Fe稳固的FeOOH@NiOOH电催化剂的大电流极化设计与析氧研究

电解水技术是制取高纯度氢气的有效途径,为传统的氢气生产提供了一种可持续的替代方案.其中,开发性能优异的电催化材料是降低电解水制氢成本的关键.析氧反应(OER)由于涉及多个电子转移而导致的动力学缓慢,是克服高过电位的主要挑战.镍铁羟基/氢氧化物(NiFe(oxy)hydroxides)是近期研究的热点,其在碱性条件下具有极低的OER过电位,部分材料性能甚至超过了贵金属基催化剂,如IrO_(2)和RuO_(2).然而,NiFe(oxy)hydroxides的长期催化稳定性,尤其是在大电流下的长期催化稳定性,成为限制其实际应用的主要问题,这主要是由于铁元素的严重流失导致的.因此,如何有效控制和利用电化学溶解/沉积动力学成为稳定铁位点的关键.为克服该挑战,本文提出了一种大电流极化重构方法来固定活性铁位点.通过在大电流(1.5 A cm^(-2))下对材料进行表面快速极化重构,成功制备了FeOOH@NiOOH(eFNO_(L))电催化剂.eFNO_(L)不仅具有稳定的铁位点,还暴露出高指数晶面,因此eFNO_(L)同时展现出较好的OER催化活性和稳定性.同时,密度泛函理论计算结果表明,与具有低指数晶面的FeNiOOH相比,大电流极化工程制备的分相eFNO_(L)对铁位点表现出更高的结合能,可以有效抑制OER过程中的铁流失,且高指数晶面在改变速率决定步骤和减少吸附能垒上具有更大的优势.电化学测试结果表明,经过优化后的eFNO_(L)催化剂在产生100和500 mA cm^(-2)大电流密度仅需234和27 mV的过电位,并且具有较小的Tafel斜率(35.2 mV dec^(-1)).由于铁位点结合能的提高,eFNO_(L)催化剂在500 mA cm^(-2)的电流密度下能够稳定催化超过100 h,且仅有1.5%的性能衰减,优于近期报道的大多数镍铁基OER催化剂.综上,本文为开发高活性和高稳定性能的催化剂提供了一种有效的大电流电化学重构策略,在电解水制氢领域实现其工业化的大规模应用方面显示出巨大潜力,有望降低可持续电解水制氢成本.

Carbon dioxide reforming of methane over mesoporous nickel aluminate/γ-alumina composites

A series of xNiAl2O4/γ-Al2O3composites with various Ni contents have been prepared via one-step partial hydrolysis of metal nitrate salts in the absence of surfactants and used for carbon dioxide reforming of methane. The characterization results demonstrated that the NiAl2O4/γ-Al2O3materials possessed mesoporous structures of uniform pore sizes; and the Ni2+ions were completely reacted with alumina to NiAl2O4spinel in the matrices using N2sorption, XRD, TEM, and XPS. The NiAl2O4/γ-Al2O3materials exhibited excellent catalytic properties and superior long-term stability for carbon dioxide reforming of methane. The effects of Ni content on the intrinsic activities and the amounts of coke disposition of the xNiAl2O4/γ-Al2O3catalysts were discussed in detail for the carbon dioxide reforming of methane. The results revealed that the Ni particle sizes did not affect the intrinsic activity of metallic Ni, but smaller Ni particles could reduce the rate of coke deposition. © 2016 Science Press

Influence of Conductivity of Slag on Decarburization Reaction

By altering the electrochemical properties of slag, the decarburization reaction of Fe3+-based slag withFe-C droplet was studied. The results showed that a lot of free electrons and holes exist in the slag containing transition metal oxides (such as TiO2 and Fe2O3). So electronic conduction in the slag increases. Finally, it led to the increment of the decarburization reaction rate between slag and Fe-C droplet, and mass fraction of carbon remaining indroplet decreases to a lower level.

