Hydrogen storage over alkali metal hydride and alkali metal hydroxide composites

Alkali metal hydroxide and hydride composite systems contain both protic （H bonded with O） and hydridic hydrogen. The interaction of these two types of hydrides produces hydrogen. The enthalpy of dehydrogenation increased with the increase of atomic number of alkali metals, i.e., -23 kJ/molnz for LiOH-LiH, 55.34 kJ/moln： for NaOH-NaH and 222 kJ/molH2 for KOH-KH. These thermodynamic calculation results were consistent with our experimental results. H2 was released from LiOH-LiH system during ball milling. The dehydrogenation temperature of NaOH-NaH system was about 150 ℃; whereas KOH and KH did not interact with each other during the heating process. Instead, KH decomposed by itself. In these three systems, NaOH-NaH was the only reversible hydrogen storage system, the enthalpy of dehydrogenation was about 55.65 kJ/molHz, and the corresponding entropy was ca. 101.23 J/（molHz .K）, so the temperature for releasing 1.0 bar H2 was as high as 518 ℃, showing unfavorable thermodynamic properties. The activation energy for hydrogen desorption of NaOH-NaH was found to be 57.87 kJ/mol, showing good kinetic properties.

Formation and Aggregation Kinetics of Mixed Metal Hydroxides Agglomerates

The aggregation and fractal structure of mixed metal hydroxides ( MMH ) agglomerates with increasing ionic strength have been studied by dynamic light scattering ( DLS ) and SEM techniques. The experiments indicate that the MMH agglomerates have two different structures in RLA regime and DLA regime, and also give the proof that the transition region between RLA and DLA may occur.

Flame retardancy effect of surface-modified metal hydroxides on linear low density polyethylene

Metal hydroxides （MAH） consisting of magnesium hydroxide and aluminum hydroxide with a mass ratio of 1：2 were surface-modified by y-diethoxyphosphorous ester propyldiethoxymethylsilane, boric acid and diphenylsilanediol in xylene under dibutyl tin dilaurate catalyst at 140 ℃. Phosphorus, silicon and boron elements covalently bonded to metal hydroxide particles were detected by X-ray photoelectron spectroscopy. The degradation behavior of the surface-modified MAH was characterized by thermogravimetric analysis. The results show that linear low density polyethylene （LLDPE） composite, filled with 50% （mass fraction） of MAH modified by 5.0% （mass fraction） of modifiers, passes the V-0 rating of UL-94 test and shows the limited oxygen index of 34%, and its heat release rate and average effective heat combustion in a cone calorimeter measurement decrease obviously; The mechanical properties of MAH can be improved by surface-modification. The uniform dispersion of particles and strong interfacial bonding between particles and matrix are obtained.

Mild hydrothermal preparation of a layered metal hydroxide salt with microtube/rod morphology

Microtubes/rods of the layered metal hydroxide salt compound Cd2（OH）3（DS）·nH2O, where DS stands for dodecyl sulfate sandwiched between two adjacent inorganic sheets, have been synthesized for the first time through a mild hydrothermal reaction route. The microtubes/rods have a diameter of about 1 μm and a length ranging from several microns to 20μm. The growth process of microtubes/rods under the experimental conditions employed follows a dissolution-recrystallization route.

Studies on Colloidal Properties of Mixed Metal Hydroxide－Clay Aqueous Suspension

he electrical property,stability and rheological property of mixed metal hydroxide(MMH)-clay aqueous suspensions were studied via determining elec- trophoretic mobilities,heterocoagulation and rheological parameters. The suspen- sions of MMH-Na-montmorillonite and MMH-Kaolinite may be transformed from negatively charged systems into positively charged systems through changing the ratio of MMH to clav. The increase of MMH content makes the stability of dilute MMH-clay suspensions decreased in negatively chrged systems and increased in positively chrged systems. The complete coagulations at near neutral systems oc- curs. In the concentrated MMH-clay suspension,the steric network structures may be formed between MMH and clay particles,which cause the apparent viscosity(AV)and Bingham yield point(YP) of the suspentqion to increase. There is a suit- able ratio of MMH to clay at which the AV and YP of the suspension attain a maximum value,which in agreement with “bridging theory”of polymer flocculation.

