Anion Exchange Process Research Articles

Engineering Sulfur Vacancies in Spinel-Phase Co3S4 for Effective Electrocatalysis of the Oxygen Evolution Reaction

Restricted by the sluggish kinetics of the oxygen evolution reaction (OER), efficient OER catalysis remains a challenge. Here, a facile strategy was proposed to prepare a hollow dodecahedron constructed by vacancy-rich spinel Co3S4 nanoparticles in a self-generated H2S atmosphere of thiourea. The morphology, composition, and electronic structure, especially the sulfur vacancy, of the cobalt sulfides can be regulated by the dose of thiourea. Benefitting from the H2S atmosphere, the anion exchange process and vacancy introduction can be accomplished simultaneously. The resulting catalyst exhibits excellent catalytic activity for the OER with a low overpotential of 270 mV to reach a current density of 10 mA cm–2 and a small Tafel slope of 59 mV dec–1. Combined with various characterizations and electrochemical tests, the as-proposed defect engineering method could delocalize cobalt neighboring electrons and expose more Co2+ sites in spinel Co3S4, which lowers the charge transfer resistance and facilitates the formation of Co3+ active sites during the preactivation process. This work paves a new way for the rational design of vacancy-enriched transition metal-based catalysts toward an efficient OER.

Characterization and investigation of intermediate stages during anion-exchange reaction between CsPbBr3 and CsPbI3 nanocrystal solution and film via photoluminescence and electroluminescence spectroscopy

All-inorganic cesium-lead-halide CsPbX3 (X = Cl, Br, and I) perovskite nanocrystals (NCs) have attracted great attention due to their outstanding photoelectric properties in recent years. However, the unsatisfactory optical stability and undesirable anion-exchange reaction between different halides of perovskite NCs seriously hinder their further development and application in optoelectronic devices. Herein, the intermediate stages during anion-exchange processes between as-prepared perovskite NCs after mixing into solution and film were respectively studied and characterized by using photoluminescence and electroluminescence (EL) spectroscopy. In our case, the physical collision and solvent bridge effect together affect the anion-exchange reaction of the mixed solution, while the physical collision mechanism is dominant in the mixed film. More importantly, a thin polystyrene layer was inserted between CsPbBr3 and CsPbI3 to efficiently prevent the halogen anion-exchange reaction. Color-tunable EL performance and stable white emission were successfully achieved by employing the optimized CsPbI3/PS/CsPbBr3 structures onto the blue-violet heterojunctions.

Free-Standing Metal Halide Perovskite Nanowire Arrays with Blue-Green Heterostructures.

Vertically aligned metal halide perovskite (MHP) nanowires are promising for various optoelectronic applications, which can be further enhanced by heterostructures. However, present methods to obtain free-standing vertically aligned MHP nanowire arrays and heterostructures lack the scalability needed for applications. We use a low-temperature solution process to prepare free-standing vertically aligned green-emitting CsPbBr3 nanowires from anodized aluminum oxide templates. The length is controlled from 1 to 20 μm by the precursor amount. The nanowires are single-crystalline and exhibit excellent photoluminescence, clear light guiding and high photoconductivity with a responsivity of 1.9 A/W. We demonstrate blue-green heterostructured nanowire arrays by converting the free-standing part of the nanowires to CsPbCl1.1Br1.9 in an anion exchange process. Our results demonstrate a scalable, self-aligned, and lithography-free approach to achieve high quality free-standing MHP nanowires arrays and heterostructures, offering new possibilities for optoelectronic applications.

Amino Acid Complexes of Zirconium in a Carbon Composite for the Efficient Removal of Fluoride Ions from Water.

