NiFe LDH Research Articles

One-step synthesis of IrOx-decorated ultrathin NiFe LDH nanosheets for efficient oxygen evolution reaction

The oxygen evolution reaction (OER) is a vital proton donor for various clean energy technologies. Here, we synthesized IrOx-decorated ultrathin NiFe-LDH nanosheets (thickness 1-2 nm) by a one-step co-precipitation method. The IrOx was uniformly dispersed on the surface of ultrathin NiFe-LDH nanosheets, greatly increasing the active sites and the electric conductivity for NiFe-LDH. As a result, the IrOx/U-NiFe-LDH exhibited excellent OER performance with a low overpotential (236 mV) and a Tafel slope (74.3 mA dec-1).

3D amorphous NiFe LDH nanosheets electrodeposited on in situ grown NiCoP@NC on nickel foam for remarkably enhanced OER electrocatalytic performance.

NiFe LDH (layered double hydroxide) is currently attracting increasing attention as a type of promising electrocatalyst for oxygen evolution reaction (OERs); however, the biggest obstacle to its large-scale practical application is its poor conductivity and limited active sites. Herein, we report a three-dimensional NiFe LDH with high conductivity and dense active sites, where amorphous NiFe LDH nanosheets are directly electrodeposited on the surface of a hierarchical porous NiCoP@NC derived from the calcination and phosphorization of metal-organic frameworks (ZIF-67) in situ grown on nickel foam. Based on the 3D porous structure, abundant exposed active sites, fast electron and mass transfer rates and strong synergetic effects between NiCoP@NC and NiFe LDH, the resultant NiFe LDH/NiCoP@NC/NF catalysts exhibited significantly enhanced OER catalytic performances compared with NiFe LDH on nickel foam and most of the reported NiFe LDH-based catalysts: a low overpotential of 210 mV for yielding a current density of 10 mA cm-2, an extremely small Tafel slope (35 mV dec-1) and excellent durability. For overall water splitting, with NiFe LDH/NiCoP@NC/NF as the anode and NiCoP@NC/NF as the cathode, the assembled two-electrode system only required 1.54 V to obtain a stable current density of 10 mA cm-2 in 1 M KOH for at least 40 h. This research provided a simple and facile way to develop non-noble-metal oxygen evolution catalysts for replacing high-cost noble metal catalysts.

Interfacial synergy between dispersed Ru sub-nanoclusters and porous NiFe layered double hydroxide on accelerated overall water splitting by intermediate modulation.

Construction of an efficient bifunctional electrocatalyst through a rational interface-engineering strategy to optimize the adsorption energy of H* and OH* species at the atomic/molecular level is of great importance for water splitting. Although conventional NiFe layered double hydroxide (LDH) shows excellent performance for alkaline oxygen evolution reactions (OERs), it shows extremely poor activity toward hydrogen evolution reactions (HERs) due to weak hydrogen adsorption and sluggish kinetics. In this work, integration of sub-nanoscale Ru species with NiFe LDH can dramatically enhance the adsorption energy of H* and improve their HER kinetics. Besides, benefitting from the desired potential-induced strategy, the Ru-NiFe LDH interfaces will convert to RuO2-NiFe(OOH)x interfaces to optimize the adsorption energy of OH* to meet the requirement of strengthening the OER performance. Strikingly, the Ru-NiFe LDH-F/NF sample (NF: Ni foam) shows an excellent OER and HER performance with an overpotential of 230.0 mV and 115.6 mV at a current density of 10 mA cm-2, respectively, as well as outstanding durability. The overall water splitting device was fabricated by using Ru/NiFe LDH-F/NF as both the HER and OER electrode with a potential of 1.53 V to achieve a current density of 10 mA cm-2. In addition, the theoretical calculations demonstrated that the Ru-NiFe LDH interfaces could optimize the adsorption energy of H* and OH*. This study provides a new insight into the development of highly efficient bifunctional electrocatalysts for water electrolysis.