Ultrathin Metal Silicate Hydroxide Nanosheets with Moderate Metal-Oxygen Covalency Enables Efficient Oxygen Evolution

Exploring efficient,cost-effective,and durable electrocatalysts for electrochemical oxygen evolution reaction(OER)is pivotal for the large-scale application of water electrolysis.Recent advance has demonstrated that the activity of electrocatalysts exhibits a strong dependence on the surface electronic structure.Herein,a series of ultrathin metal silicate hydroxide nanosheets(UMSHNs)M_(3)Si_(2)O_(5)(OH)_(4)(M=Fe,Co,and Ni)synthesized without surfactant are introduced as highly active OER electrocatalysts.Cobalt silicate hydroxide nanosheets show an optimal OER activity with overpotentials of 287 and 358 m V at 1 and 10 m A cm^(-2),respectively.Combining experimental and theoretical studies,it is found that the OER activity of UMSHNs is dominated by the metal-oxygen covalency(MOC).High OER activity can be achieved by having a moderate MOC as reflected by aσ^(*)-orbital(e_(g))filling near unity and moderate[3d]/[2p]ratio.Moreover,the UMSHNs exhibit favorable chemical stability under oxidation potential.This contribution provides a scientific guidance for further development of active metal silicate hydroxide catalysts.

Chemical interaction motivated structure design of layered metal carbonate hydroxide/MXene composites for fast and durable lithium ion storage

Rational architecture design has turned out to be an effective strategy in improving the electrochemical performance of electrode materials for batteries.However,an elaborate structure that could simultaneously endow active materials with promoted reaction reversibility,accelerated kinetic and restricted volume change still remains a huge challenge.Herein,a novel chemical interaction motivated structure design strategy has been proposed,and a chemically bonded Co(CO_(3))_(0.5)OH·0.11 H_(2)O@MXene(CoCH@MXene)layered-composite was fabricated for the first time.In such a composite,the chemical interaction between Co^(2+)and MXene drives the growth of smaller-sized CoCH crystals and the subsequent formation of interwoven CoCH wires sandwiched in-between MXene nanosheets.This unique layered structure not only encourages charge transfer for faster reaction dynamics,but buffers the volume change of CoCH during lithiation-delithiation process,owing to the confined crystal growth between conductive MXene layers with the help of chemical bonding.Besides,the sandwiched interwoven CoCH wires also prevent the stacking of MXene layers,further conducive to the electrochemical performance of the composite.As a result,the as-prepared CoCH@MXene anode demonstrates a high reversible capacity(903.1 mAh g^(-1)at 100 mA g^(-1))and excellent cycling stability(maintains 733.6 mAh g^(-1)at1000 mA g^(-1)after 500 cycles)for lithium ion batteries.This work highlights a novel concept of layerby-layer chemical interaction motivated architecture design for futuristic high performance electrode materials in energy storage systems.

A new approach for the aerobic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid without using transition metal catalysts

The organic compound 2,5-furandicarboxylic acid（FDCA） has been identified by the US Department of Energy（DOE） as a valuable platform chemical for a wide range of industrial applications. Currently, the most popular route for FDCA synthesis is reported to be the oxidation of 5-hydroxymethylfurfural（HMF）by O_2 over the catalysis of noble metals（e.g., Au, Pt, Ru, and Pd）. However, the high costs of noble metal catalysts remain a major barrier for producing FDCA at an industrial scale. Herein, we report a transition metal-free synthesis strategy for the oxidation of HMF to FDCA under O_2 or ambient air. A simple but unprecedented process for the aerobic oxidation of HMF was carried out in organic solvents using only bases as the promoters. According to the high performance liquid chromatography（HPLC） analysis, excellent product yield（91%） was obtained in the presence of NaOH in dimethylformamide（DMF） at room temperature（25 ℃）. A plausible mechanism for the NaOH-promoted aerobic oxidation of HMF in DMF is also outlined in this paper. After the reaction, the sodium salt of FDCA particles were dispersed in the reaction mixture, making it possible for product separation and solvent reuse. The new HMF oxidation approach is expected to be a practical alternative to current ones, which depend on the use of noble metal catalysts.

