Efficient C-N coupling in electrocatalytic urea generation on copper carbonate hydroxide electrocatalysts

Urea generation through electrochemical CO_(2) and NO_(3)~-co-reduction reaction(CO_(2)NO_(3)RR)is still limited by either the low selectivity or yield rate of urea.Herein,we report copper carbonate hydroxide(Cu_2(OH)_2CO_(3))as an efficient CO_(2)NO_(3)RR electrocatalyst with an impressive urea Faradaic efficiency of45.2%±2.1%and a high yield rate of 1564.5±145.2μg h~(-1)mg_(cat)~(-1).More importantly,H_(2) evolution is fully inhibited on this electrocatalyst over a wide potential range between-0.3 and-0.8 V versus reversible hydrogen electrode.Our thermodynamic simulation reveals that the first C-N coupling follows a unique pathway on Cu_2(OH)_2CO_(3) by combining the two intermediates,~*COOH and~*NHO.This work demonstrates that high selectivity and yield rate of urea can be simultaneously achieved on simple Cu-based electrocatalysts in CO_(2)NO_(3)RR,and provide guidance for rational design of more advanced catalysts.

Electron modulation of cobalt carbonate hydroxide by Mo doping for urea-assisted hydrogen production

Combining urea oxidation reaction(UOR) with hydrogen evolution reaction(HER) is an effective method for energy saving and highly efficient electrocatalytic hydrogen production. Herein, molybdenumincorporated cobalt carbonate hydroxide nanoarrays(CoxMoyCH) are designed and synthesized as a bifunctional catalyst towards UOR and HER. Benefiting from the Mo doping, the dispersed nanoarray structure and redistributed electron density, the CoxMoyCH catalyst display outstanding catalytic performance and durability for both HER and UOR, affording the overpotential of 82 m V for HER and delivering a low potential of the 1.33 V for UOR(vs. reversible hydrogen electrode, RHE) to attain a current density of 10 m A cm^(-2), respectively. Remarkably, when CoxMoyCH was applied as bifunctional catalyst in a twoelectrode electrolyzer, a working voltage of 1.40 V is needed in urea-assisted water electrolysis at10 m A cm^(-2) and without apparent decline for 40 h, outperforming the working voltage of 1.51 V in conventional water electrolysis.

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.

Preparation of ultrafine α-Al_2O_3 powders by catalytic sintering of ammonium aluminum carbonate hydroxide at low temperature

The precursor of ammonium aluminum carbonate hydroxide was synthesized by using aluminum sulfate（Al2（SO4）3） and ammonium carbonate（（NH4）2CO3）. The effects of α-Al2O3 seeds and mixture composed of α-Al2O3 and ammonium nitrate, as well as multiplex catalysts （AT） on phase transformation of alumina in sintering process were investigated respectively. The results show that the α-Al2O3 seeds and the mixture of α-Al2O3 and ammonium nitrate can lower the phase transformation temperature of α-Al2O3 to different extents while the particles obtained agglomerate heavily. AT has great potential synergistic effects on the phase transformation of alumina and reduces the phase transformation temperature of α-Al2O3 and the trends of necking-formation between particles. Therefore the dispersion of powder particles is improved significantly.

Ternary non-noble metal zinc-nickel-cobalt carbonate hydroxide cocatalysts toward highly efficient photoelectrochemical water splitting

TiO2 photoanodes have aroused intensive research interest in photoelectrochemical （PEC） water splitting. However, they still suffer from poor electron-hole separation and sluggish oxygen evolution dynamics, leading to the low photoconversion efficiency and limiting commercial application. Here, we designed and fabricated novel ternary non-noble metal carbonate hydroxide （ZNC-CH） nanosheet cocatalysts and integrated them with TiO2 nanorod arrays as highly efficient photoanodes of PEC cells. Compared with the pristine TiO2, the photocurrent of photoanode with the optimal amount of ZNC-CH represents 3.2 times enhancement, and the onset potential is shifted toward the negative potential direction of 62 mV, The remarkable enhancement is attributed to the suppressed carrier recombination and enhanced charge transfer efficiency at the interface of TiO2, ZNC-CH and electrolyte, which is closely related to the zinc elements modulated intrinsic activity of catalysts. Our results demonstrate that the introduction of multimetallic ZNC-CH cocatalysts onto photoanodes is a promising strategy to improve the PEC efficiency.

