3D-architectured nickel–cobalt–manganese layered double hydroxide/reduced graphene oxide composite for high-performance supercapacitor

In situ growth of ZIF-67-derived nickel-cobalt-manganese hydroxides on 2D V2CTx MXene for dual-functional orientation as high-performance asymmetric supercapacitor and electrochemical hydroquinone sensor

Designing dual-functional electrode materials for supercapacitors and pollutant sensors has attracted great interest from researchers for urgent demand in green energy and the environment. In this work, a novel electrode material V2CTx@NiCoMn-OH was successfully constructed for dual-functional orientation via a two-step synthesis strategy, in which the NiCoMn-OH with a three-dimensional (3D) hollow structure was fabricated by employing ZIF-67 as a template and simple anion exchange and composited with the two-dimensional (2D) layered V2CTx MXene. The intercalation of NiCoMn-OH can effectively limit the self-accumulation of V2CTx MXene nanosheets and build a 3D cross-linked hollow structure, thereby broadening the ion transport channel, exposing more active sites of V2CTx@NiCoMn-OH, and simultaneously improving the conductivity of NiCoMn-OH. Benefiting from the unique 3D cross-linked hollow structure, the optimized V2CTx@NiCoMn-OH-20 electrode material exhibits an excellent specific capacitance of 827.45 C g-1 at 1 A g-1. Furthermore, the electrode material has excellent capacitance retention of 88.44% after 10,000 cycles. Moreover, the V2CTx@NiCoMn-OH-20//AC ASC device displays a high energy density of 88.35 Wh kg-1 as well as high power density of 7500 W kg-1 during operation. Additionally, the V2CTx@NiCoMn-OH-20 exhibited excellent electrocatalytic performance in the detection of hydroquinone, including the low detection limit of 0.559 μM (S/N = 3) and the wide linear range of 2-1050 μM. Therefore, the prepared V2CTx@NiCoMn-OH-20 has great potential applications in the fields of supercapacitors and hydroquinone sensors.

Design of a high-performance ternary LDHs containing Ni, Co and Mn for arsenate removal

To cope with the current serious arsenate pollution problem, a new ternary layered double hydroxides (LDHs) containing Ni, Co and Mn with good performance was developed, guiding by DFT calculations. First, Ni, Co and Mn were screened as the metal sources to constitute the LDHs, due to their high ionic charge density. Then, Ni(II), Co(II) and Mn(III)-O octahedra were selected as the primary units for structuring the LDHs, because of their good chemical activity. Meanwhile, the ratio of metals in the ternary LDHs, favoring for arsenate removal, was optimized at 1:2:1. In addition, the synergistic effect among various metals in the LDHs was considered. The results suggested that in the case of single doping, all three metals can act as the center to promote chemical activity independently. On the contrary, when combined together, there is only one unilateral active center. Moreover, the existence of ligand covalent bonds between arsenate and LDHs was confirmed. Finally, a promising new NiCo₂Mn-LDHs with the maximum adsorption capacity of 407.23 mg/g for arsenate removal had been prepared.

Rationally engineered 3D-dendritic cell-like morphologies of LDH nanostructures using graphene-based core-shell structures

Functionalization of graphene-based materials using chemical moieties not only modify the electronic structure of the underlying graphene but also enable in limited enhancement of targeted properties. Surface modification of graphene-based materials using other nanostructures enhances the effective properties by minimally modifying the properties of pristine graphene backbone. In this pursuit, we have synthesized bio-inspired hierarchical nanostructures based on Ni-Co layered double hydroxide on reduced graphene oxide core-shells using template based wet chemical approach. The material synthesized have been characterized structurally and electrochemically. The fabricated dendritic morphology of the composite delivers a high specific capacity of 1056 Cg^-1. A cost effective solid state hybrid supercapacitor device was also fabricated using the synthesized electrode material which shows excellent performance with high energy density and fast charging capability.

A simple strategy to prepare a layer-by-layer assembled composite of Ni–Co LDHs on polypyrrole/rGO for a high specific capacitance supercapacitor

A facile and novel electrode material of nickel–cobalt layered double hydroxides (Ni–Co LDHs) layered on polypyrrole/reduced graphene oxide (PPy/rGO) is fabricated for a symmetrical supercapacitor via chemical polymerization, hydrothermal and vacuum filtration. This conscientiously layered composition is free from any binder or surfactants which is highly favorable for supercapacitors. The PPy/rGO serves as an ideal backbone for Ni–Co LDHs to form a free-standing electrode for a high-performance supercapacitor and enhanced the overall structural stability of the film. The well-designed layered nanostructures and high electrochemical activity from the hexagonal-flakes like Ni–Co LDHs provide large electroactive sites for the charge storage process. The specific capacitance (1018 F g⁻¹ at 10 mV s⁻¹) and specific energy (46.5 W h kg⁻¹ at 464.9 W kg⁻¹) obtained for the PPy/rGO|Ni–Co LDHs symmetrical electrode in the current study are the best reported for the two-electrode system for PPy- and LDHs-based composites. The outstanding performance in the prepared LBL film is a result of the LBL architecture of the film and the combined effect of redox reaction and electrical double layer capacitance.

