Display omitted
•A 3D hydrangea-like ZnCo2O4/NiCoGa-layered double hydroxide@polypyrrole core–shell heterostructure was successfully constructed.•Density functional theory (DFT) calculations were ...adopted to authenticate the charge redistribution at the heterointerfaces.•ZnCo2O4/NiCoGa-layered double hydroxide@polypyrrole exhibits satisfactory electrochemical performance for supercapacitors.
Rationally constructing advanced battery-type electrodes with hierarchical core–shell heterostructure is essential for improving the energy density and cycling stability of hybrid supercapacitors. Herein, this work successfully constructs hydrangea-like ZnCo2O4/NiCoGa-layered double hydroxide@polypyrrole (denoted as ZCO/NCG-LDH@PPy) core–shell heterostructure. Specifically, the ZCO/NCG-LDH@PPy employs ZCO nanoneedles clusters with large open void space and rough surfaces as the core, and NCG-LDH@PPy composite as the shell, comprising hexagonal NCG-LDH nanosheets with rich active surface area, and conductive PPy films with different thicknesses. Meanwhile, density functional theory (DFT) calculations authenticate the charge redistribution at the heterointerfaces between ZCO and NCG-LDH phases. Benefiting from the abundant heterointerfaces and synergistic effect among different active components, the ZCO/NCG-LDH@PPy electrode acquires an extraordinary specific capacity of 381.4 mAh g−1 at 1 A g−1, along with excellent cycling stability (89.83% capacity retention) after 10,000 cycles at 20 A g−1. Furthermore, the prepared ZCO/NCG-LDH@PPy//AC hybrid supercapacitor (HSC) exhibits a remarkable energy density (81.9 Wh kg−1), an outstanding power density (17,003.7 W kg−1), and superior cycling performance (a capacitance retention of 88.41% and a coulombic efficiency of 93.97%) at the end of the 10,000th cycle. Finally, two ZCO/NCG-LDH@PPy//AC HSCs in series can light up a LED lamp for 15 min, indicating its excellent application prospects.
Novel layered double hydroxides (LDHs) based coatings developed in-situ on aluminum alloys are recognized to provide the substrate with improved corrosion protection. LDH layers have gained prominent ...attention due to their barrier properties and ions exchange capability, together with compositional flexibility and low environmental impact. In this work, diverse MgAl LDHs layers are developed on AA5005 as a surface conversion treatment prior to applying an acrylic clearcoat. The work aims to assess the potential LDH layers of to improve the filiform corrosion (FFC) resistance of the AA500 substrate. The effect of the synthesis time and the presence of urea on the FFC susceptibility are investigated. The performance of the different synthesis conditions was compared and shown to be more effective to increase FFC resistance when well-defined crystals are formed. The findings suggest that MgAl-LDHs mitigate the extent of filiform corrosion of acrylic paint coated AA5005. The FFC inhibition was found to be qualitatively proportional to the pitting potential measured over the LDHs conversion layers.
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.
The sluggish hydrogen evolution reaction (HER) kinetics on a NiFe layered double hydroxide (LDH) are substantially sped up in a novel approach by tailoring its water dissociation active sites in alkaline solutions. The resultant Ru‐doped NiFe‐LDH nanosheet exhibits a greatly enhanced HER activity in alkaline solution, which is superior to those of Pt/C and state‐of‐the‐art Pt‐free electrocatalysts.
The development of a high‐performance electrocatalyst for oxygen evolution reaction (OER) is imperative but challenging. Here, a partial sulfidation route to construct Ni2Fe‐LDH/FeNi2S4 ...heterostructure on nickel foam (Ni2Fe‐LDH/FeNi2S4/NF) by adjusting the hydrothermal duration is reported. The heterostructures afford abundant hydroxide/sulfide interfaces that offer plentiful active sites, rapid charge and mass transfer, favorable adsorption energy to oxygenated species (OH− and OOH) evidenced by the density functional theory calculations, which synergistically boost the alkaline water oxidation. In the 1.0 m KOH solution, Ni2Fe‐LDH/FeNi2S4/NF exhibits an excellent OER catalytic activity with a much smaller overpotential (240 mV) to reach the current density of 100 mA cm−2 than single‐phase Ni2Fe‐LDH/NF (279 mV) or FeNi2S4/NF (271 mV). More impressively, 2000 cycles of cyclic voltammetry scan for water oxidation results in the formation of a sulfate layer over the catalyst. The corresponding post‐catalyst demonstrates better OER activity and durability than the initial one in the alkaline simulated seawater electrolyte. The post‐Ni2Fe‐LDH/FeNi2S4/NF delivers smaller overpotential (250 mV) at 100 mA cm−2 and longer stability time than the original form (260 mV). The post‐formed sulfate passivating layer is responsible for the outstanding corrosion resistance of the salty‐water oxidation anode since it can effectively repel chloride.
