Discovering a new 2D photocatalyst: DFT Prediction of Hydrogen-Evolution activity in a janus MoSSe Monolayer

Abstract

This research focuses on the discovery of a new two-dimensional photocatalyst for hydrogen evolution, motivated by the broader search for functional materials that can address water decontamination and clean energy storage/generation challenges. Solar-driven hydrogen production offers a route to both clean fuel generation and sustainable water treatment, but conventional photocatalysts such as symmetric MoS₂ suffer from weak internal polarization and inefficient separation of photogenerated charge carriers, limiting their real-world performance. Janus monolayers, formed by replacing one chalcogen layer of a transition metal dichalcogenide with a different element, break structural symmetry and introduce an intrinsic electric field that can improve charge separation and catalytic activity. Using this idea, the hydrogen evolution reaction (HER) activity of a Janus MoSSe monolayer was investigated using density functional theory (DFT) calculations performed in Quantum ESPRESSO, employing the PBE-GGA exchange-correlation functional, a plane-wave cutoff of 60 Ry, a 12×12×1 k-point mesh, and a vacuum spacing of ~15Å to eliminate spurious interlayer interactions. The relaxed structure was visualized using VESTA, and the electronic band structure and density of states were analyzed using XCrySDen. Band-edge positions relative to the water redox potentials and the Gibbs free energy of hydrogen adsorption (ΔG_H*) were computed to evaluate photocatalytic suitability. Results show that MoSSe has a band gap of 1.68 eV, straddles the water redox potentials, and exhibits a ΔG_H* of -0.08 eV, indicating near-optimal HER activity. These findings identify Janus MoSSe as a promising noble-metal-free 2D material for solar hydrogen generation, with future work aimed at strain and doping engineering to further tune its performance for integrated water-treatment and energy applications.

Keywords: 2D Photocatalysts; Janus MoSSe; Density Functional Theory