Hydrogen Evolution, Piezoelectricity, and Optical Properties of Monolayer Semimetal (α,β)–S₂C₂N₂ and Janus (α,β)–SCN/CN

Abstract

Herein, the density functional theory is used to study the structural, mechanical, electrical, optical, and hydrogen evolution reaction (HER) properties of monolayer structures and . They are claimed to be stable monolayer structures by phonon dispersion and ab initio molecular dynamics (AIMD). Compared to graphene (≈340 N m−1), the shows a higher Young's modulus (≈429, 414 N m−1). Moreover, the piezoelectric stress coefficient of α‐ (=2.65 pm V−1) is comparable with bulk piezoelectric α‐quartz (=2.3 pm V−1). Exciton effect at M point causes redshift and enhancement of light absorption of α‐ and . The overpotential of is only –0.072 V. Besides, the gives a small effective electron mass of about 0.2(m0). It is worth mentioning that the monolayer structures show the semimetal phases. Due to the unique semimetal phase, the absorption of has an excellent performance in the near‐infrared (NIR) region. It can be enhanced at the NIR region and extended to the middle infrared region when applying tensile stress. These results provide more choices for 2D materials in electrocatalysis, piezoelectric sensors, visible light devices, and infrared photodetectors.