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1.
本文运用电化学扫描隧道显微术研究了离子液体OMIPF6中Pt(100)表面结构在电化学双层区随电极电位的变化. OMI+阳离子在Pt(100)表面形成有序吸附结构,并且在约1.2 V宽的电位区间内稳定地存在Pt(100)表面。在电位负于-0.6 V时,有序吸附结构会发生向无序吸附结构的转变. 在电位正于+0.6 V时,较强的静电排斥力才能克服OMIPF6与Pt(100)表面之间的化学作用,从而导致OMI+阳离子的脱附. 研究表明,OMI+阳离子具有的较长烷基侧链与Pt金属产生的较强化学相互作用是影响该Pt(100)/ OMIPF6界面结构的重要因素.  相似文献   

2.
We report a molecular investigation of a cobalt phthalocyanine (CoPc)‐catalyzed CO2 reduction reaction by electrochemical scanning tunneling microscopy (ECSTM). An ordered adlayer of CoPc was prepared on Au(111). Approximately 14 % of the adsorbed species appeared with high contrast in a CO2‐purged electrolyte environment. The ECSTM experiments indicate the proportion of high‐contrast species correlated with the reduction of CoIIPc (?0.2 V vs. saturated calomel electrode (SCE)). The high‐contrast species is ascribed to the CoPc‐CO2 complex, which is further confirmed by theoretical simulation. The sharp contrast change from CoPc‐CO2 to CoPc is revealed by in situ ECSTM characterization of the reaction. Potential step experiments provide dynamic information for the initial stage of the reaction, which include the reduction of CoPc and the binding of CO2, and the latter is the rate‐limiting step. The rate constant of the formation and dissociation of CoPc‐CO2 is estimated on the basis of the in situ ECSTM experiment.  相似文献   

3.
We report a molecular investigation of a cobalt phthalocyanine (CoPc)-catalyzed CO2 reduction reaction by electrochemical scanning tunneling microscopy (ECSTM). An ordered adlayer of CoPc was prepared on Au(111). Approximately 14 % of the adsorbed species appeared with high contrast in a CO2-purged electrolyte environment. The ECSTM experiments indicate the proportion of high-contrast species correlated with the reduction of CoIIPc (−0.2 V vs. saturated calomel electrode (SCE)). The high-contrast species is ascribed to the CoPc-CO2 complex, which is further confirmed by theoretical simulation. The sharp contrast change from CoPc-CO2 to CoPc is revealed by in situ ECSTM characterization of the reaction. Potential step experiments provide dynamic information for the initial stage of the reaction, which include the reduction of CoPc and the binding of CO2, and the latter is the rate-limiting step. The rate constant of the formation and dissociation of CoPc-CO2 is estimated on the basis of the in situ ECSTM experiment.  相似文献   

4.
采用控电位电解、循环伏安法和交流阻抗法研究了FeCl2-K2MoS4体系对乙炔在石墨电极上还原为乙烯的电催化活性及反应机理。实验结果表明,当石墨阴极的电位控制在-1.50V(vs.SCE)时,FeCl2+K2MoS4的DMF溶液对C2H2还原为C2H4表现出明显的电催化活性和高的选择性。在-0.5~-1.0V时Mo(Ⅵ)还原为Mo(Ⅴ);在按连串的电子传递机理进行的Mo(Ⅴ)→Mo(Ⅲ)反应的电位区间(-1.0~-1.50V)溶液中所形成的络合品种传递电子的能力更强。Mo(Ⅲ)可能是络合物的电活性成分。  相似文献   

