Two-Dimensional Nanocapacitors from Pristine and Hydrogenated Carbon Biphenylene Networks

Two-dimensional nanocapacitors provide a promising route toward ultra-thin energy-storage devices, in which electrostatic screening and dielectric thickness play a central role. In this work, vertical metal–insulator–metal nanocapacitors based on carbon biphenylene networks are investigated using first-principles density functional theory. Pristine biphenylene is employed as the metallic electrode, while fully hydrogenated biphenylene serves as the dielectric layer, enabling a structurally compatible heterostructure. The electronic and electrostatic responses of C-BPN/CH-BPN/C-BPN nanocapacitors are examined for dielectric thicknesses ranging from one to five atomic layers. Under an applied vertical electric field, a clear and reversible charge separation develops across the metallic electrodes, while the dielectric layers remain essentially charge neutral, confirming polarization-dominated capacitive behavior. The excess charge scales linearly with the applied electric field, whereas the stored energy exhibits a quadratic dependence, consistent with classical electrostatics. The gravimetric capacitance shows a weak dependence on electric field strength and decreases systematically with increasing dielectric thickness. A maximum gravimetric capacitance of is obtained for the thinnest dielectric configuration. These results establish biphenylene-based heterostructures as a robust platform for nanoscale capacitive energy storage and demonstrate that device geometry provides an effective design space for optimizing capacitive performance in two-dimensional nanocapacitors.