La_(0.8)Sr_(0.2)MnO_3/YSZ电极氧电化学还原反应动力学

用线性极化、循环伏安、电位阶跃等方法详细研究了La0.8Sr0.2MnO3／YSZ高温电极上进行的氧电化学还原反应．实验结果表明，该反应存在两条路径：低温下氧还原反应主要发生在气相-LSM电极-YSZ电解质接触的三相界面（TPB），速度控制步骤为氧原子在LSM表面的浓差扩散，高温下由于氧空位在LSM表面的形成，氧还原反应区扩展至LSM电极表面，速度控制步骤为氧的电荷转移反应．实验同时发现：氧空位的形成受反应温度、氧分压及阴极电位的影响，氧空位在高温及高氧分压下对反应贡献很大．

电化学去合金化Pt(Pd)-Cu对氧的电催化还原活性的研究

应用电化学去合金法制备了表面覆盖有Pt(Pd)原子层的Pt(Pd)-Cu合金催化剂.研究该催化剂在0.1mol.L-1HClO4酸性溶液中对氧气电化学还原的催化活性,并采用同步辐射反常X-射线衍射法(Anomalous X-ray Diffraction,AXRD)和表面X-射线散射法(Surface X-ray Scattering,SXS)从原子尺度研究了去合金化后催化剂的结构.分析对比纳米颗粒、薄膜和单晶3种不同形式的去合金化Pt-Cu的结构和催化活性以及Pt-Cu和Pd-Cu两种不同合金薄膜的结构和催化活性.结果表明,表面应力是影响催化剂催化活性的关键因素,而应力大小则与去合金化后所形成的表面Pt(Pd)层的厚度相关,材料尺寸和组成元素等都影响表面Pt(Pd)层的厚度.提出可利用调控材料表面的应力来设计高催化活性的催化剂.

中温固体氧化物燃料电池La_(1.6)Sr_(0.4)Ni_(1-x)Cu_xO_4阴极材料的制备及电化学性能

采用甘氨酸-硝酸盐法合成了中温固体氧化物燃料电池阴极材料La1.6Sr0.4Ni1-xCuxO4(x=0.2,0.4,0.6,0.8),利用X射线衍射(XRD)和扫描电子显微镜(SEM)对其结构和微观形貌进行了表征.结果表明,该阴极材料与固体电解质Ce0.9Gd0.1O1.95(CGO)在1000℃烧结时不发生化学反应,且烧结4h后,二者之间可形成良好的接触界面.利用电化学交流阻抗谱技术对阴极材料的电化学性能进行研究,结果显示,当Cu离子掺杂量(x)为0.6时,La1.6Sr0.4Ni0.4Cu0.6O4阴极具有最小的极化电阻,在空气中当测试温度为750℃时,极化电阻为0.35Ω·cm2.在不同氧分压条件下电化学阻抗谱分析结果表明,电极上的两个氧还原反应主要包含氧离子从三相界面向电解质CGO转移的过程和电荷的迁移过程,其中电荷的迁移过程为电极反应的速率控制步骤.La1.6Sr0.4Ni0.4Cu0.6O4电极在空气中700℃和阴极电流密度为45mA·cm-2时,阴极过电位为45mV.本研究的初步结果表明La1.6Sr0.4Ni1-xCuxO4材料是一种电化学性能较为优良的新型中温固体氧化物燃料电池(IT-SOFC)阴极材料.

Chalcogen heteroatoms doped nickel-nitrogen-carbon single-atom catalysts with asymmetric coordination for efficient electrochemical CO_(2) reduction

The electronic configuration of central metal atoms in single-atom catalysts(SACs)is pivotal in electrochemical CO_(2) reduction reaction(eCO_(2)RR).Herein,chalcogen heteroatoms(e.g.,S,Se,and Te)were incorporated into the symmetric nickel-nitrogen-carbon(Ni-N_(4)-C)configuration to obtain Ni-X-N_(3)-C(X:S,Se,and Te)SACs with asymmetric coordination presented for central Ni atoms.Among these obtained Ni-X-N_(3)-C(X:S,Se,and Te)SACs,Ni-Se-N_(3)-C exhibited superior eCO_(2)RR activity,with CO selectivity reaching~98% at-0.70 V versus reversible hydrogen electrode(RHE).The Zn-CO_(2) battery integrated with Ni-Se-N_(3)-C as cathode and Zn foil as anode achieved a peak power density of 1.82 mW cm^(-2) and maintained remarkable rechargeable stability over 20 h.In-situ spectral investigations and theoretical calculations demonstrated that the chalcogen heteroatoms doped into the Ni-N_(4)-C configuration would break coordination symmetry and trigger charge redistribution,and then regulate the intermediate behaviors and thermodynamic reaction pathways for eCO_(2)RR.Especially,for Ni-Se-N_(3)-C,the introduced Se atoms could significantly raise the d-band center of central Ni atoms and thus remarkably lower the energy barrier for the rate-determining step of ^(*)COOH formation,contributing to the promising eCO_(2)RR performance for high selectivity CO production by competing with hydrogen evolution reaction.

