to 1.95-2.05 eV. Our theoretical predictions suggest that controlling the atomic configuration of dopants provides opportunities for engineering single-layered GaSe1-xOx materials with surface reactivity and bandgaps that suit photocatalytic water splitting.
Keywords
GaSe, water splitting, photocatalysis, hydrogen absorption, surface reactivity
Divisions
rms
Funders
Hong Kong Research Grants Council (CityU 11301421)
Publication Title
ACS Applied Energy Materials
Volume
5
Issue
5
Publisher
American Chemical Society
Publisher Location
1155 16TH ST, NW, WASHINGTON, DC 20036 USA