Nickel-iron Layered Double Hydroxide Research Articles

Oxygen Isotopologues Resolved from Water Oxidation Electrocatalysis by Electron Paramagnetic Resonance Spectroscopy.

Electrocatalytic water oxidation is a key transformation in many strategies designed to harness solar energy and store it as chemical fuels. Understanding the mechanism(s) of the best electrocatalysts for water oxidation has been a fundamental chemical challenge for decades. Here, we quantitate evolved dioxygen isotopologue composition via gas-phase EPR spectroscopy to elucidate the mechanisms of water oxidation on metal oxide electrocatalysts with high precision. Isotope fractionation is paired with computational and kinetic modeling, showing that this technique is sensitive enough to differentiate O-O bond-forming steps. Strong agreement between experiment and theory indicates that for the nickel-iron layered double hydroxide─one of the best earth-abundant electrocatalysts to be studied─water oxidation proceeds via a dioxo coupling mechanism to form a side-bound peroxide rather than a hydroxide attack to form an end-bound peroxide.

Ruthenium decorated nickel-iron layered double hydroxides (NiFe-LDH) for promoting peroxymonosulfate activation and atrazine degradation

With the extensive use of atrazine (ATZ), its potential hazards to ecological environment and human health have raised public concerns. This study reports the effective degradation of ATZ via advanced oxidation processes (AOPs) using peroxymonosulfate (PMS) activated by heterogeneous catalysts of Ru loaded NiFe-LDH blossom nanosheets (Ru/NiFe-LDH). During AOPs, the highly dispersed Ru sites as the main catalytic centers and the NiFe-LDH substrate synergistically stimulated PMS to efficiently produce reactive oxygen species to oxidize ATZ. Under optimal conditions, the degradation activity of ATZ by 5.8Ru/NiFe-LDH/PMS system reached 100% within 90 min. Additionally, it also exhibited good environmental applicability. Besides, electron paramagnetic resonance along with quenching experiments illustrated the production of 1O2, O2• −, •OH, SO4• − and surface-bond radicals during the degradation, where 1O2, •OH and surface-bond radicals were further identified as the dominant oxygen species for the oxidation. The ATZ degradation pathway was determined using the liquid chromatography-mass spectrometry to discern the intermediate products, e.g., dealkylation, alkylic-hydroxylation and dechlororination-hydroxylation processes. This work holds a potential application value for the removal of atrazine and other pollutants.

Electron Accumulation Induced by Electron Injection-Incomplete Discharge on NiFe LDH for Enhanced Oxygen Evolution Reaction.

Optimizing the local electronic structure of electrocatalysts can effectively lower the energy barrier of electrochemical reactions, thus enhancing the electrocatalytic activity. However, the intrinsic contribution of the electronic effect is still experimentally unclear. In this work, the electron injection-incomplete discharge approach to achieve the electron accumulation (EA) degree on the nickel-iron layered double hydroxide (NiFe LDH) is proposed, to reveal the intrinsic contribution of EA toward oxygen evolution reaction (OER). Such NiFe LDH with EA effect results in only 262mV overpotential to reach 50 mAcm-2, which is 51mV-lower compared with pristine NiFe LDH (313mV), and reduced Tafel slope of 54.8mVdec-1 than NiFe LDH (107.5mVdec-1). Spectroscopy characterizations combined with theoretical calculations confirm that the EA near concomitant Vo can induce a narrower energy gap and lower thermodynamic barrier to enhance OER performance. This study clarifies the mechanism of the EA effect on OER activity, providing a direct electronic structure modulation guideline for effective electrocatalyst design.

A novel NiFe-LDH/AC three-dimensional particle electrode system and its application for degradation of N-nitrosamines: Condition optimization and degradation mechanism

A green and sustainable three-dimensional particle electrodes system with nickel-iron layered double hydroxide mixing activated carbon particles (NiFe-LDH/AC) as particle electrodes is used in this work. Its employment in degradation of N-Nitrosodiethylamine (NDEA), A type of nitrosamines disinfection byproducts (NAs) widely present in water bodies, exhibiting significant degradation efficiency at close to neutral pH. Response surface methodology (RSM) is used to analyze the interaction effects and predict optimal conditions of four operating parameters (influent water flow, electrolyte concentration, current density and initial concentration) on the NDEA degradation efficiency. Calculated coefficients of determination (R2) are higher than 0.997 for all responses according to analysis of variance. At optimum conditions, a maximum degradation efficiency of 71.88% is achieved for NDEA. The results of electron paramagnetic resonance (EPR) and free radical quenching experiments indicate that the degradation of NDEA in the 3D AER system is dominated by •OH. Furthermore, based on the recognition of main reaction intermediates by GC-MS and density functional theory (DFT), possible degradation pathway is proposed and toxicological evaluation of degradation products is made. Our research provides a promising alternative method for the efficient and environmentally friendly removal of NAs from water.

