Self-templated pseudomorphic transformation of ZIF into layered double hydroxides for improved supercapacitive performance

Abstract

Zeolitic imidazole frameworks (ZIFs) have been researched as excellent templates for synthesizing functional materials to be used in various fields. However, direct adoption of ZIFs as electrode material shows dissatisfactory electrochemical performance due to their limited exposed electroactive sites, poor chemical stability and sluggish charging dynamics. Herein, we demonstrate in situ transformation of ZnCo-ZIF frameworks decorated on ZnCo nanorod array (ZnCo-NA) into three-dimensional (3D) spatially distributed ZnCo-LDH/ZnCo-NA heterostructure. Owing to this unique structure that can provide abundant electroactive sites and ion transport paths in all directions, the resulting ZnCo-LDH/ZnCo-NA electrode exhibits an improved supercapacitive performance with a high capacity of 15.76 F cm−2 (1576 F g−1, 788 C g−1) at 20 mA cm−2 (2 A g−1), and maintains the capacity of 13.855 F cm−2 (1385.5 F g−1, 692.75 C g−1) at 150 mA cm−2 (15 A g−1), showing a high rate capability of 87.9%. A coin cell asymmetric supercapacitor (aSC) is assembled by employing ZnCo-LDH/ZnCo-NA as cathode and active carbon as anode, which exhibits an energy density of 21.3 Wh kg−1 and superb cycling performance with capacitance retention of 88.1% after 5000 cycles. More importantly, such a simple in-situ pseudomorphic transformation of ZIF templates into novel class LDH materials demonstrates a new generation of bimetallic heterostructure for applications in energy-related fields and beyond.