Amino acid complexes of zirconia represent an entirely new class of materials that were synthesized and studied for the first time for the decontamination of fluoride ion containing aqueous solutions. Glutamic and aspartic acid complexes of zirconia assembled with thin carbon (stacked graphene oxide) platelets deriving from graphite oxide (GO) were synthesized by a two-step method to prepare adsorbents. The characterization of the complexes was carried out using infrared spectroscopy to determine the functional groups and the types of interaction between the composites and fluoride ions. To reveal the mechanisms and extent of adsorption, two types of batch adsorption measurements were performed: (i) varying equilibrium fluoride ion concentrations to construct adsorption isotherms at pH = 7 in the absence of added electrolytes and (ii) using fixed initial fluoride ion concentrations (10 mg/L) with a variation of either the pH or the concentration of a series of salts that potentially interfere with adsorption. The experimental adsorption isotherms were fitted by three different theoretical isotherm equations, and they are described most appropriately by the two-site Langmuir model for both adsorbents. The adsorption capacities of Zr-glutamic acid-graphite oxide and Zr-aspartic acid-graphite oxide are 105.3 and 101.0 mg/g, respectively. We found that two distinct binding modes are combined in the Zr-amino acid complexes: at low solution concentrations, F− ions are preferentially adsorbed by coordinating to the surface Zr species up to a capacity of ca. 10 mg/g. At higher concentrations, however, large amounts of fluoride ions may undergo anion exchange processes and physisorption may occur on the positively charged ammonium moieties of the interfacially bound amino acid molecules. The high adsorption capacity and affinity of the studied dicarboxylate-type amino acids demonstrate that amino acid complexes of zirconia are highly variable materials for the safe and efficient capture of strong Lewis base-type ions such as fluoride.

Effect of time, pH, and temperature on kinetics for adsorption of methyl orange dye into the modified nitrate intercalated MgAl LDH adsorbent

• Nitrate intercalated MA LDH nanopowder was synthesized using coprecipitation method under refluxing condition. • The adsorption of MO dye onto MA LDH reached equilibrium within 1 hour and exhibited saturation adsorption of 583 mg/g. • Adsorption kinetics and isotherm were governed by the pseudo-second-order kinetic model and Langmuir model, respectively. The present work evaluated the potential of nitrate intercalated pristine MgAl layered double hydroxide (MA LDH) powder, for adsorption of methyl orange (MO) dye from an aqueous solution for reducing health hazards. Nitrate intercalated pristine MA LDH was synthesized in the particle size range between 60 and 120 nm by co-precipitation method in nitrogen atmosphere using reflux process. MO dye was adsorbed into MA LDH by the process of anion exchange to promote formation of MO intercalated MA LDH (MAMO LDH). Both MA LDH and MAMO LDH powders were characterized using XRD, FTIR, FESEM, and TGA analysis. In the adsorption process, all effective parameters such as adsorbent dose, adsorption time, temperature, pH, and MO dye concentration were studied in the batch process using UV visible spectroscopy. It was observed that the pH and temperature of the dye solution exerted a major impact on the kinetics of adsorption of MO dye into 10 mg of MA LDH. The adsorption kinetics at different temperatures such as 25, 40, and 50 °C were investigated, and found that pseudo second order kinetic fitted well with the kinetic data. Maximum adsorption percentage of MO dye into MA LDH nanoparticles hardly varied with an increase in temperature as suggested by 98.22% of MO adsorption at 25 °C as opposed to 98.66% adsorption at 40 and 50 °C within a maximum of 1-hour incubation time from 50 ml of aqueous solution containing 0.03 mg/ml of MO dye. Upto three regeneration cycles, nitrate intercalated MA LDH dye showed no significant decrease in adsorption capacity of MO dye from its aqueous solution. The adsorption isotherm was measured at a temperature of 40 °C and indicated that the Langmuir isotherm model fitted well with experimental data with a maximum adsorption capacity of 583 mg/g. Thermodynamic parameters, such as high negative value of ΔG and positive value of ΔH suggested that the adsorption process was spontaneous and endothermic in nature.

Reconstruction and intercalating anion exchange of ZnAl-layered double hydroxide

Layered double hydroxides (LDHs) have recently attracted considerable attention as a promising multi-functional material due to their controllable properties depending on the type and composition ratio of metal cations and interlayer anions. Despite active research on controlling the composition to improve the properties of LDHs, anion intercalation techniques capable of obtaining the desired morphologies of LDHs have rarely been investigated. Herein, we report the anion exchange of ZnAl-LDHs grown on a silicon substrate using a post-treatment-based reconstruction process. Structural and chemical investigations verified that the calcined ZnAl-LDH was reconstructed by a NaCl solution during the anion exchange process. The anion exchange rate and the reconstructed fraction of the ZnAl-LDH increased as the NaCl concentration increased from 0.15 M to 0.60 M, though they decreased when the NaCl concentration exceeded 0.90 M. Therefore, the anion composition and morphology of the ZnAl-LDHs could be modulated by controlling the NaCl concentration during the reconstruction process. These results provide important information about the probability of controlling the structure and composition of LDHs intercalated with desired anions for a wide variety of device applications, such as memory, sensor, and energy storage.

