Hierarchical Nanocages Assembled by NiCo-Layered Double Hydroxide Nanosheets for a High-Performance Hybrid Supercapacitor

Abstract

Layered double hydroxides (LDHs) have attracted broad attention as cathode materials for hybrid supercapacitors (HSCs) because of their ultrahigh theoretical specific capacitance, high compositional flexibility, and adjustable interlayer spacing. However, as reported, specific capacitance of LDHs is still far below the theoretical value, inspiring countless efforts to these ongoing challenges. Herein, a hierarchical nanocage structure assembled by NiCo-LDH nanosheet arrays was rationally designed and fabricated via a facile solvothermal method assisted by the ZIF-67 template. The transformation from the ZIF-67 template to this hollow structure is achieved by a synergistic effect involving the Kirkendall effect and the Ostwald ripening process. The enlarged specific surface area co-occurred with broadened interlayer spacing of LDH nanosheets by finely increasing the Ni concentration, leading to synchronous improvement of electron/ion transfer kinetics. The optimized NiCo-LDH-210 electrode displays a maximum specific capacitance of 2203.6 F g–1 at 2 A g–1, excellent rate capability, and satisfactory cycling stability because of the highly exposed active sites and shortened ion transport paths provided by vertically aligned LDH nanosheets together with the cavity. Furthermore, the assembled HSC device achieves a superior energy density of 57.3 Wh kg–1 with prominent cycling stability. Impressively, the design concept of complex construction derived from metal-organic frameworks (MOF) derivatives shows tremendous potential for use in energy storage systems.

Magnetic Amine-Functionalized ZIF-8 with Hierarchical Pores for Efficient Covalent Immobilization of α-Amylase

“…28 The Au 4f XPS spectrum (Figure 3d) has two characteristic bands at 84.71 and 88.40 eV, respectively, corresponding to Au(0) 4f 5/2 and Au(0) 4f 7/2 . 23,28 The presence of Au(0) nanoparticles could also be confirmed by the black dots decorated on the HZIF shell in Figure 2c. This phenomenon might be ascribed to due to two reasons: (1) strong coordination between Au 3+ and nitrogen atoms of ZIF-8 make Au 3+ atoms electron-rich and reduce Au 3+ to Au(0) 22,23 and (2) the subsequent introduction of reducing agent β-mercaptoethylamine may also reduce Au 3+ to Au(0) and form Au nanoparticles.…”

“…23,28 The presence of Au(0) nanoparticles could also be confirmed by the black dots decorated on the HZIF shell in Figure 2c. This phenomenon might be ascribed to due to two reasons: (1) strong coordination between Au 3+ and nitrogen atoms of ZIF-8 make Au 3+ atoms electron-rich and reduce Au 3+ to Au(0) 22,23 and (2) the subsequent introduction of reducing agent β-mercaptoethylamine may also reduce Au 3+ to Au(0) and form Au nanoparticles. From the high-resolution XPS spectrum of C 1s and O 1s (Figure 3e,f), the presence of C�O was confirmed, indicating successful immobilization of α-Amy.…”

“…Then, the ZIF-8 shell was transformed into an HZIF-8 layer with large pores on the surface by the Kirkendall effect. 22,23 As shown in Figure 2b,c, lots of large pores could be obviously observed on the surface of Fe 3 O 4 @HZIF-8. After covalent immobilization of α-Amy, large pores on the FHA surface are still present in Figure 2d, almost the same as that in Figure 2b.…”

Hierarchical Nickel–Cobalt Hydroxide Composite Nanosheets-Incorporated Nitrogen-Doped Carbon Nanotubes Embedded with Nickel–Cobalt Alloy Nanoparticles for Driving a 2 V Asymmetric Supercapacitor

“…LDHs, like NiAl-LDH, NiMn-LDH, NiCo-LDH, , and NiCoFe-LDH, have reached owing performance along with are broadly applied in SCs. Of these electrode materials, the LDH containing transition-metal elements (Co 2+ and Ni 2+ ) is considered one of the most prospective substitute electrode materials because of its unusual energy densities, excellent stability, low cost, and versatility in composition and morphology. , However, cobalt or nickel-based oxides or hydroxide electrodes suffer from poor electronic conductivity and easy aggregation during the charging and discharging process, which hinders the mass/charge transport, prevents the rate capacity of electrodes, and limits the development of the SC. , To solve the aforementioned drawbacks of cobalt or nickel-based hydroxide or oxide electrodes, nanocarbon hybridization and endowment of three-dimensional self-supported monolithic structure should be efficient strategies, which would improve the capacitance and stability of these electrode materials simultaneously.…”

NiCo layered double hydroxide nanocages for high-performance asymmetric supercapacitors

“…However, the poor structural stability of nickel-cobalt layered double hydroxides makes their layered structure easily agglomerated, which seriously hinders the ion transport and shows poor conductivity and low cycling stability. 25,26 An effective method to solve these problems is the preparation of a nickel-cobalt layered double hydroxide with a hollow structure. The hollow three-dimensional nanocage structure can effectively avoid the accumulation of the nickel-cobalt layered hydroxide and provide a large specific surface area to expose more active centers, and the three-dimensional hollow structure also shortens the ion transport path and is beneficial for fast ion transport; they are ideal for high performance supercapacitors because they can reduce structural strain and adapt to volume changes in charge-discharge cycles.…”