A Ni-Fe layered double hydroxide anchored FeCo nanoalloys and Fe-Co dual single-atom electrocatalysts for rechargeable and flexible zinc-air and aluminum-air batteries

Developing bifunctional catalysts for the ORR and OER, along with a unique cathode structure, is essential for advancing rechargeable zinc-air batteries (ZABs) and aluminum-air batteries (AABs). Our catalyst (NiFe LDH A-FeSACoSA-FeCoAlloy-CNT/NC) integrates nickel-iron layered double hydroxide (NiFe LDH), iron-cobalt dual single atoms (FeSACoSA), and iron-cobalt nanoalloy (FeCoAlloy) within carbon nanotubes (CNTs) on a nitrogen-doped carbon framework (NC). Due to its distinctive features, this catalyst excels, achieving an ORR half-wave potential of 0.84 V and an OER potential of 1.56 V (Ej=10mAcm−2). In ZABs, it outperforms the Pt/C+RuO2, reaching a power density of 266 mWcm−2 and demonstrating impressive rechargeability over 495 h (1484 cycles). Flexible ZABs achieve 173 mWcm−2 and over 270 cycles (90 h), while flexible AABs reach 145 mWcm−2, surpassing Pt/C+RuO2. Exceptional performance in terms of capacity, power density, rechargeability, and lifespan is attributed to the catalyst's design and the cathode configuration's unique attributes.

Boosting Oxygen Evolution Performance of Nickel-Iron Layered Double Hydroxides by Controlling Oxygen Vacancies and Structural Disorder via n-Butyllithium Treatment.

Nickel-iron-based layered double hydroxides (NiFe-LDHs) are promising catalysts for the oxygen evolution reaction (OER) because of their high activity, availability, and low cost. Defect engineering, particularly the formation of oxygen vacancies, can improve the catalytic activity of NiFe-LDHs. However, the controllable introduction of uniform oxygen vacancies remains challenging. Herein, an n-butyllithium treatment method is developed to tune oxygen vacancy defects and change the degree of amorphization in NiFe-LDHs via deep reduction, followed by partial oxidization at low temperatures. Interestingly, the Ni in the NiFe-LDHs is selectively reduced to the alloy state by n-butyllithium, whereas Fe is not. The different structural transformations of Ni and Fe during the treatment successfully produce an oxygen-defect-rich amorphous/crystalline electrocatalyst. Under optimal conditions, the treated NiFe-LDHs exhibit high OER activity with an overpotential of 223 mV at 10 mA cm-2 (68 mV lower than that of a commercial IrO2 electrocatalyst) and long-term stability. Notably, the n-butyllithium treatment can be applied to other electrocatalysts, such as CoFe-LDHs and IrO2 (treated IrO2 with an overpotential of 197 mV at 10 mA cm-2). This n-butyllithium reduction/partial oxidization treatment constitutes a novel top-down strategy for the controllable modification of metal oxide structures, with various energy-related applications.

Bioinspired trimesic acid anchored electrocatalysts with unique static and dynamic compatibility for enhanced water oxidation

Layered double hydroxides are promising candidates for the electrocatalytic oxygen evolution reaction. Unfortunately, their catalytic kinetics and long-term stabilities are far from satisfactory compared to those of rare metals. Here, we investigate the durability of nickel-iron layered double hydroxides and show that ablation of the lamellar structure due to metal dissolution is the cause of the decreased stability. Inspired by the amino acid residues in photosystem II, we report a strategy using trimesic acid anchors to prepare the subsize nickel-iron layered double hydroxides with kinetics, activity and stability superior to those of commercial catalysts. Fundamental investigations through operando spectroscopy and theoretical calculations reveal that the superaerophobic surface facilitates prompt release of the generated O2 bubbles, and protects the structure of the catalyst. Coupling between the metals and coordinated carboxylates via C‒O‒Fe bonding prevents dissolution of the metal species, which stabilizes the electronic structure by static coordination. In addition, the uncoordinated carboxylates formed by dynamic evolution during oxygen evolution reaction serve as proton ferries to accelerate the oxygen evolution reaction kinetics. This work offers a promising way to achieve breakthroughs in oxygen evolution reaction stability and dynamic performance by introducing functional ligands with static and dynamic compatibilities.

