Heterointerface engineering and phosphorus doping dual-regulation enabled P-CoO/Co₉S₈@activated carbon for...

Supercapacitor performance is largely determined by electrode materials. Transition metal compounds (TMCs) have high theoretical capacities but suffer from sluggish charge transport and volume-induced structural degradation, which limits their practical applications in energy storage. To overcome the inherent bottlenecks of TMCs in energy storage, this work reports a novel dual-regulation strategy to construct a P-doped CoO/Co₉S₈ heterostructure anchored on activated carbon (P-CoO/Co₉S₈@AC). The formation of the P-doped CoO/Co₉S₈@AC heterostructure enables close coupling between macroscopic structural buffering and atomic-scale electronic modulation. Introducing activated carbon (AC) suppresses particle agglomeration and buffers volume expansion, while the synergistic effect of heterointerface engineering and P doping significantly reduces the charge-transfer resistance to 0.27 Ω. Benefiting from these multidimensional advantages, the as-prepared material delivers a specific capacity of 1697.3 C g^-1 (3394.6 F g^-1) at 1 A g^-1, outperforming previously reported nickel sulfide/nickel oxide heterostructures (2278 F g^-1) and P-doped ternary cobalt-based sulfide electrodes (2716 F g^-1). Density functional theory (DFT) calculations show that the P-doped heterostructure has an OH^- adsorption energy of -4.82 eV and an upshifted d-band center, thereby improving intrinsic conductivity and OH^- interfacial adsorption. Furthermore, the assembled hybrid supercapacitor (HSC) achieves a high energy density of 90.4 Wh kg^-1 at a power density of 750 W kg^-1, while retaining 86.1% of its capacity after 20,000 cycles. This study provides a design strategy for constructing high-performance composite electrodes by integrating heterointerface engineering and heteroatom doping.