Ni2Fe‐LDH/FeNi2S4/NF is prepared by a partial sulfidation of Ni2Fe‐LDH/NF. Abundant hydroxide/sulfide interfaces boost the alkaline water oxidation. Impressively, cyclic voltammetry activation results in the formation of a sulfate layer that largely enhances the corrosion resistance of the catalyst in the alkaline salty‐water electrolytes.
Display omitted
•Layered double hydroxides (LDH) were embedded in PVA and SA, cross-linked by La3+.•La3+ also modified PS-La-LDH hydrogels to improve the phosphate adsorption.•The adsorption capacity ...of PS-La-LDH is 34.2 mg/g, which converted to 91.2 mg/g LDH.•PS-La-LDH removes P by electrostatic adsorption, ligand exchange and ion exchange.
Lanthanum modified compounds and Layered double hydroxides (LDH) are promising adsorbents for phosphate. However, the nano-scale LDH is challenging to separate, and conventional immobilization methods weaken the adsorption performance. With the affinity between metal ions and phosphate, polyvinyl alcohol/metal ions sodium alginate (PS-M−LDH) hydrogel beads for the improvement of phosphate removal were prepared by in-situ crosslinking with different metal ion (M) solutions. Through screening, the PS-M−LDH crosslinked by La (PS-La-LDH) has the preferable phosphate adsorption performance. The phosphate adsorption behavior of PS-La-LDH hydrogel was further investigated. Results showed that the adsorption process of phosphate by PS-La-LDH hydrogel was in accordance with the pseudo-second-order kinetic model and Freundlich model. The maximum experimental adsorption capacity of PS-La-LDH was 34.2 mg P/g, converting to an equivalent LDH of 91.2 mg P/g LDH, which was 1.6 times of pristine LDH powder (58.0 mg P/g LDH). The removal of phosphate by PS-La-LDH performed well at a wide range of pH 3 ∼ 8. PS-La-LDH showed selective adsorption to phosphate with the existence of competing anions (Cl-, NO3–, and SO42–). The phosphate adsorption by PS-La-LDH hydrogel only reduced 16.57 % when the concentration of SO42– was increased to 2882 mg/L. SEM, XRD, FTIR, and XPS results showed that the electrostatic interaction, ligand exchange, and ion exchange jointly facilitated the adsorption of phosphate.
Display omitted
•Fe/Mg-LDH was dispersed on commercial high surface area Douglas fir biochar (LDHBC).•LDHBC phosphate capacity (1279 mg/g) was six-fold greater than LDH (234 mg/g).•1 M NaOH stripped ...phosphate but reduced following P uptake.•Ion-exchange, chemisorption and precipitation mechanisms were considered.
Phosphate is a primary plant nutrient, serving integral role in environmental stability. Excessive phosphate in water causes eutrophication; hence, phosphate ions need to be harvested from soil nutrient levels and water and used efficiently. Fe-Mg (1:2) layered double hydroxides (LDH) were chemically co-precipitated and widely dispersed on a cheap, commercial Douglas fir biochar (695 m2/g surface area and 0.26 cm3/g pore volume) byproduct from syn gas production. This hybrid multiphase LDH dispersed on biochar (LDHBC) robustly adsorbed (~5h equilibrium) phosphate from aqueous solutions in exceptional sorption capacities and no pH dependence between pH 1–11. High phosphate Langmuir sorption capacities were found for both LDH (154 to 241 mg/g) and LDH-modified biochar (117 to 1589 mg/g). LDHBC was able to provide excellent sorption performance in the presence of nine competitive anion contaminants (CO32–, AsO43−, SeO42−, NO3–, Cr2O72−, Cl−, F−, SO42−, and MoO42−) and also upon remediating natural eutrophic water samples. Regeneration was demonstrated by stripping with aqueous 1 M NaOH. No dramatic performance drop was observed over 3 sorption-stripping cycles for low concentrations (5 ppm). The adsorbents and phosphate-laden adsorbents were characterized using Elemental analysis, BET, PZC, TGA, DSC, XRD, SEM, TEM, and XPS. The primary sorption mechanism is ion-exchange from low to moderate concentrations (10–500 ppm). Chemisorption and stoichiometric phosphate compound formation were also considered at higher phosphate concentrations (>500 ppm) and at 40 °C. This work advances the state of the art for environmentally friendly phosphate reclamation. These phosphate-laden adsorbents also have potential to be used as a slow-release phosphate fertilizer.
