Highly dispersed ultrafine Pt nanoparticles on nickel-cobalt layered double hydroxide nanoarray for enhanced electrocatalytic methanol oxidation

Highly dispersed ultrafine Pt nanoparticles (NPs) were loaded on a nickel-cobalt layered double hydroxide (NiCo-LDH) nanoarray that was grown on Ni foam (NF) via an in situ redox reaction without any external agent between Co²⁺ (Co(OH)₂) in NiCo-LDH and PtCl₆^2-. The obtained Pt/NiCoLDH/NF composite was used as a catalyst for methanol oxidation in alkaline media, showing much higher electrocatalytic activity and better anti-poisoning ability and stability for methanol oxidation than commercial Pt/C, mainly because of the uniform dispersion of ultrafine Pt NPs, the synergistic effect and stable support of NiCoLDH. The NiCoLDH nanoarray effectively increased the specific surface area and location sites for supporting Pt NPs and enhanced the catalytic performance and tolerance to intermediate species. This enhancement was probably due to the synergistic effect between Pt and the NiCo-LDH nanosheets, in which the LDH can provide adequate OH^?_ads species for accelerating the methanol oxidation reaction (MOR).     

Defective layered double hydroxide formed by H2O2 treatment act as highly efficient electrocatalytic for oxygen evolution reaction

Electrocatalytic reaction is the important electrode reaction for many new generation electrochemistry energy and storage devices. However, the poor reaction kinetics of those electrode reaction severely restricts its application. Highly efficient electrocatalyst is essential to resolve the problem of commercial application of those electrochemistry energy and storage devices. Herein, by simple H₂O₂ treatment, the highly efficient CoFe-Layered Double Hydroxides (LDHs) electrocatalysts with multiple defects have been synthesized (noted as D-LDHs). The D-LDHs show a low overpotential of 283 mV at 10 mA cm⁻² and small Tafel slope of 39 mV dec⁻¹ for the oxygen evolution reaction (OER). The work offers a new strategy to create defects in LDHs as highly efficient electrocatalysts for OER.     

Ultrathin NiZrAl layered double hydroxide nanosheets derived catalyst for enhanced CO2 methanation

It is challenging to fabricate supported Ni catalysts with more active sites to improve their low-temperature catalytic performance in CO₂ methanation. Herein, firstly, ultrathin (～4 nm) NiZrAl layered double hydroxide (LDH) nanosheets were synthesized by co-precipitation method, followed by aqueous miscible organic solvent treatment (AMOST), and applied as catalyst precursors for CO₂ methanation. After H₂ reduction, the surface area of Ni particles in NiZrAl-LDH-AMO-R was significantly higher than that of NiZrAl-LDH-R without AMOST. As a result, the NiZrAl-LDH-AMO-R showed higher catalytic activity than NiZrAl-LDH-R owing to its higher H₂ and CO₂ chemisorption capacity and lower activation energy. During the 100 h-lifetime test, NiZrAl-LDH-AMO-R maintained a steady CO₂ conversion of about 92.3%. Moreover, NiZrAl-LDH-AMO-R maintained its catalytic activity after a 600 °C-hydrothermal treatment, suggesting its high stability. In situ DRIFTS results reveal that CO₂ methanation on both NiZrAl-LDH-R and NiZrAl-LDH-AMO-R followed the HCOO1 route. Interestingly, more active sites obtained after AMOST strongly promoted the generation and decomposition of HCOO1, and thus significantly improved the activity of NiZrAl-LDH-AMO-R at low temperatures.     

NiCo layered double hydroxide/hydroxide nanosheet heterostructures for highly efficient electro-oxidation of urea

Urea oxidation is an important reaction for direct urea fuel cells as well as hydrogen production and/or water remediation via electrolysis using urea-rich wastewater. The key to efficient urea oxidation is to explore a well-designed high-performing catalyst. Herein, NiCo layered double hydroxide/hydroxide (NiCo LDH/NiCo(OH)₂) microspheres composed of ultrasmall nanosheets have been grown on Ni foam by a solution method at room temperature. The NiCo LDH/NiCo(OH)₂ heterostructures have been confirmed by TEM and XRD analysis. The high activity with a small onset potential of 0.29 V vs. Hg/HgO is mainly attributed to the rich NiCo LDH-NiCo(OH)₂ interfaces and the bimetallic nature of the catalysts. The NiCo LDH/NiCo(OH)₂ heterostructures can be promising catalysts for urea oxidation and offer new insights into the design of high-performance nickel-based catalysts.     

