Anion Exchange of Ni–Co Layered Double Hydroxide (LDH) Nanoarrays for a High‐Capacitance Supercapacitor Electrode: A Comparison of Alkali Anion Exchange and Sulfuration

Abstract

A facile and new anion exchange process is presented, which involves the conversion of NiCo‐CO3 layered double hydroxide (LDH) nanosheet arrays in an alkaline solution. The anion exchange between CO32− and OH− results in the construction of a reservoir for OH− anions, and the decoration of thin nanoflakes on the surface of nanosheets effectively enlarges the surface area of NiCo LDH nanoarrays. The capacitance of the as‐soaked NiCo LDH nanoarrays electrode increases from 1.78 F cm−2 (684 F g−1) to 6.22 F cm−2 (2391 F g−1) at 2 mA cm−2 after soaking for 12 h. Moreover, the soaked NiCo‐OH LDH electrode exhibits an enhanced rate capacity, high coulombic efficiency, and good cycling stability compared with the Ni–Co‐S nanosheet electrode synthesized through a hydrothermal sulfuration process. The as‐assembled all‐solid‐state NiCo LDH//active carbon asymmetric supercapacitor shows a maximum energy density of 83.4 W h kg−1 at a power density of 1066 W kg−1.

Significant Role of Al in Ternary Layered Double Hydroxides for Enhancing Electrochemical Performance of Flexible Asymmetric Supercapacitor

“…A combination of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies reveals that the NiCo 2 ‐OH nanowire is of ≈2 µm in length, while the NiCo 2 Al‐LDH nanosheets exhibit a 2D hexagonal morphology. High‐resolution TEM (HRTEM) investigations of NiCo 2 ‐OH and NiCo 2 Al‐LDH (Figure c2,d2) disclose two lattice spacing of ≈0.26 nm which is assigned to the (100) facets of NiCo 2 ‐OH and the (012) facet of NiCo 2 Al‐LDH, respectively. A combined study of high‐angle annular dark field (HAADF) imaging and energy dispersive X‐ray spectroscope (EDS) mapping (Figure e,f) shows that the atomic species in the NiCo 2 ‐OH and NiCo 2 Al‐LDH nanostructures are uniformly distributed.…”

Electrochemical Deposition Enables Freestanding CoNi Layered Double Hydroxide/MnOX Electrode with Enhanced Electrochemical Properties for Asymmetric Supercapacitors

“…The EIS Nyquist is constituted of semicircles and oblique lines at the high‐frequency and low‐frequency areas, respectively. The semicircle is related to Faradic reactions, and its diameter represents the interfacial charge‐transfer resistance; then, the slope is related to the diffusion resistance of the electrolyte in the electrode pores . From Figure , the diameter of the semicircles for either CoNi LDH/MnO X /CFP or MnO X /CFP is very small, therefore indicating a low interfacial charge‐transfer resistance.…”

Sulfur and phosphorus co-doped nickel–cobalt layered double hydroxides for enhancing electrochemical reactivity and supercapacitor performance

“…In a diffusion-controlled process and capacitive process, b equals 0.5 and 1, respectively. 35 Accordingly the above eqn (9) can be summarized as follows: i ( V ) = k 1 v + k 2 v 0.5 where i is the measured current (A) at a fixed potential (V) and v is the scan rate (V s −1 ); k 1 and k 2 represent capacitive and diffusion-controlled process. Eqn (10) can be arranged as follows: i ( V )/ v 0.5 = k 1 v 0.5 + k 2 The slope and intercept of a linear plot of i ( V )/ v 0.5 versus v 0.5 correspond to k 1 and k 2 , respectively.…”

“…The S 2p 3/2 (161.4 eV) and S 2p 1/2 (162.8 eV) peaks correspond to the metal-sulfur bonding and low coordination surface S 2À , respectively. 35 In Fig. 2f, the P 2p spectrum shows deconvoluted peaks with P 2p 3/2 (132.4 eV) and P 2p 1/2 (134.5 eV), corresponding to the positively shied metal-phosphorus bonding by a more electronegative S ligand and to the P-O bonding, respectively.…”

“…In a diffusion-controlled process and capacitive process, b equals 0.5 and 1, respectively. 35 Accordingly the above eqn (9) can be summarized as follows:…”