Electrochemically reduced graphene oxide with enhanced electrocatalytic activity toward tetracycline detection

An electrochemically reduced graphene oxide sample, ERGO_0.8v, was prepared by electrochemical reduction of graphene oxide （GO） at -0.8 V, which shows unique electrocatalytic activity toward tetracycline （TTC） detection compared to the ERGO-12v （GO applied to a negative potential of-1.2 V）, GO, chemically reduced GO （CRGO）-modified glassy carbon electrode （GC） and bare GC electrodes. The redox peaks of TTC on an ERGO-0.8v-modifled glass carbon electrode （GC/ERGO-0.8v） were within 0-0.5 V in a pH 3.0 buffer solution with the oxidation peak current correlating well with TTC concentration over a wide range from 0.1 to 160 mg/L Physical characterizations with Fourier transform infrared （FT-IR）, Raman, and X-ray photoelectron spectroscopies （XPS） demonstrated that the oxygen-containing functional groups on GO diminished after the electrochemical reduction at -0.8 V, yet still existed in large amounts, and the defect density changed as new sp2 domains were formed. These changes demonstrated that this adjustment in the number of oxygen-containing groups might be the main factor affecting the electrocatalytic behavior of ERGO. Additionally, the defect density and sp2 domains also exert a profound influence on this behavior. A possible mechanism for the TTC redox reaction at the GC/ERGO-0.8v electrode is also presented. This work suggests that the electrochemical reduction is an effective method to establish new catalytic activities of GO by setting appropriate parameters.

Preparation of nitrogen-doped carbon nanoblocks with high electrocatalytic activity for oxygen reduction reaction in alkaline solution

The oxygen reduction reaction （ORR） is traditionally performed using noble‐metals catalysts, e.g. Pt. However, these metal‐based catalysts have the drawbacks of high costs, low selectivity, poor stabili‐ties, and detrimental environmental effects. Here, we describe metal‐free nitrogen‐doped carbon nanoblocks （NCNBs） with high nitrogen contents （4.11%）, which have good electrocatalytic proper‐ties for ORRs. This material was fabricated using a scalable, one‐step process involving the pyrolysis of tris（hydroxymethyl）aminomethane （Tris） at 800℃. Rotating ring disk electrode measurements show that the NCNBs give a high electrocatalytic performance and have good stability in ORRs. The onset potential of the catalyst for the ORR is-0.05 V （vs Ag/AgCl）, the ORR reduction peak potential is-0.20 V （vs Ag/AgCl）, and the electron transfer number is 3.4. The NCNBs showed pronounced electrocatalytic activity, improved long‐term stability, and better tolerance of the methanol crosso‐ver effect compared with a commercial 20 wt%Pt/C catalyst. The composition and structure of, and nitrogen species in, the NCNBs were investigated using Fourier‐transform infrared spectroscopy, scanning electron microscopy, X‐ray photoelectron spectroscopy, and X‐ray diffraction. The pyroly‐sis of Tris at high temperature increases the number of active nitrogen sites, especially pyridinic nitrogen, which creates a net positive charge on adjacent carbon atoms, and the high positive charge promotes oxygen adsorption and reduction. The results show that NCNBs prepared by pyrolysis of Tris as nitrogen and carbon sources are a promising ORR catalyst for fuel cells.

Magneli phase titanium sub-oxide conductive ceramic Ti_nO_(2n-1) as support for electrocatalyst toward oxygen reduction reaction with high activity and stability

