Ni-based Layered Double Hydroxides Research Articles

Unraveling the crucial contribution of additive chromate to efficient and stable alkaline seawater oxidation on Ni-based layered double hydroxides

Seawater electrolysis to generate hydrogen offers a clean, green, and sustainable solution for new energy. However, the catalytic activity and durability of anodic catalysts are plagued by the corrosion and competitive oxidation reactions of chloride in high concentrations. In this study, we find that the additive CrO42− anions in the electrolyte can not only promote the formation and stabilization of the metal oxyhydroxide active phase but also greatly mitigate the adverse effect of Cl− on the anode. Linear sweep voltammetry, accelerated corrosion experiments, corrosion polarization curves, and charge transfer resistance results indicate that the addition of CrO42− distinctly improves oxygen evolution reaction (OER) kinetics and corrosion resistance in alkaline seawater electrolytes. Especially, the introduction of CrO42− even in the highly concentrated NaCl (2.5 M) electrolyte prolongs the durability of NiFe-LDH to almost five times the case without CrO42−. Density functional theory calculations also reveal that the adsorption of CrO42− can tune the electronic configuration of active sites of metal oxyhydroxides, enhance conductivity, and optimize the intermediate adsorption energies. This anionic additive strategy can give a better enlightenment for the development of efficient and stable oxygen evolution reactions for seawater electrolysis.

Insights on Ni-based layered double hydroxides for electrochemical supercapacitors: Underlying aspects in rational design and structural evolution

Insights on Ni-based layered double hydroxides for electrochemical supercapacitors: Underlying aspects in rational design and structural evolution

Synthesis of defective Ni-Mn layered double hydroxides nanosheets via alkali-assisted Mo doping for urea electro-oxidation

Urea oxidation reaction (UOR) with favorable thermodynamic potential provides a good application prospect in renewable energy infrastructure. However, the sluggish kinetics caused by 6e- transfer greatly hinders the usage of urea as fuel, efficient catalysts are urgently needed in consequence. In response, alkali-assisted Mo doped into Ni-Mn layered double hydroxides (Mo-NiMnLDH-OH) with laminate structure is synthesized via one-pot hydrothermal method. The alkali-assisted Mo doping contributes the modified morphology and microstructure, the tuned chemical states of Ni and Mn species, simultaneously generates defects and more active sites. The existence of alkali plays a vital role in promoting the Mo doping. Without alkali, the Mo doping should damage the laminate structure, and the chemical states of active sites cannot be efficiently tuned. When used as catalyst for UOR, the current density of 45.3 mA cm−2 and a specific current activity of 1132.8 mA cm−2 mg−1 for Mo-NiMnLDH-OH can be achieved at the potential of 1.623 V (vs. RHE), which is 4-fold higher than that for Ni-Mn layered double hydroxides without doping. Both indirect electrochemical and direct urea oxidation processes occur when using Mo-NiMnLDH-OH as catalyst, and the existence of Mo species will facilitate the occurrence of direct urea oxidation process. This work paves an effective way to synergistically engineer of Mo doping and defects into Ni-based layered double hydroxides for UOR.

Inert Mg Incorporation to Break the Activity/Stability Relationship in High-Entropy Layered Hydroxides for the Electrocatalytic Oxygen Evolution Reaction

Ni-based layered double hydroxides (LDHs) have been demonstrated as the most active catalyst for the oxygen evolution reaction in alkaline media but suffer from poor stability. Herein, we report the rational breaking of the activity/stability trade-off by a strategy of inert Mg-involved high-entropy coordination. The as-developed high-entropy FeCoNiMg-LDH nanosheets exhibit not only high catalytic activity (302 mV at 100 mA cm–2) but also an unprecedented stability with almost no performance decline at a large current density of 300 mA cm–2. The combined structural investigations and theoretical calculations reveal that the synergistic electronic coupling provides active Ni in desired electronic states, leading to an optimized adsorption energy of intermediates, while the construction of high configuration entropy as well as the formation of the Mg–O interfacial bond can effectively mitigate phase segregation and transformation and thus improve the stability. The current insights into unveiling the composition–activity–stability of high-entropy coordination may provide valuable guidance for the design of catalysts for various electrochemical reactions.