Activating Inert Sites in Cobalt Silicate Hydroxides for Oxygen Evolution through Atomically Doping

Metal silicate hydroxides have been recognized as efficient oxygen evolution reaction(OER)electrocatalysts,yet tailoring of their intrinsic activity remains confused.Herein,Fe had been incorporated into cobalt silicate hydroxide nanosheets and the resulted material achieves a competitive OER catalytic activity.It is found that the doping state obviously affects the electrical transport property.Specifically,highly dispersed Fe atoms(low-concentration Fe doping)trigger slight electron transfer to Co atoms while serried Fe(highconcentration Fe doping)attract vast electrons.By introducing 6 at.%Fe doping,partial relatively inert Co sites are activated by atomically dispersed Fe,bearing an optimal metal 3d electronic occupation and adsorption capacity to oxygen intermediate.The introduced Co-O-Fe unit trigger the p-donation effect and decrease the number of electrons in p*-antibonding orbitals,which enhance the Fe-O covalency and the structural stability.As a result,the sample delivers a low overpotential of 293 mV to achieve a current density of 10 mA cm^(-2).This work clarifies the superiority of atomically dispersed doping state,which is of fundamental interest to the design of doped catalyst.

Superhydrophilic nickel hydroxide ultrathin nanosheets enable high-performance asymmetric supercapacitors

Superhydrophilic surfaces have been applied for supercapacitor;however,during energy storage reaction,how the wettability affects the process of electrochemical reaction specifically is still unclear.Herein,we demonstrate superhydrophilic surface for promotion of electrochemical reactions by liquid affinity and further explain the mechanism,where the transition of the wettability state caused by the change in surface free energy is the main reason for the obvious increase in specific capacitance.Through citric acid assistance strategy,an intrinsically hydrophobic Ni(OH)_(2)thick nanosheets(HNHTNs,16 nm)can be transitioned into superhydrophilic Ni(OH)_(2)ultrathin nanosheets(SNHUNs,6.8 nm),where the water contact angle was 0°and the surface free energy increased from 8.6to 65.8 mN·m^(-1),implying superhydrophilicity.Compared with HNHTNs,the specific capacitance of SNHUNs is doubled:from 1230 F·g^(-1)(HNHTNs)to 2350 F·g^(-1)(2A·g^(-1))and,even at 20 A·g^(-1),from 833 F·g^(-1)(HNHTNs)to 1670 F·g^(-1).The asymmetric capacitors assembled by SNHUNs and activated carbon show 52.44 Wh·kg^(-1)at 160W·kg^(-1)and excellent stability with~90%retention after5000 cycles(~80%retention after 9500 cycles).The promotion of electrochemical performances is ascribed to the change of surface wettability caused by surface free energy,which greatly increase affinity of electrode to the surrounding liquid environment to reduce the interface resistance and optimize the electron transport path.

Research progress in rare earths and their composites based electrode materials for supercapacitors

Supercapacitor is an imminent potential energy storage system,and acts as a booster to the batteries and fuel cells to provide necessary power density.In the last decade,carbon and carbonaceous materials,conducting polymers and transition metal oxide/hydroxide based electrode materials have been made to show a remarkable electrochemical performance.Rare-earth materials have attracted significant research attention as an electrode material for supercapacitor applications based on their physicochemical properties.In this review,rare earth metals,rare earth metal oxides/hydroxides,rare-earth metal chalcogenides,rare-earth metal/carbon composites and rare-earth metal/metal oxide composites based electrode materials are discussed for supercapacitors.We also discuss the energy chemistry of rare-earth metal-based materials.Besides the factors that affect the performance of the electrode materials,their evaluation methods and supercapacitor performances are discussed in details.Finally,the future outlook in rare-earth-based electrode materials is revealed towards its current developments for supercapacitor applications.

