Green and scalable electrochemical routes for cost‐effective mass production of MXenes for supercapacitor electrodes

One of the most unique properties of two-dimensional carbides and nitrides of transition metals(MXenes)is their excellent water dispersibility and yet possessing superior electrical conductivity but their industrial-scale application is limited by their costly chemical synthesis methods.In this work,the niche feature of MXenes was capitalized in the packed-bed electrochemical reactor to produce MXenes at an unprecedented reaction rate and yield with minimal chemical waste.A simple NH4F solution was employed as the green electrolyte,which could be used repeatedly without any loss in its efficacy.Surprisingly,both fluoride and ammonium were found to play critical roles in the electrochemical etching,functionalization,and expansion of the layered parent materials(MAXs)through which the liberation of ammonia gas was observed.The electrochemically produced MXenes with excellent conductivity,applied as supercapacitor electrodes,could deliver an ultrahigh volumetric capacity(1408 F cm^(−3))and a volumetric energy density(75.8 Wh L^(−1)).This revolutionary green,energy-efficient,and scalable electrochemical route will not only pave the way for industrial-scale production of MXenes but also open up a myriad of versatile electrochemical modifications for improved functional MXenes.

Charge transfer in plasma assisted dry reforming of methane using a nanosecond pulsed packed-bed reactor discharge

This paper is aimed to investigate the effect of packing material on plasma characteristic from the viewpoint of charge transfer process.Both the charge accumulation and release processes in the dielectric barrier discharge reactor and packed-bed reactor were investigated by measuring voltage and current waveforms and taking ICCD images.The packing material was ZrO2 pellets and the reactors were driven by a parameterized nanosecond pulse source.The quantity of transferred charges in the dielectric barrier discharge reactor was enhanced when decreasing pulse rise time or increasing pulse width(within 150 ns),but reduced when the gas gap was packed with pellets.The quantity of accumulated charges in the primary discharge was larger than the quantity of released charges in the secondary discharges in the dielectric barrier discharge reactor,but they were almost equal in the packed-bed reactor.It indicates that the discharge behavior has been changed from the view of charge transfer process once the gas gap was packed with pellets,and the ICCD images confirmed it.

Reaction Selectivity Improvement for Reduction of Nitrobenzene in a Packed-Bed Electrode Reactor under Periodic-Current Control

Rectangular wave current control of the electrochemical reduction of nitrobenzene im-proves the selectivity for p-aminophenol(PAP) compared to direct current(d.c.) control at thesame average current density in a flow-by packed-bed reactor.Optimal increase in PAP selectivitycan be obtained at about a frequency of 50Hz and a duty cycle of 0.2.A mathematical model isset up to incorporate the effects of mass transfer,hydrogen evolution and double layer charging,and is solved using the Duhamel’s superposition principle and the modified Crank-Nicolson methodwith the upwind scheme.The conventional d.c.control cases are also calculated for comparison.Calculations can be applied to predict the reaction results under periodic current and d.c.control,but both display the same trends compared to experimental data.

Ozone generation enhanced by silica catalyst in packed-bed DBD reactor

In this paper,three dielectric barrier discharge(DBD)configurations,which were plain DBD with no packing,DBD with packed pure quartz fibers and DBD with packed loaded quartz fibers,were employed to investigate the effect and catalytic mechanism of catalyst materials in a packed-bed ozone generator.From the experimental results,it was clear that the DBD configuration with packed pure fibers and packed loaded fibers promotes ozone generation.For the packed-bed reactor,ozone concentration and ozone yield were enhanced by an increase of electric field in the discharge gap with the packed-bed effect.Meanwhile,the enhancement of ozone concentration and yield for the DBD reactor packed by loaded fibers with silica nanoparticles was due to the catalysis of silica nanoparticles on the fiber surface.The adsorption of silica nanoparticles on the fiber surface can prolong the retention time of active species and enhance surface reactions.