Controlled moderative sulfidation-fabricated hierarchical heterogeneous nickel sulfides-based electrocatalyst with tripartite Mo doping for efficient oxygen evolution

An electrocatalyst with heterogeneous nanostructure, especially the hierarchical one, generally shows a more competitive activity than that of its single-component counterparts for oxygen evolution reaction(OER), due to the synergistically enhanced kinetics on enriched active sites and reconfigured electronic band structure. Here this work introduces hierarchical heterostructures into a NiMo@NiS/MoS_(2)@Ni_(2)S_(2)/MoO_(x)(NiMoS) composite by one-pot controlled moderative sulfidation. The optimal solvent composition and addition of NaOH enable NiMoS to own loose and porous structures, smaller nanoparticle sizes, optimal phase composition and chemical states of elements, improving the OER activity of NiMoS. To achieve current densities of 50 and 100 mA cm^(-1), small overpotentials of 275 and 306 mV are required respectively, together with a minor Tafel slope of 58 mV dec^(-1), which outperforms most reported sulfide catalysts and IrO_(2). The synergistic effects in the hierarchical heterostructures expose more active sites,adjust the electronic band structure, and enable the fast charge transfer kinetics, which construct an optimized local coordination environment for high OER electrocatalytic activity. Furthermore, the hierarchical heterostructures suppress the distinct lowering of electrical conductivity and collapse of pristine structures resulted from the metal oxidation and synchronous S leaching during OER, yielding competitive catalytic stability.

Highly efficient and stable electrocatalyst for hydrogen evolution by molybdenum doped Ni-Co phosphide nanoneedles at high current density

There is an increasingly urgent need to develop cost-effective electrocatalysts with high catalytic activity and stability as alternatives to the traditional Pt/C in catalysts in water electrolysis.In this study,microspheres composed of Mo-doped NiCoP nanoneedles supported on nickel foam were prepared to address this challenge.The results show that the nanoneedles provide sufficient active sites for efficient electron transfer;the small-sized effect and the micro-scale roughness enhance the entry of reactants and the release of hydrogen bubbles;the Mo doping effectively improves the electrocatalytic performance of NiCoP in alkaline media.The catalyst exhibits low hydrogen evolution overpotentials of 38.5 and 217.5 mV at a current density of 10 mA·cm^(-2) and high current density of 500 mA·cm^(-2),respectively,and only 1.978 V is required to achieve a current density of 1000 mA·cm^(-2) for overall water splitting.Density functional theory(DFT)calculations show that the improved hydrogen evolution performance can be explained as a result of the Mo doping,which serves to reduce the interaction between NiCoP and intermediates,optimize the Gibbs free energy of hydrogen adsorption(△G_(*H)),and accelerate the desorption rate of *OH.This study provides a promising solution to the ongoing challenge of designing efficient electrocatalysts for high-current-density hydrogen production.

Effect of CeO_2 addition on Ni/Al_2O_3 catalysts for methanation of carbon dioxide with hydrogen

The Ni-CeO2/Al2O3 catalysts with a nickel content of 15 wt% prepared via impregnating boehmite were found to be highly active and stable for methanation of carbon dioxide with hydrogen at a H2/CO2 molar ratio of 4. The effects of CeO2 content and reaction temperature on the performance of the Ni-CeO2/Al2O3 catalysts were studied in detail. The results showed that the catalytic performance was strongly dependent on the CeO2 content in Ni-CeO2/Al2O3 catalysts and that the catalysts with 2 wt% CeO2 had the highest catalytic activity among the tested ones at 350 ℃. The XRD and H2-TPR characterizations revealed that the addition of CeO2 decreased the reduction temperature by altering the interaction between Ni and Al2O3, and improved the reducibility of the catalyst. Preliminary stability test of 120 h on stream over the Ni-2CeO2/Al2O3 catalyst at 350 ℃ revealed that the catalyst was much better than the unpromoted one.