Influence of Sodium Carbonate Amount on Crystalline Phase and Structure Stability for Doping Nickel Hydroxide

Alpha nickel hydroxide has better performances than commercial beta nickel hydroxide. However, the main defect is that α-phase is difficult to synthesize and easily transformed to β-phase Ni（OH）2 upon aging in a strong alkaline solution. In this study, the Al-Co, Al-Yb, Yb-Co and Al-Yb-Co multiple doping was used respectively. By controlling the amount of sodium carbonate, the α-Ni（OH）2 was prepared by ultrasonic-assisted precipitation. And the influence of sodium carbonate on the crystalline phase and structure stability for alpha nickel hydroxide was studied. The results demonstrate that, with increasing amount, the biphase nickel hydroxide transforms to pure alpha nickel hydroxide gradually, and the structure stability is also improved. When the amount of sodium carbonate is 2 g, the sample still keeps α-Ni（OH）2 after being aged for 30 days, for Al-Yb-Co-Ni（OH）2. And when the amount is less than 2 g, the phase transformations exist in the samples with different extents. These results demonstrated that the amount of sodium carbonate is a critical factor to maintain the structural stability of α-Ni（OH）2.

PRODUCTION OF ULTRA-FINEα-AL_2O_3 PO WDERSFROM AMMONIUM A LUMINUM CARBONATE HY DROXIDE

Synthesis of a m m oniu m alu min u m carbonate hydroxide ( A A C H) w as investigated usinga m m oniu m alu min u m sulfate and a m moniu m hydro carbonate as the starting m aterials . Itw as found that A A C Hcan be synthesized by adding a m m oniu m alu m inu m sulfate solution torapidly stirred a m moniu m hydro - carbonate solution at a tem perature of 30 ℃. A A C Hcantransfor m to α Al2 O3 co m pletely by calcining at 1100 ℃ for 1 hour , and the obtained po w ders , with a particle size of 100 n m , can be sintered to 98 99 % relative density at 1500 ℃for 2 hours .

Influence of Compaction Pressure on the Accelerated Carbonation of Calcium Hydroxide

Mineral carbonation using waste cement is a promising method to solve the problems caused by CO_2 emission and waste cement. Compaction pressure is an important parameter for mineral carbonation of calcium hydroxide, one of the most dominant composite of waste cement that can be carbonated. The carbonation degree, morphology of products and compressive strength of carbonated compacts are influenced by compaction pressure significantly. Results show that the carbonation degree of calcium hydroxide increases at first（0-8 MPa） and then decreases in the higher compaction pressure range（10-14 MPa）. At the meantime, results also indicate that lower compaction pressure accelerates the early carbonation but hinder carbonation in the later stages. For the morphologies of carbonation products, calcium carbonate tends to form typical crystal morphology of calcite（rhombohedral） under lower compaction pressure, while it will become ellipsoidlike when compaction pressure reaches 8 MPa. TGA and water content results show that there is an optimal water content for the carbonation. In addition, lower water content is adverse to the carbonation at later stage and the CO_2 is difficult to penetrate into the inside of compacts when water content is high, which will hinder the carbonation. XRD and TGA results show that the carbonation products are calcite and small amount of amorphous calcium carbonate.

Multicomponent mixed metallic hierarchical ZnNi@Ni@PEDOT arrayed structures as advanced electrode for high-performance hybrid electrochemical cells