5.
Ohura H  Imato T  Yamasaki S 《Talanta》1999,49(5):1383-1015
A rapid potentiometric flow injection technique for the simultaneous determination of oxychlorine species such as ClO3–ClO2 and ClO3–HClO has been developed, using both a redox electrode detector and a Fe(III)–Fe(II) potential buffer solution containing chloride. The analytical method is based on the detection of a large transient potential change of the redox electrode due to chlorine generated via the reaction of the oxychlorine species with chloride in the potential buffer solution. The sensitivities to HClO and ClO2 obtained by the transient potential change were enhanced 700–800-fold over that using an equilibrium potential. The detection limit of the present method for HClO and ClO2 is as low as 5×10−8 M with use of a 5×10−4 M Fe(III)–1×10−3 M Fe(II) buffer containing 0.3 M KCl and 0.5 M H2SO4. On the other hand, sensitivity to ClO3 was low when a potential buffer solution containing 0.5 M H2SO4 was used, but could be increased largely by increasing the acidity of the potential buffer. The detection limit for ClO3 was 2×10−6 M with the use of a 5×10−4 M Fe(III)–1×10−3 M Fe(II) buffer containing 0.3 M KCl and 9 M H2SO4. By utilizing the difference in reactivity of oxychlorine species with chloride in the potential buffer, a simultaneous determination method for a mixed solution of ClO3–ClO2 or ClO3–HClO was designed to detect, in a timely manner, a transient potential change with the use of two streams of potential buffers which contain different concentrations of sulfuric acid. Analytical concentration ranges of oxychlorine species were 2×10−5–2×10−4 M for ClO3, and 1×10−6–1×10−5 M for HClO and ClO2. The reproducibility of the present method was in the range 1.5–2.3%. The reaction mechanism for the transient potential change used in the present method is also discussed, based on the results of batchwise experiments. The simultaneous determination method was applied to the determination of oxychlorine species in a tap water sample, and was found to provide an analytical result for HClO, which was in good agreement with that obtained by the o-tolidine method and to provide a good recovery for ClO3 added to the sample.  相似文献   

6.
The objective of this work was to describe the characteristics of chemically and electrochemically deposited Pd surface layers on HOPG and polycrystalline gold electrode, using in situ ECSTM and EIS measurements, and SEM-EDX element analysis. Pd surface layers were deposited, in successive voltammetric cycles, and anodically dissolved in 0.01 M HCl+0.01 M (NH4)2PdCl4 aqueous electrolyte. Both of the electrode materials used in the study were treated as standard testing electrodes: (i) HOPG for STM/ECSTM measurements, and (ii) polycrystalline Au as the well known working electrode in various electro-analytical applications. The elements surface analysis and nano-surface pictures were used to interpret the EIS diagrams and electrical equivalent circuits. Pd chemical and electrochemical deposition on the HOPG surface was compared with the same process on the polycrystalline gold electrode, on which palladium can be electrodeposited only by means of electrochemical cathodic deposition. Surface topographies of the electrodeposited palladium layers on HOPG and Au were completely different. The equivalent electrical circuits were fitted and the surface roughness of the investigated electrodes calculated. Relations between the surface topography, EIS and SEM-EDX, and interface model of the electrolyte solution electrodeposited Pd layer matrix electrode were proposed.  相似文献   

7.
将二氧化碳转化为高附加值的燃料和化学品是缓解当前能源危机和控制温室气体排放的有效策略之一,但此法受限于缺乏高活性与高选择性的电催化剂。因此,我们通过热解含镍金属有机框架结构(MOF)和二氰二胺制得负载高含量镍单原子(7.77% (w))的超薄氮掺杂二维碳纳米片用于电催化还原CO2生成CO。研究发现高温热解能将MOF中Ni2+转化为Ni+-N-C和Ni2+-N-C结构,且Ni+-N-C含量依赖于热解温度——其含量随热解温度增加呈现火山型变化。800 ℃下,Ni2+到Ni+-N-C的转化和石墨化的C生成达到最优水平。Ni+-N-C结构有适宜的*CO中间体结合能,能有效地抑制析氢反应的同时还能促进CO生成。因此,800 ℃热处理制得的材料(Ni-N-C-800)催化CO2生成CO效率最高。调节电解液浓度,能进一步优化电催化性能。当电解液(碳酸氢钾)浓度为0.5 mol·L-1时,Ni-N-C-800的CO生成选择性在较宽电压窗口内(-0.77到-1.07 V vs. RHE)都高于90%,且具有优良的稳定性。这些结果表明,选择合适的前躯体通过调控热解温度以及氮掺杂可以有效提高镍基MOF衍生催化剂的二氧化碳电催化性能。  相似文献   