Molten salt synthesis of porous carbon and its application in supercapacitors: A review

Carbon materials have taken an important role in supercapacitor applications due to their outstanding features of large surface area,low price,and stable physicochemical properties.Considerable research efforts have been devoted to the development of novel synthesis strategy for the preparation of porous carbon materials in recent years.In particular,molten salt strategy represents an emerging and promising method,whereby it has shown great potential in achieving tailored production of porous carbon.It has been proved that the molten salt-assisted production of carbon via the direct carbonization of carbonaceous precursors is an effective approach.Furthermore,with the incorporation of electrochemical technology,molten salt synthesis of porous carbon has become flexible and diversiform.Here,this review focuses on the mainstream molten salt synthesis strategies for the production of porous carbon materials,which includes direct molten salt carbonization process,capture and electrochemical conversion of CO_(2)to value-added carbon,electrochemical exfoliation of graphite to graphene-based materials,and electrochemical etching of carbides to new-type carbide-derived carbon materials.The reaction mechanisms and recent advances for these strategies are reviewed and discussed systematically.The morphological and structural properties and capacitive performances of the obtained carbon materials are summarized to reveal their appealing points for supercapacitor applications.Moreover,the opportunities and challenges of the molten salt synthesis strategy for the preparation of carbon materials are also discussed in this review to provide inspiration to the future researches.

Gasification of iron coke and cogasification behavior of iron coke and coke under simulated hydrogen-rich blast furnace condition

To explore the iron coke application in hydrogen-rich blast furnace,which is an effective method to achieve the purpose of low carbon emissions,the initial gasification temperature of iron coke in CO_(2) and H_(2)O atmosphere and its cogasification reaction mechanism with coke were systematically studied.Iron coke was prepared under laboratory conditions,with a 0-7wt%iron ore powder addition.The properties of iron cokes were tested by coke reactivity index(CRI)and coke strength after reaction(CSR),and their phases and morphology were evolution discussed by scanning electron microscopy and X-ray diffraction analysis.The results indicated that the initial gasification temperature of iron coke decreased with the increase in the iron ore powder content under the CO_(2) and H_(2)O_((g))atmosphere.In the 40vol%H_(2)O+60vol%CO_(2) atmosphere,CRI of iron coke with the addition of 3wt%iron ore powder reached 58.7%,and its CSR reached 56.5%.Because of the catalytic action of iron,the reaction capacity of iron coke was greater than that of coke.As iron coke was preferentially gasified,the CRI and CSR of coke were reduced and increased,respectively,when iron coke and coke were cogasified.The results showed that the skeleton function of the coke can be protected by iron coke.

Continuous electrodeposition of silicon and germanium micro/nanowires from their oxides precursors in molten salt

In recent years,silicon(Si)and germanium(Ge)materials have been considered as promising highperformance anode materials for lithium-ion batteries due to their high theoretical capacities.It is of great importance to design and synthesize micro/nanostructured Si and Ge materials.In this work,we demonstrated that Si,Ge and SiGe micro/nanowires can be continuously synthesized from their oxides precursors through molten salt electrodeposition.The electrochemical synthesis processes have been investigated systematically,and the deposited Si,Ge and SiGe micro/nanowires have been characterized and compared.The results show that the micro/nanostructured Si and Ge materials with tunable morphology can be facilely and continuously produced via molten salt electrodeposition.The electrodeposition process generally includes calcium oxide-assisted dissolution and electrodeposition processes,and the morphologies of the deposited Si and Ge products can be controlled by varying conditions.Si micro/nanowires,Si films,Ge micro/nanowires,and Ge particles can be continuously synthesized in a controlled manner.