Optical modulation properties of the Ni-based layered double hydroxides for dual-wavelength Q-switched Er:YAP laser at 2.7 μm

The Nickel-vanadium layered double hydroxide (NiV-LDH) saturable absorber (SA) and the Nickel-cobalt layered double hydroxide (NiCo-LDH) SA were fabricated based on the liquid-phase exfoliation (LPE) method. The nonlinear optical modulation properties at 3 μm of the these two different SAs were investigated for the first time. The dual-wavelength Q-switched Er:YAP lasers at 2.7 μm were realized with the Ni-based LDH SAs. The shortest pulse duration of the generated dual-wavelength laser pulses was 141 ns with the peak power of 6.05 W and the repetition rate of 295 kHz, under the absorbed pump power of 4.8 W. The experimental results indicate the Ni-based LDHs can be the promising optical modulators for the 3-μm pulsed laser generation.

In situ coupled nickel-based layered double hydroxides with MXene to enhance supercapacitor performance

Sandwich-like Ti3C2@LDHs were synthesized in a hydrothermal manner. The mass-specific capacitance of Ti3C2@NiV-LDHs and Ti3C2@NiCo-LDHs composite electrodes were improved thanks to the excellent electrical conductivity of Ti3C2.

Modulation of Trivalent/Tetravalent Metallic Elements in Ni-Based Layered Double Hydroxides for Photocatalytic CO2 Reduction.

Herein, by modulating trivalent/tetravalent metallic elements, NiMLDHs (M = Al, Co, Fe, Mn, and Ti) were successfully prepared and evaluated in photocatalytic CO2 reduction reaction (PCRR). Photocatalytic results declared that the electronic yields followed the order of NiTiLDH > NiCoLDH > NiFeLDH > NiMnLDH > NiAlLDH. Multiple characterizations affirmed that the introduction of various trivalent/tetravalent metallic elements could visibly affect the three critical aspects: (i) light harvesting; (ii) charge separation and transfer; and (iii) surface reactions, thus governing PCRR performance. Importantly, an in-depth mechanistic investigation was conducted by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments. These layered double hydroxides (LDHs) exhibited different adsorption/activation behaviors toward CO2 molecule: NiAlLDH primarily converted CO2 into b-CO32- species; NiCoLDH, NiFeLDH, and NiMnLDH could induce c-CO32- intermediate; NiTiLDH could generate a higher proportion of •CO2- species, which was an important intermediate to produce CO. More favorable carries separation and adsorption/activation process was presented upon NiTiLDH, thus more markedly enhancing photoactivity.

Hydroxyl vacancies triggered high methanol oxidation activity of monolayered layered double hydroxides for energy-saving hydrogen production

Monolayered Ni-based layered double hydroxides (LDHs) enriched with hydroxyl vacancies are synthesized and first applied in the methanol-assisted energy-saving hydrogen production system including independent electrolysis and photovoltaic-electrolysis. The rich hydroxyl vacancies are revealed to endow monolayered LDHs with significantly superior performance in the aspects of the activity for methanol oxidation reaction and the boosting effect for cathodic hydrogen production compared to the bulk counterparts. The theoretical and experimental results confirm that the hydroxyl vacancies can increase density of states near Fermi level of LDH (i.e. elevate electrical conductivity to form favorable charge transportation during electrocatalysis), and promote its adsorption and further cleavage for methanol, thus leading to the enhanced methanol oxidation reaction performance.