Engineering multicomponent nanomaterials as an electrode with rationalized ordered structures is a promising strategy for fulfilling the high-energy storage needs of supercapacitors(SCs).Even now,the fundamental barrier to utilizing hydroxides/hydroxyl carbonates is their poor electrochemical performance,resulting from the significantly poor electrical conductivity and sluggish charge storage kinetics.Hence,a multilayered structural approach is primarily and successfully used to construct electrodes as one of the efficient approaches.This method has made it possible to develop well-ordered nanostructured electrodes with good performance by taking advantage of tunable approach parameters.Herein,we report the design of multilayered heterostructure porous zinc-nickel nanosheets@nickel flakes hydroxyl carbonates and/or hydroxides integrated with conductive PEDOT fibrous network(i.e.,ZnNi@Ni@PEDOT) via facile synthesis methods.The combined hybrid electrode acquires the features of high electrical conductivity from one part and various valance states from another one to develop a well-organized nanosheet/flake/fibrous-like heterostructure with decent mechanical strength,creating robust synergistic results.Thus,the designed binder-free ZnNi@Ni@PEDOT electrode delivers a high areal capacity value of 1050.1 μA h cm^(-2) at 3 mA cm^(-2) with good cycling durability,significantly outperforming other individual electrodes.Moreover,its feasibility is also tested by constructing a hybrid electrochemical cell(HEC).The assembled HEC exhibits a high areal capacity value of 783.8 μA h cm^(-2) at5 mA cm^(-2).and even at a high current density of 100 mA cm^(-2)(484.6 μA h cm^(-2)),the device still retains a rate capability of 61,82%,Also,the HEC shows maximum energy and power densities of0.595 mW h cm^(-2) and 77.23 mW cm^(-2),respectively,along with good cycling stability.The obtained energy storage capabilities effectively power various electronic components.These results provide a viable and practical way to construct a positive electrode with innovative heterostructures for highperformance energy storage devices and profoundly influence the development of electrochemical SCs.

Fibrous activated alumina prepared through phase transformation using dawsonite as a template

Fibrous activated alumina is widely applied in catalysts,adsorbents,and composite materials.This work presents a green approach in preparing the fibrous activated Al_(2)O_(3) with high purity and specific surface area through multistep phase transformation of aluminum-bearing substances using intermediate dawsonite as a template.Thermodynamic calculations and experimental results show that increasing the concentration of Na_(2)CO_(3) and(NH_(4))_(2)CO_(3) is remarkably beneficial to the formation of dawsonite and ammonium aluminum carbonate hydroxide,respectively.Based on determination of dissolution and precipitation mechanism,the ultrafine granular gibbsite is converted to the uniform fibrous dawsonite with a ratio of length to diameter over 50,and the fibrous dawsonite changes into the long fibrous ammonium aluminum carbonate hydroxide with a ratio of length to diameter is about 80 in above 70 g/L(NH_(4))_(2)CO_(3) solution.Furthermore,the activated alumina remains fibrous morphology after roasting ammonium aluminum carbonate hydroxide at a slow heating rate,plentiful open mesopore and weak aggregation of particles,which contributes to the high specific surface area of 159.37 m^(2)/g at 1273 K for the activated alumina.The complete transformation of dawsonite to ammonium aluminum carbonate hydroxide and high specific surface area contribute to the purity of the activated fibrous alumina above 99.9%with low Na and Fe content.

Preparation of γ-Al2O3 via Hydrothermal Synthesis Using ρ-Al2O3 as Raw Material for Propane Dehydrogenation

γ-Al2O3 was prepared by hydrothermal synthesis usingρ-Al2O3 and urea as raw materials.In this work,the eff ects of the molar ratio of CO(NH2)2/Al and reaction temperature were investigated,and a Pt–Sn–K/γ-Al2O3 catalyst was prepared.The ammonium aluminum carbonate hydroxide(AACH),γ-Al2O3,and Pt–Sn–K/γ-Al2O3 were characterized by X-ray diff raction,scanning electron microscopy,transmission electron microscopy,N2 adsorption–desorption,thermogravimetry–differential thermal analysis,and NH3 temperature-programmed desorption techniques.The reactivity of Pt–Sn–K/γ-Al2O3 for propane dehydrogenation was tested in a micro-fixed-bed reactor.The results show thatγ-Al2O3 with a specific surface area of 358.1 m 2/g and pore volume of 0.96 cm 3/g was obtained when the molar ratio of CO(NH2)2/Al was 3:1 and the reaction temperature was 140℃.The alumina obtained by calcination of AACH has a higher specific surface area and larger pore volume than the industrial pseudo-boehmite does.The catalyst prepared from AACH as precursor showed high selectivity and conversion,which can reach 96.1%and 37.6%,respectively,for propane dehydrogenation.