Electrochemical properties of nickel-aluminum layered double hydroxide/carbon composite fabricated by liquid phase deposition

Nickel-aluminum layered double hydroxide/carbon (Ni-Al LDH/C) composites have been fabricated using a mixed solution of {Al(NO₃)₃·9H₂O and H₃BO₃} as fluoride scavengers in the liquid phase deposition (LPD) process. The amount of divalent Ni²⁺ substituted by trivalent Al³⁺ within the lattice of α-Ni(OH)₂ was controlled by the concentration of Al(NO₃)₃·9H₂O solution. X-ray diffraction studies reveal pure phase Ni-Al LDH, isostructural and isomorphic to α-Ni(OH)₂ with higher interlayer distance. The electrochemical properties of the cathode materials containing 0, 8.6, 13.8, 17.8, 21.3 and 23.4 Al% were evaluated by the means of charge-discharge and cyclic voltammetry measurements. The overall comparison indicates that Ni-Al LDH/C composites have higher electrochemical performance than pure α-Ni(OH)₂/C composite. The cathode with 17.8 Al% exhibits the best performance at 1 C compared to other Al³⁺ contents; a much lower voltage plateau, well separated from the oxygen evolution at the end of the charging as well as a single flat and high discharge plateau with a discharge capacity of 376.9 mAh g_comp⁻¹. Short term durability test for 80 cycles showed that the electrode containing 13.8 Al% has the highest discharge rate at 2 C. The range of Al substitution 13.8-17.8 Al% provides a good electrochemical response.     

MoSe2 regulates Ce-doped NiFe layered double hydroxide for efficient oxygen evolution reaction: The increase of active sites

Oxygen evolution reaction (OER) is a common reaction in many sustainable energy conversion systems. However, it has become a bottleneck in the development of sustainable energy conversion systems because of its slow kinetics, especially in the common electrolytic water reaction. At present, although there are a lot of researches on OER's catalysts, it is still a great challenge. In this work, a new type of composite was prepared by simple co-precipitation method and Hydrothermal, which is composed of Ce-doped NiFe Layered Double Hydroxide (LDH) and MoSe₂. The electrochemical test results of OER show that the overpotential of 6.7%Ce–NiFe LDH@MoSe₂ is 221 mV at 10 mA/cm², which is better than that of NiFe LDH (409 mV). And it is better than most of the reported OER catalysts in literature, including precious metal catalysts. Simultaneously, 6.7%Ce–NiFe LDH@MoSe₂ also has smaller Tafel slope (35.8mV/dec), larger ESCA (6689 cm²), long-time stability and selectivity with 92.1% Faraday efficiency. The excellent OER performance of 6.7%Ce–NiFe LDH@MoSe₂ benefits from the increase of active and defective sites and the interface coordination between MoSe₂ and Ce–NiFe LDH.     

Facile layer-by-layer self-assembly of 2D perovskite niobate and layered double hydroxide nanosheets for enhanced photocatalytic oxygen generation

Photocatalytic O₂-generation reaction is recognized as a crucial step in water splitting and has drawn great attention of researchers. In this work, a hetero-layered composite photocatalyst was successfully prepared by a facile self-assembly method based on electrostatic interaction between oppositely charged Zn/Cr-layered double hydroxide (Zn/Cr-LDH) and lead niobate nanosheets. The layer-by-layer stacking of Zn/Cr-LDH and HPb₂Nb₃O₁₀ nanosheets was beneficial for rapid migration of photo-induced charge carriers inside the photocatalyst because of large contact area. In the meantime, Zn/Cr-LDH and HPb₂Nb₃O₁₀ components exhibited suitable energy-band alignment, which led to efficient separation of photo-induced charge carriers. The composite photocatalyst showed enhanced photocatalytic O₂-generation activity under visible-light irradiation without loading cocatalyst. Briefly, this work expanded the applications of AB₂Nb₃O₁₀-based materials in photocatalytic energy conversion and proved that constructing composites based on electrostatic self-assembly of complementary 2D materials is a promising strategy for development of more efficient photocatalysts.     