Magneli phase titanium sub-oxide conductive ceramic Tin O2n-1 was used as the support for Pt due to its excellent resistance to electrochemical oxidation, and Pt/Tin O2n-1 composites were prepared by the impregnation-reduction method. The electrochemical stability of Tin O2n-1 was investigated and the results show almost no change in the redox region after oxidation for 20 h at 1.2 V(vs NHE) in 0.5 mol/L H2SO4 aqueous solution. The catalytic activity and stability of the Pt/Tin O2n-1 toward the oxygen reduction reaction(ORR) in 0.5 mol/L H2SO4 solution were investigated through the accelerated aging tests(AAT), and the morphology of the catalysts before and after the AAT was observed by transmission electron microscopy. At the potential of 0.55 V(vs SCE), the specific kinetic current density of the ORR on the Pt/Tin O2n-1 is about 1.5 times that of the Pt/C. The LSV curves for the Pt/C shift negatively obviously with the half-wave potential shifting about 0.02 V after 8000 cycles AAT, while no obvious change takes place for the LSV curves for the Pt/Tin O2n-1. The Pt particles supported on the carbon aggregate obviously, while the morphology of the Pt supported on Tin O2n-1 remains almost unchanged, which contributes to the electrochemical surface area loss of Pt/C being about 2times that of the Pt/Tin O2n-1. The superior catalytic stability of Pt/Tin O2n-1 toward the ORR could be attributed to the excellent stability of the Tin O2n-1 and the electronic interaction between the metals and the support.

Kinetics and Modeling of Chemical Leaching of Sphalerite Concentrate Using Ferric Iron in a Redox-controlled Reactor

This work presents a study for chemical leaching of sphalerite concentrate under various constant Fe3+ concentrations and redox potential conditions. The effects of Fe3+ concentration and redox potential on chemical leaching of sphalerite were investigated. The shrinking core model was applied to analyze the experimental results. It was found that both the Fe3+ concentration and the redox potential controlled the chemical leaching rate of sphalerite. A new kinetic model was developed, in which the chemical leaching rate of sphalerite was proportional to Fe3+ concentration and Fe3+ /Fe2+ ratio. All the model parameters were evaluated from the experimental data. The model predictions fit well with the experimental observed values.

Electrocatalytic H_(2)O_(2)generation for disinfection

Epidemics are threatening public health and social development.Emerging as a green disinfectant,H_(2)O_(2)can prevent the breakout of epidemics in migration.Electrochemical H_(2)O_(2)production powered by renewable electricity provides a clean and decentralized solution for on-site disinfection.This review firstly discussed the efficacy of H_(2)O_(2)in disinfection.Then necessary fundamental principles are summarized to gain insight into electrochemical H_(2)O_(2)production.The focus is on exploring pathways to realize a highly efficient H_(2)O_(2)production.Progress in advanced electrocatalysts,typically single-atom catalysts for the two-electron oxygen reduction reaction(2e−ORR),are highlighted to provide high H_(2)O_(2)selectivity design strategies.Finally,a rational design of electrode and electrolytic cells is outlined to realize the on-site disinfection.Overall,this critical review contributes to exploiting the potentials and constraints of electrochemical H_(2)O_(2)generation in disinfection and pinpoints future research directions required for implementation.

Amorphous Fe Nanoclusters Embedded inside Balloon-Like N-Doped Hollow Carbon for Efficient Electrocatalytic Oxygen Reduction

Rational designs of electrocatalytic active sites and architectures are of great importance to develop cost-efficient non-noble metal electrocatalysts towards efficient oxygen reduction reaction(ORR)for high-performance energy conversion and storage devices.In this work,active amorphous Fe-based nanoclusters(Fe NC)are elaborately embedded at the inner surface of balloonlike N-doped hollow carbon(Fe NC/Csphere)as an efficient ORR electrocatalyst with an ultrathin wall of about 10 nm.When evaluated for electrochemical performance,Fe NC/Csphere exhibits decent ORR activity with a diffusionlimited current density of~5.0 mA/cm^(2)and a half-wave potential of~0.81 V in alkaline solution,which is comparable with commercial Pt/C and superior to Fe nanoparticles supported on carbon sheet(Fe NP/C sheet)counterpart.The electrochemical analyses combined with electronic structure characterizations reveal that robust Fe-N interactions in amorphous Fe nanoclusters are helpful for the adsorption of surface oxygen-relative species,and the strong support effect of N-doped hollow carbon is benefitial for accelerating the interfacial electron transfer,which jointly contributes to improve ORR kinetics for Fe NC/Csphere.

Transition metal-nitrogen sites for electrochemical carbon dioxide reduction reaction

Electrochemical CO2 reduction reaction(CO2RR)powered by renewable electricity has emerged as the most promising technique for CO2 conversion,making it possible to realize a carbon‐neutral cycle.Highly efficient,robust,and cost‐effective catalysts are highly demanded for the near‐future practical applications of CO2RR.Previous studies on atomically dispersed metal‐nitrogen(M‐Nx)sites constituted of earth abundant elements with maximum atom‐utilization efficiency have demonstrated their performance towards CO2RR.This review summarizes recent advances on a variety of M‐Nx sites‐containing transition metal‐centered macrocyclic complexes,metal organic frameworks,and M‐Nx‐doped carbon materials for efficient CO2RR,including both experimental and theoretical studies.The roles of metal centers,coordinated ligands,and conductive supports on the intrinsic activity and selectivity,together with the importance of reaction conditions for improved performance are discussed.The mechanisms of CO2RR over these M‐Nx‐containing materials are presented to provide useful guidance for the rational design of efficient catalysts towards CO2RR.