Anion Exchange in Lead Halide Perovskites: An Overview

Precise tuning of the bandgap of lead halide perovskites by the postsynthetic anion exchange reaction has been considered as one of the best methods to customize their optical/electronic properties. The anion exchange reaction of lead halide perovskites is very fast and occurs at room temperature. The crystal structure of the lead halide perovskites is soft, and hence it facilitates diffusion of the halide ions through the crystal lattice. Through this anion exchange reaction, emission of lead halide perovskites can be tuned in the entire visible range, by varying the amounts of chloride, bromide, and iodide ions from the same synthesis in a cost‐effective manner. Herein, the mechanism involved in the anion exchange reactions and the factors influencing the same are discussed. Also, the discussion is extended to demonstrate how anion exchange process can make lead halide perovskite a more promising candidate for various applications.

Impacts of chloride-form anion exchange seawater regeneration performance

ABSTRACT Seawater was investigated as an alternative regenerant source to conventional salt-imported brine solutions in an anion exchange process treating surficial Florida coastal groundwater for the removal of sulfate and organics. Bench-scale column testing revealed that filtered Sarasota Bay seawater efficiently regenerated the anion resin media; however, sulfate exchange capacity decreased by 8.42% compared with conventional 10% salt regeneration methods. Addition of 3% sodium chloride increased regeneration efficiency, reduced exchange capacity losses to 2.4% as compared to conventional 10% salt regeneration methods. Regeneration resulted in 2.13 mg/L of bromide leakage; however, addition of 3% sodium chloride to seawater reduced bromide leakage to 1.25 mg/L. A correlation between bromide exchange and the regenerant chloride-to-bromide molar ratio (CBMR) was observed, yielding less bromide exchange at higher CBMRs. Bromide adsorption followed pseudo 2nd order kinetics and chemisorption was the rate controlling step. Increasing the CBMR of the regenerant was found to shift adsorption behaviour, allowing intra-particle diffusion to occur sooner. Bromide equilibrium appeared to follow a logarithmic decay as the CBMR of the regenerant increased. Intra-particle and film diffusion mechanisms were evaluated that indicated the presence of diffusion-based processes and more than one rate controlling step. An empirical function was derived to approximate bromide equilibrium adsorption in relation to a regenerant’s CBMR. Seawater as a regenerant when enhanced with sodium chloride shows promise as an anion exchange regenerant; additionally, classification of a seawater regenerant’s CBMR can provide insight into the kinetic and equilibrium relationships of bromide exchange.

In situ detection of an unstable C,N-Au(III) chelate by 15N NMR methods

Au(III)-NHC-oxazolyl complexes are prepared by oxidation and anion exchange of the corresponding Au(I)Cl-NHC-oxazolyl precursors, which are synthesized from appropriate imidazolium pre-ligands. As the Au(III) complexes are too unstable for proper isolation and spectroscopic characterization, selective 15N NMR techniques provide valuable knowledge of N-coordination to gold by formation of N-ligated Au(III) complexes. The changes in 15N-shift values (Δδ15N), observed by 1H,15N-HMBC 2D NMR studies, going from Au(I)Cl, via Au(III)Cl3 to the C,N-Au(III) NHC-oxazolyl complexes, afford important information of the oxidation and the anion exchange processes. In particular, the huge up-field shift of the oxazoline-N by anion exchange (Δδ15NAE: −71.3 ppm), represents significant evidence that oxazoline-N-coordination to Au(III) takes place by anion exchange, and, hence, that the target six-membered bidentate C,N-Au(III)-NHC-oxazoline chelated complex is formed.

Desalination and Detoxification of Textile Wastewater by Novel Photocatalytic Electrolysis Membrane Reactor for Ecosafe Hydroponic Farming.

In this study, a novel photoelectrocatalytic membrane (PECM) reactor was tested as an option for the desalination, disinfection, and detoxification of biologically treated textile wastewater (BTTWW), with the aim to reuse it in hydroponic farming. The anionic ion exchange (IEX) process was used before PECM treatment to remove toxic residual dyes. The toxicity evaluation for every effluent was carried out using the Vibrio fischeri, Microtox® test protocol. The disinfection effect of the PECM reactor was studied against E. coli. After PECM treatment, the 78.7% toxicity level of the BTTWW was reduced to 14.6%. However, photocatalytic desalination during treatment was found to be slow (2.5 mg L−1 min−1 at 1 V potential). The reactor demonstrated approximately 52% COD and 63% TOC removal efficiency. The effects of wastewater reuse on hydroponic production were comparatively investigated by following the growth of the lettuce plant. A detrimental effect was observed on the lettuce plant by the reuse of BTTWW, while no negative impact was reported using the PECM treated textile wastewater. In addition, all macro/micronutrient elements in the PECM treated textile wastewater were recovered by hydroponic farming, and the PECM treatment may be an eco-safe wastewater reuse method for crop irrigation.

