Platinum modification of gold and electrocatalytic oxidation of ethylene glycol on Pt-modified Au electrodes

The surface modification of gold electrodes with platinum and the electrocatalytic oxidation of ethylene glycol on Pt-modified Au electrodes are investigated by cyclic voltammetry. Platinum modification is performed by the electrochemical deposition of platinum on polycrystalline gold electrodes, and the Pt-modified Au electrodes with different amount of the deposited platinum are used for the ethylene glycol oxidation in alkaline and acidic solutions. It is shown that oxidation potential for the ethylene glycol oxidation on the Pt-modified Au electrodes shifts significantly negative compared with that on Au electrodes, nearly same oxidation potentials as that on Pt electrodes are observed, and peak current density of the ethylene glycol oxidation is dependent on the amounts of the deposited platinum on gold surface, much higher peak current densities than that on Au and Pt electrodes can be obtained. The low oxidation potential and high peak current density indicate the enhanced reactivity of Au electrodes by the platinum modification. The characteristics of the Pt-modified Au electrodes are found to be similar to that of Pt electrodes, and the reactivity of the Pt-modified Au electrodes is mainly attributed to the deposited platinum.     

几种芳香化合物电化学性质的研究

采用循环伏安法考察了苯胺在铂电极上不同浓度、pH值和不同扫描速率等条件下的电化学反应特性。结果表明:在中性条件下,苯胺未出现明显的氧化还原峰,氯苯、苯甲酸分别出现了2个氧化峰和1个还原峰;随着硫酸浓度的增大,氯苯和苯甲酸峰电流密度呈减小趋势,而苯胺峰电流密度增大,这可能与氨基、氯、羧基的Hammet常数和溶液的pH值有关,Hammet常数越小易于发生亲电攻击;苯胺的氧化峰和还原峰相比大约为1,接近于可逆反应,苯胺的可逆性最强。     

Catalysed titanium mesh electrodes for ethylene glycol fuel cells

Electrodes comprising thermally deposited Pt, PtRu and PtRuW on titanium mesh were evaluated for the oxidation of ethylene glycol in acidic electrolyte. The electrodes were characterised using cyclic voltammetry, scanning electron microscopy and X-ray diffraction and the effect of reactant concentration and temperature were examined. Single fuel cell tests employing the titanium mesh anode with the PtRuW catalyst showed better performance than that of the PtRu catalyst. A peak power density of 15 mW cm⁻² was obtained at a temperature of 90 °C with 1.0 M ethylene glycol solution. The performance of the catalysed PtRu mesh electrode was comparable to that of a commercial, alcohol oxidation, PtRu carbon supported catalyst.     

Anodic Oxidation of Polyhydric Alcohols on a Pt Electrode in Alkaline Solution

The electrochemical oxidation of various polyhydric alcohols, ethylene glycol, glycerol, meso-erythoritol, and xylitol, on a platinum electrode was investigated systemematically in acidic H₂SO₄, and in alkaline KOH and K₂CO₃ solutions to evaluate the potential of these polyhydric alcohols as fuels in micro-fuel cells for portable electronic devices. All polyhydric alcohols tested in the present study showed high reactivities in both alkaline solutions. Ethylene glycol showed the highest reactivity. Although the reactivity of ethylene glycol was lower in K₂CO₃ than in KOH, the carbonate solution is a potential candidate as an electrolyte solution due to its resistance to solution carbonation. Furthermore, ethylene glycol showed much less significant electrode poisoning by adsorbed CO upon oxidation in alkaline solution.     

纳米铂修饰玻碳电极对乙二醇的电催化氧化研究

采用化学原位一步还原法制得纳米铂修饰玻碳电极,并测试比较了其在酸性介质和碱性介质中对乙二醇氧化的电催化作用.结果表明,相比铂片电极,纳米铂修饰玻碳电极对乙二醇表现出更好的电催化性能,且该修饰电极在碱性介质中对乙二醇的催化作用更明显.     

PdNi/C催化剂的制备及对甲酸的电催化氧化

采用化学还原法,在乙二醇体系中制备了碳载PdNi催化剂(PdNi/C),与相同方法制备的Pd/C催化剂比较,发现PdNi/C催化剂对甲酸氧化具有较负的峰电位和较高的峰电流,且起始氧化电位也较低。计时电流曲线测试表明,与Pd/C催化剂相比,甲酸在PdNi/C催化剂上的氧化电流密度随时间衰减得比较慢,且具有较高的稳定电流。     

Au/C catalyst prepared by polyvinyl alcohol protection method for direct alcohol alkaline exchange membrane fuel cell application