Facile synthesis of Ni-based layered double hydroxides with superior photocatalytic performance for tetracycline antibiotic degradation

The purpose of this study was to investigate the photocatalytic performance of Ni-based layered double hydroxides (LDHs) in degradation of tetracycline (TC) as a model antibiotic pollutant. Two kinds of Ni-based LDHs (NiFe-LDH and NiCr-LDH) with chloride and carbonate ions in the interlayer region were facile fabricated by chemical co-precipitation method at room temperature and characterized using Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy disperse spectroscopy (EDS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) techniques. The results showed that the as-prepared LDHs materials performed superior photocatalytic efficiency to eliminate TC from aqueous water solution under UV–vis light irradiation. The photocatalytic efficiency depends on the catalyst dosage and TC concentration. Furthermore, the plausible photocatalytic degradation mechanism was proposed by means of radical trapping and electron spin resonance (ESR) tests. It is found that the photocatalytic degradation of TC by Ni-based LDHs follows an oxygen-induced pathway, and the superoxide radical (•O2−) and hydroxyl radical (•OH) play a major role in the photocatalytic degradation process. The study provided a valuable insight into fabricating high-performance and environmentally friendly LDHs for removal of antibiotics in waste water.

Cu-doped Ni-LDH with abundant oxygen vacancies for enhanced methyl 4-hydroxybenzoate degradation via peroxymonosulfate activation: key role of superoxide radicals

Oxygen vacancies (OVs) were introduced into Ni-based layered double hydroxides (LDHs) through Cu doping, and the catalytic performance of the resulting NixCu-LDHs were investigated for peroxymonosulfate (PMS) activation and methyl 4-hydroxybenzoate (MeP) degradation. Compared with that of Ni-LDH, the catalytic performance of NixCu-LDHs were significantly enhanced and increased with increasing OV content in the catalysts, indicating that Cu doping introduced OVs into NixCu-LDHs and greatly improved their catalytic activity with PMS. Quenching experiments and EPR analyses confirmed that oxidation processes dominated by superoxide radicals (O2•−) and singlet oxygen (1O2), rather than sulfate radicals (SO4•−) or hydroxyl radicals (•OH) used by traditional LDH catalysts, were responsible for MeP degradation by Ni15Cu-LDHs. In addition, quenching experiments with different systems showed the fate of reduced SO4•−and •OH, and demonstrated that O2•− and 1O2 concentrations grew with increasing OV content, confirming that the presence of OVs affected the process of PMS activation. Notably, O2•− mainly originated from adsorbed oxygen or dissolved oxygen (DO) by acquiring electrons from OVs in Ni15Cu-LDHs, since OVs possess abundant localized electrons. Consequently, an OV-mediated oxidative mechanism was proposed for Ni15Cu-LDHs/PMS. This study provides new clues for enhancing the catalytic performance of LDH catalysts by introducing OVs via metal doping in PMS-based AOPs systems.

Designing bimetallic Ni-based layered double hydroxides for enzyme-free electrochemical lactate biosensors

Lactate concentration in the human body is the crucial index to be monitored for evaluating exercise levels under anaerobic metabolism conditions. To solve the unstable nature of enzymes in biosensors for lactate detection, in this study, Ni-based layered double hydroxide (LDH) with various secondary transition metals (Fe and Co) was proposed as electrocatalysts in an enzyme-free electrochemical lactate sensor. According to the mechanism of lactate oxidation on the transition metal-based electrocatalyst, secondary transition metal of Co could serve as the active site for lactate oxidation and facilitate the adsorption of OH− in the alkaline electrolyte. After exploring the influence of secondary metal in Ni-based LDH, NiCo LDH modified screen-printed carbon electrodes (SPCEs) reached the high sensitivity of 30.59 ± 0.34 μA mM-1 cm-2 at an applied potential of 0.55 V (vs. Ag/AgCl KCl sat’d) in the concentration range from 5 to 25 mM, which is relatively higher than pristine Ni LDH (23.51 ± 0.45 μA mM-1 cm-2) and NiFe LDH (3.03 ± 0.06 μA mM-1 cm-2). This study proposes a new category of electrocatalyst to be utilized in enzyme-free electrochemical lactate sensors with reliable and stable performance as one of the non-invasive biosensors.

Effect of Binding Affinity of Crystal Water on the Electrochemical Performance of Layered Double Hydroxides.

