乙醇在钯电极上的电氧化机理

利用循环伏安与现场傅里叶变换红外(FTIR)光谱对乙醇在Pd电极上的电氧化机理进行了研究. 循环伏安测量表明, 乙醇在Pd上氧化的性能受pH值与乙醇浓度的影响. 当溶液pH>11.0时, Pd对乙醇才具有催化性能, 而且乙醇在Pd上氧化的性能随着pH值和乙醇浓度的增加而提高. 现场红外光谱电化学测量结果证明, 乙醇在不同pH 溶液中的氧化反应机理和产物不同. 当溶液pH>13.0 时, 产物只有乙酸盐, 说明乙醇仅发生部分氧化, 乙醇中的C—C键没有断裂. 当溶液pH≤13.0时, 尽管乙醇在Pd电极上的氧化活性受到抑制, 却发生完全氧化而产生二氧化碳, 说明乙醇的C—C键在低碱环境中容易断裂, 最后乙醇被完全氧化. 实验中没有检测到CO, 表明该反应途径是一个非毒化过程.     

Pt-Mo2C/GC催化甲醇氧化的现场电化学-红外光谱研究

应用离子交换法制备了40%Pt在Mo2C/GC上的电催化剂.X射线衍射(XRD)显示,Pt在Mo2C载体上有较好的分散度,平均粒径为3 nm.循环伏安、计时电位测试表明,酸性溶液中,Pt-Mo2C/GC具有良好的甲醇氧化性能.其催化甲醇氧化的起始电位比Pt/C的负移了90 mV.这一优异性能与Pt和载体Mo2C之间的协同作用有关.现场红外光谱电化学测量显示,甲醇在Pt/C电极氧化的中间产物是桥式吸附COB和线性吸附COL,而在Pt-Mo2C/GC电极则未检测到有害中间产物CO,其氧化终产物均为CO2.     

乙醇在不同介质中电氧化的原位表面增强拉曼光谱研究

采用常规电化学伏安技术和电化学原位表面增强拉曼光谱(in-situ SERS)技术研究了不同介质中乙醇在粗糙铂电极上的电催化氧化行为. 发现不论在酸性、中性还是碱性介质中, 乙醇均能在粗糙铂电极上自发氧化解离生成强吸附中间体CO; 碱性介质中, CO在粗糙铂电极上基本氧化完全的电位(0.20 V)比中性和酸性介质中(0.50 V)负移了约0.30 V. 而乙醇在粗糙铂电极上CV正向扫描的氧化峰电位(-0.20 V)比酸性介质中(0.65 V)负移了约0.85 V. 比较不同介质中乙醇和CO在粗糙铂电极上的氧化峰电流和峰电位可以发现, 粗糙铂电极在碱性介质中对乙醇和CO的电催化氧化活性比中性和酸性介质中更强; 可以推测, 不论在酸性、中性还是碱性介质中, 乙醇在粗糙铂电极上的氧化过程均按双途径机理进行.     

碱性介质中甲醇在铂电极表面吸附和氧化的电化学原位FTIR反射光谱和EQCM研究

运用电化学循环伏安、原位FTIR反射光谱和石英晶体微天平(EQCM)等方法研究了碱性介质中甲醇在Pt电极表面吸附和氧化行为. 结果表明: 甲醇电氧化与溶液酸碱性有密切的关系. 酸性介质中甲醇在Pt电极上的CV曲线有两个正向氧化峰, 而碱性介质中只有一个正向氧化峰, 第二个氧化峰的消失可能是由于碱性介质中Pt电极在高电位下形成高氧化态的氧物种毒化其表面引起的. 碱性介质中甲醇解离吸附产物的数量比酸性介质的明显减少, 对甲醇氧化的第一个氧化峰表现出更高的电催化活性. 目前实验条件下, 原位FTIR反射光谱检测到: 碱性介质中甲醇电氧化的最终产物是CO₂和CO₃^2－, 反应中间体主要为HCOO^－物种. 从电极表面质量定量变化的角度提供了甲醇反应机理的新数据.     