Preparation of Nano-Alumina with Aluminum Scraps as Raw Materials

Ammonium aluminum carbonate hydroxide (AACH) was synthesized by the reaction of ammonium aluminum sulphate (AA) with ammonium hydrogen carbonate (AHC). AA was obtained by the reaction of NH4HSO4 with aluminum scraps as the raw materials. According to this method, AACH samples prepared were used to fabricate nano alumina powders by thermal decomposition. The microstructural properties of as-formed alumina were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), special surface analysis and inductively coupled plasma-atomic emission spectrometry (ICP-AES). Experimental observations revealed that highly pure (99.99%) α-alumina with mean diameter of 49 nm could be obtained.

Biodegradable Poly(propylene carbonate)/Layered Double Hydroxide Composite Films with Enhanced Gas Barrier and Mechanical Properties

Relatively well crystallized and high aspect ratio Mg-Al layered double hydroxides（LDHs） were prepared by coprecipitation process in aqueous solution and further rehydrated to an organic modified LDH（OLDH） in the presence of surfactant. The intercalated structure and high aspect ratio of OLDH were verified by X-ray diffraction（XRD） and scanning electron microscopy（SEM）. A series of poly（propylene carbonate）（PPC）/OLDH composite films with different contents of OLDH were prepared via a melt-blending method. Their cross section morphologies, gas barrier properties and tensile strength were investigated as a function of OLDH contents. SEM results show that OLDH platelets are well dispersed within the composites and oriented parallel to the composite sheet plane. The gas barrier properties and tensile strength are obviously enhanced upon the incorporation of OLDH. Particularly, PPC/2%OLDH film exhibits the best barrier properties among all the composite films. Compared with pure PPC, the oxygen permeability coefficient（OP） and water vapor permeability coefficient（WVP） is reduced by 54% and 17% respectively with 2% OLDH addition. Furthermore, the tensile strength of PPC/2%OLDH is 83% higher than that of pure PPC with only small lose of elongation at break. Therefore, PPC/OLDH composite films show great potential application in packaging materials due to its biodegradable properties, superior oxygen and moisture barrier characteristics.

Preparation and modification of activated carbon for benzene adsorption by steam activation in the presence of KOH

A series of activated carbons from Taixi anthracite were prepared by steam activation in the presence of KOH and then they were modified by different methods. The regulation of porosity and the modification of surface chemistry were carried out with the aim to improve the benzene adsorption capacity of activated carbon. The influences of KOH and activation process parameters including activation temperature, activation time and steam flow rate on porosity of activated carbon were evaluated, and the effect of modification methods on surface chemistry was investigated. Also, the relationship between benzene adsorption capacity and porosity and surface chemistry was analyzed. Results show that activation temperature is the dominant factor in the activation process; the introduction of KOH into the raw material can enhance the reactivity of char in activation process, meanwhile it shows a negative effect on the porosity development, especially on the mesopore development. Results of FTIR analysis indicate that anthracite-based activated carbon with condensed aromatics and chemically inert oxygen does not present the nature to be surface modified. Besides, benzene adsorption capacity has an approximate linear relationship with surface area and in our preparation, benzene adsorption capacity and surface area of activated carbon are up to 1210 m 2 /g and 423 mg/g, respectively.

Study on Capacitance of Zn-Based Electrode in Redox Electrolyte System

Electrode material is one of the most important factors affecting the performance of supercapacitors, and electrolyte solution is another. In this work, electrochemical properties of hydroxide zinc carbonate composite electrode (HZC) in KOH + K3[Fe(CN)6] electrolyte were studied. It was proved that [Fe(CN)6]3−in electrolyte participated in electrochemical reactions and promoted electron transfer. The specific capacitance of HZC electrode was as high as 920.5 F·g−1 at 1.0 A·g−1 in 1 mol·L−1 KOH and 0.04 mol·L−1 K3[Fe(CN)6] electrolyte, which is 172.9% higher than that in KOH. The combination of HZC electrode and low alkalinity aqueous electrolyte provided the supercapacitor system with good capacitance performance, safety, and environmentally friendly.

