Polarization-direction-controlled Z-scheme photocatalytic switch in ${\mathrm{Sc}}_2{\mathrm{CO}}_2/{\mathrm{Pt}\mathrm{S}}_2$ heterostructures: A first-principles study

Constructing van der Waals (vdW) heterostructures is the most commonly used method for separating photogenerated carriers, which can effectively improve photocatalytic water-splitting efficiency. Although many vdW heterostructure photocatalysts have been proposed, there is still a lack of effective strategies to regulate the photocatalytic reaction ability. In this work, we propose a ${\mathrm{Sc}}_2{\mathrm{CO}}_2/{\mathrm{Pt}\mathrm{S}}_2$ heterostructure that can achieve the photocatalytic switch with different polarization directions (P ↑ and P ↓). Both the P ↑ and P ↓ ${\mathrm{Sc}}_2{\mathrm{CO}}_2/{\mathrm{Pt}\mathrm{S}}_2$ heterostructures are semiconductors with type-II band-edge distribution. Remarkably, through the analysis of band arrangement and the built-in electric field, we found two completely different carrier-migration mechanisms inside the two heterostructures. The ${\mathrm{Sc}}_2{\mathrm{CO}}_2/{\mathrm{Pt}\mathrm{S}}_2$ heterostructure with P ↑ can be used as a direct Z-scheme photocatalyst, showing great application prospect for water splitting. In contrast, the P ↓ ${\mathrm{Sc}}_2{\mathrm{CO}}_2/{\mathrm{Pt}\mathrm{S}}_2$ heterostructure cannot undergo photocatalytic reactions affected by the direction of the built-in electric field. Therefore, based on ${\mathrm{Sc}}_2{\mathrm{CO}}_2/{\mathrm{Pt}\mathrm{S}}_2$ heterostructure, the “on” and “off” of photocatalysis are successfully achieved in a single material. Additionally, Gibbs free-energy calculation, high light absorption, and strain tunable band gap indicate that the ${\mathrm{Sc}}_2{\mathrm{CO}}_2/{\mathrm{Pt}\mathrm{S}}_2$ heterostructure is a promising candidate for photocatalytic applications.

Figure 1

The top and side views of the structures of (a) ${\mathrm{Sc}}_2{\mathrm{CO}}_2\mathrm{and}{\mathrm{Pt}\mathrm{S}}_2$ monolayers. (b)–(i) The ${\mathrm{Sc}}_2{\mathrm{CO}}_2/{\mathrm{Pt}\mathrm{S}}_2$ heterostructures with different configurations. P ↑ states are shown in (b)–(e) while P ↓ states are shown in (f)–(i).

Figure 2

(a),(c) are the AIMD simulation at 300 K of ${\mathrm{Sc}}_2{\mathrm{CO}}_2/{\mathrm{Pt}\mathrm{S}}_2$ heterostructure with P ↑ and P ↓ configurations, respectively. (b),(d) are the phonon spectrum of the ${\mathrm{Sc}}_2{\mathrm{CO}}_2/{\mathrm{Pt}\mathrm{S}}_2$ heterostructure with P ↑ and P ↓ configurations, respectively.

Figure 3

The band structure of the ${\mathrm{Sc}}_2{\mathrm{CO}}_2/{\mathrm{Pt}\mathrm{S}}_2$ heterostructure with (a) P ↑ and (c) P ↓ states. The DOS and PDOS of ${\mathrm{Sc}}_2{\mathrm{CO}}_2/{\mathrm{Pt}\mathrm{S}}_2$ heterostructure with (b) P ↑ and (d) P ↓ states.

Figure 4

Plane-averaged electrostatic potential of (a) P ↑ and (b) P ↓ states in ${\mathrm{Sc}}_2{\mathrm{CO}}_2/{\mathrm{Pt}\mathrm{S}}_2$. Average charge-density difference along the Z axis of (c) P ↑ and (d) P ↓ states in ${\mathrm{Sc}}_2{\mathrm{CO}}_2/{\mathrm{Pt}\mathrm{S}}_2$.

Figure 5

The band arrangement versus the redox potential of water in (a) P ↑ and (b) P ↓ states of the ${\mathrm{Sc}}_2{\mathrm{CO}}_2/{\mathrm{Pt}\mathrm{S}}_2$ heterostructure. (c) The minimal energy pathway from P ↑ to P ↓ states. (d) Different photocatalytic mechanism in the ${\mathrm{Sc}}_2{\mathrm{CO}}_2/{\mathrm{Pt}\mathrm{S}}_2$ heterostructure.

Figure 6

The (a) HER pathway and (b) OER pathway with the most stable absorbed intermediates. Gibbs free-energy steps with implicit solvation scheme of (c) HER and (d) OER in the P ↑ configuration of ${\mathrm{Sc}}_2{\mathrm{CO}}_2/{\mathrm{Pt}\mathrm{S}}_2$ heterostructure.

Figure 7

(a) Light-absorption coefficient of ${\mathrm{Sc}}_2{\mathrm{CO}}_2\mathrm{and}{\mathrm{Pt}\mathrm{S}}_2$ monolayers and the P ↑ ${\mathrm{Sc}}_2{\mathrm{CO}}_2/{\mathrm{Pt}\mathrm{S}}_2$ heterostructure. (b) Band gap and total energy as functions of biaxial strain from −2% to 4%.