An Au/C catalyst was prepared by means of the polyvinyl alcohol-protected Au sol method. Highly dispersed Au nanoparticles with an average particle size of around 3.7 nm were obtained as confirmed by transmission electron microscopy. The cyclic voltammogram of Au/C was similar to that of a bulk Au electrode, but a small shift of Au oxide reduction and oxidation potential peaks were observed. The electrooxidation of methanol, ethanol, ethylene glycol, and glycerol on the Au/C catalyst in an alkaline solution was analyzed. Using a cyclic voltammogram, the maximum current density toward alcohol electrooxidation was found to decrease in the order of glycerol > ethylene glycol > ethanol, while methanol was not oxidized. Compared with PtRu/C, the maximum current densities obtained from the Au/C catalyst for ethylene glycol and glycerol electrooxidation were increased by 1.6 and 3.3 times, respectively. The reaction heavily progressed through a C–C bond dissociation path. It was found that main product of glycerol electrooxidation was formic acid, which accounted for more than 60 % of the total product. Using chronoamperometry, the Au/C catalyst showed much better stability than that of PtRu/C for the reaction without C–C bond dissociation and better stability for the reaction with C–C bond dissociation.     

Electrocatalytic Oxidation of Glucose on Gold Nanocomposite Electrodes

The electrocatalytic oxidation of glucose on gold nanocomposite electrodes was investigated with cyclic voltammetry. The gold nanocomposite electrodes were prepared by precipitating gold nanoparticles of different sizes from the corresponding colloidal solutions onto planar substrates, and the electrodes exhibited higher catalytic activity for the oxidation of glucose in alkaline solution with a negative shift in oxidation potential and a larger current as compared with bare gold electrodes. The high catalytic activity of the gold nanocomposite electrodes also resulted in easy oxidation of gluconolactone produced in the reaction. The modification of the gold nanocomposite electrodes with silver underpotential deposition led to a further negative shift in potential but a drop in current for the glucose oxidation.     

Electrochemical oxidation of ethylene glycol on Pt-based catalysts in alkaline solutions and quantitative analysis of intermediate products

Electrocatalytic activities of Pt/C, Pt-Ru/C, and Pt-Ni/C for the oxidation of ethylene glycol in a basic solution are evaluated by cyclic voltammetry and quasi-steady state polarization. Based on the results of Tafel slopes from quasi-steady state polarization, the catalytic activities for ethylene glycol oxidation are in the order of Pt-Ru/C > Pt-Ni/C > Pt/C. The analysis of intermediate products for ethylene glycol oxidation by higher performance liquid chromatograph (HPLC) demonstrates that the degree of ethylene glycol oxidation is dependent on catalysts. Pt-Ru/C shows the highest current densities for ethylene glycol oxidation, but shows lower fuel utilization. On the other hand, Pt-Ni/C shows higher ability to cleavage C–C bonds, but is suffered from catalyst poisoning. To improve the tolerance for catalyst poisoning, we construct a novel Pt-Ni-SnO₂/C catalyst, compare its catalytic activities, and evaluate the intermediates. Pt-Ni-SnO₂/C shows superior catalytic activities for ethylene glycol oxidation, resulting in the highest degree of complete electro-oxidation of ethylene glycol to CO₂.     

Pd-Co/CNT复合催化剂的制备及甲醇电氧化性能

以Pd Cl₂和Co(NO₃)₂为原料，采用分步乙二醇还原法制备了多壁碳纳米管负载Pd-Co复合纳米催化剂Pd-Co/CNT。利用TEM、XRD和XPS对催化剂的结构进行了表征，考察了其甲醇电氧化性能。结果显示，Co的引入使Pd催化剂的分散性得到改善，其电化学表面积可达39.7 m²/g。循环伏安测试表明，当Pd∶Co物质的量比为1∶0.2时，Pd-Co/CNT的甲醇氧化峰电流密度约为Pd/CNT的2.7倍。计时电流结果表明，Co的添加使催化剂的活性衰减比例由Pd/CNT的63.8%降至54.2%，显示出较强的抗中毒能力。Pd-Co复合催化剂性能的改善归因于Pd与Co之间的协同相互作用。     

Electrooxidation of methanol and ethylene glycol on gold and on gold modified with an electrodeposited polyNiTSPc film