High-Performance Alkaline Seawater Electrolysis with Anomalous Chloride Promoted Oxygen Evolution Reaction.

A highly selective and durable oxygen evolution reaction (OER) electrocatalyst is the bottleneck for direct seawater splitting because of side reactions primarily caused by chloride ions (Cl-). Most studies about OER catalysts in seawater focus on the repulsion of the Cl- to reduce its negative effects. Herein, we demonstrate that the absorption of Cl- on the specific site of a popular OER electrocatalyst, nickel-iron layered double hydroxide (NiFe LDH), does not have a significant negative impact; rather, it is beneficial for its activity and stability enhancement in natural seawater. A set of in situ characterization techniques reveals that the adsorption of Cl- on the desired Fe site suppresses Fe leaching, and creates more OER-active Ni sites, improving the catalyst's long-term stability and activity simultaneously. Therefore, we achieve direct alkaline seawater electrolysis for the very first time on a commercial-scale alkaline electrolyser (AE, 120 cm2 electrode area) using the NiFe LDH anode. The new alkaline seawater electrolyser exhibits a reduction in electricity consumption by 20.7 % compared to the alkaline purified water-based AE using commercial Ni catalyst, achieving excellent durability for 100 h at 200 mA cm-2.

Simple Method to Enhance the Oxidation–Reduction Reaction Activity of a Carbon Nanotube-Based Nickel–Iron Layered Double Hydroxide as a Bifunctional Electrocatalyst

Simple Method to Enhance the Oxidation–Reduction Reaction Activity of a Carbon Nanotube-Based Nickel–Iron Layered Double Hydroxide as a Bifunctional Electrocatalyst

Selective adsorption of nitrate in water by organosilicon quaternary ammonium salt modified derived nickel-iron layered double hydroxide: Adsorption characteristics and mechanism

Nitrate (NO3−) is a widespread pollutant in the water environment. Due to its physicochemical properties, such as negative monovalent charge, traditional adsorption treatment processes have low selectivity for NO3− removal, resulting in low removal efficiency of NO3− by adsorbents in the presence of interfering ions. Therefore, to improve the adsorption selectivity and efficiency of NO3−. In this study, we used organosilicon quaternary modified derived nickel–iron layered double hydroxide (NiFe-MLDH/OQAS) for selective removal of NO3−. NiFe-MLDH/OQAS has a flowery globular structure, with interconnected nanosheets on the surface providing more adsorption sites for NO3−, which improves the adsorption rate and adsorption amount. What's more, the nitrate removal rate of NiFe-MLDH/OQAS only decreased by about 14.36% in the presence of the same concentration of interfering ions, and the maximum adsorption amount reached 61.05 mg/g, showing good selectivity and adsorption amount. Various characterization analyses indicate that the nitrate selectivity of NiFe-MLDH/OQAS is attributed to its unique layer spacing, as well as the abundant functional groups on the material surface. Finally, we demonstrated through experiments that NiFe-MLDH/OQAS has good cyclic regeneration ability and environmental safety. These findings demonstrate the great potential of NiFe-MLDH/OQAS for selective adsorption of NO3−.