Nitrogen modification enhances the electrocatalytic overall water splitting of NiFe layered double hydroxides in alkaline media

NiFe materials have been favored for electrocatalysis because of their high activity and high stability in oxygen evolution reaction (OER). However, achieving high hydrogen evolution reaction (HER) properties remains challenging. Herein, NiFe layered double hydroxide (NiFe LDH) was prepared by one-step hydrothermal method. The N-modified NiFe LDH electrocatalyst was prepared using ammonia as a nitrogen source. The introduced N atom imparts the catalyst with suitable water separation energy and changes the electronic structure of the material. N12-NiFe LDH exhibits excellent total hydrolysis in alkaline medium. The overpotentials of HER and OER are 52 and 136 mV, respectively, at a current density of 10 mA cm−2. The overall water separation overpotential can reach up to 240 mV at a current density of 10 mA cm−2 when using N12-NiFe LDH as anode and cathode.

Electro catalytic Performance of bimetallic LDH on Mxene Adsorbed Nickle Foam

Mxene is a typical two-dimension material which have widely applied in many fields. Following the design strategy of electrostatic adsorption, coupled with bimetallic LDH, the layered Mxene is successfully used in electrochemical system. A large number of negative groups on the surface of Mxene are used to let Mxene monolayer adsorb on self-supporting materials. The comparison of the electrocatalytic performance before and after the adsorption of Mxene showed that a small amount of absorbed Mxene did have the effect on the reaction activity. The different bimetallic LDH synthesised by hydrothermal method was supported on this new material NF@Mxene. After exploring various combinations, the NF@Mxene with NiFe LDH was proved to be the best OER catalyst. This strategy will provide possibilities for subsequent Mxene electrocatalytic applications.

Process Optimization Studies of Congo Red Dye Adsorption onto Nickel Iron Layered Double Hydroxide Using Response Surface Methodology

Layer double hydroxide materials have many applications in areas such as biomedical, catalytic, sensor, adsorption. Recently, the LDH synthesis methods used have been increasingly developed. In this study, the Ni-Fe LDH material was synthesized by hydrothermal method and parameters affecting CR adsorption were maximized by surface response method (RSM). The results showed that the CR removal capacity reached a maximum value of 244.87 mg/g at a concentration of 136.63 mg/L, pH of 5.94 and reaction time 233.84 min. In addition, ANOVA analysis for the second-order model gave favorable results with high R2 (R2 = 0.991), F and p values in accordance with the proposed standards, all indicating that this model has significance between experimental variables and predict.

Bifunctional NiFe layered double hydroxide@Ni3S2 heterostructure as efficient electrocatalyst for overall water splitting

The tailored construction of non-noble metal bifunctional electrocatalysts for high-efficiency oxygen/hydrogen evolution reactions (OER/HER) is vital for the development of electrochemical energy conversion. Herein, we report a powerful combined wet chemical method to fabricate a novel binder-free NiFe layered double hydroxide@Ni3S2 (NiFe LDH@Ni3S2) heterostructure as an efficient bifunctional electrocatalyst for overall water splitting. The hydrothermal-synthesized NiFe LDH nanosheets are uniformly coated on the Ni3S2 nanosheet skeleton forming 3D porous heterostructure arrays. By virtue of its synergistic advantages, including its binder-free characteristics, increased catalysis sites and structural stability, the as-obtained NiFe LDH@Ni3S2/NF electrode exhibits low overpotentials of 184 and 271 mV at 20 mA cm−2 for HER and OER in 1 M KOH, respectively. Notably, a low operation potential of 1.74 V at a current density of 20 mA cm−2 is achieved for overall water splitting with a stable cycling life. In addition, the intimate composite structure and sensitive interface of NiFe LDH@Ni3S2 are responsible for the good electrocatalytic activity with a low Tafel slope, fast reaction kinetics and high stability. The versatile fabrication protocol and heterostructure interface engineering provide a new way to construct other bifunctional and cost-effective electrocatalysts for electrocatalysis.

