NiFe-layered Double Hydroxide Nanosheets Research Articles

Active-Site-Enriched Iron-Doped Nickel/Cobalt Hydroxide Nanosheets for Enhanced Oxygen Evolution Reaction

Highly active, durable, and inexpensive nanostructured catalysts are crucial for achieving efficient and economical electrochemical water splitting. However, developing efficient approaches to further improve the catalytic ability of the well-defined nanostructured catalysts is still a big challenge. Herein, we report a facile and universal cation-exchange process for synthesizing Fe-doped Ni(OH)2 and Co(OH)2 nanosheets with enriched active sites toward enhanced oxygen evolution reaction (OER). In comparison with typical NiFe layered double hydroxide (LDH) nanosteets prepared by the conventional one-pot method, Fe-doped Ni(OH)2 nanosheets evolving from Ni(OH)2 via an Fe3+/Ni2+ cation-exchange process possess nanoporous surfaces with abundant defects. Accordingly, Fe-doped Ni(OH)2 nanosheets exhibit higher electrochemical active surface area (ECSA) and improved surface wettability in comparison to NiFe LDH nanosheets and deliver significantly enhanced catalytic activity over NiFe LDH. Specifically, a low o...

Tuning Surface Electronic Configuration of NiFe LDHs Nanosheets by Introducing Cation Vacancies (Fe or Ni) as Highly Efficient Electrocatalysts for Oxygen Evolution Reaction.

Intrinsically inferior electrocatalytic activity of NiFe layered double hydroxides (LDHs) nanosheets is considered as a limiting factor to inhibit the electrocatalytic properties for oxygen evolution reaction (OER). Proper defect engineering to tune the surface electronic configuration of electrocatalysts may significantly improve the intrinsic activity. In this work, the selective formation of cation vacancies in NiFe LDHs nanosheets is successfully realized. The as-synthesized NiFe LDHs-VFe and NiFe LDHs-VNi electrocatalysts show excellent activity for OER, mainly attributed to the introduction of rich iron or nickel vacancies in NiFe LDHs nanosheets, which efficiently tune the surface electronic structure increasing the adsorbing capacity of OER intermediates. Density functional theory (DFT) computational results also further indicate that the OER catalytic performance of NiFe LDHs can be pronouncedly improved by introducing Fe or Ni vacancies.

Effects of redox-active interlayer anions on the oxygen evolution reactivity of NiFe-layered double hydroxide nanosheets

Nickel-iron layered double hydroxide (NiFe-LDH) nanosheets have shown optimal oxygen evolution reaction (OER) performance; however, the role of the intercalated ions in the OER activity remains unclear. In this work, we show that the activity of the NiFe-LDHs can be tailored by the intercalated anions with different redox potentials. The intercalation of anions with low redox potential (high reducing ability), such as hypophosphites, leads to NiFe-LDHs with low OER overpotential of 240 mV and a small Tafel slope of 36.9 mV/dec, whereas NiFe-LDHs intercalated with anions of high redox potential (low reducing ability), such as fluorion, show a high overpotential of 370 mV and a Tafel slope of 80.8 mV/dec. The OER activity shows a surprising linear correlation with the standard redox potential. Density functional theory calculations and X-ray photoelectron spectroscopy analysis indicate that the intercalated anions alter the electronic structure of metal atoms which exposed at the surface. Anions with low standard redox potential and strong reducing ability transfer more electrons to the hydroxide layers. This increases the electron density of the surface metal sites and stabilizes their high-valence states, whose formation is known as the critical step prior to the OER process.

Accelerated Hydrogen Evolution Kinetics on NiFe-Layered Double Hydroxide Electrocatalysts by Tailoring Water Dissociation Active Sites.

Owing to its earth abundance, low kinetic overpotential, and superior stability, NiFe-layered double hydroxide (NiFe-LDH) has emerged as a promising electrocatalyst for catalyzing water splitting, especially oxygen evolution reaction (OER), in alkaline solutions. Unfortunately, as a result of extremely sluggish water dissociation kinetics (Volmer step), hydrogen evolution reaction (HER) activity of the NiFe-LDH is rather poor in alkaline environment. Here a novel strategy is demonstrated for substantially accelerating the hydrogen evolution kinetics of the NiFe-LDH by partially substituting Fe atoms with Ru. In a 1 m KOH solution, the as-synthesized Ru-doped NiFe-LDH nanosheets (NiFeRu-LDH) exhibit excellent HER performance with an overpotential of 29 mV at 10 mA cm-2 , which is much lower than those of noble metal Pt/C and reported electrocatalysts. Both experimental and theoretical results reveal that the introduction of Ru atoms into NiFe-LDH can efficiently reduce energy barrier of the Volmer step, eventually accelerating its HER kinetics. Benefitting from its outstanding HER activity and remained excellent OER activity, the NiFeRu-LDH steadily drives an alkaline electrolyzer with a current density of 10 mA cm-2 at a cell voltage of 1.52 V, which is much lower than the values for Pt/C-Ir/C couple and state-of-the-art overall water-splitting electrocatalysts.