Sulphur- and nitrogen-codoped layered double hydroxides with expanded interlayer distance for enhanced overall water splitting

Developing highly active, durable, and non-noble electrocatalysts for water-splitting is critical for efficient renewable energy conversion. Nickel-iron layered double-hydroxide (NiFe-LDH) materials show potential in achieving good catalytic performance, however, which was restricted by the scarce active sites and poor conductivity. Herein, we report a series of NiFe-LDH-based materials of expanded interlayer spacing constructed through S/N co-doping with rich active sites, used as a high-efficient bifunctional electrocatalyst for the oxygen and hydrogen evolution reactions (OER and HER). The experimental results indicate that the intercalation/decoration on the interlayer structure of NiFe-LDH can efficiently reduce the energy barrier and accelerate reaction kinetics. Combining with the structural advantages, including the expanded lattice spacing and exposed active surface sites, the resulting S-N/NiFe-LDH anchored in nickel foam (NF) drives an alkaline electrolyzer with a cell voltage of 1.67 V at a current density of 100 mA cm−2, as well as robust stability over 100 h, which is much superior to the state-of-the-art Pt/C-RuO2 electrocatalysts.

Layered double hydroxides as a robust catalyst for water oxidation through strong substrate-catalytic layer interaction

Electrochemical preparation of hydrogen permits a way to meet our energy and environmental issues, but the anodic reaction is kinetically slow and thus is the bottleneck in the overall water splitting. Achieving cost-effective electrocatalysts represents a big challenge for practical water oxidation. Herein, We report the tuning of the local electron structure of nickel-iron layered double hydroxides (NiFe LDH) by achieving a highly coupled interface between active sites and the current collector. Our developed NiFe-LDH/Fe catalysts as the anode can provide 10 mA cm−2 at 1.455 V vs. RHE with a Tafel slope of only 32.7 mV dec−1. Simultaneously, the catalyst has high catalytic stability. Combined with the X-ray photoelectron spectroscopy and density functional theory calculation, the coupling interface between the substrate and catalytic layer can effectively regulate the electron density of the Fe sites, which is the main reason for the high catalytic ability of the layered double hydroxide catalyst.

In Situ Synthesis of NiFeLDH/A-CBp from Pyrolytic Carbon as High-Performance Oxygen Evolution Reaction Catalyst for Water Splitting and Zinc Hydrometallurgy.

Nickel-iron-layered double hydroxide (NiFeLDH) is one of the promising catalysts for the oxygen evolution reaction (OER) in alkaline electrolytes, but its conductivity limits its large-scale application. The focus of current work is to explore low-cost, conductive substrates for large-scale production and combine them with NiFeLDH to improve its conductivity. In this work, purified and activated pyrolytic carbon black (CBp) is combined with NiFeLDH to form an NiFeLDH/A-CBp catalyst for OER. CBp not only improves the conductivity of the catalyst but also greatly reduces the size of NiFeLDH nanosheets to increase the activated surface area. In addition, ascorbic acid (AA) is introduced to enhance the coupling between NiFeLDH and A-CBp, which can be evidenced by the increase of Fe-O-Ni peak intensity in FTIR measurement. Thus, a lower overvoltage of 227 mV and larger active surface area of 43.26 mF·cm-2 are achieved in 1 M KOH solution for NiFeLDH/A-CBp. In addition, NiFeLDH/A-CBp shows good catalytic performance and stability as the anode catalyst for water splitting and Zn electrowinning in alkaline electrolytes. In Zn electrowinning with NiFeLDH/A-CBp, the low cell voltage of 2.08 V at 1000 A·m-2 results in lower energy consumption of 1.78 kW h/KgZn, which is nearly half of the 3.40 kW h/KgZn of industrial electrowinning. This work demonstrates the new application of high-value-added CBp in hydrogen production from electrolytic water and zinc hydrometallurgy to realize the recycling of waste carbon resources and reduce the consumption of fossil resources.

A hierarchical cactus-like nanostructure as a bifunctional catalyst for overall water splitting

In this study, a hierarchical cactus-like nanostructure with cobalt doped iron disulfide (Co-FeS2) needle nanowires as trunks and nickel-iron layered double hydroxide (NiFe-LDH) nanosheets as branches was constructed as a self-supporting electrode for overall water splitting in alkaline electrolytes. A low electron density NiFe-LDH derived from the strong electronic interaction between sulfides and NiFe-LDH is remarkably effective in facilitating the adsorption of H2O and OH−, while the presence of Co atoms in FeS2 facilitates the hydrogen adsorption. Such a synergetic effect improved the HER performance in alkaline electrolytes significantly. In terms of the OER process, the Fe/Co oxyhydroxides produced from in situ phase transition from Co-FeS2 in conjunction with NiFe-LDH endow the electrode with excellent OER activity. Furthermore, the Co-FeS2 needle nanowires with metal-like conductivity allow for rapid electron transfer during electrochemical processes, and the hierarchical structure exposes substantial active sites and facilitates electrolyte penetration. In alkaline media, the electrode demonstrated outstanding HER and OER catalytic activity, requiring small overpotentials of 131 mV and 220 mV to reach current densities of 10 mA cm−2 and 20 mA cm−2, respectively. Moreover, it only needed 1.58 V to drive 10 mA cm−2 when utilized simultaneously as both cathode and anode for overall water splitting.