Ultrasound-induced elevation of interlayer spacing and conductivity of CoNi hydroxides for high-performance Ni–Zn batteries

Nickel–zinc(Ni–Zn) batteries hold a lot of promise for energy storage thanks to their high output voltage, plentiful Zn supply, and low toxicity. Achieving the facile preparation of high-performance cathodes at ambient temperature remains a challenge, it is however essential for practical applications. Here, in the present study, an efficient ultrasound-assisted one-step fabrication of CoNi double hydroxide(UACoNi DH) microspheres at room temperature that performs well as a cathode for Ni–Zn batteries was proposed. This designed ultrasound-assisted method induces the formation of metal double hydroxide with an elevation of interlayer spacing and bulk conductivity while maintaining the structure features of CoNi DH prepared without ultrasound assistance. As a result, the UA-CoNi DH as an electrode material displays highly enhanced electrochemical properties relative to CoNi DH prepared without ultrasound assistance. Benefitting from the improved performance of our UA-CoNi DH electrode, the Ni–Zn battery with UA-CoNi DH as the cathode(UA-CoNi DH//Zn) delivers a good specific capacity(202.36 mAh/g) and rate performance(70.49% capacity maintained at a 10-fold higher current), presenting more than 71.61%and 21.99% improvement relative to the CoNi DH//Zn battery, respectively. This work offers guidelines for constructing high-performance Ni–Zn battery cathodes in an open environment.

CeO2 quantum dots doped Ni-Co hydroxide nanosheets for ultrahigh energy density asymmetric supercapacitors

By integrating the merits of lanthanide elements and quantum dots,we firstly design CeO2 quantum dots doped Ni-Co hydroxide nanosheet via a controllable synthetic strategy,which exhibits a large specific capacitance(1370.7 F/g at 1.0 A/g) and a good cyclic stability(90.6% retention after 4000 cycles).Moreover,we assemble an aqueous asymmetric supercapacitor with the obtained material,which has an extremely high energy density(108.9 Wh/kg at 378 W/kg) and outstanding cycle stability(retaining88.1% capacitance at 2.0 A/g after 4000 cycles).

In situ electrochemical dehydrogenation of ultrathin Co(OH)_(2) nanosheets for enhanced hydrogen evolution

Transition metal hydroxides/oxyhydroxides have recently emerged as highly active electrocatalysts for oxygen evolution reaction in alkaline water electrolysis,while have not yet been widely investigated for hydrogen evolution electrocatalysts owing to their unfavorable H*-adsorption,making it difficult to construct an overall-water-splitting cell for hydrogen production.In this work,we proposed a straightforward and effective approach to develop an efficient in-plane heterostructured CoOOH/Co(OH)_(2) catalyst via in-situ electrochemical dehydrogenation method,in which the dehydrogenated–CoOOH and Co(OH)_(2) at the surface synergistically boost the hydrogen evolution reaction(HER)kinetics in base as confirmed by high-resolution transmission electron microscope,synchrotron X-ray absorption spectroscopy,and electron energy loss spectroscopy.Due to the in-situ dehydrogenation of ultrathin Co(OH)_(2) nanosheets,the catalytic activity of the CoOOH/Co(OH)_(2) heterostructures is progressively improved,which exhibit outstanding hydrogen-evolving activity in base requiring a low overpotential of 132 m V to afford 10 m A/cm^(2)with very fast reaction kinetics after 60 h dehydrogenation.The gradually improved catalytic performance for the CoOOH/Co(OH)2is probably due to the enhanced H*-adsorption induced by the synergistic effect of heterostructures and better conductivity of Co OOH relative to electrically insulating Co(OH)_(2).This work will open the opportunity for a new family of transition metal hydroxides/oxyhydroxides as active HER catalysts,and also highlight the importance of using in situ techniques to construct precious metal-free efficient catalysts for alkaline hydrogen evolution.