Efficient development of Type-Ⅱ TiO_2 heterojunction using electrochemical approach for an enhanced photoelectrochemical water splitting performance

Type‐II‐heterojunction TiO2nanorod arrays(NAs)are achieved by a combination of reduced and pristine TiO2NAs through a simple electrochemical reduction.The heterojunction‐structured TiO2NAs exhibit an enhanced photo‐efficiency,with respect to those of pristine TiO2NAs and completely reduced black TiO2.The improved efficiency can be attributed to a synergistic effect of two contributions of the partially reduced TiO2NAs.The light absorption is significantly increased,from theUV to the visible spectrum.Moreover,the type II structure leads to enhanced separation and transport of the electrons and charges.The proposed electrochemical approach could be applied to various semiconductors for a control of the band structure and improved photoelectrochemical performance.

Guanine-regulated proton transfer enhances CO_(2)-to-CH_(4) selectivity over copper electrode

Electrocatalytic CO_(2) reduction has attracted growing attention as a promising route to realize artificial carbon recycling.Proton transfer plays an essential role in CO_(2) reduction and dramatically impacts product distribution.However,the precise control of proton transfer during CO_(2) reduction remains challenging.In this study,we present a well-controlled proton transfer through the modification of several purines with similar molecular structures,and reveal a direct correlation between surface proton transfer capability and CO_(2) reduction selectivity over Cu electrode.With a moderate proton transfer capability,the guanine modification can remarkably boost CH_(4) production and suppress C2 products formation.In-situ ATR-SEIRAS suggests a weakened^(*)CO intermediate adsorption and a relatively low local pH environment after the guanine modification,which facilitates the^(*)CO protonation and detachment for CH_(4) generation.

Study on Kinetics of Cathodic Reduction of Dissolved Oxygen in 3.5% Sodium Chloride Solution

Electrochemical reduction of dissolved oxygen in seawater on metals is of great importance for corrosion studies. The present paper studied cathodic reduction of dissolved oxygen on Q235 carbon steel in 3.5% sodium chloride （NaCl） solutions by cyclic voltammetry （CV）, electrochemical impedance spectroscopy （EIS）, rotating disk electrode （RDE） and rotating ring-disk electrode （RRDE）. The cyclic voltammetric results demonstrated the cathodic process on Q235 carbon steel in O2-saturated 3.5% NaCl solution contains three reactions： dissolved oxygen reduction, iron oxides reduction and hydrogen evolution. The peak potential of oxygen reduction reaction （ORR） is - 0.85 V vs Ag/AgCl, 3 molL^-1 KCI. The EIS results indicated that the ORR occurring on Q235 carbon steel is a 4-electron process and that no finite diffusion is caused by the intermediate of H2O2 produced by ORR. The RDE and RRDE voltammograms confirmed the EIS results and it was found that the number of transferred electrons for ORR was nearly 4, i.e., dissolved oxygen reduced to water.

Carbon Foam Anode Modified by Urea and Its Higher Electrochemical Performance in Marine Benthic Microbial Fuel Cell

Electrode materials have an important effect on the property of microbial fuel cell(MFC). Carbon foam is utilized as an anode and further modified by urea to improve its performance in marine benthic microbial fuel cell(BMFC) with higher voltage and output power. The electrochemical properties of plain carbon foam(PC) and urea-modified carbon foam(UC) are measured respectively. Results show that the UC obtains better wettability after its modification and higher anti-polarization ability than the PC. A novel phenomenon has been found that the electrical potential of the modified UC anode is nearly 100 m V lower than that of the PC, reaching-570 ±10 m V(vs. SCE), and that it also has a much higher electron transfer kinetic activity, reaching 9399.4 m W m-2, which is 566.2-fold higher than that from plain graphite anode(PG). The fuel cell containing the UC anode has the maximum power density(256.0 m W m-2) among the three different BMFCs. Urea would enhance the bacteria biofilm formation with a more diverse microbial community and maintain more electrons, leading to a lower anodic redox potential and higher power output. The paper primarily analyzes why the electrical potential of the modified anode becomes much lower than that of others after urea modification. These results can be utilized to construct a novel BMFC with higher output power and to design the conditioner of voltage booster with a higher conversion ratio. Finally, the carbon foam with a bigger pore size would be a potential anodic material in conventional MFC.