碱性介质中甲醇氧化红外光谱电化学循环伏吸研究

本文利用红外光谱电化学循环伏吸法,对碱性体系下甲醇在Pt电极上的氧化过程的中间产物进行分析和研究。结果表明,碱性体系中,CH3OH在Pt电极上具有较好的电化学活性,存在和在酸性体系中不同的反应机理。利用现场红外差谱对氧化过程的产物进行分析,对生成的产物进行指认,并未发现毒化中间产物COL的生成。运用红外光谱电化学循环伏吸及导数伏吸法,对生成的中间体的生成过程进行分析和指认,结果表明:CH3OH的氧化中间产物为HCOO-,在碱性体系下,会继续转化为CO2,CO32-和HCO3-。     

不同介质中甲醛在Aucore@Ptshell/Pt电极上氧化的原位SERS研究

应用化学还原法合成了Au_core@Pt_shell纳米粒子, 并用扫描电子显微镜(SEM)和能量色散光谱(EDS)对其进行了表征; 采用电化学原位表面增强拉曼散射(SERS)光谱技术研究了不同介质中甲醛在Au_core@Pt_shell/Pt电极上的电催化氧化行为, 获得了不同介质中甲醛在Au_core@Pt_shell/Pt电极上电催化氧化行为的原位SERS谱. 研究结果表明, 不论在酸性、中性还是碱性介质中, 甲醛均能在Au_core@Pt_shell/Pt电极上自发氧化解离出强吸附中间体CO, 只是在碱性介质中桥式吸附CO的比例明显增大, 且桥式吸附比线形吸附CO更易被氧化, 使CO在碱性介质中基本氧化完毕的电位比在中性及酸性介质中提前了约950 mV. 分子水平的研究结果表明, CO和甲醛在碱性介质中比在中性和酸性介质中更易被氧化.     

吸附态和溶液相CO在Pt(110)电极上氧化过程的CV和in situ FTIRS 研究

应用电化学原位傅里叶变换红外反射光谱(in situ FTIRS)研究了酸性介质中Pt(110)单晶电极上吸附态CO(COad)和溶液相CO(COsol)的氧化过程.循环伏安测试表明,COsol氧化的峰电位比COad氧化的正移了168mV,其峰电流密度为后者的6.7倍.电化学原位红外光谱检测到CO主要生成线型的吸附态物种(COL),均匀分布在Pt(110)表面上.当溶液中不存在CO时,COL仅在电位高于0.15V才发生氧化.而且,该谱峰在其稳定吸附的电位区间内随电位增加蓝移,Stark系数为30cm-1·V-1;在COL发生氧化的电位区间,其谱峰强度随电位增加减小、峰位红移,线性变化率为-56cm-1·V-1.溶液中饱和CO时,原位红外光谱在-0.05V即可检测到CO2的存在,显示COL起始氧化的电位提前了200mV;电位高于-0.05V,该谱峰即发生红移,对应的线性变化率为-26.5cm-1·V-1.     

乙二醇在铂电极上吸附和氧化过程的现场FTIR反射光谱研究(Ⅰ)──酸性介质

运用循环伏安法和现场FTIR反射光谱研究了酸性介质中乙二醇在铂电极上的吸附和氧化行为,指出乙二醇电催化氧化是通过解离吸附产物和反应中间体双途径机理进行的。经FTIR反射光谱检测,解离吸附产物为CO,反应中间体主要有CH₂OH─COOH和HOOC─COOH等。本文还在分子水平上解释了铂电极上乙二醇吸附和氧化循环伏安特征的内在原因。     

利用原位红外光谱与微分电化学质谱联用技术研究在Pt以及PtRu电极上发生的甲醇氧化反应

利用电化学衰减全反射原位傅里叶变换红外光谱与微分电化学质谱联用技术,在流动电解池环境以及恒电位条件下研究了Pt电极和Pt电极通过表面电沉积Ru形成的PtRu电极（PtxRuy）上发生的甲醇氧化反应（反应电解质溶液为0.1 mol/L HClO4＋0.5 mol/L MeOH）. 在0.3-0.6 V（参比电极为可逆氢参比）实验用到的所有电极上,CO是唯一能从红外光谱观察到的与甲醇相关的表面吸附物;在Pt0.56Ru0.44电极上可以观察到CO吸附在Ru原子形成的岛上和CO线式吸附在Pt电极表面红外波段,而其他电极上只能观察到Pt表面上线式吸附的CO;甲醇氧化活性按Pt0.73Ru0.27〉Pt0.56Ru0.44〉Pt0.83Ru0.17〉Pt的顺序递减;在0.5V时,甲醇在Pt0.73Ru0.27电极上的氧化反应的CO2电流效率达到了50%.     