The ever-increasing demand for safe batteries has driven research efforts to develop aqueous rechargeable batteries. In this regard, Ni-based layered double hydroxides (LDHs) have received marked attention owing to their adequate operating potential, high specific capacity, and decent cycling performance. Nevertheless, the effect of immobile intercalants (e. g., crystal water and anions) that are inherently present in the interlayer galleries is barely understood. In this paper, we report that the electrochemical performance of LDH largely depends on the extent to which the crystallinity is affected by the binding strength of crystal water to the transition metal slabs. A series of infrared spectroscopy and in-situ X-ray absorption analyses reveal that the lattice disordering in LDHs is beneficial for accommodating the stress during the (de)intercalation of carrier ions, which serves as the origin of their superior specific capacities and cycle life. This study presents a useful structure-property relationship of the way in which the binding affinity of crystal water affects the key electrochemical properties of the host electrode materials.

Hydrogen production via water-gas shift reaction over gold supported on Ni-based layered double hydroxides

Co-precipitated NiAl and NiMgAl layered double hydroxides (LDHs) were prepared at M2+/Al3+ molar ratio of 2.5/1 and subsequently promoted with gold targeting to be studied as catalysts and supports of gold particles in the hydrogen production via water-gas shift (WGS) reaction. Powder X-ray diffraction and N2 physisorption before and after WGS tests were applied to investigate the impacts of Mg and Au on the structure and catalytic behavior of the systems. Partial replacement of Ni by Mg resulted in moderate activity of NiMgAl and Au/NiMgAl catalysts than NiAl analogues due to: (i) smaller Ni amount that could not supply sufficient number catalytically active sites; (ii) higher thermal stability leading to the creation of the active Ni species at higher temperatures, and (iii) partial regeneration of the layered structure with the assistance of small Au particles, Mg, and the reaction medium as well. Favorable role of gold on Au/NiAl WGS activity was elucidated.

High-performance flexible hybrid supercapacitor based on NiAl layered double hydroxide as a positive electrode and nitrogen-doped reduced graphene oxide as a negative electrode

Herein, we investigated the influence of Fe, Cr and Al incorporation in Ni-based layered double hydroxides (LDHs) supported on nickel foam (NF) electrodes, prepared through a one-step hydrothermal, on their electrochemical performance. The resulting NiFe, NiCr and NiAl (LDHs) were further coated on carbon spheres (CS) supported on NF using a facile two-step hydrothermal process to produce NiFe LDHs@CS/NF, NiCr LDHs@CS/NF and NiAl LDHs@CS/NF. The performance of the prepared materials as binder-free electrodes in supercapacitors was assessed. Among all the prepared electrodes, NiAl LDHs@CS/NF electrode material achieved the largest areal capacity (1042.2 mC cm−2 at 1 mA cm−2), as compared to the areal capacity values attained by NiFe LDHs@CS/NF (705.8 mC cm−2) and NiCr LDHs@CS/NF (814.9 mC cm−2) at 1 mA cm−2. Therefore, a hybrid supercapacitor device comprising NiAl LDHs@CS/NF as the positive electrode and N-doped reduced graphene/NF as the negative electrode was successfully fabricated. The device exhibited favorable flexibility, good mechanical properties and stability; the areal capacity remained ∼75% and ∼67% of the original value after 5000 and 10,000 cycles, respectively. The hybrid supercapacitor attained an energy density of 43 μWh cm−2 at a power density of 0.805 mW cm−2 and was applied successfully to operate a home-made windmill device continuously for 32 s. Moreover, two flexible NiAl LDHs@CS/NF//N-rGO/NF hybrid supercapacitors, connected in series, were able to light up a green, a red and a yellow LED in parallel, lasting for 37 s, 542 s and 199 s, respectively, indicating their potential application for flexible energy storage devices.