Numerical simulation of packed-bed reactor for oxidative coupling of methane

A three-dimensional geometric model of the oxidative coupling of methane （OCM） packed-bed reactor loaded with Na2WO4-Mn/SiO2 partic- ulate catalyst was set up, and an improved Stansch kinetic model was established to calculate the OCM reactions using the computational fluid dynamics method and Fluent software. The simulation conditions were completely the same with the experimental conditions that the volume velocity of the reactant was 80 mL/min under standard state, the ratio of CH4/O2 was 3, the temperature and pressure were 800 ℃ and 1 atm, respectively. The contour of the characteristics parameters in the catalyst bed was analyzed, such as the species mass fractions, temperature, the heat flux on side wall surface, pressure, fluid density and velocity. The results showed that the calculated values matched well with the experimental values on the conversion of CH4 and the selectivity to products （C2H6, C2H4, CO2, CO） in the reactor outlet with an error range of 4-2%. The mass fractions of CH4 and O2 decreased from 0.6 and 0.4 in the catalyst bed inlet to 0.436 and 0.142 in the outlet, where the mass fractions of C2H6, C2H4, CO and CO2 were 0.035, 0.061, 0.032 and 0.106, respectively. Due to the existence of laminar boundary layer, the contours of each component bent upwards in the vicinity of the boundary layer. This OCM reaction was volume increase reaction and the total moles of products were greater than those of reactants. The flow field in the catalyst bed maintained constant temperature and pressure. The fluid density decreased gradually from 2.28 kg/m3 in the inlet of the catalyst bed to 2.22 kg/m3 in the outlet of the catalyst bed, while the velocity increased from 0.108 m/s to 0.115 m/s.

Electrochemical analysis and convection-enhanced mass transfer synergistic effect of MnO_x/Ti membrane electrode for alcohol oxidation

The different electrocatalytic reactors could be constructed for the electrocatalytic oxidation of 2,2,3,3-tetrafluoro-1-propanol(TFP) with two typical MnO_x/Ti electrodes, i.e.the electrocatalytic membrane reactor(ECMR) with the Ti membrane electrode and the electrocatalytic reactor(ECR) with the traditional Ti plate electrode.For the electro-oxidation of TFP, the conversion with membrane electrode(70.1%) in the ECMR was 3.3 and 1.7 times higher than that of the membrane electrode without permeate flow(40.8%) in the ECMR and the plate electrode(21.5%) in the ECR, respectively.Obviously, the pore structure of membrane and convection-enhanced mass transfer in the ECMR dramatically improved the catalytic activity towards the electro-oxidation of TFP.The specific surface area of porous electrode was 2.22 m^2·g^(-1).The surface area of plate electrode was 2.26 cm^2(1.13 cm^2× 2).In addition, the electrochemical results showed that the mass diffusion coefficient of the MnO_x/Ti membrane electrode(1.80 × 10^(-6) cm^2·s^(-1)) could be increased to 6.87 × 10^(-6) cm^2·s^(-1) at the certain flow rate with pump, confirming the lower resistance of mass transfer due to the convection-enhanced mass transfer during the operation of the ECMR.Hence, the porous structure and convection-enhanced mass transfer would improve the electrochemical property of the membrane electrode and the catalytic performance of the ECMR,which could give guideline for the design and application of the porous electrode and electrochemical reactor.

Electrochemical Detection of Horseradish Peroxidase at Zeptomole Level

An electrochemical method for determination of horseradish peroxidase (HRP) was developed using a capillary catalytic system. HRP can be measured in several minutes with a detection limit of 4.8 x 10(-12) mol/L or 47 zmol (S/N=3).

High-Con cent rat ion Electrosynthesis of Formic Acid/Formate from CO_(2):Reactor and Electrode Design Strategies

The electrochemical CO_(2)reduction reaction(CO_(2)RR),driven by renewable energy,provides a potential carbon-neutral avenue to convert CO_(2)into valuable fuels and feedstocks.Conversion of CO_(2)into formic acid/formate is considered one of the economical and feasible methods,owing to their high energy densities,and ease of distribution and storage.The separation of formic acid/formate from the reaction mixtures accounts for the majority of the overall CO_(2)RR process cost,while the increment of product concentration can lead to the reduction of separation cost,remarkably.In this paper,we give an overview of recent strategies for highly concentrated formic acid/formate products in CO_(2)RR.CO_(2)RR is a complex process with several different products,as it has different intermediates and reaction pathways.Therefore,this review focuses on recent study strategies that can enhance targeted formic acid/formate yield,such as the all-solid-state reactor design to deliver a high concentration of products during the reduction of CO_(2)in the electrolyzer.Firstly,some novel electrolyzers are introduced as an engineering strategy to improve the concentration of the formic acid/formate and reduce the cost of downstream separations.Also,the design of planar and gas diffusion electrodes(GDEs)with the potential to deliver high-concentration formic acid/formate in CO_(2)RR is summarized.Finally,the existing technological challenges are highlighted,and further research recommendations to achieve high-concentration products in CO_(2)RR.This review can provide some inspiration for future research to further improve the product concentration and economic benefits of CO_(2)RR.

