Theoretical study on vertical B2CSe/Mg(OH)2 van der Waals heterostructures with high solar-to-hydrogen efficiency†

The search for efficient and stable photocatalysts for solar-driven water splitting remains a critical challenge in renewable energy research. In this study, the B₂CSe/Mg(OH)₂ van der Waals heterostructure (vdWH) was investigated as a promising candidate using first-principles simulations. The heterostructure demonstrated exceptional thermal, kinetic, and mechanical stability, as confirmed through ab initio molecular dynamics, phonon dispersion, and mechanical property analyses. The B₂CSe/Mg(OH)₂ vdWH exhibited a reduced indirect bandgap compared to the Mg(OH)₂ monolayer, facilitating efficient photogenerated electron–hole pair separation. A type-II band alignment, supported by charge density difference, electronic structure, and built-in electric field analyses, further enhanced redox capacity and carrier separation efficiency. The heterostructure achieved a remarkable solar-to-hydrogen (STH) conversion efficiency of 34.58%, outperforming many existing systems, and demonstrated strong optical absorption across the visible light spectrum. Strain engineering revealed the potential for adaptive photocatalyst design, with compressive strain inducing a transition from type-II to type-I band alignment and tensile strain effectively redshifting the absorption edge to harness a broader range of solar energy. This tunability allows for precise control over the electronic and optical properties of the heterostructure, enabling optimization for specific photocatalytic applications. A potential drop of 8.06 eV across the interface and a charge transfer of 0.0045 electrons from Mg(OH)₂ to B₂CSe further enhanced the heterostructure's photocatalytic potential. These findings not only highlight the B₂CSe/Mg(OH)₂ vdWH as a highly efficient and stable photocatalyst for overall water splitting but also underscore the transformative role of strain engineering in designing adaptive photocatalysts. This approach offers a promising pathway for advancing solar energy utilization and hydrogen production, paving the way for next-generation renewable energy technologies.