Rational design of hierarchical zeolitic imidazolate framework-67@Cu2CoO3 core-shell architectures for hybrid supercapacitor applications

Hierarchical core-shell architectures constructed with zeolitic imidazolate frameworks (ZIFs) and binary metal oxides are attracting much attention as an efficient electrode material for supercapacitors (SCs). In this regard, we reported the ZIF-67 amorphous nanoparticles (NPs)@Cu2CoO3 (ZIF-67@CCO) via a two-step synthesis pro-cess. Initially, the CCO electrode material with soap nuts-like core-shell hollow sphere (SNHS) morphology was synthesized by a facile solvothermal method and post-annealing treatment. The optimized CCO SNHS (CCO-9 h (9 h growth time)) electrode demonstrated higher areal capacity (CA)/specific capacity (CS) values than the CCO-6 h and CCO-12 h electrodes. Next, ZIF-67 NPs were deposited on the CCO-9 h material using the solvothermal method. The resulting ZIF-67@CCO-9 h electrode exhibited improved electrochemical properties of CA = 176.3 mu Ah cm-2 (CS = 117.5 mAh g-1) at 1 mA cm-2 and superb cycling stability after 25,000 cycles (83.4% retention). The ZIF-67 layer on the CCO-9 h with SNHS structure may provide faster electron transfer as well as more active sites, benefiting the electrochemical characteristics. Furthermore, the hybrid supercapacitor (HSC) cell was assembled using ZIF-67@CCO-9 h and activated carbon/Ni foam as positive (+) and negative (-) electrodes, respectively. The as-constructed HSC cell revealed high energy density value of 25.2 Wh kg -1. Also, the com-mercial application of the fabricated HSC cell was verified by driving different electronic components.

Automated summary

In this study, hierarchical core-shell architectures were constructed using zeolitic imidazolate frameworks (ZIFs) and binary metal oxides, leading to improved electrochemical properties. The resulting electrode material, ZIF-67 amorphous nanoparticles (NPs)@Cu2CoO3 (ZIF-67@CCO), demonstrated higher areal capacity and specific capacity values. When assembled into a hybrid supercapacitor cell, it exhibited high energy density and showed potential for commercial applications.