Integration of ZnCo2S4 nanowires arrays with NiFe-LDH nanosheet as water dissociation promoter for enhanced electrocatalytic hydrogen evolution

Developing high-efficiency but nonprecious electrocatalysts for hydrogen evolution reaction (HER) in basic media is of great importance for energy conversion. Bimetallic transition metal sulphide (TMS) nanoarrays have been regarded as promising HER electrocatalyst owing to its high conductivity and synergy of different active sites. However, the reaction kinetic of HER for bimetallic TMS is sluggish probably due to the limited active sites for the dissociation of H2O molecule. Herein, NiFe-LDH (NFL) nanosheets are anchored on the ZnCo2S4 (ZCS) nanowire arrays supported on nickel foam (NF) to form core-shell hierarchical ZnCo2S4@NiFe-LDH architecture (ZCS@NFL/NF). Resulting from the 3D core-shell architectures and synergy between ZCS and NFL, the ZCS@NFL/NF needs a low overpotential of 110 mV to deliver 10 mA cm−2 for HER in 1 M KOH, which is about 135 mV lower than the bare ZCS/NF and superior to many reported Co-/Ni-based-electrocatalysts. We anticipated that this work could open up an avenue for development of core-shell hierarchical architecture HER electrocatalysts by using LDHs materials as the H2O dissociation promoter.

Ultrasonic exfoliation of NiFe LDH/CB nanosheets for enhanced oxygen evolution catalysis.

The oxygen evolution reaction (OER) is an important reaction in water splitting. Nickel-iron layered double hydroxide (NiFe LDH) has been considered a potential catalyst for OER. Herein, we report a simple/green approach to improve the oxygen evolution activity of NiFe LDH supported on carbon black (CB). Specifically, ultrasonic exfoliation (UIP500hd, 20 kHz, 500 W) in pure water has been applied to boost the activity of NiFe LDH/CB towards OER. The exfoliated NiFe LDH/CB nanosheets display significantly higher OER activity than their corresponding bulk NiFe LDH/CB in an alkaline solution, with an overpotential of 220 mV at a current density of 10 mA cm-2, which is 60 mV lower than the 280 mV of the bulk NiFe LDH/CB. Notably, it is comparable with the current record overpotential (~200 mV) and superior than other non-precious catalysts. Additionally, after exfoliation, it possesses outstanding kinetics (Tafel slope of 35 mV dec-1) for OER. Besides the improved activity, the exfoliated NiFe LDH/CB has shown a high stability with nearly a constant potential through 12 h electrolysis at a current density of 10 mA cm-2. The characterization analysis reveal that the improved electrochemical performance is closely related to the synergistic effects of the Ni2+ and Fe2+ enriched surface of the exfoliated NiFe LDH/CB, as well as single/few layers structure after exfoliation.

Novel Ni–Fe‐Layered Double Hydroxide Microspheres with Reduced Graphene Oxide for Rechargeable Aluminum Batteries

Rechargeable aluminum batteries (RABs) have been intensively studied recently in virtue of high volumetric energy density and cheapness. However, limited options for suitable cathode materials is the major obstacle to their large‐scale application. Herein, nickel‐iron layered double hydroxide (NiFe–LDH) microspheres with reduced graphene oxide (rGO) are reported as cathode for RABs. It is demonstrated that NiFe–LDH can provide large interlayer spacing for aluminum ions to interact, and the introduction of rGO endows NiFe–LDH with excellent structure stability, electronic conduction, and electrochemical reaction kinetics. The aluminum battery with a NiFe–LDH/rGO cathode delivers a high reversible capacity of 131 mA h g−1 at 1 A g−1 with nearly 100% coulombic efficiency after 100 cycles. The characterization results reveal that the reversible Al3+ insertion/extraction along with the multielectron redox reactions occurs in the NiFe–LDH/rGO during the cycling process. The aforementioned strategies shed new light on the selection of compatible cathodes for RABs.

One-Step Synthesis of NiFe Layered Double Hydroxide Nanosheet Array/N-Doped Graphite Foam Electrodes for Oxygen Evolution Reactions.

Developing cost‐effective and highly efficient oxygen evolution reaction (OER) electrocatalysts is vital for the production of clean hydrogen by electrocatalytic water splitting. Here, three dimensional nickel‐iron layered double hydroxide (NiFe LDH) nanosheet arrays are in‐situ fabricated on self‐supporting nitrogen doped graphited foam (NGF) via a one‐step hydrothermal process under an optimized amount of urea. The as prepared NiFe LDH/NGF electrode exhibits a remarkable activity toward OER with a low onset overpotential of 233 mV and a Tafel slope of 59.4 mV dec−1 as well as a long‐term durability. Such good performance is attributed to the synergy among the doping effect, the binder‐free characteristic, and the architecture of the nanosheet array.