Gold nanoparticle-coated Ni/Al layered double hydroxides on glassy carbon electrode for enhanced methanol electro-oxidation

We report a facile electrochemical strategy for the synthesis of Ni/Al layered double hydroxides (LDHs) and gold nanoparticle (AuNPs)-coated glassy carbon electrode (GCE). The new electrode is named LDH/AuNPs/GCE. The new electrode is named LDH/AuNPs/GCE. The electrocatalytic activity of LDH/AuNPs toward methanol electro-oxidation was studied by cyclic voltammetry and chronoamperometry. Compared to the Ni/Al-LDH modified GCE without AuNPs film (LDH/GCE), the LDH/AuNPs/GCE exhibits remarkably higher catalytic activity for methanol electro-oxidation, e.g. the lower oxidation potential (0.57 V vs. SCE) and the higher current density (6-fold). The enhancement may be attributed to the higher electrocatalytic activity of Ni/Al-LDHs in the presence of AuNPs, the synergy effect between them, or both. The results presented here may be of broad interest not only for developing fuel cells but also for understanding of OH⁻ electro-generated on noble metal surfaces.     

In situ growth of NiCoFe-layered double hydroxide through etching Ni foam matrix for highly enhanced oxygen evolution reaction

It is of great significance to develop the nonprecious metal oxide electrocatalysts toward oxygen evolution reaction (OER) for water splitting. Herein we report an in-situ growth of the ternary NiCoFe-layered double hydroxide nanosheets on surface etching nickel foam (NiCoFe LDHs/NF) without adding any nickel precursor. In this method, etching Ni matrix by Fe³⁺ not only provides the slowly released nickel ions, but also intensifies the Fe–Ni interaction between the directly grown active species and Ni foam. Therefore the composition, electronic structure, and morphology of the electrocatalysts can be easily regulated only by adjusting Co²⁺:Fe³⁺ ratio in the precursor solution. The obtained NiCo₁Fe₁ LDH/NF, which is formed in 1:1 Co²⁺:Fe³⁺ solution, has highest content of Ni³⁺ and Co³⁺ active sites and the largest electrochemical active area. It exhibits an outstanding OER performance with a small overpotential of 231 mV at 10 mA cm^?2 and excellent durability at 50 mA cm^?2 in 1.0 M KOH solution.     

K (Na)-promoted Ni,Al layered double hydroxide catalysts for the steam reforming of methanol

Production of hydrogen by methanol steam reforming has been studied over a series of Ni/Al layered double hydroxide catalysts prepared by the co-precipitation method, with the aim to develop a stable catalyst that can be used in a membrane-joint performer at temperatures greater than 300 °C. H₂, CO and CO₂ are generally the major products together with trace amounts of CH₄. The presence of potassium and/or sodium cations was found to improve the activity of methanol conversion. The selectivity for CO₂ rather than CO was better with K ions than Na ions, especially at higher temperatures (e.g. 390–400 °C). Methanol steam reforming over a K-promoted Ni/Al layered double hydroxide catalyst resulted in better activity and similar stability compared to a commercial Cu catalyst.     

In situ direct growth of flower-like hierarchical architecture of CoNi-layered double hydroxide on Ni foam as an efficient self-supported oxygen evolution electrocatalyst

Exploring economical, efficient and robust electrocatalysts toward the oxygen evolution reaction (OER) is one of the key issues in water splitting technology. Nanostructure engineering of electrocatalysts and hybridizing active species with a conductive support represent powerful strategies to enhance the electrocatalytic performance. Herein, we report a facile one-step solvothermal method to directly grow 3D CoNi-layered double hydroxide (LDH) flower-like architectures onto porous and conductive Ni foam (NF) substrate (denoted as CoNi-LDH(2:1)@NF hereafter). The flower-like hierarchical architecture of CoNi-LDHs with open configurations endows CoNi-LDH microflowers with sufficient accessible active sites and efficient mass diffusion paths. Moreover, the in situ direct growth manner ensures an intimate contact between the electroactive CoNi-LDHs and NF substrate and thus the charge transfer resistance is reduced. Consequently, the as-formed self-supported and binder-free electrode of CoNi-LDH(2:1)@NF exhibits an outstanding OER performance with a small overpotential of 283 mV at a relatively large current density of 50 mA cm⁻² and a remarkable long-term electrochemical durability in 0.1 M KOH solution, holding great promise in practical scale-up water electrolysis. The present study may open a new avenue to design and fabricate cost-effective and high-efficiency electrocatalysts for energy conversion applications.     