Corrosion-resistant Mg(OH)2/Mg-Fe layered double hydroxide (LDH) composite films on magnesium alloy WE43

BackgroundA new synthesis approach was developed for Mg-Fe layered double hydroxide (LDH) film on oxidised magnesium (Mg) alloy WE43 surface by cathodic electrodeposition. MethodsThe synthesised Mg(OH)2 surface layer provides essential divalent cations and a foundation for the direct growth of an Mg-Fe LDH film through the electrodeposition process with trivalent cations containing solution. FindingsThe cross-section analysis results disclosed that the Mg(OH)2 layer altered the typical morphology of LDH film, leading to structured LDH nanoplates with a thickness of approximately 3.5 µm. The formation of structured LDH nanoplates resulted from the perpendicular arrangement of the ab-faces of the crystallites to the WE43 surface, as seen from Field Emission Scanning Electron Microscopy (FE-SEM) images. Electrochemical tests in Hank's Balanced Salt Solution (HBSS) report the Ecorr value increased by 0.24 V and a decrease in icorr by one order of magnitude of Mg(OH)2/Mg-Fe LDH composite films against its substrate. Furthermore, the impedance modulus values of Mg(OH)2/Mg-Fe LDH composite films can achieve a magnitude of three times greater than its substrate. These results indicate that the Mg-Fe LDH film can effectively capture the corrosion anions during corrosion through the anion-exchange process, making it a promising surface modification for Mg alloy.

Sulfur Vacancies‐Engineered Ni3S4‐x Hollow Microspheres with Optimized Anionic Adsorption Energy for High‐Performance Supercapacitor

AbstractNickel sulfides with high theoretical capacitance have aroused tremendous attention for next‐generation supercapacitors. Unfortunately, the structural durability of nickel sulfides is insufficient to support the long‐term working situation. Herein, Ni3S4‐x hollow microspheres with sulfur vacancies (Ni3S4‐x HMs) are constructed by a liquid‐phase anion exchange process using the Ni‐MOF as the precursor. Both experimental investigation and theoretical analysis suggest that the deliberately introduced sulfur vacancies effectively improve the anionic adsorptive ability of nickel sulfides in the KOH electrolyte, significantly enhancing the reversible capacitance and structural durability (1884 F g‐1 at 2 A g‐1, capacity retention of 97.9% after 10 000 cycles). In addition, an asymmetrical solid‐state supercapacitor consisting of Ni3S4‐x HMs cathode and activated carbon anode shows infusive energy/power density (33.05 Wh kg‐1/1.68 kW kg‐1) and remains 82.4% over 10 000 repeated charging/discharging processes in the KOH‐PVA gel electrolyte. The strategies can be developed to enlighten the structural design of various metal sulfides materials adopted in electrochemical energy storage devices including alkali ion batteries, supercapacitors, and electrocatalysts.

Membrane distillation and dispersive solvent extraction in a closed-loop process for water, sulfuric acid and copper recycling from gold mining wastewater

Membrane distillation (MD) and dispersive liquid–liquid extraction (d-LLE) were integrated for gold mining wastewater beneficiation and better use of natural resources. MD presented an average permeate flux of 5.51 ± 0.14 L/m2·h, without a significant flux decay (p < 0.001), and rejection efficiencies for acid and metallic species>98.7%. Five different extractants were studied for sulfuric acid recovery from MD concentrate. Considering the extraction and stripping efficiency, tris-2-ethylhexylamine (TEHA) was the most appropriate alternative for sulfuric acid extraction, requiring 2 stages of extraction and 1 of striping to achieve a recovery>95%. The endothermic nature of acid extraction contributed to the integration of d-LLE and MD, designating a proper destination for MD concentrate, a stream often forgotten while discussing membrane separation processes for wastewater treatment. Copper was then selectively recovered from the raffinate from acid extraction (βCu/Fe = 4,274, βCu/Al = 176, and βCu/Mg = 1,262) by Lix 84-I. A single contact stage ensured that 99.3% of copper was recovered. Fourier-transform infrared spectra demonstrated that the acid extraction mechanisms involve amine salts formation, whereas copper is extracted by anion exchange processes. The economic assessment was favorable for water (US$/m3 0.23) and copper (US$/kgCu 4.25) recovery, with prices lower than currently practiced for both commodities. For sulfuric acid, the operational expenditures corresponded to US$/kgH2SO4 0.423, slightly higher than its marketable price. Overall, the integrated system could be inserted in a perspective that departs from the linear focus of raw material utilization, prioritizing recycling and reuse processes.

