Free-Standing Leaf-LikeCoNiSe₂/NC@Ni₃(PO₄)₂ Core–ShellNanoarray Heterostructuresfor Flexible Asymmetric Supercapacitors

The rational design of a porous core–shell heterostructure with open spaces is an effective strategy to mitigate the aggregation and volume expansion of active nanoelectrodes during charging/discharging processes. Herein, the leaf-like CoNiSe₂/NC@Ni₃(PO₄)₂ core–shell heterostructure with hierarchical pores is <i>in situ</i> grown on activated carbon cloth (CC) as a free-standing electrode for flexible supercapacitors. The open spaces collectively formed by both the interspaces among adjacent leaf-like CoNiSe₂/NC@Ni₃(PO₄)₂ structures and the channels among vertically crossed Ni₃(PO₄)₂ nanosheets not only significantly enhance the electrode and electrolyte contact areas to promote rapid electrolyte penetration and ion diffusion but also effectively buffer the agglomeration and volume expansion of the active nanoelectrode. Such unique spatial arrangement and structure endow CoNiSe₂/NC@Ni₃(PO₄)₂/CC with a high specific capacitance of 2505 F g^–1 (1 A g^–1) and an extended cycle life with 91.1% capacity retention after 10,000 cycles, surpassing most reported electrodes with similar compositions. A combined experimental and band structure analysis signifies that the integrated CoNiSe₂/Ni₃(PO₄)₂ interfaces featuring an optimized electronic structure accelerate the charge transport and improve the redox-reaction kinetics, resulting in a significant enhancement in electrochemical performance compared to the two individual components.