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.
ABSTRACT
Constructing hierarchical structure is an effective strategy to boost the electrochemical performance of layered double hydroxide (LDH) materials, but the rational design of such delicate architectures is still challenging. Herein, a unique hierarchical core/shell homostructure with NiCo-LDH nanorods (NCNRs) as core and NiCo-LDH nanosheets (NCNSs) as shell is constructed via in-situ ZIF shell growth and subsequent ion exchange-coprecipitation process. Such novel hierarchical structure provides a large accessible surface area and more exposed electrochemical active sites. The in-situ growth and conversion process contribute to the formation of robust adhesion between the core and the shell, which could facilitate the effective charge and ion diffusion, as well as improve the mechanical stability. Benefiting from the unique structure, the NCNRs@NCNSs electrode exhibits a high capacitance of 2640.2 F g-1, along with the good rate performance and cyclic stability. Furthermore, the as-assembled asymmetric supercapacitor of NCNRs@NCNSs//AC device displays a high energy density of 22.81 Wh kg-1 at the power density of 374.95 W kg-1. This work demonstrates a new strategy for designing hierarchical LDH with core/shell structure as electrode materials for superior electrochemical energy storage.
ABSTRACT
MXene is a neoteric type of bidimensional (2D) transition metal carbide/nitride with broad application prospects, in particular with electrochemical energy storage. The electrochemical performance of MXene is unsatisfactory because it is easy to stack resulting in the difficulty of electrolyte penetration and ion transport. In this study, the cobaltous sulfide-modified 3D MXene/N-doped carbon foam (CoS@MXene/CF) hybrid aerogel is projected and manufactured via simple in situ growth and thermal annealing strategies. The capacitance of the as-fabricated 300-CMC-31:1 electrode material reaches 250 F g-1 (1 A g-1), which is obviously higher than those of MXene, CoS@CF, 400-CMC-31:1, 300-CMC-10:1, 300-CMC-50:1, CF, and MXene/CF electrode materials. Moreover, it can hold 97.5% of the original capacitance after 10,000 cycles and the internal resistance (Rs) is only 0.50 Ω. A green bulb can be lit by two all-solid asymmetric supercapacitors installed in series. The prepared CoS@MXene/CF hybrid aerogel exhibits promising potential for practical application in energy storage areas.