The electrooxidation of methanol and ethylene glycol on Au and on polynickeltetrasulphophthalocyanine-modified gold (polyNiTSPc/Au/Q) electrodes in a pH 11 carbonate/hydrogen carbonate buffer electrolyte was studied by cyclic voltammetry (CV) and with an electrochemical quartz crystal microbalance (EQCM). Au shows negligible activity for methanol oxidation, in agreement with the fact that methanol does not adsorb on Au, since it does not affect the potential at which the mass increase due to Au oxidation starts. On the contrary, ethylene glycol (EG) is electrooxidized on Au at a significant rate, probably because it adsorbs rather strongly on Au, as evidenced by the positive shift by 0.35 V of the mass increase attending Au monolayer oxidation. The polyNiTSPc-modified Au electrodes are hydrophobic, as inferred from the disappearance of the large mass decrease in the double-layer region typical of the bare Au electrode, a decrease which is due to the desorption of the water molecules adsorbed at the negative potential limit. On the polyNiTSPc/Au/Q electrodes the current at the positive potential limit (at which only Ni(III) exists) of methanol oxidation, and the peak current of EG oxidation (at a potential at which only Ni(II) exists), show a Langmuir dependence on the concentration, which indicates that in both cases the reactive species are adsorbed, and that their oxidation rate is much lower than the adsorption rate. As is well known, the oxidation of Ni(II) to Ni(III) in the polyNiTSPc film is accompanied by a large mass decrease, due mostly to the expulsion of water from the film by the hydrophobic Ni(III). This mass decrease is independent of the scan rate, but in the presence of methanol or ethylene glycol it increases with increasing scan rate, which indicates that the oxidation of the alcohols involves a chemical reaction of the alcohols with Ni(III) ions, the extent of which decreases with increasing rate. Consequently, the amount of the hydrophobic Ni(III) will increase, and so will the mass loss. The mass decrease of Ni(II) oxidation decreases with increasing concentration of methanol or ethylene glycol, which again shows that there is a chemical reaction between the alcohols and Ni(III) ions, since the concentration of the latter would decrease with increasing alcohol concentration.     

A microelectrode study of the reduction of formaldehyde in neutral concentrated aqueous solutions

Voltammetry at Hg microelectrodes has been used to investigate the mechanism of the reduction of formaldehyde in conditions close to those employed for the electrosynthesis of ethylene glycol (that is, a very high concentration of formaldehyde in a neutral buffer at high temperature). It is shown that, even with a 40% formaldehyde solution, it is possible to record a well formed reduction wave, limiting current densities up to 30 A cm^–2. The variations in half-wave potential, limiting current density and wave shape with formaldehyde concentration are reported and the influence of pH, temperature and electrolyte are considered. With increasing formaldehyde concentration, the transition from 2e^– reduction to 1e^– reduction is clearly observed. The results led to a re-examination of the influence of cathode material on the yield of ethylene glycol and it is confirmed that graphite is definitely the best choice.     

乙腈-水相1,4-二氯苯在铂电极上的电氧化行为

为有效去除化工废水中的1,4-二氯苯,研究了Pt电极上乙腈-水混合溶剂中1,4-二氯苯电氧化机理。计时电流法研究表明,氧化过程中既有电极表面失电子的直接电化学氧化,又有基于活性自由基的间接氧化。通过SEM表征和Pt电极表面观察,证明Pt电极在2.3 V(vs. SCE)的电位下氧化p-DCB过程中,表面存在黄色有机聚合物膜,致使体系的导电性变差。降解途径推断表明,反应首先经历了脱氯和对氯酚、对苯醌等芳香类中间体的生成;接着开环生成小分子有机酸;最后小分子羧酸进一步氧化成CO₂。     

Electropolymerization of phenol on a vitreous carbon electrode in acidic aqueous solution at different temperatures

Electrochemical oxidation of phenol in acidic aqueous solution was studied on a vitreous carbon electrode at different temperatures in the range of 25–85 °C by cyclic voltammetry and chronoamperometry. The kinetic aspect of the phenol oxidation was investigated as a function of its concentration and temperature. The electrode deactivation by formation of an adherent, compact, and insulating polymeric film was examined by monitoring the decrease in the peak current of phenol oxidation during the course of successive potential scans. Repeated potential scans in the region of water stability did not reactivate the electrode whatever the temperature used. Chronoamperometric curves recorded at different potentials in the region of water decomposition shown that the electrochemical activity of the electrode was partially restored even when performed at low temperature (25 °C).     

Electrochemical behaviour of 1024 mild steel in slightly alkaline bicarbonate solutions

The electrochemical behaviour of 1024 mild steel electrodes is investigated in the presence of 0.05–0.5 M sodium bicarbonate in aqueous solution at pH 8.9 and 25°C. Voltammograms are obtained with a rotating gold ring-mild steel electrode and the effect of the NaHCO3 concentration, the potential limits and the rotation speed of the disc electrode is considered. The voltammograms display an oxidation peak current at low potentials, a passivity region and a transpassive region at high potentials for the potential sweep in the anodic direction. The oxidation current in the passivity region is practically independent of the applied potential and the NaHCO3 concentration. The rate-determining step of the oxidation reaction in both the oxidation peak current region and the transpassive region is determined.     