8.
Seneviratne J  Holmstrom SD  Cox JA 《Talanta》2000,52(6):1025-1031
An electrocatalytic amperometric detector for the ion chromatographic determination of CN is described. A conducting composite that is based on a graphite-loaded sol–gel material comprises the working electrode. The composite is doped with a RuII metallodendrimer which is demonstrated to promote the electrochemical oxidation of CN at potentials positive of 0.5 V vs. Ag/AgCl. In 6 mM NaOH, 0.05 M NaCl flowed at 1.0 ml min−1, a 5-point calibration curve with the following linear least squares parameters is obtained over the range, 1.0–30 M CN: slope, 24.2±0.1 nA M−1; intercept, −6±2 nA; and r, 0.9997. The detection limit, 0.7 μM CN, compares favorably to that obtained by amperometry at a silver electrode, 0.5 μM CN, under comparable experimental conditions. A 60-min preconcentration by Donnan dialysis increases the sensitivity by a factor of 23.6.  相似文献   

9.
在240℃水热体系中首次合成出系列纳米晶固溶体(CeO2)1-x(BiO1.5)x(x=0.0~0.50).产物采用X射线衍射,扫描电子显微镜和X射线光电子能谱仪进行表征.Bi2O3在CeO2中的固溶限约为50%.所有固溶体结晶属立方萤石结构,粒度范围为10~18nm.当Bi2O3掺杂量小于固溶限时,于800℃烧结不会导致结构转变.而对于(CeO2)0.5(BiO1.5)0.5,于800℃在空气中烧结将导致固溶限降低.Bi2O3含量低于固溶限时,固溶体只具有体电导,而(CeO2)0.6(BiO1.5)0.4的总电导可分为体电导和晶界电导.体电导为氧离子,而晶界为来自电极的银离子.  相似文献   

10.
Understanding the structure and formation dynamics of the solid electrolyte interphase (SEI) on the electrode/electrolyte interface is of great importance for lithium ion batteries, as the properties of the SEI remarkably affect the performances of lithium ion batteries such as power capabilities, cycling life, and safety issues. Herein, we report an in situ electrochemical scanning tunnelling microscopy (ECSTM) study of the surface morphology changes of a highly oriented pyrolytic graphite (HOPG) anode during initial lithium uptake in 1 M LiPF(6) dissolved in the solvents of ethylene carbonate plus dimethyl carbonate. The exfoliation of the graphite originating from the step edge occurs when the potential is more negative than 1.5 V vs. Li(+)/Li. Within the range from 0.8 to 0.7 V vs. Li(+)/Li, the growth of clusters on the step edge, the decoration of the terrace with small island-like clusters, and the exfoliation of graphite layers take place on the surface simultaneously. The surface morphology change in the initial lithium uptake process can be recovered when the potential is switched back to 2.0 V. Control experiments indicate that the surface morphology change can be attributed to the electrochemical reduction of solvent molecules. The findings may lead to a better understanding of SEI formation on graphite anodes, optimized electrolyte systems for it, as well as the use of in situ ECSTM for interface studies in lithium ion batteries.  相似文献   

11.
A simple method is described to distinguish between As species that react with sodium tetrahydroborate (III) to form AsH3 and the naturally occurring As species that are unreactive. Results for this rudimentary or “first order” speciation scheme are reported for biological tissue, aquatic plant material, urine and natural water samples. Biological tissue and aquatic plant samples were briefly solubilized in a mixture of 50% nitric acid, no sample preparation was required for the urine or natural water samples. Organoarsenic species which do not react with sodium borohydride under acidic conditions such as arsenobetaine, arsenocholine and tetramethylarsenic, are converted to As(V) by on-line photo-oxidation or microwave heating in a mixture of 0.5 M NaOH and 0.05 M K2S2O8. The sample is subsequently acidified, reduced with sodium borohydride and the generated arsine is trapped in a heated graphite furnace prior to atomization. The superior detection limit (0.14 ng) of the trapping technique permits the dilution of most types of samples, minimizing or eliminating interference effects. Without photolysis or microwave heating a combined result for As(III), As(V), monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) is obtained. Results are reported for the first order speciation of As in a suite of certified reference materials (CRMs) including National Research Council (NRC) biological tissues and natural water samples, Community Bureau of Reference (BCR) aquatic plant materials and the National Institute of Standards and Technology (NIST) SRM 267ON urine sample. The determination of a non-hydride forming As fraction in untreated urine and natural water certified reference materials (CRMs) has revealed a species of As previously undetected in NRC seawater CRMs.  相似文献   