新型电化学反应器降解苯酚废水的研究

以自制钛基PbO_(2)电极为阳极,以碳纤维管为阴极成功开发了一种基于电磁感应无线供电技术的微型电解池填充式电化学反应器,从电解质浓度、pH值和输入电压等等方面探究了新型电化学反应器对苯酚废水的最佳降解条件,当电解质浓度为0.012 5 mol/L,pH值为5,输入电压为8 V时进行降解100 min,苯酚降解率可达92%,处理效果最佳。与传统平板式电化学反应器相比具有明显优势。

基于三维生物膜电极的难生化有机化工废水处理研究进展

近年来,难降解有机化工污染物在自然水体中被广泛检出,对水生态环境和人体健康构成了严重威胁。生物膜电极技术因具备环境友好、去除效率高、适用范围广等优点,在难降解污染物处理领域应用前景日渐广阔。对此,介绍了三维生物膜电极(3D-BERs)反应器构建方法,阐述了三维生物膜电极对有机污染物的降解机理,分析了电化学催化氧化与电活性微生物(EAMs)的协同降解作用,从电子迁移强化角度解析了污染物强化降解机制,并概述了3D-BERs的构建方法与运行参数对反应器效率的影响。本文系统综述了3D-BERs在难生化有机化工废水处理领域中的应用与优势,提出了三维生物膜电极技术的发展前景和今后研究工作的重点方向,为难生化有机化工废水的高效处理提供新思路与技术选择。

模拟压水堆一回路环境下冷应变对321不锈钢高温电化学行为和应力腐蚀开裂行为的影响

321不锈钢是常用的压水堆结构材料之一,在成型加工和服役期间易因各种因素发生冷应变,使其性能发生改变。本文在模拟压水堆一回路水化学环境中,测量了不同冷应变量321不锈钢的电化学阻抗谱,并用热应变样品作为对比;采用慢应变速率拉伸测试了冷应变试样应力腐蚀开裂性能。使用X射线衍射(XRD)、扫描电子显微镜(SEM)、能谱仪(EDS)对样品微观特征进行了分析。XRD分析表明,冷应变使基体发生了由奥氏体到马氏体的转变,而高温抑制了这一过程。随着应变程度的增大(至20%),电荷转移电阻增大,膜电阻随马氏体含量的升高而降低。裂纹萌生实验结果表明,马氏体优先发生氧化腐蚀,保护了奥氏体基体,抑制了应力腐蚀裂纹萌生。

Conversion enhancement of tubular fixed-bed reactor for Fischer-Tropsch synthesis using static mixer

Recently, Fischer-Tropsch synthesis （FTS） has become an interesting technology because of its potential role in producing biofuels via Biomass- to-Liquids （BTL） processes. In Fischer-Tropsch （FT） section, biomass-derived syngas, mainly composed of a mixture of carbon monoxide （CO） and hydrogen （H2）, is converted into various forms of hydrocarbon products over a catalyst at specified temperature and pressure. Fixed-bed reactors are typically used for these processes as conventional FT reactors. The fixed-bed or packed-bed type reactor has its drawbacks, which are heat transfer limitation, i.e. a hot spot problem involved highly exothermic characteristics of FT reaction, and mass transfer limitation due to the condensation of liquid hydrocarbon products occurred on catalyst surface. This work is initiated to develop a new chemical reactor design in which a better distribution of gaseous reactants and hydrocarbon products could be achieved, and led to higher throughput and conversion. The main goal of the research is the enhancement of a fixed-bed reactor, focusing on the application of KenicsTM static mixer insertion in the tubular packed-bed reactor. Two FTS experiments were carried out using two reactors i.e., with and without static mixer insertion within catalytic beds. The modeled syngas used was a mixed gas composed of H2/CO in 2 ： 1 molar ratio that was fed at the rate of 30 mL（STP）·min^- 1 （GHSV ≈ 136 mL·gcat^-1 ·h^-1） into the fixed Ru supported aluminum catalyst bed of weight 13.3 g. The reaction was carried out at 180 ℃ and atmospheric pressure continuously for 36 h for both experiments. Both transient and steady-state conversions （in terms of time on stream） were reported. The results revealed that the steady-state CO conversion for the case using the static mixer was approximately 3.5 times higher than that of the case without static mixer. In both cases, the values of chain growth probability of hydrocarbon products （α） for Fischer-Tropsch synthesis were 0.92 and 0.89 for the case with and without static mixer, respectively.