As a promising bifunctional electrocatalyst for water splitting, NiFe-layered double hydroxide (NiFe LDH) demonstrates an excellent activity toward oxygen evolution reaction (OER) in alkaline ...solution. However, its hydrogen evolution reaction (HER) activity is challenged owing to the poor electronic conductivity and insufficient electrochemical active sites. Therefore, a three-dimensional self-supporting metal hydroxide/oxide electrode with abundant oxygen vacancies is prepared by electrodepositing CeO x nanoparticles on NiFe LDH nanosheets. According to the density functional theory calculations and experimental studies, the oxygen vacancies at the NiFe LDH/CeO x interface can be introduced successfully because of the positive charges accumulation resulting from the local electron potential difference between NiFe LDH and CeO x . The oxygen vacancies accelerate the electron/ion migration rates, facilitate the charge transfer, and increase the electrochemical active sites, which give rise to an efficient activity toward HER in alkaline solution. Furthermore, NF@NiFe LDH/CeO x needs a lower potential of 1.51 V to drive a current density of 10 mA cm–2 in overall water splitting and demonstrates a superior performance compared with the benchmark Pt/C and RuO2, which is indicated to be a promising bifunctional electrode catalyst.
Oxygen evolution reaction (OER) is a significant half-reaction in varied energy conversion devices. Ni-based layered double hydroxides (LDHs) have attracted immense attention recently for OER. ...Herein, we have provided a comprehensive overview of the recent development of the Ni-based LDHs for OER. We firstly introduced some fabrication strategies and in situ characterization followed by some typical Ni-based LDHs as electrocatalysts for OER. Then the structure modifications such as exfoliation, layer composition tuning, interlayer space adjustment and integrating Ni-based LDHs with complementing functional materials were overviewed. Some obstacles that hinder the practical applications of Ni-based LDHs were also discussed and it was pointed out that more efforts should be given to structure rational design and the catalyst application in the real water electrolysis technique. This review can help readers understand the recent development of the Ni-based LDHs and get some insights into the rational design of Ni-based LDHs catalyst and catalytic performance improvement strategy.
TOC:. Display omitted
•Ni-based LDHs were reviewed for oxygen evolution reaction.•Fabrication strategy and in situ characterization overview for some typical Ni-based LDHs materials.•Structure modification and activity correlation for Ni-based LDHs materials.•Problems and challenges for practical application of Ni-based LDHs.
Layered double‐hydroxide (LDH) has been considered an important class of electrocatalysts for the oxygen evolution reaction (OER), but the adsorption‐desorption behaviors of oxygen intermediates on ...its surface still remain unsatisfactory. Apart from transition‐metal doping to solve this electrocatalytic problem of LDH, rare‐earth (RE) species have sprung up as emerging dopants owing to their unique 4f valence‐electronic configurations. Herein, the Er is chosen as a RE model to improve OER activity of LDH via constructing nickel foam supported Er‐doped NiFe‐LDH catalyst (Er‐NiFe‐LDH@NF). The optimal Er‐NiFe‐LDH@NF exhibits a low overpotential (191 mV at 10 mA cm−2), high turnover frequency (0.588 s−1), and low activation energy (36.03 kJ mol−1), which are superior to Er‐free sample. Electrochemical in situ Raman spectra reveal the facilitated transition of Ni‐OH into Ni‐OOH for promoted OER kinetics through the Er doping effect. Theoretical calculations demonstrate that the introduction of Er facilitates the spin crossover of valence electrons by optimizing the d band center of NiFe‐LDH, which leads to the GO‐GHO closer to the optimal activity of the kinetic OER volcano by balancing the bonding strength of *O and *OH. Moreover, the Er‐NiFe‐LDH@NF presents high practicability in electrochemical water‐splitting devices with a low driving potential of and a well‐extended driving period.
An effective valence electronic perturbation strategy is proposed for tuning the electrocatalytic performance of NiFe‐layered double hydroxide (LDH) for oxygen evolution reaction (OER) through the construction of the Er‐doped NiFe‐LDH model. The theory analysis and experiment demonstrate that Er doping leads to the GO‐GHO closer to the peak in the kinetic OER volcano for NiFe‐LDH by balancing the scaling relation between *O and *OH.
