Heterojunction‐Induced Facet Reorientation: Decoupling Thermodynamics and Kinetics for Ultrastable Ni ₂ P‐Based Flexible Supercapacitors

ABSTRACT Practical application of nickel‐based phosphides is severely impeded by material oxidation and parasitic oxygen evolution reactions (OER) under high voltage. This work proposes a Ni ₂ P@Ni‐Co PBA heterojunction to synergistically suppress both degradation pathways. Electrostatic self‐assembly induced a crystal facet reorientation of the Ni ₂ P nanosheets, enhancing the exposure of the highly active (400) facet. Density Functional Theory (DFT) calculations reveal this interfacial reconstruction achieves a decoupled modulation of the electronic structure. The d‐band center downshifts, thermodynamically inhibiting OER and deep oxidation. Simultaneously, the density of states (DOS) at the Fermi level surges, kinetically establishing an efficient pathway for charge transfer. This mechanism manifests as a self‐limiting passivation layer, confirmed by High‐Resolution Transmission Electron Microscopy (HRTEM) to be thinner at the heterointerface than at the bulk edges. Consequently, the heterojunction electrode exhibits a wide voltage window and a high specific capacitance (1674.91 F g ⁻¹ ). The assembled asymmetric supercapacitor (ASC) demonstrates exceptional cycling stability (97.14% after 10 000 cycles), and flexible solid‐state ASC realizes a wide 1.8 V window and 53.44 Wh kg ⁻¹ energy density. This strategy of establishing dynamic equilibrium through interfacial facet and electronic reconstruction opens a new paradigm for designing high‐stability electrode materials.