Transition metal phosphides exhibit excellent energy storage characteristics in the field of supercapacitors. However, in practical applications, due to their relatively weak electron conduction ability, these materials lead to the blocking of charge transport inside the material and at the electrode/electrolyte interface, thereby limiting the power density of supercapacitors; more importantly, in the long-term charge-discharge cycle, transition metal phosphides are prone to structural degradation, which will seriously affect the long-term stability and service life of supercapacitors. In this work, MOF was used as a self-sacrificing template to construct a hierarchical NC@MOF@NCP composite (~25.4 mg·cm^-2) with high active material load by hydrothermal method combined with controllable electrodeposition technology. The skeleton structure of the NC@MOF @NCP composite has 3D conductive channel and mesoporous characteristics, which significantly reduces the charge transfer impedance of the material when improving its energy density and stable cycle.

Preparation of NiCo-LDH: 0.290 79 g of Ni(NO₃)₂·6H₂O, 0.582 06 g of Co(NO₃)₂·6H₂O, 0.074 08 g of NH₄F and 0.300 30 g of CO(NH₂)₂ were dissolved separately in 50 mL of deionized water. After stirring for 20 min, a 3 cm×4 cm piece of nickel foam (NF) was transferred, together with the precursor solution, into a stainless-steel autoclave lined with polytetrafluoroethylene (PTFE). The mixture was then heated to 120 ℃ and left to react for 5 h, yielding NiCo-LDH nanorods (NC). To prepare NiCo-LDH@Co-MOF: 0.873 1 g of Co(NO₃)₂·6H₂O and 0.210 1 g of 1,3,5-benzenetricarboxylic acid were dissolved in 20 mL of a mixture of N,N-dimethylformamide (DMF) and ethanol (volume ratio 1:1) to form Solution A. Subsequently, 0.5 g of polyvinylpyrrolidone was dispersed in 10 mL of deionized water to yield Solution B, which was then slowly added to Solution A with thorough mixing. The mixture was then transferred, together with the Ni foam bearing the deposited NiCo-LDH, to a stainless-steel reactor lined with polytetrafluoroethylene. The mixture was then maintained at 180 ℃ for 10 h, yielding the purple product, NiCo-LDH@Co-MOF (NC@MOF). To prepare NiCo-LDH@Co-MOF@NiCoP: 5.815 8 g of dissolve Ni(NO₃)₂·6H₂O, 5.820 6 g of Co(NO₃)₂·6H₂O and 2.119 8 g of NaH₂PO₂·H₂O separately in a 100 mL mixture of ethanol and deionized water (volume ratio 1:1). NiCoP nanosheets were then electrodeposited onto the NC@MOF framework via cyclic voltammetry. In a three-electrode system, the NC@MOF served as the working electrode, Pt as the counter electrode and Ag/AgCl as the reference electrode. Within the -1.2 to 0.2　V potential window, 20 cycles were performed at a scan rate of 10 mV·s^-1, yielding the product NiCo-LDH@Co-MOF@NiCoP (NC@MOF@NCP). The loading mass of NC, NC@MOF and NC@MOF@NCP were 2.7, 10.5 mg·cm^-2 and 25.4 mg·cm^-2 respectively.

After 20 cycles of electrochemical deposition, the product NC@MOF@NCP primarily consists of a mixed phase comprising MOF, Ni(OH)₂ and Co_3.5(OH)·0.11H₂O, Ni(HPO₃)H₂O and (Ni_0.65Co_0.35)₃(PO₄). FESEM and TEM images reveal that the NC@MOF nanorods are encapsulated by ultrathin, low-crystallinity NiCoP nanosheets, forming a highly loaded core-shell structure of NC@MOF@NCP. The Co-MOF serves as a sacrificial template that provides skeletal support for the deposition of high-loading NiCoP, and also effectively increases the electrode's specific surface area, offering more active sites for rapid, reversible Faradaic reactions. Electrochemical impedance spectroscopy (EIS) results indicate that the NC@MOF@NCP composite electrode exhibits low R_s (0.74 Ω) and R_ct (0.34 Ω) values. This low electrode-electrolyte interface charge transfer resistance contributes to the electrode's enhanced overall electrochemical performance.

A hierarchical NC@MOF@NCP nanorod electrode loaded with a highly active material has been constructed. This electrode's mesoporous system synergizes with the phosphide's metallic electronic structure, significantly reducing charge transfer impedance to 0.34 Ω. The optimized electrode exhibits a surface capacitance of 21.49 F·cm^-2 and high-capacity retention of 79.65% at 50 mA·cm^-2. Its outstanding rate performance is attributed to rapid charge redistribution mechanisms at the layered heterointerfaces. The assembled asymmetric supercapacitor of NC@MOF@NCP//AC achieved an energy density of 1.55 mW·h·cm^-2 at a power density of 8 mW·cm^-2 and demonstrated excellent cycling stability, retaining 86.8% of its capacity after 8000 cycles.