12.
镉离子在H2SO4溶液中极谱行为的研究   总被引:1,自引:0,他引:1  
周本省  吴瑞鉴 《化学学报》1983,41(12):1121-1126
本文研究了在没有动物胶的0.5M H_2SO_4溶液中镉离子的极谱行为,得到了如下的结果:(1)在0.050~20.0mM CdSO_4 0.5M H_2SO_4的十种溶液中测得的电流-电位曲线都有良好的波形、恒定的极限扩散电流和易于确定的半波电位.这些曲线上都没有极谱极大出现;其极限扩散电流(波高)与镉离子的浓度成正比.在镉离子低浓度(0.050~0.20mM)时,半波电位保持不变,在镉离子高浓度(1.00~20.0mM)时,也仅有很小的变化.故镉离子在0.5MH_2SO_4,溶液中的电流-电位曲线可供定量和定性测定之用.(2)镉离子在低浓度时的极谱波是一种可逆波.(3)前人在H_2SO_4溶液中研究镉离子时之所以没有能得到令人满意的极谱行为的原因是他们在H_2SO4溶液中添加了动物胶的缘故.(4)作者从得到的波形良好的电流-电位曲线上,测定了25±0.2℃时镉离子在0.5M H_2SO_4溶液中的扩散电流常数、半波电位和电极反应中得失的电子数.结果如下: i_d/cm~(2/3)t~(1/6)=3.97μA/mM·mg~(2/3)·s~(-1/2) E_(1/2)=-1.011V(0.5M硫酸亚汞电极)=-0.559V(饱和甘汞电极) n=2 这些数据比Lingane的数据,扩散电流常数2.6μA/mM·mg~(2/3)·s~(-1/2)和半波电位-0.59V(饱和甘汞电极)],要合理些.  相似文献   

13.
The electrochemical behavior of three heteroaromatic thiols (MBs) (2-mercaptobenzimidazole (MBI), 2-mercaptobenzothiazole (MBT), and 2-mercaptobenzoxazole (MBO)) on a Au(111) surface has been investigated by electrochemical scanning tunneling microscopy (ECSTM) and cyclic voltammetry (CV) in 0.1 M HClO(4) solution. All three thiols form oriented molecular cluster lines along the reconstruction line direction at 0.55 V. With the electrode potential shifting negatively, the molecules undergo a disordered-ordered structural transition. Molecularly resolved STM images show that all three molecules form striped adlayers in the desorption region on the Au(111) surface. The different heteroatoms in the heteroaromatic rings result in different electrochemical behavior of the MB self-assembled monolayers (SAMs). MBI, MBT, and MBO are proposed to interact with the substrate via the S-Au bonds from thiol group and the coordination interaction of N, S, and O with the substrate from the heteroaromatic ring, respectively. These results provide direct evidence of the electrochemical behavior and the adlayer structures of MB SAMs on the Au electrode.  相似文献   

14.
The spirocyclic silylamides M[(NR)2SiMe2]2 (R = t-Bu: M = Hf (III), V (IV); R = SiMe3: M = V (V), NbCl (VI), TaCl (VII)) have been prepared by reaction of the HfCl4, VCl4, NbCl5 and TaCl5, respectively, with Me2Si[N(Li)R]2. Methylation of VI and VII with MeLi yields the respective NbCH3 and TaCH3 derivatives (VIII and IX). The effective magnetic moments of IV and V are 1.67 and 1.66 μB respectively. Infrared and Raman spectra are given, and the 1H, 13C and 29Si chemical shifts for the diamagnetic compounds are reported. Single-crystal X-ray studies have been performed on III, IV and VIII. The structures of III and IV possess distorted tetrahedral symmetry (D2d), with mean M---N distance of 2.030(4) and 1.853(5) Å, respectively. Distorted trigonal-bipyramidal coordination with an equatorial methyl group is found for each Nb atom of the two crystallographically independent molecules of VIII. Mean Nb---C, Nb---N (equatorial) and Nb---N (axial) bond lengths are 2.218(9), 1.997(4) and 2.026(5) Å, respectively.  相似文献   