Oxygen permeability and CO_2-tolerance of Ce_(0.8)Gd_(0.2)O_(2-δ)-Ln BaCo_2O_(5+δ) dual-phase membranes

A series of oxygen permeable dual-phase composite oxides 60 wt% Ce0.8Gd0.2O2-δ-40 wt% LnBaCo2O5＋δ （CGO-LBCO, Ln = La, Pr, Nd, Sin, Gd and Y） were synthesized through a sol-gel route and effects of the Ln3＋ cations on their phase structure, oxygen permeability and chemical stability against CO2 were investigated systemically by XRD, SEM, TG-DSC and oxygen permeation experiments. XRD patterns reveal that the larger Ln3＋ cations （La3＋, Pr3＋ and Nd3＋） successfully stabilized the double-layered perovskite structure of sintered LBCO, while the smaller ones （Sm3＋, Gd3＋, and Y3＋） resulted in the partial decomposition of LBCO with some impurities formed. CGO-PBCO yields the highest oxygen permeation flux, reaching 2.8× 10^-7 mol.s-1.cm-2 at 925 ℃ with 1 mm thickness under air/He gradient. The TG-DSC profiles in 20 mol% CO2/N2 and oxygen permeability experiments with CO2 as sweep gas show that CGO-YBCO demonstrates the best chemical stability against CO2, possibly due to its minimum basicity. The stable oxygen permeation flux of CGO-YBCO under CO2 atmosphere reveals its potential application in the oxy-fuel combustion route for CO2 capture.

All-climate aqueous supercapacitor enabled by a deep eutectic solvent electrolyte based on salt hydrate

Aqueous supercapacitors(SCs)have received considerable attention owing to the utilization of low-cost,non-flammable,and low-toxicity aqueous electrolytes thus could eliminate the safety and cost concerns,but their wide temperature range applications have generally suffered from frozen of electrolyte and insufficient ionic conductivity at low temperatures.Herein,we demonstrate the feasibility of using an unconventional Deep Eutectic Solvent(DES)based on H2O-Mg(ClO4)2·6 H2O binary system as electrolyte to construct all-climate aqueous carbon-based SC.This unconventional class DES completely base on inorganic substances and achieving simply mix inexpensive salts and water together at the right proportions.Attributed to the attractive feature of extremely low freeze temperature of-69℃,this electrolyte can enable the 1.8 V carbon-based SC to fully work at-40℃with outstanding cycling stability.This DES electrolyte comprising of a single salt and a single solvent without any additive will open up an avenue for developing simple and green electrolytes to construct all-climate SC.

An integrated strategy towards the facile synthesis of core-shell SiC-derived carbon@N-doped carbon for high-performance supercapacitors

Porous active core-shell carbon material with excellent synergistic effect has been regarded as a prospective material for supercapacitors.Herein,we report an integrated method for the facile synthesis of carbide-derived carbon(CDC)encapsulated with porous N-doped carbon(CDC@NC)towards highperformance supercapacitors.Polydopamine(PDA)as nitrogen and carbon sources was simply coated on SiC nanospheres to form SiC@PDA,which was then directly transformed into CDC@NC via a onestep molten salt electro-etching/in-situ doping process.The synthesized CDC@NC with hierarchically porous structure has a high specific surface area of 1191 m^(2) g^(-1).The CDC core and NC shell are typical amorphous carbon and more ordered N-doped carbon,respectively.Benefitting from its unique dual porous structures,the CDC@NC demonstrates high specific capacitances of 255 and 193 F g^(-1) at 0.5 and20 A g^(-1),respectively.The reaction mechanism of the electro-etching/in-situ doping process has also been investigated through experimental characterizations and theoretical density functional theory calculations.It is suggested that the molten salt electro-etching/in-situ doping strategy is promising for the synthesis of active core-shell porous carbon materials with synergistic properties for supercapacitors without the need for additional doping/activation processes.