Constructing microstructures in nickel-iron layered double hydroxide electrocatalysts by cobalt doping for efficient overall water splitting

The development of Ni–Fe layered double hydroxide (NiFe LDH) catalysts for overall water splitting (OWS) is urgently required. NiFe LDHs are promising catalysts for the oxygen evolution reaction (OER). However, their hydrogen evolution reaction (HER) performance is restricted by slow kinetics. The construction of multiple types of active sites to simultaneously optimise the OER and HER performance is significant for OWS using NiFe LDHs. Hence, a Co-doped NiFe LDH electrocatalyst with dislocations and stacking faults was designed to modulate the electronic structure and generate multiple types of activity sites. The Co0.03-NiFe0.97 LDH catalyst only required overpotentials of 280 (50 mA cm−2, OER) and 170 mV (10 mA cm−2, HER). However, it reached a current density of 50 mA cm−2 at 1.53 V during OWS. Co0.03-NiFe0.97 LDHs could be stabilised for 140 h at 1.52 V. Furthermore, Co0.03-NiFe0.97 LDHs exhibited a higher electrocatalytic activity than commercial Raney nickel and Pt/C||IrO2 under industrial conditions. The significant specific surface area, high conductivity, and unique microstructures are the major factors contributing to the excellent OWS performance. This study suggests an efficient strategy for introducing microstructures to fabricate catalysts with high activity for application in OWS.

Monodispersed Pt Sites Supported on NiFe-LDH from Synchronous Anchoring and Reduction for High Efficiency Overall Water Splitting.

Precise design of low-cost, efficient and definite electrocatalysts is the key to sustainable renewable energy. Herein, this work develops a targeted-anchored and subsequent spontaneous-redox strategy to synthesize nickel-iron layered double hydroxide (LDH) nanosheets anchored with monodispersed platinum (Pt) sites (Pt@LDH). Intermediate metal-organic frameworks (MOF)/LDH heterostructure not only provides numerous confine points to guarantee the stability of Pt sites, but also excites the spontaneous reduction for PtII . Electronic structure, charge transfer ability and reaction kinetics of Pt@LDH can be effectively facilitated by the monodispersed Pt moieties. As a result, the optimized Pt@LDH that with the 5% ultra-low content Pt exhibits the significant increment in electrochemical water splitting performance in alkaline media, which only afford low overpotentials of 58mV at 10 mAcm-2 for hydrogen evolution reaction (HER) and 239mV at 10 mAcm-2 for oxygen evolution reaction (OER), respectively. In a real device, Pt@LDH can drive an overall water-splitting at low cell voltage of 1.49V at 10 mAcm-2 , which can be superior to most reported similar LDH-based catalysts. Moreover, the versatility of the method is extended to other MOF precursors and noble metals for the design of ultrathin LDH supported monodispersed noble metal electrocatalysts promoting research interest in material design.

NiFe Layered Double Hydroxide-Derived Catalysts with Remarkable Selectivity for the Oxidation of 5-Hydroxymethylfurfural to 2,5-Furanedicarboxylic Acid under Base-Free Conditions

