MOF-On-MOF Heterostructure Coupled with Polyaniline as Advanced Electrode for High-Energy-Density Supercapacitors

This study designs a MOF-on-MOF heterostructure coupled with polyaniline as a high-performance electrode for high-energy-density supercapacitors. Flower-like BTC-Ni was synthesized by a hydrothermal method, followed by in situ growth of ZIF-67 to construct a hierarchical heterojunction, and then coated with polyaniline via electropolymerization to obtain the ternary composite BTC-Ni/ZIF-67@PANI. Systematic characterizations including X-ray absorption fine structure (EXAFS) and wavelet transform reveal that Ni exists in the form of Ni−O coordination and Co exists in the form of Co−N coordination, both highly dispersed without metal agglomeration, providing abundant bimetallic active sites. The heterointerface optimizes the electronic structure, strengthens OH− adsorption, and accelerates charge transfer. The PANI layer forms a continuous conductive network, improves conductivity, supplies extra pseudocapacitance, and alleviates volume expansion during cycling. Electrochemical tests show that the composite exhibits high specific capacitance, excellent rate performance, and 85.9% capacitance retention after 10,000 cycles at 5 A/g. The assembled asymmetric supercapacitor achieves a voltage window of 1.6 V and an energy density of 67.28 Wh/kg at 800 W/kg. This work provides a feasible strategy for constructing advanced MOF-based electrodes with clear coordination environment and excellent energy storage performance.