Understanding the incorporating effect of Co2+/Co3+ in NiFe-layered double hydroxide for electrocatalytic oxygen evolution reaction

NiFe-layered double hydroxide (NiFe-LDH) has been widely accepted as promising catalyst candidates for the oxygen evolution reaction (OER). Recently, incorporating Co atoms in NiFe laminates has been recognized as an effective way to enhance the OER activity, but their roles have been rarely studied. Herein, density functional theory plus U (DFT + U) calculations are employed to evaluate the OER thermodynamics after introducing bivalent Co2+ or trivalent Co3+ and consequent sites sensitivity in NiFe-LDH catalyst. Generally, based on computational results, incorporation of Co2+/Co3+ into NiFe-LDH could modulate the electronic structure of metal sites and thus reducing their OER overpotential. Moreover, Co3+-doped NiFe-LDH has the lowest overpotential of η = 0.413 eV among the above proposed structure. This point was fully demonstrated by Co2+ and Co3+-incorporated NiFe-LDH nanosheets made by a co-precipitation method, by showing OER onset overpotential of 249 mV for Co3+-doped NiFe-LDH, 264 mV for Co2+-doped NiFe-LDH, which are 33 mV and 18 mV lower than that of pristine NiFe-LDH (282 mV), respectively. Such improved OER activity were attributed to the lowered overpotential at the *OOH formation step for Co2+-doped NiFe-LDH and the deprotonation step for Co3+-doped NiFe-LDH, which was the potential limiting step for their OER process. This work should be inspiring for future designing of more efficient NiFe-based oxygen evolution electrocatalysts.

Hierarchical Hollow Nanoprisms Based on Ultrathin Ni-Fe Layered Double Hydroxide Nanosheets with Enhanced Electrocatalytic Activity towards Oxygen Evolution.

The oxygen evolution reaction (OER) is involved in various renewable energy systems, such as water-splitting cells and metal-air batteries. Ni-Fe layered double hydroxides (LDHs) have been reported as promising OER electrocatalysts in alkaline electrolytes. The rational design of advanced nanostructures for Ni-Fe LDHs is highly desirable to optimize their electrocatalytic performance. Herein, we report a facile self-templated strategy for the synthesis of novel hierarchical hollow nanoprisms composed of ultrathin Ni-Fe LDH nanosheets. Tetragonal nanoprisms of nickel precursors were first synthesized as the self-sacrificing template. Afterwards, these Ni precursors were consumed during the hydrolysis of iron(II) sulfate for the simultaneous growth of a layer of Ni-Fe LDH nanosheets on the surface. The resultant Ni-Fe LDH hollow prisms with large surface areas manifest high electrocatalytic activity towards the OER with low overpotential, small Tafel slope, and remarkable stability.

Ar Plasma Exfoliated Nickel Iron Layered Double Hydroxide Nanosheets into Ultrathin Nanosheets as Highly-Efficient Electrocatalysts for Water Oxidation

Layered double hydroxides (LDHs) as a electrocatalyst had exhibited a good oxygen evolution reaction (OER) performance. However, the bulk NiFe LDHs nanosheets with a large lateral size and bulk thickness hindering the exposure of active sites and reducing the electrocatalytic activity of reactive sites. Herein, the bulk NiFe LDHs nanosheets were successfully exfoliated into 2D ultrathin NiFe LDHs nanosheets by one-step Ar plasma. This unique structure of NiFe LDH increased the surface area and the exposure of active sites improving the electrocatalytic performance for OER. Moreover, Ar plasma also further etched the basal planes of 2D crystals leading to production of more edge and corner sites which had much higher catalytic activity than positions in the basal planes. Therefore, this ultrathin NiFe LDHs nanosheets with rich edges and corners as electrocatalyst showed a good OER activity with a low overpotential of 278 mV at 10 mA/cm2.

