MOF-on-MOF Derived\nCo<sub>2</sub>P/Ni<sub>2</sub>P\nHeterostructures for High-Performance Supercapacitors

Metal–organic\nframeworks (MOFs) have been widely\nused as\nversatile precursors to fabricate functional nanomaterials with well-defined\nstructures for various applications. Herein, the presynthesized Ni-MOF\nnanosheets were grown on a Ni foam (NF) substrate, which then guided\nthe nucleation and further growth of Prussian blue analogues (PBA)\nnanocubes to form MOF-on-MOF of the PBA/Ni-MOF film. This film was\nsubsequently converted into a Co<sub>2</sub>P/Ni<sub>2</sub>P heterostructure.\nThe NF-supported Co<sub>2</sub>P/Ni<sub>2</sub>P composites exhibited\nexcellent supercapacitor performance, delivering a high specific capacity\nof 5124.2 mF cm<sup>–2</sup> at 1 mA cm<sup>–2</sup> and a remarkable capacity retention of 80.69% after 3000 cycles\nat 10 mA cm<sup>–2</sup>. An asymmetric supercapacitor assembled\nusing Co<sub>2</sub>P/Ni<sub>2</sub>P/NF as the cathode and activated\ncarbon as the anode yielded a maximum energy density of 0.34 mWh cm<sup>–2</sup> at a power density of 1.50 mW cm<sup>–2</sup>. The enhanced supercapacitor performance is attributed to the synergistic\neffects of the Ni<sub>2</sub>P and Co<sub>2</sub>P components with\nmultiple valence states as well as the unique hierarchical structure,\nwhich provides efficient pathways for electron and ion transport while\nmitigating volume expansion during energy storage. This synthetic\nstrategy demonstrates an effective approach to fabricate phosphide-based\nhybrid materials for high-performance supercapacitor applications.