Unraveling role of double-exchange interaction in electrochemical water oxidation by external magnetic field

Double-exchange(DE) interaction plays an important role in electrocatalytic oxygen evolution reaction(OER).However,precise achievement of DE interaction often requires foreign dopants or vacancy engineering,leading to destabilization of the catalysts and deterioration of performance.By contrast,the utilization of environmentally friendly,contactless,and continuously adjustable magnetic fields to study the OER process is profitable to avoid aforementioned interference factors and further elucidate the direct relationship_(0.5)between DE interaction and OER activity.Here,by using cobalt hydroxide carbonate(Co(OH)(CO_(3))·xH_(2)O,CoHC) nanostructures as a proof-of-concept study,external magnetic fields are carefully implemented to verify the role of DE interaction during water oxidation reaction.Detailed studies reveal that external magnetic fields effectively enhance the reaction rate of the catalyst,the overpotential decreases from 386 to 355 mV(100 mA·cm^(-2)),while Tafel slopes drastically decline from 93 to 67 mV·dec^(-1)(1.0 T).Moreover,magnetic field increment exhibits robust durability.Through in situ Raman and impedance measurements under external field,it can be found that magnetic field promotes the electron migration between Co^(2+) and Co^(3+) in the CoHC catalysts with the assistance of DE interactions,thus boosting the OER efficiency.

Hydrothermal synthesis of single-crystal CeCO_3OH and their thermal conversion to CeO_2

Hexagonal single-crystalline cerium carbonate hydroxide （CeCO3OH） precursors with dendrite morphologies have been synthesized by a facile hydrothermal method at 180 C using CeCl3-7H2O as the cerium source, triethylenetetramine as both an alkaline and carbon source, with triethylenete- tramine also playing an important role in the formation of the dendrite structure. Polycrystalline ceria （CeO2） have been obtained by calcining the precursor at 500 C for 4 h. Tile morphology of the precursor was partly maintained during the heating process. The optical absorption spectra indicate the CeO2 nano/microstructures have a direct band gap of 2.92 eV, which is lower than values of the bulk powder due to the quantum size effect. The high absorption in the UV region for CeO2 nano/microstructure indicated that this material was expected to be used as UV-blocking materials.

Preparation of porous sea-urchin-like CuO/ZnO composite nanostructure consisting of numerous nanowires with improved gas-sensing performance

A sea-urchin-like CuO/ZnO porous nanostructure is obtained via a simple solution method followed by a calcination process.There are abundant pores among the resulting nanowires due to the thermal decomposition of copper-zinc hydroxide carbonate.The specific surface area of the as-prepared CuO/ZnO sample is determined as 31.3 m^(2)·g^(-1).The gas-sensing performance of the sea-urchin-like CuO/ZnO sensor is studied by exposure to volatile organic compound(VOC)vapors.With contrast to a pure porous sea-urchin-like ZnO sensor,the sea-urchin-like CuO/ZnO sensor shows superior gas-sensing behavior for acetone,formaldehyde,methanol,toluene,isopropanol and ethanol.It exhibits a high response of 52.6-100 ppm acetone vapor,with short response/recovery time.This superior sensing behavior is mainly ascribed to the porous nanowireassembled structure with abundant p-n heterojunctions.

Catalytic action of rare earth oxide(La_(2)O_(3),CeO_(2),Pr_(6)O_(11))on electrochemical oxidation of activated carbon in molten KOH-NaOH

The oxidation of anode carbon fuel directly affects the electrochemical performance of molten hydroxide direct carbon fuel cell(MHDCFC).In general,the anode carbon fuel can be oxidized at high temperature,thus the direct carbon fuel cell(DCFC)can show great electrochemical performance.In this study,rare earth oxides(La_(2)O_(3),CeO_(2),Pr_(6)O_(11))were prepared by the method of precipitation.Activated carbon was prepared by pretreatment of lignite.Rare earth oxides and activated carbon were mixed as anode carbon fuel,and rare earth oxides were used to catalyze the electrochemical oxidation of anode carbon fuel.The results show that CeO_(2)has better electrocatalytic activity compared with La_(2)O_(3)and Pr_(6)O_(11) in the MHDCFC.The electrochemical test results show that the current density(at 0.4 V)increases from 81.02 to 112.90 mA/cm^(2)and the maximum power density increases from 34.78 to 47.05 mW/cm^(2)at 450℃,when the mass fraction of CeO_(2)is increased from 0 to 40%.When the mass fraction of CeO_(2)is 30%,the current density(82.55 mA/cm^(2)at 0.4 V)at 400℃is higher than that(81.02 mA/cm^(2)at 0.4 V)without CeO_(2)at 450℃.The electrochemical oxidation mechanism of CeO_(2)catalyzed anode carbon fuel is discussed.