15.
为在固体氧化物燃料电池中有效利用干甲烷为燃料,需制作多孔立体阳极。采用硬模板法和浸渍法制备Ni_(0.5)Cu_(0.5)Ba_(0.05)O_x包覆管状SDC阳极材料(Ni_(0.5)Cu_(0.5)Ba_(0.05)O_x/SDC),为作对比,用溶胶凝胶法制备粉末状Ni_(0.5)Cu_(0.5)Ba_(0.05)O_x,机械混合SDC粉末制备Ni_(0.5)Cu_(0.5)Ba_(0.05)O_x-SDC。将这两种阳极材料分别制作电解质支撑的单电池Ni_(0.5)Cu_(0.5)Ba_(0.05)O_x/SDC|YSZ|LSMYSZ与Ni_(0.5)Cu_(0.5)Ba_(0.05)O_x-SDC|YSZ|LSM-YSZ,并进行发电性能测试以及长期稳定性实验。结果表明,800℃下,干甲烷环境中,Ni_(0.5)Cu_(0.5)Ba_(0.05)O_x-SDC为阳极的单电池最大功率密度为324.99 m W/cm2,运行10 h后,电压下降5.60%;而以Ni_(0.5)Cu_(0.5)Ba_(0.05)O_x/SDC为阳极的单电池最大功率密度达到384.54 m W/cm2,运行100 h后,电压未严重衰减。实验后阳极的SEM照片表明,Ni_(0.5)Cu_(0.5)Ba_(0.05)O_x-SDC阳极内孔隙狭小,易被积炭堵塞;而Ni_(0.5)Cu_(0.5)Ba_(0.05)O_x/SDC阳极呈立体多孔结构,有利于燃料气体与反应后气体的扩散。催化剂颗粒均匀地包覆在SDC纤维管表面,有利于增加三相界面,提高电池的稳定性。  相似文献   

16.
Functional solid substrates modified by self-assembled monolayers (SAMs) have potential applications in biosensors, chromatography, and biocompatible materials. The potential-induced phase transition of N-isobutyryl-L-cysteine (L-NIBC) SAMs on Au (111) surfaces was investigated by in-situ electrochemical scanning tunneling microscopy (EC-STM) in 0.1 mol·L-1 H2SO4 solution. The NIBC SAMs with two distinct structures (α phase and β phase) can be prepared by immersing the Au (111) substrate in pure NIBC aqueous solution and NIBC solution controlled by phosphate buffer at pH 7, respectively. The as-prepared α phase and β phase of NIBC SAMs show various structural changes under the control of electrochemical potentials of the Au (111) in H2SO4 solution. The α phase NIBC SAMs exhibit structural changes from ordered to disordered structures with potential changes from 0.7 V (vs saturated calomel electrode, SCE) to 0.2 V. However, the β phase NIBC SAMs undergo structural changes from disordered structures (E < 0.3 V) to γ phase (0.4 V < E < 0.5 V) and finally to the β phase (0.5 V < E < 0.7 V). EC-STM images also indicate that the phase transition from the β phase NIBC SAMs to the α phase occurs at positive potential. Combined with density functional theory (DFT) calculations, the phase transition from the β phase to the α phase is explained by the potential-induced break of bonding interactions between ——COO- and the negatively charged gold surfaces.  相似文献   