Separation of NaCl and humic substances in anion exchange spent brine with electrodialysis

The advanced treatment process of anion exchange can be an effective approach for removing dissolved organic matter in the drinking water, but the production of anion exchange spent brine is a main drawback. Herein, electrodialysis (ED) was used to separate high-concentration NaCl and humic substances (HSs) from anion exchange spent brine. The composition and characteristics of anion exchange spent brine were systematically studied, and the impacts of ion exchange membrane type, volume ratio of initial concentrate to dilute (Vc,0/Vd,0) and flow rate on the performance of lab-scale and pilot-scale ED were investigated. Our results demonstrated the cost-effective membrane pair was TWEDC1/TWEDA1 to treat anion exchange spent brine with high degree of aromaticity and plentiful oxygen-containing functional groups, because of its special membrane structure and membrane properties. High current efficiency of 90.60% and low energy consumption of 0.91 kW h/kg NaCl were achieved by ED with TWEDC1/TWEDA1. When Vc,0/Vd,0 was 1:4, 15% (w/w) recovery NaCl solution concentrated by lab-scale first-stage ED could be used as resin regeneration agent. Furthermore, lab-scale and pilot-scale two-stage ED were simultaneously verified to effectively separate NaCl and HSs in the anion exchange spent brine.

Synthesis of two cationic Coordination polymers for the exploration of anion exchange properties

Anion exchange materials are important for their application in toxic anion control process. Coordination Polymers (CPs) with weakly coordinated anions and lattice anions may be practically useful in anion exchange process. To explore this anion exchange properties by Coordination Polymers (CPs) we have synthesized two water insoluble cationic CPs {[Mn(bix)3(H2O)2].bix.(NO3)2}n(1), {[Cd(bix)2(NO3)2].(H2O)2}n(2) by using N,N-donors linkers bix {bix = 1,4-bis(imidazol-1-ylmethyl)- benzene}. Structure of complex 1 is 1D and contains lattice NO3– anion and the complex 2 is 2D and contains weakly coordinated NO3–anion. Both these complexes along with another previously published structurally similar CP {[Cd(bix)2(NO3)2]}n (3), response in anion exchange studies with foreign anions. All the anion exchange processes have been monitored by FT-IR spectroscopy and PXRD measurements.

Mechanochemical solid state architectonics on Lead(II) coordination polymer by anion-exchange

New 2D lead(II) coordination polymers, Pb(4-bpdh)(CH3COO)(NO3)]n (1) and [Pb(4-bpdh)(ClO4)(NO3)]n (2), 4-bpdh ​= ​2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene, were prepared and characterized by single-crystal X-ray diffraction. Compound 3 with formula [Pb(4-bpdh)(NO3)2(H2O)]n (3) was obtained by solid state mechanochemical reaction of the compounds 1 and 2 via anion-exchange process. These conversions are reversible and the grinding of compound 3 with CH3COO¯ and ClO4¯ ions led to the formation of the compounds 1 and 2, respectively. Thermal decomposition of the compounds 1–3 results in the formation of different metallic composites. The composites were characterized by X-ray powder diffraction (XRD) and size and morphology of them were investigated by scanning electron microscopy (SEM).

Water-soluble ionic liquid as a fluorescent probe towards distinct binding and detection of 2,4,6-trinitrotoluene and 2,4,6-trinitrophenol in aqueous medium

Owing to the escalating threat of criminal activities and pollution aroused by 2,4,6-trinitrotoluene (TNT) and 2,4,6-trinitrophenol (TNP), development of a proficient sensor for the detection of these explosives is highly demanded. Herein, a water-soluble ionic liquid-tagged fluorescent probe, 1-ethyl-3-(3-formyl-4-hydroxybenzyl)-1H-benzimidazol-3-ium chloride (EB-IL) has been designed and synthesized for the detection of TNT and TNP in 100% aqueous medium. The EB-IL fluorescent probe displayed strong cyan-blue fluorescence at 500 nm which gets quenched upon the addition of TNT/TNP over other concomitant nitro-compounds. The distinct binding response of EB-IL towards TNT could be due to the formation of hydrogen bonding between the acidic proton of benzimidazolium (C2–H) and nitro group of TNT. Meanwhile, the selective binding of TNP with EB-IL could be due to the exchange of counter Cl− anion of EB-IL with picrate anion. The fluorescence quenching of EB-IL by TNT could be attributed to the resonance energy transfer (RET) and that of TNP is ascribed to the anion-exchange process. The developed sensor is extremely selective and sensitive towards TNT and TNP with high quenching constants of 1.94 × 105 M−1 and 2.32 × 106 M−1 and shows a lower detection limit of 159 nM and 282 nM, respectively.