High phosphate removal using La(OH)3 loaded chitosan based composites and mechanistic study

Our present study was to prepare a biomass-supported adsorbents with high adsorptive capacity and high selectivity to prevent the accelerated eutrophication in water body.To this end,different metal hydroxide(La,Zr and Fe)first was successfully loaded on chitosan microspheres.Then the quaternary ammonium group with different content was introduced into the adsorbent by polymerization.By comparison of adsorption properties,chitosanLa(OH)3-quaternary ammonium-20%(CS-La-N-20%)has strong adsorption to phosphate(160 mg/g)by immobilizing nano-sized La(OH)3 within a quaternary-aminated chitosan and it maintain high adsorption in the presence of salt ions.The pH results indicated that the CS-La-N-20%would effectively sequestrate phosphate over a wide pH range between 3 and 7 without significant La3+leaching.What’s more,adsorption capacity on the introduce of positively charged quanternary-aminated groups was significantly higher than that of the unmodified adsorbents at alkaline conditions.The column adsorption capacity reached 1300 bed volumes(BV)when phosphate concentration decreased until 0.5 mg/L at 6 BV/hr.The column adsorption/desorption reveals that no significant capacity loss is observed,indicating excellent stability and repeated use property.Characterizations revealed that phosphate adsorption on CS-La-N-20%through ligand exchange(impregnated nano-La(OH)3)and electrostatic attraction(positively charged quanternary-aminated groups).All the results suggested that CS-La-N-20%can serve as a promising adsorbent for preferable phosphate removal in realistic application.

Inhibiting effect of Al(OH)_3 and Mg(OH)_2 dust on the explosions of methane-air mixtures in closed vessel

The inhibiting effect of AI（OH）3 and Mg（OH）2 dust on explosion of methane-air mixtures was investigated by means of explosion parameter tests in a 20-liter closed vessel. The influences of varying methane concentration and dust concentration on explosion parameters were characterized based on the experimental data to determine the maximum explosion pressure, maximum rate of pressure rise, lower explosion limits and upper explosion limits. The inhibiting mechanisms of these kinds of dust were analyzed as well. The investigations indicate that AI（OH）3 and Mg（OH）2 dust can be used as inhibitors to prevent meth- ane explosion, however, their inhibiting effects are less than those of inert gas such as N2 and CO2 in that their dust can weaken the methane explosion but cannot totally eliminate it. The tests show that all of the explosion parameters with dust additives are strongly dependent on methane/air ratio and dust concentration, and AI（OH）3 dust has better performance than Mg（OH）2 dust in inhibiting methane explosion. The average percentage decreases of maximum explosion pressure and maximum rate of pressure rise with AI（OH）3 dust are 11.08% and 66.15%, respectively. Experiments also showed that there is a special phe- nomenon when methane explosion is inhibited by AI（OH）3 and Mg（OH）2 dust, in which is that during the process of explosion the maximum explosion pressure value first decreases then increases as dust concentration increases. The best dust concentrations to inhibit the explosion are 250 g/m3 with methane/air ratio at 9.5%, and 200 g/m3 with methane/air ratio at 7%. It is suggested that water vapor produced by the thermal decomposition of metal hydroxides makes the particles of descending dust combine, resulting in a decrease of the real dust concentration in the vessel. Water vapor also is the major cause of another phenomenon that the LEL curve and the UEL curve never meet with the increase of gas concentration.

