Biphenylene-Based Crystalline Foam Carbon Allotropes

Developing new allotropes with excellent properties and high synthesizability is an intriguing and challenging topic for carbon materials. Based on the experimental biphenylene monolayers, varied three-dimensional crystalline foam carbon allotropes with parallel channels in the structure are theoretically designed. These calculated foam carbon structures are mostly semimetals or semiconductors. The selected representatives possess lattice dynamic stability, high thermal stability, great mechanical performance stability, and feasible synthesizability. Moreover, the selected foam carbon structures exhibit high feasibility in ion filtration, transport, or storage for different ion species. The representative structure (3D-C₄₈-Z₂-R₄R₄-R₆-trans) exhibits a high theoretical lithium storage capacity of 930.6 mAh·g^–1, low diffusion barriers of only 0.079 eV, suitable open-circuit voltage of 0.905–0.071 V, and relatively small volume change (8.5%). Besides, a nonfoam-limit structure (BPN-diamond) is found to be a direct bandgap semiconductor with a bandgap of 4.073 eV (HSE06), exhibiting ultrahigh hardness (H_V ∼ 76.4 GPa), high carrier mobility (up to 5.97 × 10³ cm² V^–1 s^–1), good optical absorption ability in the UV region, and high synthesizability. These findings suggest that the biphenylene-based foam carbon allotropes are potentially excellent multifunctional materials with applications in flexible and ductile materials, ion electron mixed conductors, ion filtration, and anode materials for Li ion batteries.