NiFe layered double hydroxide nanosheets as an efficiently mimic enzyme for colorimetric determination of glucose and H2O2

Abstract The ultrathin NiFe-layered double hydroxide nanosheets (NiFe-LDHNS) were prepared by exfoliating bulk LDH in l -asparagine aqueous medium. The transmission electron microscopy and atomic force microscopy results reveal that NiFe-LDHNS have about 200–300 nm lateral size and less than 2 nm thickness with the broken edges rather than the original hexagon of hydrotalcite. The peroxidase-like activity of the 2D NiFe-LDHNS was investigated by using oxidation of the peroxidase substrate 3,3′,5,5′-tetramethylbenzidine in presence of H2O2. The 2D NiFe-LDHNS exhibited the superior enzyme mimic activity to the bulk NiFe-LDH, which was attributed to the more exposed active sites and more accessible inner surface of single or several layers. Thus, a simple and sensitive non-enzyme biosensor was developed for colorimetric detection of H2O2 and glucose. The proposed method was successfully applied to glucose detection in real samples with satisfactory results.

Ar Plasma Exfoliated Nickel Iron Layered Double Hydroxide Nanosheets into Ultrathin Nanosheets As Highly-Efficient Electrocatalysts for Water Oxidition

Designing electrocatalysts for oxygen evolution reaction with low cost, high activity and stable are crucial extremely to water splitting. Layered double hydroxides (LDHs) as a electrocatalyst exhibits a good oxygen evolution reaction (OER) performance because of its unique 2D lameller and electronic structure. However, the bulk NiFe LDHs nanosheets with large lateral size and bulk thickness hindering the exposition active sites reduce the electrocatalytic activity. To solve this problem, herein, the bulk NiFe LDHs nanosheets were successfully exfoliated into 2D ultrathin NiFe LDHs nanosheets by one-step Ar plasma. This electrocatalyst with a structure of ultrathin nanosheet and exposed more edge sites was synthesized by the Ar plasma treatment and was used to catalyze the oxidation of water. This unique structure of NiFe LDH increases the surface area and the exposure of active sites which extremely facilitate to improve the electrocatalytic performance for oxygen evolution reaction. In additions, Ar plasma also futher etched the basal planes of 2D crystals leading to production of more edge sites. Enormous studies have confirmed that positions in edge have much higher catalytic activity than positions in the basal planes. Therefore, this ultrathin NiFe LDHs nanosheets with rich edge sites as electrocatalyst showed a good OER activity with a low overpotential of 278 mV at 10 mA/cm2. Figure 1

Highly Sensitive Nonenzymatic Glucose Sensor Based on 3D Ultrathin NiFe Layered Double Hydroxide Nanosheets

AbstractAs a promising electrode material, Ni‐based nanomaterials exhibit a remarkable electrochemical catalytic activity for nonenzymatic glucose sensors. In this paper, Nickel–Iron layered double hydroxide (NiFe‐LDH) film electrode with ultrathin nanosheets and porous nanostructures was synthesized directly on Ni foam (NF) by a one‐step hydrothermal method. The as‐obtained NiFe‐LDH electrode was adopted for glucose detection without further treatment. As an integrated binder‐free electrode for glucose sensor, the NiFe‐LDH/NF hybrid exhibits a superior sensitivity of 3680.2 μA mM−1 cm−2 with a low limit of detection (0.59 μM, S/N=3) as well as fast response time (<1 s). An excellent selectivity from potential interference species such as ascorbic acid, uric acid and Cl− ions and acceptable stability were also achieved. The outstanding performance can be ascribed to the abundant electrochemistry active sites, facilitative diffusion of the electrolyte, high electron transfer rate and reliable stability architecture. Therefore, the NiFe‐LDH nanosheets demonstrate potential application in non‐enzymatic sensory of glucose.

The effects of Al substitution and partial dissolution on ultrathin NiFeAl trinary layered double hydroxide nanosheets for oxygen evolution reaction in alkaline solution

Recently, Ni–based layered double hydroxide (LDH) materials have attracted growing interest owing to the remarkable performance for oxygen evolution reaction (OER). Here we demonstrate the preparation of ultrathin Ni3FeAlx trinary LDH nanosheets with higher activity and stability than NiFe–LDH nanosheets for OER. The enhancement was derived from Al substitution, which increased the concentration of Ni3+ active sites on the catalyst surface. Besides, low-coordinated Ni and Fe atoms and defects were formed by partial etching/dissolution of Al3+ in alkaline solution, which further increased the activity towards OER. To improve the conductivity, Ni3FeAlx–LDH (x=0, 0.91, 1.27 or 2.73) nanosheets were also in-situ grown on three-dimensional-networked nickel foam. The binder-free Ni3FeAlx–LDH/Ni foam electrodes exhibited further improved catalytic performance compared to the electrodes made of powdery Ni3FeAlx–LDHs and nafion binder. The best OER performance was presented by Ni3FeAl0.91–LDH/Ni foam, showing a Tafel slope of 57mV/dec, a low overpotential (304mV) at the current density of 20mA/cm2, and a current density of 235mA/cm2 at 1.60V (vs. RHE). Furthermore, the Ni3FeAl0.91–LDHs/Ni foam electrode showed excellent long-term stability, maintaining a stable overpotential of 320mV at 20mA/cm2 after testing for 18h.

