Enhanced Pseudocapacitance and Supercapacitor Performance with Amorphous Cu(OH)<sub>2</sub>/ZIF-67 Composite

To address the intermittent nature of renewable energy, highly efficient high-performance energy storage devices are essential. Among various options, supercapacitors have attracted significant attention because they provide high power density, rapid charge–discharge capability, and long cycle life. In this study, a composite of amorphous Cu(OH)<sub>2</sub> grown on a metal–organic framework ZIF-67 (Cu(OH)<sub>2</sub>@ZIF-67) was successfully synthesized via a facile solvothermal method. Detailed structural and surface analyses, including scanning and transmission electron microscopy as well as X-ray diffraction measurements, revealed that ultrathin Cu(OH)<sub>2</sub> nanosheets were uniformly grown on the ZIF-67 surface. The combination of the amorphous phase with the MOF provided abundant electrochemically active sites and facilitated rapid ion transport, significantly contributing to greatly improved charge storage behavior. Electrochemical characterization demonstrated that Cu(OH)<sub>2</sub>@ZIF-67 exhibited a specific capacitance of 168 F/g at 3 A/g, approximately four times higher than that of pristine ZIF-67, while maintaining superior energy density across a wide power range. These findings demonstrate that introducing an amorphous structure onto MOF-derived metal supports not only effectively enhances the overall performance of supercapacitors but also provides valuable insights for the rational design, optimization, and potential practical and technological applications of hybrid electrode materials in next-generation high-performance energy storage systems.