Electro-oxidation of methanol and ethylene glycol on platinum in alkaline solution: Poisoning effects and product analysis

The electrochemical oxidation of ethylene glycol on platinum was investigated and compared with that of methanol in alkaline solution by using various electrochemical and analytical measurements. Ethylene glycol showed much less significant electrode poisoning than methanol at low potential (400 mV). This phenomenon was clarified by analyzing the products of ethylene glycol oxidation. In ethylene glycol oxidation, partial oxidation to glycolate was much faster than complete oxidation to CO₂. In addition, there were two paths for ethylene glycol oxidation: poisoning and non-poisoning paths. The poisoning path led to the production of C1 compounds and the non-poisoning path gave oxalate. The non-poisoning path prevented the formation of poisonous species on platinum.     

甲醇在不同方法制备的碳载Pt-TiO_2催化剂上的电催化氧化

采用TiO2溶胶法,在不同条件下制备了碳载Pt-TiO2催化剂.通过循环伏安法(CV),计时电流法(CA)对碳载Pt-TiO2催化剂在甲醇上的电氧化特性进行了研究.结果表明不同条件制备的催化剂对甲醇的电催化氧化的催化活性不同.其中加入聚乙二醇所制得的Pt-TiO2/C催化剂对甲醇的氧化具有最佳的电催化活性和稳定性.     

Electrode processes of bismuth in weakly acidic,neutral and alkaline solutions

The electrode process Bi(III)+ 3e = Bi(Hg) has been investigated in weakly acidic, neutral and alkaline solutions by means of amalgam polarography and cyclic voltammetry and chronopotentiometry with the use of hanging amalgam drop electrode. It has been found that in weakly acidic and neutral solutions, oxidation of bismuth amalgam goes through aquocomplexes of bismuth. In the cathodic step on cyclic voltammetry curves four peaks of reduction are observed, with magnitude and shape strongly dependent on pH of the solution. These peaks have been ascribed to the reduction of Bi³⁺, Bi(OH)⁺₂, Bi(OH)⁺² and Bi(OH)₃.In alkaline solutions, oxidation of bismuth amalgam leads to Bi(OH)₃. In cathodic scan on cyclic voltammetry curves only one peak is observed, which corresponds to Bi(OH)₃ reduction. Formal potentials of electrode process and solubility product of Bi(OH)₃ have been calculated and discussed. The step-wise nature of the overall electrode reaction has been ascertained and discussed. At higher concentrations of OH^? ions, Bi(OH)₃ dissolves.     

Electrooxidation of methanol on polycrystalline and single crystal gold electrodes

Oxidation of methanol has been investigated on polycrystalline and single crystal gold electrodes: Au(poly), Au(1 1 1) and Au(2 1 0), in acidic, neutral and alkaline solutions. As expected, catalytic activity of gold towards methanol oxidation increases with increasing pH of the solution. It has been found that in all studied solutions methanol is oxidised in two potential regions, prior to gold surface oxide monolayer formation and in more positive potentials, on gold surface oxide after so called “turn over”. Surface structure of the electrode has little influence on the oxidation current, however potentials at which oxidation is observed depends on the crystallographic orientation. The mechanism of electro-oxidation of methanol on gold is discussed.     

Enhanced electrooxidation of methanol,ethylene glycol,glycerol, and xylitol over a polypyrrole/manganese oxyhydroxide/palladium nanocomposite electrode

A small quantity of palladium metal (Pd, 5 wt%) nanoparticles supported by a polypyrrole/manganese oxyhydroxide (PPy/MOH) nanocomposite was developed and investigated as an electrocatalyst for the alcohol electrooxidation reaction in alkaline media. In voltammetric studies, the PPy/MOH/Pd catalyst, compared to C/Pd, exhibited improved electrocatalytic activity for methanol electrooxidation. The peak current density ratios (j ^f/j ^b) for the C/Pd and PPy/MOH/Pd nanocomposite electrodes were 0.67 and 2.43, respectively, indicating that the PPy/MOH/Pd nanocomposite electrode was much more resistant to catalytic poisoning. The electrooxidation of ethylene glycol (EG), glycerol, and xylitol was also tested using the PPy/MOH/Pd nanocomposite electrode. Among these alcohol electrooxidations, that of EG exhibited the maximum power density of 430 mA cm^?2. The intermediates formed during the electrooxidation reactions were removed by increasing the upper sweep potential from +0.2 to +1.0 V. The catalytic performance of the PPy/MOH nanocomposite is discussed in detail. The study results demonstrate that PPy/MOH acts as a superior catalytic supporting material for alcohol electrooxidation reactions in alkaline media.