Theoretical insights into the structural, electronic, photocatalytic and supercapacitor applications of pentahexoctite.

The discovery of novel two-dimensional (2D) carbon allotropes with tunable structural and electronic properties is vital for the development of next-generation energy storage and photocatalytic technologies. In this study, we present first-principle insights into the stability, electronic features, and electrochemical performance of pentahexoctite. Cohesive energy (-8.483 eV per atom) and formation energy (0.451 eV per atom) values reveal that pentahexoctite is structurally and thermodynamically more favorable than many well-known carbon allotropes, while phonon dispersion and molecular dynamics (AIMD) simulations confirm its dynamic and thermal robustness. Structural and thermodynamic feasibility under bi-axial strain further demonstrate that pentahexoctite remains stable in comparison with other 2D carbon frameworks. Pristine pentahexoctite exhibits metallic behavior; however, its electronic structure can be tailored to wide-gap semiconductors through even-numbered hydrogenation or BN doping at hexagonal sites. Multilayer stacking configurations significantly enhance its electrochemical properties, where the trilayer and tetralayer pentahexoctite achieve superior surface charge density and quantum capacitance, enabling a transition from negative-type to symmetric electrode behavior (except for the HSE06 functional). Furthermore, compressive biaxial strain and uniaxial tensile strain promote balanced charge accumulation, reinforcing its suitability for high-performance symmetric supercapacitors. Beyond energy storage, BN-doped pentahexoctite demonstrates strong photocatalytic activity for visible-light-driven water splitting. Collectively, these findings highlight pentahexoctite as a stable, tunable, and multifunctional carbon allotrope with exceptional promise for advanced energy storage and sustainable energy conversion applications.