Intrinsic Electric Field-Driven Charge Polarization Strategy in Homojunction Analogues of Graphitic Carbon Nitride for High-Performance Pseudocapacitor

Built-in electric field at semiconductor interfaces enhances the facile formation of an electric double layer, providing an effective strategy for improving power-density-based electrochemical energy storage. Building on this principle, rational design of homojunction involving nonmetal/nonmetal configuration, oxygen-doped g-C3N4 (O:g-C3N4) nanosheets exhibiting n-type characteristics combined with boron-doped g-C3N4 (B:g-C3N4) hollow nanotubes, which show a typical p-type carrier transport resulting in a well-defined homointerface (p–n). The doping strategy successfully aligns the band positions of g-C3N4, with O:g-C3N4 and B:g-C3N4 aiding in the redistribution of charges within the p–n junction, leading to the formation of space-charge regions and a built-in electric field, which promotes charge transfer at the interface. Unique hollow tubular morphology of B: g-C3N4 coupled with the 2D layered structure of O:g-C3N4 affords a high surface area and shorter ion diffusion path, enabling rapid ion transport and enhanced electrochemical performance, achieving a remarkable specific capacitance of 366 F g–1 at 1 A g–1. An asymmetric two-electrode supercapacitor using B:g-C3N4/O:g-C3N4 as a positive electrode achieves an energy density of 24 Wh kg–1 @ 700 W kg–1, demonstrating 83% capacitance retention at 100% Coulombic efficiency after 20,000 charge–discharge cycles.