A facile and novel electrode material of nickel–cobalt layered double hydroxides (Ni–Co LDHs) layered on polypyrrole/reduced graphene oxide (PPy/rGO) is fabricated for a symmetrical supercapacitor via chemical polymerization, hydrothermal and vacuum filtration.

Research Progress of NiMn Layered Double Hydroxides for Supercapacitors: A Review

The research on supercapacitors has been attractive due to their large power density, fast charge/discharge speed and long lifespan. The electrode materials for supercapacitors are thus intensively investigated to improve the electrochemical performances. Various transition metal layered double hydroxides (LDHs) with a hydrotalcite-like structure have been developed to be promising electrode materials. Earth-abundant metal hydroxides are very suitable electrode materials due to the low cost and high specific capacity. This is a review paper on NiMn LDHs for supercapacitor application. We focus particularly on the recent published papers using NiMn LDHs as electrode materials for supercapacitors. The preparation methods for NiMn LDHs are introduced first. Then, the structural design and chemical modification of NiMn LDH materials, as well as the composites and films derived from NiMn LDHs are discussed. These approaches are proven to be effective to enhance the performance of supercapacitor. Finally, the reports related to NiMn LDH-based asymmetric supercapacitors are summarized. A brief discussion of the future development of NiMn LDHs is also provided.

One-step synthesis of Nickle Iron-layered double hydroxide/reduced graphene oxide/carbon nanofibres composite as electrode materials for asymmetric supercapacitor

A novel NiFe-LDH/RGO/CNFs composite was produced by using a facile one-step hydrothermal method as electrode for supercapacitor. Compared with NiFe-LDH/CNFs, NiFe-LDH/CNTs and NiFe-LDH/RGO, NiFe-LDH/RGO/CNFs demonstrated a high specific capacitance of 1330.2 F g⁻¹ at 1 A g⁻¹ and a super rate capability of 64.2% from 1 to 20 A g⁻¹, indicating great potential for supercapacitor application. Additionally, an asymmetric supercapacitor using NiFe-LDH/RGO/CNFs composite as positive electrode material and activated carbon as negative electrode material was assembled. The asymmetric supercapacitor can work in the voltage range of 0–1.57 V. It displayed high energy density of 33.7 W h kg⁻¹ at power density of 785.8 W kg⁻¹ and excellent cycling stability with 97.1% of the initial capacitance after 2500 cycles at 8 A g⁻¹. Two flexible AC//LDH-RGO-CNFs ASC devices connected in series were able to light up a red LED indicator after being fully charged. The results demonstrate that the AC//LDH-RGO-CNFs ASC has a promising potential in commercial application.

High-Performance Flexible Asymmetric Supercapacitor Based on CoAl-LDH and rGO Electrodes

A flexible asymmetric supercapacitor (ASC) based on a CoAl-layered double hydroxide (CoAl-LDH) electrode and a reduced graphene oxide (rGO) electrode was successfully fabricated. The CoAl-LDH electrode as a positive electrode was synthesized by directly growing CoAl-LDH nanosheet arrays on a carbon cloth (CC) through a facile hydrothermal method, and it delivered a specific capacitance of 616.9 F g^-1 at a current density of 1 A g^-1. The rGO electrode as a negative electrode was synthesized by coating rGO on the CC via a simple dip-coating method and revealed a specific capacitance of 110.0 F g^-1 at a current density of 2 A g^-1. Ultimately, the advanced ASC offered a broad voltage window (1.7 V) and exhibited a high superficial capacitance of 1.77 F cm^-2 at 2 mA cm^-2 and a high energy density of 0.71 mWh cm^-2 at a power density of 17.05 mW cm^-2, along with an excellent cycle stability (92.9% capacitance retention over 8000 charge-discharge cycles).

A comparative study of Ni–Mn layered double hydroxide/carbon composites with different morphologies for supercapacitors

A variety of carbon materials varying from 0D to 2D, i.e. 0D nanoparticles, 1D carbon nanotubes (CNTs) and 2D reduced graphene oxide (rGO) are selected to in situ combine with Ni–Mn layered double hydroxide (LDH) to prepare electrode materials for supercapacitors.