Janus MoSSe/WSSe Heterobilayers as Selective Photocatalysts for Water Splitting

TL;DR

This study uses advanced first-principles calculations to identify Janus MoSSe/WSSe heterobilayers as highly efficient and tunable photocatalysts for water splitting, with potential for high solar-to-hydrogen conversion.

Contribution

It introduces a rational design framework for Janus heterobilayers as effective photocatalysts, highlighting the role of intrinsic dipoles and chemical potential differences.

Findings

Se-Se interfaced heterobilayer can drive water splitting intrinsically.

Achieves a predicted 17.1% solar-to-hydrogen efficiency.

Heterobilayers outperform homobilayers in hydrogen production.

Abstract

Identifying materials that simultaneously straddle the water redox potentials and possess an intrinsic electric field is crucial for achieving high solar-to-hydrogen (STH) efficiency. Using state-of-the-art first-principles calculations, including a range-separated hybrid functional and spin-orbit coupling, we investigate MoXY/WXY (X, Y = S, Se) Janus bilayers for overall water splitting. We find a critical competition between the metal-to-metal chemical potential difference and the intrinsic dipoles at the interface between the Janus monolayers. We find that the Se-Se interfaced heterobilayer is intrinsically capable of driving water splitting, while its S-S counterpart can meet the redox requirements through pH modulation. For both configurations, a remarkable STH efficiency of 17.1% is anticipated. Furthermore, we predict a threshold of 1.0 eV for the built-in potential gradient to govern the transition from overall water splitting to band-edge pinning. Compared to homobilayers, heterobilayers benefit from the reciprocity between layer-specific dipoles and the Mo/W chemical potential difference, which promotes spatial separation and suppresses recombination, overall enhancing hydrogen production. Our results establish specific electronic descriptors for Janus heterostructures, providing a rational design rule for maximizing solar-driven hydrogen production in asymmetric two-dimensional materials.