Modification of Nife Layered Double Hydroxide and Photocatalytic Activity

Modifying materials by ions with multiple valence states is an effective way for enhancing their properties. NiFe layered double hydroxides (NiFe LDHs) were prepared by using a hydrothermal method. Efficient LDH photocatalyst was synthesized by the modification of NiFe LDHs with Fe(III). Electron microscopy, X-ray diffraction, Brunauer-Emmett-Teller surface area, photoluminescence spectroscopy, and UV-Vis diffuse reflectance spectroscopy were used to investigate the morphology, crystal structure, and optical properties of the NiFe LDHs. The photocatalytic and adsorption performances were examined in the degradation of methyl orange. NiFe LDHs exhibited higher adsorption property but lower photocatalytic activity. After modification with Fe(III), the introducing of Fe ions and recrystallization of LDHs led to the distance decreasing between NiFe LDH sheets and exhibit higher photocatalytic performance.

Enhanced Photocatalytic Activities of RhB Degradation and H2 Evolution from in Situ Formation of the Electrostatic Heterostructure MoS2/NiFe LDH Nanocomposite through the Z-Scheme Mechanism via p-n Heterojunctions.

Designing of an efficient heterostructure photocatalyst for photocatalytic organic pollutant removal and H2 production has been a subject of rigorous research intended to solve the related environmental aggravation and enormous energy crises. Z-scheme-based charge-transfer dynamics in a p-n heterostructure could significantly replicate the inherent power of natural photosynthesis, which is the key point to affect the transportation of photoinduced exciton pairs. In this finding, a series of p-type MoS2 loaded with n-type NiFe-layered double hydroxide (LDH) forming a heterostructure MoS2/NiFe LDH were designed by electrostatic self-assembled chemistry and an in situ hydrothermal strategy for photocatalytic rhodamine B (RhB) dye degradation and H2 production. The creation of p-n heterojunctions of type-II and Z-scheme mode of charge transfer modified the optical and electronic property of the as-synthesized MSLDH3, thereafter promoting the generation, separation, and migration of photoinduced electron-hole pairs. The as-synthesized MSLDH3 showed superior photocatalytic activities in degradation of RhB with H2 evolution, which was enhanced by 3- and 4.5-fold and 10.9 and 19.2 times higher than that of NiFe LDH and MoS2, respectively. Last but not the least, heterostructure MSLDH3 possesses practical stability for its resultant enhanced photocatalytic activity with recyclability for everyday life.

Tuning the Bifunctional Oxygen Electrocatalytic Properties of Core-Shell Co3O4@NiFe LDH Catalysts for Zn-Air Batteries: Effects of Interfacial Cation Valences.

The rational design of excellent electrocatalysts is significant for triggering the slow kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in rechargeable metal-air batteries. Hereby, we report a bifunctional catalytic material with core-shell structure constructed by Co3O4 nanowire arrays as cores and ultrathin NiFe-layered double hydroxides (NiFe LDHs) as shells (Co3O4@NiFe LDHs). The introduction of Co3O4 nanowires could provide abundant active sites for NiFe LDH nanosheets. Most importantly, the deposition of NiFe LDHs on the surface of Co3O4 can modulate the surface chemical valences of Co, Ni, and Fe species via changing the electron donor and/or electron absorption effects, finally achieving the balance and optimization of ORR and OER properties. By this core-shell design, the maximum ORR current densities of Co3O4@NiFe LDHs increase to 3-7 mA cm-2, almost an order of magnitude increases compared to pure NiFe LDH (0.45 mA cm-2). Significantly, an OER overpotential as low as 226 mV (35 mA cm-2) is achieved in the designed core-shell catalyst, which is comparable to and/or even better than those of commercial Ir/C. Hence, the primary zinc-air battery employing Co3O4@NiFe LDH as an air electrode achieves a high specific capacity (667.5 mA h g-1) and first-class energy density (797.6 W h kg-1); the rechargeable battery can show superior reversibility, excellent stability, and voltage gaps of ∼0.8 V (∼60% of round-trip efficiency) in >1200 continuous cycles. Furthermore, the flexible quasi-solid-state zinc-air battery with bendable ability holds practical potential in portable and wearable electronic devices.