Rh多晶表面CO2还原过程的电化学和原位FTIR反射光谱研究

应用程序电位扫描法和电化学原位FTIR反射光谱从定量角度在分子水平 上研究了CO2在Rh电极上的电催化还原性能。红外光谱结果指出CO2还原的吸附产物为线型和桥式吸附态CO物种。在所研究和还原电位范围（－0．15－0．40V）和相同还原时间,CO2还原吸附物种的氧化电量随还原电位的负移而增大,在每个还原电位下,时间超过250s时都可达到一个相应的饱和值。原位红外光谱和电化学研究结果表明,CO2的还原与Rh电极表面氢吸附反应密切相关,同时需要一定数量相邻表面位的参与。因此生成的CO不能在Rh电极表面达到满单层吸附,而是形成均匀的亚单层分布。     

Pt-WO3/C电极表面活化对乙二醇和CO氧化的作用

用丙酮和四氢呋喃混合溶液对Pt—WO3/C电极进行表面活化处理后，乙二醇在Pt—WO3/C电极上的电催化氧化活性大幅度提高．发现无论在中性溶液中还是在酸性溶液中，表面活化处理后的Pt—WO3/C电极，乙二醇的起始氧化电位负移，氧化峰电流在酸性介质中增加到表面活化处理前的3．2倍：中性介质中增加到表面处理前的4．7倍，其主要原因是表面活化处理后，一方面增加了催化剂Pt的活性表面，另一方面也促进了电极表面吸附的CO的电氧化，减少了CO对电极表面的毒化作用．     

In situ FTIR spectroelectrochemical study on the mechanism of ethylene glycol electrocatalytic oxidation at a Pd electrode

The adsorption and electrooxidation pathways of ethylene glycol (EG) on polycrystalline palladium surfaces have been investigated in both alkaline and acidic media by in situ FTIR spectroscopy in conjunction with cyclic voltammetry. Palladium exhibits a high electrocatalytic activity in alkaline solution with low onset oxidation potentials and high current densities, depending on the pH, as well as on the supporting electrolyte. Higher potentials are required for EG oxidation in acidic solutions, where the catalytic performance decreases with increasing the pH. The products and intermediates of EG oxidation on Pd are influenced by the pH. In alkaline media, both C(2) species (glycolate, glyoxal, glyoxylate and oxalate) and C(1) species (formate and carbonate) are formed in mutual concentrations depending on the pH. In contrast, CO(2) is selectively produced in acidic aqueous solution.     

Synthesis and Performance of Polyvinylpyrrolidone‐Protected Pd Nanoparticles Supported on TiO2MWCNTs under Protection of PVP for in Alcohols Oxidation in Alkaline Media

This paper describes the synthesis and performance of Pd/p‐TiO₂‐MWCNTs for alcohol electrooxidation. Regulation of the steric repulsive forces of polyvinylpyrrolidone was used to achieve even dispersion of Pd nanoparticles over the TiO₂ surfaces. The order of the electroactivities of the Pd/p‐TiO₂? MWCNTs in alcohol oxidation was ethanol>ethylene glycol>methanol. The order of the stabilities of alcohol oxidation by Pd/p‐TiO₂? MWCNTs was ethylene glycol>ethanol>methanol. Electroimpedance spectroscopy showed that at a potential of ?0.1 V, the Pd/p‐TiO₂? MWCNTs had good tolerance of adsorbed CO in ethylene glycol oxidation, and at ?0.2 V, the Pd/p‐TiO₂? MWCNTs had good adsorbed CO tolerance in methanol oxidation.     

