Optimizing the quantum capacitance of AsXBr/AsYBr ((X ≠ Y) = S, Se and Te) Janus heterostructures for high-performance supercapacitors†

We systematically investigated the properties of AsXBr/AsYBr ((X ≠ Y) = S, Se and Te) Janus heterostructures with the goal of tailoring their characteristics for advanced supercapacitor applications. To our knowledge, this is the first reported study on these Janus heterostructures, thus offering novel insights into their properties. By employing density functional theory (DFT), we uncovered crucial insights into these materials. Notably, we found reduced indirect band gaps of 1.39 eV for AsSBr/AsSeBr, 1.08 eV for AsSBr/AsTeBr, and 1.23 eV for AsSeBr/AsTeBr, indicating their potential for efficient charge storage. Mechanical stability was confirmed, with ultra-low Young's modulus values for all structures. Our exploration of chalcogenides’ interchange effect in supercapacitors leads to the discovery of remarkable maximum quantum capacitance values: 426.62 μF cm⁻² for AsSBr/AsSeBr, 430.12 μF cm⁻² for AsSBr/AsTeBr, and 536.86 μF cm⁻² for AsSeBr/AsTeBr, respectively. Furthermore, our investigation into surface charge dynamics suggested that these materials act as cathode-type electrodes, enhancing their suitability for supercapacitor configurations. To ensure dynamical stability, we conducted detailed analysis of the phonon dispersion curves of these Janus heterostructures. These curves revealed no imaginary frequencies in the Brillouin zone, confirming the dynamical stability of AsSBr/AsSeBr and AsSeBr/AsTeBr Janus heterostructures. Additionally, our exploration extended to the assessment of the thermal properties, including the Seebeck coefficient (S), electronic conductivity (σ), and thermal conductivity (κ), of all heterostructures. The results, obtained through this methodology, utilized the SIESTA code to compute overlaps between Bloch states and trial localized orbitals. Subsequently, we employed Wannier90 to generate maximally-localized Wannier functions (MLWFs), which served as the basis set for interpolating band structures and computing transport properties via the BoltzWann module.