In this work, we report the exciting discovery of inexpensive and durable catalysts for the selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furanedicarboxylic acid (FDCA) under base-free conditions. A nickel-iron layered double hydroxide (NiFe-LDH) precursor was first prepared then subjected to hydrothermal sulfidation with thioacetamide at 120 °C or thermal phosphidation with sodium hypophosphite at 400 °C to produce NiFeS and NiFeP-400 catalysts, respectively. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) showed these catalysts to contain FeNi2S4 and FeNi2P, respectively, as the dominant phases. The catalytic activity of each catalyst was optimized by studying the effect of the solvent, reaction temperature, oxidant, and reaction time on HMF conversions and product distributions. Under optimized conditions (acetonitrile solvent, 120 °C, tert-butanol peroxide as an oxidant, 12 h, respectively), the NiFeS catalyst afforded 100% HMF conversion with an 83.2% FDCA selectivity with the performance of the NiFeP-400 catalyst being almost identical (HMF conversion of 100%; FDCA selectivity of 82.7%). Both catalysts showed excellent stability over five cycles of catalyst tests with the catalysts able to be easily collected after use with a magnet. Based on the experimental findings, the similar reaction mechanisms used are to be proposed for HMF oxidation to FDCA over the two catalysts. Results show that metal sulfide-based and metal phosphide-based catalysts are promising alternatives to traditional noble metal-based catalyst for the valorization of bio-derived HMF.

Regulation of the electronic structure of a RuNi/MoC electrocatalyst for high-efficiency hydrogen evolution in alkaline seawater.

Alkaline seawater electrolysis offers a way to generate hydrogen without carbon emissions. However, developing highly efficient catalysts that can sustain high performance and stability for the hydrogen evolution reaction (HER) in alkaline seawater is a formidable challenge. Here, a nanowire (NW) of a RuNi/MoC heterojunction embedded in N-doped carbon (RuNi/MoC@NC) was developed as a potent HER catalyst. The catalyst required only 21 mV at 10 mA cm-2 for HER in alkaline seawater, which surpasses 20% Pt/C. Moreover, using nickel foam (NF) as a catalyst carrier, an electrolyzer composed of RuNi/MoC@NC and nickel-iron layered double hydroxide (NiFe LDH) needed only 1.81 V at 500 mA cm-2 for full water splitting and showed long-term stability (over 500 h). Theoretical calculation revealed that the Ru and Ni sites in the catalyst had the optimal adsorption energy for hydrogen and water, respectively, which synergistically lowered the energy barrier for HER. This work offered an efficient method to design a highly effective HER catalyst for alkaline seawater splitting.

Electronic structure regulation of nickel-iron layered double hydroxides by tuning ternary component for overall water splitting

NiFe layer double hydroxide (LDH) preserves high electrocatalytic activities for oxygen evolution reaction (OER); however, the catalytic performance on hydrogen evolution reaction (HER) is still suffering from poor catalytic activities. In this work, zinc (Zn)-doped NiFe LDH was synthesized as an excellent bifunctional electrocatalysts in alkaline electrolyte. For OER performance, the NiFeZn LDH achieves a Tafel slope of 35.2 mV/dec, which is much lower than that of commercial IrO2 catalysts (124.3 mV/dec). Expected, NiFeZn LDH also remains enhanced HER activity with an overpotential of 236 mV at 50 mA/cm2, superior to most of reported transition metal LDHs. The density functional theory results demonstrated that the Zn dopants could effectively manipulate the electronic structure of NiFeZn LDH, which is responsible to the enhanced active sites for HER.

Synthesis of layered double hydroxide-based hybrid electrode for efficient removal of phosphate ions in capacitive deionization.

The removal of phosphate ions by capacitive deionization has become one of the most frontier research topics in the water treatment field in recent years. In this work, hybrid electrodes composed of nickel-iron layered double hydroxide (NiFe-LDH) - anchored on activated carbon fiber (ACF)-were synthesized by a hydrothermal method and subsequently applied in capacitive deionization to remove phosphate ions. The adsorption performance of the two hybrid electrodes on phosphate ions was compared by capacitive deionization experiments. The experiment was carried out for 3 hours to reach equilibrium, and the optimum adsorption of 33.48 mg/g was obtained using NiFe-LDH/ACF-2 hybrid electrode at room temperature (25 °C) and pH = 6.0. The results showed that increasing the loading capacity of NiFe-LDH on ACF might enhance the adsorption capacity of phosphate ions. Furthermore, the calculation of adsorption kinetics and adsorption isotherms elucidated that the adsorption capacity increased with the increasing of applied voltage. Meanwhile, the experimental data were fitted well with pseudo-first-order kinetics and Langmuir isotherms. Notably, it was observed that the pH first increased, then decreased during the adsorption due to the electrolysis of water, while the form of phosphate ions was transformed, with low pH favoring the adsorption of phosphate ions.