Structure–Property Relationship of Oxygen-Doped Two-Dimensional Gallium Selenide for Hydrogen Evolution Reaction Revealed from Density Functional Theory

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–x O x , 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–x O x at low O contents, where all O atoms are favorably separated by at least one -Ga-Se-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–x O x 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 ΔG 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–x O x materials with surface reactivity and bandgaps that suit photocatalytic water splitting.

Room-Temperature Optoelectronic NO2 Sensing Using Two-Dimensional Gallium Oxyselenides

“…The changes in the band state of gallium oxyselenide may be attributed to the potential development of a novel unoccupied band introduced by the oxygen atom, positioned between the conduction band maximum (CBM) and the original VBM of pure GaSe. Additionally, the Ga–O band exhibits a shorter length (2.1 Å) compared to the Ga–Se band (2.6 Å), resulting in tensile strains within the plane and compressive strains perpendicular to it. Previous studies have suggested that both tensile and compressive strains could decrease the band gap. − The flat band potentials of GaSe, GaSe 0.40 O 0.60 , GaSe 0.31 O 0.69 , and GaSe 0.19 O 0.81 were determined as 0.30, 0.32, 0.39, and 0.61 eV, respectively, from the Mott–Schottky plots depicted in Figure S6, which increased with improved annealing temperature, as demonstrated in Figure c.…”

“…positioned between the conduction band maximum (CBM) and the original VBM of pure GaSe. Additionally, the Ga−O band exhibits a shorter length (2.1 Å) compared to the Ga−Se band (2.6 Å),60 resulting in tensile strains within the plane and compressive strains perpendicular to it. Previous studies have suggested that both tensile and compressive strains could decrease the band gap.61−63 The flat band potentials of GaSe,…”

Theoretical Understanding of the Structure–Property Relationship of Oxygen-Doped Gallium Selenide as an Efficient Photocatalyst for Oxygen Evolution Reaction

“…In our previous work, not only the concentration but also the atomic configuration of O-dopants were identified as essential factors for tuning the surface catalytic activity of GaSe 1−x O x for HER; interestingly, the presence of localized dopant arrangements would play an essential role in enhancing its catalytic activity. 42 To be discussed below, the atomic configuration of the Odopants is also an important factor to improve the catalytic efficiency for the OER, as predicted with our GaSe supercell with O atoms. In this study, GaSe 1−x O x with up to 22% O content was investigated.…”

“…42 Oxygen doping can also significantly alter the electronic structure of GaSe by reducing its wide bandgap while still keeping the positions of conduction band minimum (CBM) and valence band maximum (VBM) suitable for photochemical water splitting reactions. 42 In this work, the surface activity and catalytic performance of oxygen-doped GaSe (GaSe 1−x O x ; x = 6, 11, 17, and 22%) toward the OER are also theoretically studied. The primary objective is to predict how the performance of OER may be influenced by different concentrations and atomic configurations of the dopants on the O-doped GaSe surfaces, which have been suggested to have significant effects on the complementary HER process.…”

“…The primary objective is to predict how the performance of OER may be influenced by different concentrations and atomic configurations of the dopants on the O-doped GaSe surfaces, which have been suggested to have significant effects on the complementary HER process. 42 By systematically exploring different dopant concentrations and atomic configurations, we aimed to predict whether these modifications will enhance or diminish the catalytic activity. Properly accounting the effects of varying concentrations and atomic configurations, we have identified a more localized O dopant configuration in GaSe 1−x O x structures that serves as a high efficient photocatalyst for OER.…”