Enhanced electrocatalytic methanol oxidation properties by photo-assisted Fe2O3 nanoplates

In this paper, visible-light-driven two-dimensional (2D) Fe₂O₃ nanoplates with exposed (001) facets were first adopted to act as Pt support for photo-assisted electrocatalytic methanol oxidation. Under simulated solar light and visible light illumination Pt-2D Fe₂O₃ nanoplates displayed 2.32 and 1.30 times higher electrocatalytic activities for methanol oxidation than in dark condition, respectively. Besides, 2D Fe₂O₃ nanoplates owns much better electrocatalytic activities for methanol oxidation than Fe₂O₃ particles whether in dark, visible light or simulated solar light illumination. The nice photo-assisted electrocatalytic methanol oxidation activities of Pt-2D Fe₂O₃ nanoplates can be attributed to 2D structure enhanced the oxidation activities of photogenerated holes to oxidize OH⁻ to hydroxyl radical (·OH) as well as its large specific surface area. Our experimental results suggest that photo-assisted and two-dimensional strategy of semiconductors are promising ways to further improve the electrocatalytic activities for methanol oxidation in DMFCs.     

Preparation of a novel Pd/layered double hydroxide composite membrane for hydrogen filtration and characterization by thermal cycling

A layered double hydroxide (LDH) layer was grown directly on a porous stainless steel (PSS) surface to reduce the pore opening of the PSS and to be a middle layer retarding Pd/Fe interdiffusion. A thin Pd film (∼7.85 μm) was plated on the modified PSS tube by an electroless plating method. A helium leak test proved that the thin Pd on the LDH-modified PSS substrate was free of defects. The membrane had a H₂ flux of 28–36 m³/(m² h) and H₂/He selectivity larger than 2000 at a pressure difference of 1 bar. Thermal cycling between room temperature and 673 K was performed and showed that the membrane exhibited good permeance and selectivity. Long-term evaluation (1500 h) of the membrane at 673 K showed static results of H₂ flux (∼30 m³/(m² h)) and H₂/He selectivity (∼2000) over the 1500 h test period.     

Recent advancements of layered double hydroxide heterojunction composites with engineering approach towards photocatalytic hydrogen production: A review

Photocatalytic hydrogen production has been considered as one of the most promising alternatives for providing clean, sustainable, and renewable energy sources. Tremendous investigation and efforts have been devoted to increase the efficiency of the solar to energy conversion of a photocatalyst. Layered double hydroxide (LDH) received scientific attention for its excellent compositional flexibility and controllable morphology, leading to the facile incorporation of the metal species into their layered structure. The unique multi-structure and the tunability of its band gap make LDH more prominent in the field of photocatalysis. This article highlights the recent developments in the fabrication of LDH-based photocatalyst nanocomposites and the engineering approaches for augmenting their photocatalytic hydrogen production efficiency. The thermodynamics and challenges in photocatalytic water splitting are deliberated to understand the pathways to construct efficient semiconductor photocatalysis system. The efficiency enhancement of LDH-based photocatalysts are comprehensively discussed by giving special attention to the heterojunction engineering of type I, type II, p-n junction, Z-scheme, S-scheme, and R-scheme. Fabrication of the hybrid LDH nanocomposites through band gap engineering and metal loading are summarised. The architectural and morphological tuning of LDH-based composite through the construction of the novel core-shell structure and layer-by-layer nanosheets are also demonstrated. Finally, the future recommendations are outlined to provide insights for their development in the photocatalysis field.     