Kinetics of hydrogen absorption and desorption of a mechanically milled MgH_2+5at%V nanocomposite

The experimental data in the MgH2-5at%V composite was summarized and used to investigate the kinetic mechanism of hydrogen absorption and desorption using a new model. The research results indicate that a coincidence of the theoretical calculation values with the experimental data has been reached and the rate-limiting step is hydrogen diffusion through the hydride phase （β phase） with the activation energy of 47.2 kJ per mole H2 for absorption and the diffusion of hydrogen in the a solid solution （α phase） with that of 59.1 kJ per mole H2 for desorption. In addition, the hydriding rate of the MgH2-V composite is 2.9 times faster than that of MgH2 powders when compared with their characteristic absorption time directly.

Oxygen permeation and phase structure properties of partially A-site substituted BaCo_(0.7)Fe_(0.225)Ta_(0.075)O_(3-δ) perovskites

Ba0.9R0.1Co0.TFe0.225Ta0.07503-δ （BRCFT, R = Ca, La or Sr） membranes were synthesized by a solid-state reaction. Metal cation Ca2＋, La3＋ or Sr2＋ doping on A-site partially substituted Ba2＋ in BaCoo.TFe0.225Ta0.07503-δ oxides, and its subsequent effects on phase structure stability, oxygen permeability and oxygen desorption were systematically investigated by XRD, TG-DSC, Hz-TPR, O2-TPD techniques and oxygen permeation experiments. The partial substitution with Ca2＋, La3＋ or Sr2＋, whose ionic radii are smaller than that of Ba2＋, succeeded in stabilizing the cubic perovskite structure without formation of impurity phases, as revealed by XRD analysis. Oxygen-involving experi- ments showed that BRCFT with A-site fully occupied by Ba2＋ exhibited good oxygen permeation flux under He flow, reaching about 2.3 mL.min-l .cm-2 at 900 with I mm thickness. Of all the membranes, BLCFT membrane showed better chemical stability in CO2, owing to the reduction in alkalinity of the mixed conductor oxide by La doping. In addition, we also found the stability of the perovskite structure under reducing atmospheres was strengthened by increasing the size of A-site cation （Ba2＋〉La3＋〉SrZ＋〉Ca2＋）.

Fast and extensive intercalation chemistry in Wadsley-Roth phase based high-capacity electrodes

Wadsley-Roth (W-R) structured oxides featured with wide channels represent one of the most promising material families showing compelling rate performance for lithium-ion batteries.Herein,we report an indepth study on the fast and extensive intercalation chemistry of phosphorus stabilized W-R phase PNb_(9)O_(25) and its application in high energy and fast-charging devices.We explore the intercalation geometry of PNb_(9)O_(25) and identify two geometrical types of stable insertion sites with the total amount much higher than conventional intercalation-type electrodes.We reveal the ion transportation kinetics that the Li ions initially diffuse along the open type Ⅲ channels and then penetrate to edge sites with low kinetic barriers.During the lithiation,no remarkable phase transition is detected with nearly intact host phosphorous niobium oxide backbone.Therefore,the oxide framework of PNb_(9)O_(25) keeps almost unchanged with all the fast diffusion channels and insertion cavities well-maintained upon cycling,which accomplishes the unconventional electrochemical performance of W-R structured electrodes.

Hydrogen production from simulated hot coke oven gas by catalytic reforming over Ni/Mg(Al)O catalysts

Hydrogen production by catalytic reforming of simulated hot coke oven gas （HCOG） with toluene as a model tar compound was investigated in a fixed bed reactor over Ni/Mg（Al）O catalysts. The catalysts were prepared by a homogeneous precipitation method using urea hydrolysis and characterized by ICE BET, XRD, TPR, TEM and TG. XRD showed that the hydrotalcite type precursor after calcination formed （Ni, Mg）Al2O4 spinel and Ni-Mg-O solid solution structure. TPR results suggested that the increase in Ni/Mg molar ratio gave rise to the decrease in the reduction temperature of Ni^2＋ to Ni^0 on Ni/Mg（Al）O catalysts. The reaction results indicated that toluene and CH4 could completely be converted to H2 and CO in the catalytic reforming of the simulated HCOG under atmospheric pressure and the amount of H2 in the reaction effluent gas was about 4 times more than that in original HCOG. The catalysts with lower Ni/Mg molar ratio showed better catalytic activity and resistance to coking, which may become promising catalysts in the catalytic reforming of HCOG.

