Exploration of Photocatalytic Overall Water Splitting Mechanisms in the Z-Scheme SnS₂/β-As Heterostructure

Abstract

The Z-scheme heterostructure photocatalysts have irreplaceable advantages over other heterostructures due to their ability to separate the spatial carriers and retain strong redox ability. In this study, we explored the SnS2/β-As (β-arsenene) van der Waals heterostructure with Z-scheme properties and suitable band edge positions as a potential photocatalyst for overall water splitting. Under appropriate conditions, the hydrogen evolution reaction (HER) barrier is much closer to 0. Based on the oxidation product criteria, the SnS2/β-As heterostructure photocatalyst may generate multiple end products, including •OH, H2O2, and O2. Moreover, we screen the optimal and most possible reaction pathway OER-III under irradiation among three underlying oxygen evolution reaction (OER) mechanisms, in which the intermediate species HOOH* acts as a bridge for subsequent reactions. The solar-to-hydrogen conversion efficiency of the heterostructure can reach 17.18%. This work provides new insights into designing superior photocatalysts for overall water splitting and recognizing the OER mechanism.

Forecasting the unrevealed surface-controlled photocatalytic water splitting in two-dimensional Ag2Se with ultrafast carrier mobility: a first-principles study

“…Under an external potential of U = 2.10 V, it is evident that all free-energy profiles become negative and are going downhill, indicating that the OER is exothermic and can proceed with minimal kinetic hindrance to catalyze water oxidation in this condition from an energy standpoint. The selected U value is much lower than that of other 2D photocatalysts 49–52 and requires only an overpotential of 0.56 V. It is worth noting that the required overpotential is comparable or much less than those reported for other 2D materials, such as g-C 3 N 4 (0.43 V), 53 the broadly studied catalyst γ(Ni, Fe)OOH (0.56 V), 54 GaAs (1.39 V), 55 C 2 N-based heterostructures (0.94–1.47 V), 56 β-Te 2 X (X = S, Se) (1.30–2.01 V) 57 and CuCl (1.53 V). 58 Researchers have also found that materials with intrinsically low photocurrents can be induced to better exhibit a photocurrent by applying an external voltage.…”

The Isoelectronic Dopant in the Z-Scheme SnS2/β-As Heterostructure Enhancing Photocatalytic Overall Water Splitting

“…The SnS 2 /β-As heterostructure exhibits both thermodynamic and kinetic stability. The lattice constants of SnS 2 and β-As monolayers are 3.68 and 3.61 Å, respectively, and their lattice mismatch is only 1.9%. As can be seen from Figure S1, the projected band structures and density of states reveal that the S-p orbitals of SnS 2 primarily contribute to the conduction band minimum (CBM).…”

“…Therefore, the OER cannot proceed through a traditional four-electron step. Instead, there is a possibility that the OER may proceed through a new pathway facilitated by the HOOH* intermediate, acting as a bridge for subsequent reactions . The HOOH* state can be considered as a precursor to the generation of H 2 O 2 .…”

“…Based on the staggered band structures and the built-in electric field at the interface, photoexcited electrons from the conduction band of SnS 2 will transfer to the valence band of β-As and subsequently recombine. As a result, the hydrogen reduction reaction occurs at the conduction band of β-As, while the water oxidation reaction takes place at the valence band of SnS 2 . However, the dynamic results indicate that the higher barrier of water oxidation between O* and OOH* prohibits the OER along the conventional four-electron step pathway.…”

“…The SnS 2 /β-As heterostructure has been predicted to exhibit a Z-scheme feature and hold potential as a photocatalyst for overall water decomposition . However, a relatively high reaction barrier of 3.76 eV in the OER presents a challenge in achieving the traditional four-electron step.…”