17.
In this study, the extraction of Bi(III) from synthetic solutions of 2 M H2SO4/0.5 M HCl by supported liquid membranes (SLM) using tri-n-octylphosphine oxide (Cyanex 921) as extractant is reported. First, the nature of the Bi(III)/Cyanex 921 solvates extracted to organic phase (in a solvent extraction system) was determined by the slope method. It was found that Bi(III) reacts with 2 molecules of Cyanex 921 to form the solvate BiCl3·2Cyanex 921. In the recovery of Bi(III) by the SLM system, parameters that influence extraction efficiency were evaluated, including: support, feed solution and stripping solution nature, and extractant concentration in the organic phase which impregnates the support. Results indicate that Cyanex 921 dissolved in kerosene is not able to extract Bi(III) from H2SO4 media. Moreover, transfer of H2SO4 was observed. HCl addition to the feed solution up to a maximum concentration of 0.5 M increases Bi(III) extraction. Further increase in HCl concentration causes a decrease in Bi(III) transfer. Likewise, the concentration of Cyanex 921 in the SLM organic phase which produced the maximum Bi(III) extraction was found to be 0.3 M. The performance of H2O and 0.2 M H2SO4 as stripping solutions was evaluated, and it was found that only H2SO4 enabled Bi(III) transfer.  相似文献   

18.
《Analytica chimica acta》2000,410(1-2):159-165
Modification of the luminol solution by means of addition of various complexones and surfactants has been investigated to eliminate interferences from gaseous co-pollutants in the determination of ambient nitrogen dioxide using a chemiluminescence aerosol detector. The simultaneous presence of EDTA and triton X-100 or X-405 together with sulphite and iodide in the luminol solution suppressed interferences from ozone and peroxyacetyl nitrate to a negligible level and no scrubbers or corrections of the NO2 measurements were needed.

In general, the best composition of the reagent solution included luminol, KOH, Na2SO3, KI, Na2EDTA and triton X-100. From the point of view of selectivity of NO2 determination, an optimum reagent solution consisted of luminol (0.002 M), KOH (0.5 M), Na2SO3 (0.2 M), KI (0.1 M), Na2EDTA (0.05 M) and triton X-100 (0.5 vol.%). Interferences from ozone (170 ppb (v/v)) and peroxyacetyl nitrate (81 ppb (v/v)) were 0.2 and 1.2%, respectively, for nitrogen dioxide at a concentration of 50 ppb (v/v) and 0.25 and 1.7%, respectively, for 0.5 ppb (v/v) NO2. The calibration graph was linear for NO2 concentrations ranging from 3 to 665 ppb (v/v). Below 3 ppb (v/v) NO2 the detector response to nitrogen dioxide can be fitted with a linear equation of the third order.  相似文献   


19.
高择优锌-镍合金电沉积的现场ECSTM研究   总被引:1,自引:0,他引:1  
采用"二步包封"法制备了性能良好的电化学STM针尖.以此为基础采用ECSTM现场研究了工艺条件下HOPG上高择优锌-镍合金的电沉积过程.研究结果表明这种高择优沉积层以侧向生长方式生长,而表面上电化学活性差的晶面构成了晶体生长过程的保留面,从而进一步形成了与基底表面方向一致的高择优沉积层,X射线研究表明这一择优面为(100)晶面.  相似文献   

20.
Perovskite oxide Ba0.5Sr0.5Fe0.9Nb0.1O3-δ(BSFN) as a cobalt-free cathode for intermediate-temperature solid oxide fuel cells(IT-SOFCs) on the Ce0.5Sm0.2O1.9(SDC) and La0.9Sr0.1Ga0.8Mg0.23O3-δ(LSGM) electrolytes was prepared and investigated. The single phase BSFN oxide with a cubic perovskite structure and relatively high elec- trical conductivities was obtained after sintering at 1250℃ for 10 h in air. The BSFN cathode exhibited excellent chemical stability on the SDC and LSGM electrolytes at temperatures below 950 ℃. The area specific resistance of the BSFN cathode on the SDC and LSGM electrolytes were 0.024 and 0.021 Ω·cm2 at 800℃, respectively. The maximum power densities of the single cell with BSFN cathode in 300 μm-thick SDC and LSGM electrolytes achieved 414 and 516 mW/cm2 at 800℃, respectively. These results show that the BSFN material is a promising co- bait-free cathode candidate to be used in IT-SOFCs. A combination of the BSFN cathode and LSGM electrolyte is preferred owing to its excellent electrochemical performance.  相似文献   

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