Electrochemical Characteristic of Decarburization Reaction

The electrochemical mechanism of the reaction between Fe-C melts and CaO-SiO2-Al2O3-FeOx slag systems has been carried out. The experimental results suggest that the final content of carbon in melt increases as the partial oxygen pressure of gas decreases no matter whether there is electronic conductor or not. However, the final content of carbon in the system with electronic conductor is much lower than that without electronic conductor. It can be deduced that the transfer ability of oxygen in slag is dominated by electrons. When an electronic conductor exists, an easy pathway for the electrons is provided and the oxygen transfer rate is accelerated.

Electrolysis of Converter Matte in Molten CaCl₂-NaCl

The electrolytic production of nickel-copper alloy by electrochemical reduction of converter matte in molten salt has been investigated. The sintered solid porous pellets of Ni3S2, Cu2S and converter matte were electrolyzed at a voltage of 3.0 V in molten CaCl2-NaCl under the protection of argon gas at 700℃, respectively. The electro-reduction processes were investigated and the products were characterized. The results show that the molten salt electro-reduction process can be used to produce nickel, copper and nickel-copper alloy directly from Ni3S2, Cu2S and converter matte precursors in molten CaCl2-NaCl, respectively. CaS would be formed as the intermediate compound during the electro-reduction process, and then the formed CaS can be gradually decomposed and removed with the increase of the electrolysis time. The experimental results show that the molten salt electro-reduction process has the potential to be used for the reduction of sulfide minerals in molten CaCl2-NaCl.

Suppression of multistep phase transitions of O3-type cathode for sodium-ion batteries

O3-type layered oxide cathodes have been widely investigated due to their high reversible capacities and sufficient Na+reservoirs.However,such materials usually suffer from complex multistep phase transitions along with drastic volume changes,leading to the unsatisfied cycle performance.Herein,we report a Mg/Ti co-doped O3-type NaNi_(0.5)Mn_(0.5)O_(2),which can effectively suppress the complex multistep phase transition and realize a solid-solution reaction within a wide voltage range.It is confirmed that,the Mg/Ti co-doping is beneficial to enhance the structural stability and integrity by absorbing micro-strain and distortions.Thus,the as obtained sample delivers an outstanding cyclic performance(82.3%after 200 cycles at 1 C)in the voltage range of 2.0-4.0 V,and a high discharge capacity of 86.6 mAh/g after 100 cycles within the wide voltage range(2.0-4.5 V),which outperform the existing literatures.This co-doping strategy offers new insights into high performance O3-type cathode for sodium ion batteries.

Bimetallic site substitution of NiCoP nanoneedles as bifunctional electrocatalyst for boosted water splitting

The bimetallic nickel-cobalt phosphide (NiCoP) has been confirmed as an efficient electrocatalyst in water splitting. But little attention is paid to the selectivity and affinity of metal sites on hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, we report a trace-Zn-doping (2.18 wt.%) NiCoP (Zn-NiCoP) whereby the nanoparticles self-aggregated to form elongated nanoneedles. We discover that both Co and Ni sites can be replaced by Zn. The Co substitution improves HER, while the Ni substitution dramatically reduces the energy barrier of the rate-determining step (*O → *OOH). The negative shift of d-band centers after Zn doping ameliorates the intermediate desorption. Therefore, Zn-NiCoP demonstrates superior electrocatalytic activity with overpotentials of 48 and 240 mV for HER and OER at 10 and 50 mA·cm^(−2), respectively. The cell voltage with Zn-NiCoP as both anode and cathode in water splitting was as low as 1.35 V at 10 mA·cm^(−2).