Methane Conversion to C_2 Hydrocarbons in Solid State Oxide Electrolyte Membrane Reactor

Provskite-type catalysts, Ln0.6 Sr0.4 FexCo1-x O3 (Ln = Nd,Pr, Gd, Sm, La, 0＜x＜1) and Ln0.8Na0.2CoO3(Ln= La,Gd, Sm) were synthesized, their catalytic properties in the oxidative coupling of methane (OCM) were examined in a fixed-bed reactor. The former group presented higher activity in the OCM, but the main product was carbon dioxide. While the later group showed lower activity but much higher selectivity to C2 hydrocarbons compared with the former. Electrochemical measurements were conducted in a solid oxide membrane reactor with La0.8 Na0.2CoO3 as catalyst. The results showed that methane was oxidized to carbon dioxide and ethane by two parallel reactions. Ethane was oxidized to ethene and carbon dioxide. A fraction of ethene was oxidized deeply to carbon dioxide. The total selectivity to C2 hydrocarbons exceeded 70%. Based on the experimental results, a kinetic model was suggested to describe the reaction results.

锰氧化物负载活性炭颗粒电极的制备及其对甲基橙的降解性能

颗粒电极的性质对于三维电化学反应器的运行效果至关重要。为了提高颗粒电极的催化活性,本实验通过浸渍-煅烧法制备了负载锰氧化的颗粒活性炭(MnOx/GAC),并将其作为催化颗粒电极构建三维电化学反应器处理含甲基橙的模拟染料废水。通过单因素实验考察了制备条件对MnOx/GAC电催化降解甲基橙的影响。结果表明:MnO_(x)/GAC中Mn的价态包含+2、+3和+4价,在浸渍溶液Mn2+质量分数2.4%、煅烧温度600℃、煅烧时间2 h条件下制得的颗粒电极对甲基橙降解性能良好且性质稳定;经240 min处理后,甲基橙去除率达到98.5%;循环使用4次后,染料去除率无明显下降。

电催化二氧化碳还原催化剂、电解液、反应器和隔膜研究进展

人类社会的正常运转非常依赖化石能源,然而化石能源的消耗已导致能源危机和环境污染,同时空气中CO_(2)的含量从工业革命以来一直攀升。将CO_(2)通过催化反应转化为高附加值的燃料和化学品,不仅可以缓解环境问题,还开辟了一种燃料合成新路径,其中电催化CO_(2)还原技术由于条件温和、反应可控、对环境友好和产物众多受到广泛关注。电催化CO_(2)技术有四个关键步骤:(1)电荷传输(电子从导电基底传输到电催化剂);(2)表面转化(CO_(2)吸附在催化剂表面并被活化);(3)电荷传输(电子从催化剂表面传输到CO_(2)中间体);(4)传质效应(CO_(2)从电解质扩散到催化剂表面,产物以反向路径扩散),前两个步骤依赖于具有丰富有效活性位点的催化剂,后两个步骤依赖于电解质的性质、隔膜的类型和电解池的配置。本文从工业化和商业化电催化CO_(2)技术出发,系统地归纳催化剂的发展、电解液的影响、反应器的进展和隔膜的类型,最后对电催化CO_(2)还原的产业化进行展望。