Electrochemical Energy Storage Technologies and Applications

The current need to fasten the implementation of renewable energies greatly depends on the development of competitive storage devices, and while there is not a single technology which is likely capable to competitively cover the wide range of possible demands, electrochemical technologies are one of the most promising for many of them. For the realization of this promise, new materials fulfilling criteria such as high energy density, high power density, competitive cost, reliability, and environmental compatibility need to be developed in the near future. Electrochemical energy storage devices can be classified into two main technologies： supercapacitors and batteries （including redox flow batteries）. Materials and applications for these technologies are discussed and compared, listing current status, technical and strategic challenges.

Reticular chemistry in electrochemical carbon dioxide reduction

Electrochemical CO2 reduction(ECR)represents a promising strategy for utilizing CO2,an industrial waste,as an abundant and cheap carbon source for organic synthesis as well as storing intermittent renewable electricity from renewable sources.Efficient electrocatalysts allowing CO2 to be reduced selectively and actively are crucial since the ECR is a complex and sluggish process producing a variety of products.Metal-organic frameworks(MOFs)and covalentorganic frameworks(COFs)have emerged as versatile materials applicable in many fields due to their unique properties including high surface areas and tunable pore channels.Besides,the emerging reticular chemistry makes tuning their features on the atomic/molecular levels possible,thereby lending credence to the prospect of their utilizations.Herein,an overview of recent progress in employing framework material-based catalysts,including MOFs,COFs and their derivatives,for ECR is provided.The pertinent challenges,future trends,and opportunities associated with those systems are also discussed.

Electrochemical reduction of CO_2 to CO using graphene oxide/carbon nanotube electrode in ionic liquid/acetonitrile system

Electrochemical reduction of CO_2 to CO is an interesting topic. In this work, we prepared metal-free electrodes by depositing graphene oxide(GO), multi-walled carbon nanotube(MWCNT), and GO/MWCNT composites on carbon paper(CP) using electrophoretic deposition(EPD) method. The electrodes were characterized by different methods, such as X-ray diffraction(XRD) and X-ray photoelectron spectroscopy(XPS). The electrochemical reduction of CO_2 to CO was conducted on the electrodes in 1-butyl-3-methylimidazolium tetrafluoroborate([Bmim]BF4)/acetonitrile(Me CN) electrolyte, and the composition of the electrolyte influenced the reaction significantly. It was demonstrated that GO/MWCNT-CP electrode was very effective for the reaction in IL(90 wt%)/Me CN binary mixture, the Faradaic efficiency of CO and current density were even higher than those on Au and Ag electrodes in the same electrolyte.

Electrochemical co-deposition of reduced graphene oxide-gold nanocomposite on an ITO substrate and its application in the detection of dopamine

The simultaneous deposition of rGO and gold nano structures has been achieved by electrodeposition from mixed solutions containing graphene oxide(GO)and a gold precursor.Scanning electron microscope(SEM),Raman spectroscopy and atomic force microscopy(AFM)have been employed to reveal the morphology,uniformity and practical stability of the nanocomposite films on the indium tin oxide(ITO)substrate.The AFM data showed heights of tens of nanometers of the nanocomposite,suggesting that multilayers of rGO with gold nanoparticles had been formed as a result of the electrochemical co-deposition.Differential pulse voltammetry(DPV),as a widely used analytical technique,has been carried out on the rGO-Au/ITO electrode for the quantitative detection of dopamine(DA).The detection limit(S/N=3)for the determination of DA was evaluated as 0.6μM.

Towards unlocking high-performance of supercapacitors: From layered transition-metal hydroxide electrode to redox electrolyte.

Both energy density and power density are crucial for a supereapacitor device, where the trade-off must be made between the two factors towards a practical application. Herein we focus on pseudocapacitance produced from the electrode and the electrolyte of supercapacitors to simultaneously achieve high energy density and power density. On the one hand, layered transition metal hydroxides （Ni（OH）2 and Co（OH）,,） are introduced as electrodes, followed with exploration of the effect of the active materials and the substrate on the electrochemical behavior. On the other hand, various redox electrolytes are utilized to improve the specific capacitance of an electrolyte. The roadmap is to select an appropriate electrode and a dedicated electrolyte in order to achieve high electrochemical performance of the supercapacitors.