Operational durability of three-dimensional Ni-Fe layered double hydroxide electrocatalyst for water oxidation

Water electrolysis for hydrogen and oxygen production is a key technology in next-generation energy carrier and conversion. In particular, renewable energy sources integrated water electrolysis system has emerged due to its eco-friendly and highly energy efficient process. However, inherent limitations of renewable energy sources including intermittent and unpredictable energy production restrict stable water electrolysis cell operating. Therefore, investigation on cell performance depending on various operation conditions is absolutely required. Here, we synthesized Ni-Fe layered double hydroxide (Ni-Fe LDH) electrodes and studied their oxygen evolution reaction (OER) activities under various operational conditions matching actual environmental conditions when utilizing renewable energy sources. Changes in morphology and electrocatalytic performance were systematically studied by using XRD, FE-SEM, and EIS measurement. Our results showed that operation of water electrolysis cell in an accelerated stress condition could result in changes in morphology of crystal structure of LDH, thus restricting ions to be fully utilized at active site for OER.

Transition-Metal-Doped TiO2 Decorated Nife Layered Double Hydroxide Catalyst in Alkaline Oxygen Evolution Reaction

Efficient and earth abundant electrocatalysts for high-performance oxygen evolution reaction (OER) are essential for the development of sustainable energy conversion technologies. Here, the 3d transition-metal-doped TiO2 were synthesized and used the catalysts for alkaline oxygen evolution reaction. Commercial catalyst usually uses carbon as support such as Ir/C and Ru/C. But during oxygen evolution reaction, carbon will be corroded seriously. So, catalyst will detach from carbon support cause efficiency of catalyst to decay very quickly. In order to overcome these problems, we develop TiO2 as a support because TiO2 is a very durable material in high potential region and high concentration alkaline electrolyte. However, TiO2 is not a good catalyst for oxygen evolution reaction and suffer from its poor conductivity. To solve these drawbacks, we synthesized different 3d transition metal doping TiO2 in this work. After electrochemical tests, we choose (Ni, Fe) dual doped TiO2 was chosen because of its potential for oxygen evolution reaction. First of all, different different doping compositions of Ni and Fe were investigated, and it was found that Ni:Fe in molar ratio 3:1 showed the best oxygen evolution reaction performance. Next, different doping amounts of Ni to Fe, from 6:2, 3:1 to 1.5:0.5 were also evaluated, where Ni:Fe in 6:2 was the best composition for alkaline oxygen evoution. Furthermore, we modified catalyst by adding long chain anion, hydrogen treatment and loading NiFe LDH on (Ni, Fe) dual doped TiO2. Finally, NiFe/TiNiFe perform better oxygen evolution reaction than pure NiFe LDH. At the current density reach 10 mA/cm2, the required potential of NiFe/TiNiFe was 10 mV less than for pure NiFe LDH. After chronopotentiometric stability test for 48 hours, NiFe/TiNiFe showed almost no decay during reaction and is more superior than NiFe LDH. Our work successfully solves activity and stability issue at the same time by an excessive dual doping approach.

Efficient Ni–Fe layered double hydroxides/ZnO nanostructures for photochemical water splitting

Zinc oxide (ZnO) nanostructures are widely investigated for photocatalytic applications but the functional properties are limited by the fast carrier recombination rate, which is an intrinsic property of ZnO. To optimize the recombination rate of ZnO, a study is carried out in which it is covered with Ni-Fe layered double hydroxides and synergistic effects are created which boosted the photocatalytic activity of ZnO. The nanostructured materials are synthesized by the low temperature aqueous chemical growth and electrodeposition methods. These nanostructures are characterized by scanning electron microscopy (SEM) and powder X-ray diffraction (XRD) technique. SEM study has revealed a Ni–Fe LDH coated ZnO NRs. The powder XRD has showed a cubic phase of the Ni-Fe layered double hydroxide on the ZnO NRs having an excellent crystalline quality. The optical characterization has shown low scattering of light for the Ni–Fe LDH coated ZnO NRs sample. The sample prepared with deposition time of 25 s showed excellent photochemical water splitting properties compared to counter photo-anodes in alkaline media. The photo response was highly stable and fast. The incident photon to current conversion efficiency for the photo-anode of Ni–Fe(LDHs)/ZnO over 25 s was 82% at a maximum absorption of 380 nm compared to the pristine ZnO NRs which has 70% at the same wavelength. This study is providing a simple, cost effective, earth abundant and environment friendly methodology for the fabrication of photo-anodes for diverse applications specifically water oxidation and solar radiation driven water splitting.