Technetium-99 decontamination from radioactive wastewater by modified bentonite: batch, column experiment and mechanism investigation

Technetium-99 (99Tc), as one of the important high-yield fission products, poses a significant threat to the environment and human health due to its radiotoxicity, long half-life, high solubility and mobility in the environment. Thus, removal of 99TcO4− from radioactive wastewater is considerably imminent for waste disposal and environment conservation. In this work, Hexadecylpyridinium Chloride Monohydrate modified bentonite (HDPy-bent) was synthesised and used as an adsorbent to remove 99TcO4−. The adsorption behaviours of ReO4− as an analogue for TcO4− were investigated as functions of contact time, solution pH, initial concentration, and competing anions using batch techniques. It is demonstrated that the HDPy-bent showed an excellent adsorption ability for ReO4− at the pH range of 2–11, fast adsorption kinetic (reaching equilibrium within 3 min at room temperature), and maintains desirable ReO4− adsorption in the presence of concomitant anions at an excessive concentration of 500 times (Cl−, HCO3−, NO3−, CO32−, SO42− and PO43−). As for adsorption mechanism, we propose the anion exchange process at low concentration of Re(VII) and precipitation reaction at high concentration, while the driving force of the high ReO4− adsorption ability is the interaction between ReO4− anion and pyridinium ring of HDPy+, which is confirmed by density functional theory (DFT) simulations. Additionally, DFT studies also shed light on the adsorption structure of HDPy+/ReO4− and the origin of adsorption selectivity. Moreover, four adsorption-desorption cycles suggest that the HDPy-bent has good durability and reusability. Furthermore, ReO4− can be removed completely and recovered fractionally by using the chromatography column packed with HDPy-bent from simulated groundwater samples. The work presented herein demonstrates a low-cost adsorbent which can efficiently remove 99Tc from contaminated water.

Hierarchical NiCo2O4 and NiCo2S4 nanomaterials as electrocatalysts for methanol oxidation reaction

In this work, Ni foam supported hierarchical NiCo2O4 nanomaterials are successfully prepared through a hydrothermal process and subsequent calcination process, then the hierarchical NiCo2O4 is converted to hierarchical NiCo2S4 through a hydrothermal anion exchange process. The hierarchical nanomaterials are constructed by a nanorod core and nanoribbons shell. The morphology evolution mechanism of the hierarchical NiCo2O4 is studied by exploratory experiments, the results show that the morphology evolution from nanorod to hierarchical nanostructure undergo a solid–solid process, and the calcination temperature is crucial for the formation of the hierarchical nanostructure. The hierarchical NiCo2O4 and NiCo2S4 nanomaterials are both used as electrocatalysts for methanol oxidation reaction in alkaline electrolyte, and the electrocatalytic activity of the NiCo2S4 is higher than that of the NiCo2O4. Cycling test shows the good stability of the NiCo2S4, and the slight loss of activity during cycling is caused by the surface oxidation of NiCo2S4 in alkaline electrolyte. This work indicate that the hierarchical NiCo2S4 is a promising non-noble metal electrocatalyst for direct methanol fuel cells.

Effect of physical barrier and anion-exchange process of nitrate-intercalated ZnAl layered double hydroxide films grown on Al on corrosion protection

ZnAl layered double hydroxide (ZnAl-LDH) film loaded with nitrates was prepared on the surface of pure Al plate by hydrothermal reaction. The anion-exchange process of ZnAl-LDH in corrosive NaCl solution was demonstrated by the X-ray Diffraction (XRD). The corrosion protection behavior of this fabricated film was monitored by performing electrochemical impedance spectroscopy (EIS) up to 39 d. It was revealed that the physical barrier effect of nitrate-intercalated ZnAl-LDH film played a significant role in its corrosion protection and the anion-exchange had a limited influence on final corrosion protection.