Mesoporous silica template-derived nickel-cobalt bimetallic catalyst for urea oxidation and its application in a direct urea/H2O2 fuel cell

Ni-based catalysts are considered as an efficient anode material for urea fuel cells due to the low cost and high activity in alkaline media. Herein, we demonstrate that Ni-Co bimetallic hydroxide particles with highly porous nanostructures can be synthesized using mesoporous silica nanoparticles as templates. The replicated nanostructures of the Ni-Co hydroxide samples from the mesoporous silica templates are observed. The porous Ni_0.8Co_0.2(OH)₂ particles exhibited considerably enhanced electro-catalytic activity for urea oxidation reaction by providing a high surface area and fast mass transport for urea oxidation reaction. It is also found that the Co-doping at 20% significantly reduce the overpotential and increase the peak current of urea oxidation reaction. A direct urea/H₂O₂ fuel cell with the porous Ni_0.8Co_0.2(OH)₂ as anode material shows an excellent performance with maximum power densities of 11.2 and 25.6 mW cm⁻² at 20 °C and 70 °C with 0.5 M urea in 5 M KOH, respectively. Thus, this work suggests that the highly porous Ni_0.8Co_0.2(OH)₂-derived from the mesoporous silica templates can be used for urea oxidation and as an efficient anode material for urea-based fuel cells.     

Metal-introduced NiCuAl-LDH using chelating agent for steam reforming of methanol

In this study, we focus on NiCuAl-LDH and introduce various metal ion species (Ga, Ni, Fe, Nd, Zn, Mg, and Cu) using a chelating agent into calcined NiCuAl-LDH. We obtained a maximum methanol conversion of 82.6% and H₂ yield of 53.5%. In addition, we found that the metal surface area of Ni and Cu increased compared to NiCuAl-LDH. On the other hand, results demonstrated that the presence of Ni(OH)₂ and Cu(OH)₂ on the catalyst surface had a positive effect on the MSR. We also tested the catalytic stability, introducing Cu by EDTA into calcined NiCuAl-LDH.     

Facile synthesis of nanometer-sized NiFe layered double hydroxide/nitrogen-doped graphite foam hybrids for enhanced electrocatalytic oxygen evolution reactions

We report a self-standing NiFe layered double hydroxide/nitrogen doped graphite foam (NiFe LDH/NGF) electrode for the oxygen evolution reaction (OER) prepared via a facile electrodeposition method. The electrode showed high electrocatalytic activity towards OER, exhibiting a low onset overpotential of 0.239 V and a small Tafel slope of 57.9 mV dec^?1 in basic electrolytes, as well as a good stability during the long-term cycling test. The outstanding electrocatalytic activity is mainly attributed to the synergy between the abundant catalytically active sites through good dispersion of NiFe LDH across NGF and fluent electron transport arising from NGF.     

CuAl layered double hydroxide as a highly efficient electrocatalyst for the electrolysis of water into hydrogen and oxygen fuels

The production of green H₂ through water electrolysis processes has become a prominent technology to deal with energy and environmental crisis worldwide. The total energy consumption of electrolysis processes can be reduced by the development of low-cost electrocatalysts. In this paper, we report first time the synthesis of a highly efficient 2D CuAl LDH electrocatalyst to produce the green H₂. The electrocatalyst was characterized with the help of various analytical instruments such as FT-IR, XRD, BET, TGA, ICP-OES, and XPS. The morphological characterization was done by SEM and TEM. The electrochemical characterization such as CV, LSV, Tafel plot, and EIS was done in acidic, basic, seawater, and alkaline seawater medium. It was found that CuAl LDH electrocatalyst exhibits a good current density of 100 mA/cm² at a potential of 1.178 V in acidic medium and 10 mA/cm² at 1.114V in seawater medium. It was investigated that the CuAl LDH behaves as a bifunctional electrocatalyst and exhibits excellent HER and OER activity in an acidic medium. The effect of temperature on the efficiency of the electrocatalyst under the above electrolyte mediums was also studied. The electrochemical data suggests that the CuAl LDH electrocatalyst can be utilized in an alkaline/PEM electrolyzer to produce the green H₂ at an industrial scale with optimum cost.     

Synthesis and characterization of polysulfone/layered double hydroxides nanocomposite membranes for fuel cell application

In the present study, sulfonated polysulfone (SPSU)/layered double hydroxide (LDH) composite membranes for use in proton exchange membrane fuel cells (PEMFCs) were investigated. Polysulfone (PSU) was sulfonated with trimethylsilyl chlorosulfonate in 1,2 dichloroethane at room temperature.