Electrooxidation Mechanism of Methanol at Pt-Ru Catalyst Modified GC Electrode in Electrolytes with Different pH Using Electrochemical and SERS Techniques

The electrochemical and in-situ surface-enhanced Raman spectroscopy （SERS） techniques were used to investigate the electrooxidation behavior of methanol in acidic, neutral and alkaline media at a Pt-Ru nanoparticle modified glassy carbon （Pt-Ru/GC） electrode. The results showed that methanol could be dissociated spontaneously at the Pt-Ru/GC electrode to produce a strongly adsorbed intermediate, CO. It was found that CO could be oxidized more easily in the alkaline medium than in the acidic and neutral media. The peak potential of methanol oxidation was shifted from 0.663 and 0.708 V in the acidic and neutral media to -0.030 V in the alkaline medium, which is due to that the adsorption strength of CO on the Pt surface in the alkaline medium is weaker than that in the acidic and neutral media. The final product of the methanol oxidation is CO2. However, in the alkaline medium, CO2 produced would form CO3^2- and HCO3^- resulting in the decrease in the alkaline concentration and then in the decrease in the performance of DMFC. Therefore, the performance of the alkaline DMFC is not Stable.     

In situ transmission difference FTIR spectroscopic investigation on anodic oxidation of methanol in aqueous solution

In situ transmission difference FTIR spectroscopy method was introduced for studying the anodic oxidation of methanol in acid aqueous solution. A minigrid Pt optically transparent thin layer electrode was used as working electrode. This method has the ability to clarify the identity of species involved in the oxidation process both in solution and adsorbed at the surface of electrode. From the results of in situ transmission difference FTIR spectroscopy measurement it was found that HCHO, HCOOH, HCOOCH₃ and CH₂(OCH₃)₂ could be formed in the oxidation process of methanol. The final product was CO₂. The adsorbed poisonous intermediate CO was detected. It was formed at near 0.6 V and became significant at 0.9 V, where the oxidation current was inhibited. The in situ transmission difference FTIR spectroscopy method is a very convenient, relative simplicity and efficient method for investigating the electrochemical process, and could be as a good candidate for further application.     

Relationship between the reactions of hydrogen sorption/desorption and methanol oxidation on bifunctional Ni/Pd electrode in alkaline solution

The present paper is aimed at studying the influence of the hydrogen sorption/desorption process occurring on the layered nickel–palladium (Ni/Pd) electrode on the kinetics of the reaction of methanol oxidation in strong alkaline KOH solution. The electrodes were prepared by chemical deposition of a thin layer of porous palladium on a nickel foam support. A scanning electron microscope was used for studying the morphology of both the nickel support and the porous palladium layer. The mechanism of the anodic desorption of hydrogen changes depending on whether or not 6 M KOH electrolyte is admixed with methanol. It was shown that, in the first cycle of the cyclic voltammetry (CV) measurements, the anodic peak current and peak charge related to the oxidative desorption of hydrogen significantly decrease due to the presence of methanol in KOH. This effect is attributed to the obstacles in hydrogen sorption due to the formation of a passivating layer on the Pd surface composed of both adsorbed methanol molecules and the intermediate products involving adsorbed CO. On the other hand, hydrogen desorbing from Pd electrode exerts influence on the kinetics of the reaction of methanol oxidation. Ni/Pd electrode undergoes considerable reactivation due to the potentiostatic saturation with hydrogen at ?1.1 V, followed by the ease in hydrogen desorption. The CV measurements proved that, after such a treatment, the peak of hydrogen desorption partially overlaps the double peak of methanol oxidation and, in consequence, the rate of methanol oxidation is enhanced. The positive effect of hydrogen releasing from the electrode on the kinetics of the reaction of methanol oxidation is ascribed to the anti-poison behavior consisting in the reaction of hydrogen radicals with intermediates adsorbed on the Pd surface.     

Construction,assessment and applications of a dichromate-selective liquid membrane electrode based on tetrapentylammonium dichromate

A dichromate-selective liquid-membrane electrode based on tetrapentylammonium dichromate dissolved in 2-nitrotoluene is described. The electrode exhibits rapid and linear response to the activity of Cr(VI) anions in the range 5 × 10^?4–2 × 10.2 M dichromate; the slopes of the calibration graphs depend on the acidity. The electrode is useful for end-point indication in titrations of iron(II), arsenic(III), ascorbic acid, thiobarbituric acid, thiourea, and cysteine with dichromate. The electrode is also used as indicator electrode in a potentiometric reaction-rate method for the determination of hydroxyl-containing organic compounds, based on their oxidation by dichromate in acidic solution; ethanol, isopropanol, ethylene glycol, propylene glycol, butylene glycol, and several carbohydrates were determined with a mean error of 1%. The method is applied to determine the ethanol content of alcoholic beverages. Kinetic data are given for the dichromate/ethanol reaction.