Bifunctional Ni1−xFex layered double hydroxides/Ni foam electrodes for high-efficient overall water splitting: A study on compositional tuning and valence state evolution

Toward both hydrogen (HER) and oxygen evolution reaction (OER) in alkaline electrolyte, bifunctional Ni1−xFex layered double hydroxides (LDHs) on Ni foam (NF) have been systematically developed for high-efficient water splitting by changing Fe content. The interlaced NiFe LDHs nanosheets consist of ultra-small γ-NiOOH-like nanoparticles with size of 2–5 nm interconnected by amorphous domains. By tuning Fe content from 15% to 25% and 36%, optimized μ10 values (μ10 is the overpotential required to reach a current density of 10 mA/cm2) of 169 mV (HER) and 140 mV (OER), and Tafel slope of 31 mV/dec have been achieved at x = 0.25. A hydrogen generation rate of 170 μmol/h/cm2 with H2/O2 ratio nearly to 2:1 and Faradic efficiency of 93% have been realized at 1.7 V by using two Ni0.75Fe0.25 LDHs/NF as respective anode and cathode in a 2-electrode system. Based on the valence state evolution of the electrodes, undergoing respectively H2 and O2 generation, tremendous transformation of NiFe(OH)2 to NiFeOOH is deduced, which reaches a Ni3+/Ni2+ ratio of ∼2.35 for the Fe content of 25%. Further or less Fe incorporation will depress the electrocatalytic property. The effective Ni3+ active sites on the NiFe-based nanosheets endow the Ni0.75Fe0.25 LDHs/NF with high bifunctional catalytic property.

Water Splitting: Ni3FeN Nanoparticles Derived from Ultrathin NiFe‐Layered Double Hydroxide Nanosheets: An Efficient Overall Water Splitting Electrocatalyst (Adv. Energy Mater. 10/2016)

In article number 1502585, Tierui Zhang and co-workers report Ni3FeN nanoparticles with a particle size of 100 nm and a thickness of ≈9 nm synthesized by thermal ammonolysis of ultrathin NiFe-layered double hydroxide nanosheets. The Ni3FeN nanoparticles show extraordinarily high performance and stability for overall water splitting into hydrogen and oxygen with low overpotentials, which exhibited better activity than most other noble-metal-free electrocatalysts and commercial Pt/C.

Facile synthesis of thin NiFe-layered double hydroxides nanosheets efficient for oxygen evolution

Ultrathin NiFe-layered double hydroxide (LDH) nanosheets are facilely and cost-effectively fabricated. The as-prepared NiFe-LDH nanosheets are highly active and stable electrocatalysts for water oxidation in alkaline environment, exhibiting a much higher oxygen evolution activity and lower overpotential with the enhanced stability, much superior to the previously reported LDH-derived catalysts. This work provides a facile methodology for the fabrication of thin nanosheets, which are promising in the renewable energy conversion.

A Superlattice of Alternately Stacked Ni–Fe Hydroxide Nanosheets and Graphene for Efficient Splitting of Water

Cost-effective electrocatalysts based on nonprecious metals for efficient water splitting are crucial for various technological applications represented by fuel cell. Here, 3d transition metal layered double hydroxides (LDHs) with varied contents of Ni and Fe were successfully synthesized through a homogeneous precipitation. The exfoliated Ni-Fe LDH nanosheets were heteroassembled with graphene oxide (GO) as well as reduced graphene oxide (rGO) into superlattice-like hybrids, in which two kinds of oppositely charged nanosheets are stacked face-to-face in alternating sequence. Heterostructured composites of Ni2/3Fe1/3 LDH nanosheets and GO (Ni2/3Fe1/3-GO) exhibited an excellent oxygen evolution reaction (OER) efficiency with a small overpotential of about 0.23 V and Tafel slope of 42 mV/decade. The activity was further improved via the combination of Ni2/3Fe1/3 LDH nanosheets with more conductive rGO (Ni2/3Fe1/3-rGO) to achieve an overpotential as low as 0.21 V and Tafel plot of 40 mV/decade. The catalytic activity was enhanced with an increased Fe content in the bimetallic Ni-Fe system. Moreover, the composite catalysts were found to be effective for hydrogen evolution reaction. An electrolyzer cell powered by a single AA battery of 1.5 V was demonstrated by using the bifunctional catalysts.