A novel septenary high-entropy(oxy)hydroxide electrocatalyst for boosted oxygen evolution reaction

High-entropy materials(HEMs)have attracted extensive attention in the field of electrochemical catal-ysis due to their unique properties.However,the preparation of high-entropy catalysts typically relies on high-temperature,energy-intensive,and time-consuming synthesis methods due to their compositional complexity.In this study,a facile low-temperature electrochemical reconstruction approach is adopted to synthesize Ag-decorated septenary Co-Cu-Fe-Mo-Zn-Ag-Ru high-entropy(oxy)hydroxide electro-catalysts for oxygen evolution reaction(OER).By introducing Ag and Ru elements and implanting Ag nanoparticles to co-regulate the electronic structure of the catalysts,the as-prepared catalyst achieves remarkable OER performance with a low overpotential of 298 mV at 100 mA/cm^(2)and a small Tafel slope of 30.1 mV/dec in 1 mol/L KOH.This work offers a valuable strategy for developing high-performance high-entropy OER electrocatalysts.

Improved utilization of active sites for phosphorus adsorption in FeOOH/anion exchanger nanocomposites via a glycol-solvothermal synthesis strategy

Metal oxide/hydroxide-based nanocomposite adsorbents with porous supporting matrices have been recognized as efficient adsorbents for phosphorus recovery.Aiming at satisfying increasingly restrictive environmental requirements involving improving metal site utilization and lowering metal leakage risk,a glycol-solvothermal confined-space synthesis strategy was proposed for the fabrication of Fe OOH/anion exchanger nanocomposites(Fe/900s)with enhanced metal site utilization and reduced metal leakage risk.Compared to composites prepared using alkaline precipitation methods,Fe/900s performed comparably,with a high adsorption capacity of 19.05 mg-P/g with an initial concentration of 10 mg-P/L,a high adsorption selectivity of 8.2 mg-P/g in the presence of 500 mg-SO_(4)^(2-)/L,and high long-term resilience(with a capacity loss of~14%after five cycles),along with substantially lower Fe loading amount(4.11 wt.%)and Fe leakage percentage.Mechanistic investigation demonstrated that contribution of the specific Fe OOH sites to phosphate adsorption increased substantially(up to 50.97%under the optimal conditions),in which Fe(Ⅲ)-OH was the dominant efficient species.The side effects of an excessively long reaction time,which included quaternary ammonium decomposition,Fe OOH aggregation,and Fe(Ⅲ)reduction,were discussed as guidance for optimizing the synthesis strategy.The glycol-solvothermal strategy provides a facile solution to environmental problems through nanocrystal growth engineering in a confined space.

Synthesis of Co/SiO2 hybrid nanocatalyst via twisted Co3Si2O5（OH）4 nanosheets for high-temperature Fischer- Tropsch reaction

A cobalt-silica hybrid nanocatalyst bearing small cobalt particles of diameter -5 nm was prepared through a hydrothermal reaction and hydrogen reduction. The resulting material showed very high CO conversion （〉82%） and high hydrocarbon productivity （-1.0gHC·gcat^-1·h^-1 ） with high activity （-8.5 × 10^-5 molco.gco^-1.s-1） in the Fischer-Tropsch synthesis reaction.

Atomic-level correlation between the electrochemical performance of an oxygen-evolving catalyst and the effects of CeO_(2) functionalization

Herein,we prepared a bimetallic layered double hydroxide(FeCo LDH)featuring a dandelion-like structure.Anchoring of CeO_(2)onto FeCo LDH produced interfaces between the functionalizing CeO_(2)and the parent LDH.Comparative electrochemical studies were carried out.Onset potential,overpotential,and Tafel slope point to the superior oxygen-evolving performance of CeO_(2)-FeCo LDH with respect to FeCo LDH,therefore,demonstrating the merits of CeO_(2)functionalization.The electronic structures of Fe,Co,and Ce were analyzed by X-ray photoelectron spectroscopy(XPS)and electron energy loss spectroscopy(EELS)from which the increase of Co^(3+)and the concurrent lowering of Ce^(4+)were established.With the use of CeO_(2)-FeCo LDH,accelerated formation at a sizably reduced potential of Co-OOH,one of the key intermediates preceding the release of O_(2)was observed by in situ Raman spectroscopy.We now have the atomic-level and location-specific evidence,the increase of the active Co^(3+)across the interface to correlate the enhanced catalytic performance with CeO_(2)functionalization.