Effect of low loading of yttrium on Ni-based layered double hydroxides in CO2 reforming of CH4

Ni/Al/Mg layered double hydroxides (LDHs) modified with low loading of yttrium (0.2 and 0.4 wt%) were used in dry reforming of methane at 700 °C. Physicochemical characterization, such as: X-ray fluorescence, N2 sorption, X-ray diffraction, temperature programmed reduction in H2, temperature programmed desorption of CO2, H2 chemisorption, thermogravimetry analysis coupled by mass spectrometry and Raman spectroscopy, showed that the introduction of low loadings of yttrium lead to a smaller Ni° crystallite size, a decrease in reducibility of the nickel, and a decreased number of basic sites in the modified Ni/LDHs catalysts. The doping with 0.4 wt% of Y improves catalytic activity resulting in higher CH4 and CO2 conversions at 700 °C, i.e., ca. 84% and ca. 87%, respectively with no clear deactivation observed after 5 h run. The increase in CO2 conversion and a decrease of H2/CO ratio indicates that side reactions occurs during DRM.

Enhanced degradation of an azo dye by catalytic ozonation over Ni-containing layered double hydroxide nanocatalyst

• For the first time catalytic activity of Ni-based LDH was studied in ozonation. • Catalytic degradation of methyl orange showed a COD removal of 72%. • Ozone-Ni ions interaction on catalyst surface generated active complexes. • Active complexes are the key for achieving such high catalytic performance. The catalytic activity of Ni-based layered double hydroxides (Ni-LDHs) nanomaterials was studied for the first time in ozonation of simulated dyeing wastewater for dye degradation (methyl orange (MO)). For the purpose of comparison, degradation of MO by non-catalyzed ozonation was also considered. The degradation experiments were performed in a laboratory scale cylindrical batch reactor. The effect of catalyst was studied using UV–Vis, chemical oxygen demand (COD) and ion chromatography (IC) analyses. The influence of various operating factors such as reaction temperature, dye concentration, catalyst dosage and hydroxyl radical scavengers (bicarbonate-carbonate) on the MO dye degradation rate were investigated. The catalytic ozonation exhibits total discoloration with faster reaction rate and clearly enhances the COD removal. In optimized conditions, after 60 min reaction, COD removal has reached 72% in the catalytic ozonation process, while it reached only 30% in non-catalytic ozonation. Additionally, the characterization results of Ni-LDH catalyst before and after ozonation experiments were discussed. A possible mechanism of degradation was suggested.

Theoretical and Experimental Study on MIIMIII-Layered Double Hydroxides as Efficient Photocatalysts toward Oxygen Evolution from Water

Recently, layered double hydroxides (LDHs) have attracted extensive attention in the field of energy storage and conversion, and an in-depth understanding of their semiconducting properties is rather limited. In this work, the electronic properties (band structure, density of states (DOS), and band edge placement) of MIIMIII-LDHs (MII = Mg, Co, Ni and Zn; MIII = Al and Ga) were studied in detail. The thermodynamic mechanism toward oxygen evolution reaction (OER) was investigated by using the density functional theory plus U (DFT + U) method. The calculation results of band structure indicate that Mg and Zn-based LDHs (band gap energies larger than 3.1 eV) are ultraviolet responsive, while Co and Ni-based LDHs are responsive to visible light (band gap energies less than 3.1 eV). The DOS calculations reveal that the photogenerated hole localizes on the surface hydroxyl group of LDHs, facilitating the oxidization of a water molecule without a long transportation route. The band edge placements of MIIMIII-LDH...

Tunable composition of Ni II–Al III and Ni II–Fe III layered hydroxides within a wide range of layer charge

In this paper we investigated the particular behaviour of the nickel ion to serve as divalent cations for M II/Fe III and M II/Al III layered double hydroxides. To this end, we showed by careful TEM/EDX, PXRD and infrared analysis the possibility to accurately tune the composition of Ni-based layered double hydroxides in the range 0.09 ≤ M III/(Ni II + M III) ≤ 0.33. The morphology of the crystals was strongly correlated to the net charge of the layer. Finally, we confirmed the trends of structural parameters observed in literature for other M II/M III LDHs synthesized in narrower ranges of composition.