三维生物电化学法提高污染物去除效能的研究进展

通过对三维生物膜电化学系统的特性进行剖析,总结出该系统具有提高氧化功能的羟基自由基水平、加速电子传递效能、增加降解功能微生物群落富集和活性的能力。通过剖析该系统对污染物高效去除的机理,从反应器构建的工艺参数(电极材料、反应器结构以及电极形状)方面提出了优化方案,对比了系统运行条件对污染物去除性能的影响,并评价其经济性能,最后提出了三维生物膜电化学法未来的发展方向。

Recent progress in electrochemical C–N coupling reactions

Electrochemical C–N coupling has generated intense research interest as a promising approach to reduce carbon and nitrogen emissions and store excess renewable electricity in valuable chemicals(e.g.,urea,amides,and amines).In this review,we discuss the emerging trends in electrocatalytic C–N coupling reactions using CO_(2) and inorganic nitrogenous species(i.e.,dinitrogen(N_(2))),nitrate(NO_(2)^(-)),nitrite(NO_(3)^(-)),and ammonia(NH_(3))as raw materials.The related reaction mechanisms and potential design principles for advanced electrocatalysts are outlined.In addition,the effects of different reactors,including H-cells,membrane-based flow reactors,and membrane electrode assembly electrolyzers,on the coupling reactions are emphasized.Finally,the current challenges and future opportunities in this field are described.We aim to provide an up-to-date overview of the electrochemical C–N coupling system to advance progress toward its practical application.

甲烷转化制乙烯技术研究进展

根据目前甲烷制乙烯技术的现状,阐述现阶段甲烷偶联的几种反应途径与各自特点以及目前甲烷偶联反应器的设计。具体论述甲烷偶联的氧化偶联、非氧化偶联两种途径,并基于不同的反应温度对每种途径下的化学方法和电化学方法分别进行概括总结。并讨论目前甲烷偶联的反应器设计趋势与调整策略。针对目前甲烷偶联制乙烯几种反应途径的难点和反应器设计趋势,提出未来催化剂设计和反应器设计方面的研究重点。

Electrochemical oxidation of recalcitrant organic compounds in biologically treated municipal solid waste leachate in a flow reactor

Biologically-treated municipal solid waste （MSW） leachate still contains many kinds of bit-recalcitrant organic matter. A new plate and frame electrochemical reactor was designed to treat these materials under flow conditions. In the electrochemical oxidation process, NH3 and color could be easily removed by means of electro-generated chlorinefaypochlorite within 20 min. The effects of major process parameters on the removal of organic pollutants were investigated systematically. Under experimental conditions, the optimum operation parameters were current density of 65 mA/cm^2, flow velocity of 2.6 cm/sec in electrode gap, and initial chloride ion concentration of 5000 mg/L. The COD in the leachate could be reduced below 100 mg/L after 1 hr of treatment. The kinetics and mechanism of COD removal were investigated by simultaneously monitoring the COD change and chlorine/hypochlorite production. The kinetics of COD removal exhibited a two-stage kinetic model, and the decrease of electro-generated chlorine/hypochlorite production was the major mechanism for the slowing down of the COD removal rate in the second stage. The narrowing of the electrode gap is beneficial for COD removal and energy consumption.

A structured packed-bed reactor designed for exothermic hydrogenation of acetone

Fixed-bed reactors randomly packed with catalysts have many disadvantages that may adversely affect the desired chemical reaction.The increasingly used monolithic reactor,in contrast,has many operational advantages;however,for a kinetically-controlled reaction,it does not contain sufficient catalyst to sustain the reaction.To address the problems associated with both randomly packed-bed reactor and the monolithic reactor,a structured packed-bed reactor was proposed and mathematical models were built for randomly packed-bed reactor and structured packed-bed reactor.Their respective performances were compared when applied to the exothermic reaction of the isopropanol-acetone-hydrogen chemical heat pump system.The results showed that the structured packed-bed reactor performed better in terms of pressure drop and heat transfer capacity,and had a lower radial temperature gradient,indicating that this reactor had a higher effective heat conductivity.Isopropanol on the catalyst particle surfaces was more concentrated near the tube wall because a wall effect existed in the boundary layer around the particle-wall contact points.