Deciphering Z-scheme Charge Transfer Dynamics in Heterostructure NiFe-LDH/N-rGO/g-C3N4 Nanocomposite for Photocatalytic Pollutant Removal and Water Splitting Reactions

A series of heterostructure NiFe LDH/N-rGO/g-C3N4 nanocomposite were fabricated by combining calcinations-electrostatic self-assembly and hydrothermal steps. In this method, negatively charged N-rGO was electrostaticaly bonded to the self-assembled interface of n-n type g-C3N4/NiFe LDH hybrid. XRD and AFM results revealed successful formation of heterostructure nanocomposite due to the coupling effect of exfoliated NiFe LDH nanosheets with N-rGO and g-C3N4. Among the as synthesized heterostructure, CNNG3LDH performed superior photocatalytic activities towards 95 and 72% mineralization of RhB and phenol. Furthermore, CNNG3LDH could achieve the highest photocatalytic H2 evolution rate of 2508 μmolg−12h−1 and O2 evolution rate of 1280 μmolg−12h−1 under visible light irradiation. The CNNG3LDH possess lowest PL intensity, reduced arc of the Nyquist plot (43.8 Ώ) and highest photocurrent density (−0.97 mA cm−2) which revealed effective charge separation for superior photocatalytic activities. TRPL spectral results reveal the synergistic effect of layered component in CNNG3LDH for achievable higher life time of excitons of ~16.52 ns. In addition, N-rGO mediator based Z-scheme charge transfer mechanisms in CNNG3LDH were verified by the ESR and TA-PL studies. Enriched oxygen vacancy type defects in NiFe LDH and N-rGO mediated Z-scheme charge transfer mechanistic path strongly manifest the superior photocatalytic activities of the heterostructure materials.

3D hierarchical graphene oxide-NiFe LDH composite with enhanced adsorption affinity to Congo red, methyl orange and Cr(VI) ions.

Three-dimensional (3D) hierarchical graphene oxide-NiFe layered double hydroxide (GO-NiFe LDH) composite with sandwich-like structure is fabricated using a facile one-pot hydrothermal reaction. Electron microscopy images demonstrate that the GO-NiFe LDH composite possesses a highly porous and well-ordered structure. Both sides of the GO are fully covered by the LDH nanosheets, resulting in the sandwich-like architecture. The adsorption performance of the GO-NiFe LDH composite and pure NiFe LDH for three anionic pollutants, namely, Congo red (CR), methyl orange (MO) and hexavalent chromium ion [Cr(VI)] is systematically investigated. The presence of GO in the GO-NiFe LDH composite leads to the better adsorption capability and faster adsorption kinetics of this composite compared with the NiFe LDH microspheres. The pseudo-second-order kinetic model can well represent the adsorption kinetics, and the Langmuir isotherm model provides a better description for the adsorption isotherms. The GO-NiFe LDH composite demonstrates appreciable potential in alleviating anionic pollutants from the aquatic environment as shown by its excellent adsorption capability towards CR, MO and Cr(VI).

2D-2D growth of NiFe LDH nanoflakes on montmorillonite for cationic and anionic dye adsorption performance

NiFe layered double hydroxides nanoflakes decorated montmorillonite (MMT@NiFe LDH) was successfully prepared by a one-pot hydrothermal method. The 2D-2D growth MMT@NiFe LDH was utilized as an effective adsorbent for removal of anionic dye of methyl orange (MO) and cationic dye of methylene blue (MB). The mole ratio of Ni2+/Fe3+ could quite influence the interlayer spacing, surface area per unit charge and the ultrathin hexagonal laminated morphology of NiFe LDH decorated on the surface of MMT. Various characterization techniques were conducted to identify it, such as XRD, FT-IR, TG-DTA, BET, XPS and SEM. Under the optimal conditions, the Langmuir-fitted maximum adsorption capacities for MO and MB are 108.80 mg g−1 and 99.18 mg g−1, respectively. Adsorption kinetics for MO and MB are both verified to be fit in with pseudo-second-order model. This work suggests a facile pathway to synthesize desirable bifunctional adsorbent for cationic and anionic dyes, which provides the potential application for the actual wastewater purification.