Pt/laponite clay-modified gold electrode for direct methanol fuel cells

This work employs a novel technique in which laponite clay-modified gold electrodes are used as the anode for direct methanol fuel cells. The platinum/laponite clay (Pt/Clay) films on indium tin oxide electrode were characterized by using scanning electron microscope and energy-dispersive X-ray spectroscopy. Various contents of laponite clay (0.1, 0.5, 1.0, and 2.0?wt%) with constant platinum (Pt) catalyst content on modified gold electrodes were studied as an anode catalyst for methanol oxidation. The catalyst poisoning was observed as a function of time. The 1.0?wt% Pt/Clay-modified gold electrode shows the highest activity for methanol oxidation, 27.73?% higher than Pt only modified gold electrode at 2.5?min. The peak current of 1?% Pt/Clay-modified gold electrode is 3.50?% higher than the peak current of Pt only modified gold electrode at 57.5?min. The higher content of Pt/Clay-modified gold electrode shows strong resistance to catalyst poisoning. The Pt/Clay-modified gold electrode is a new and promising electrode for a direct methanol fuel cell and can replace existing commercial catalysts.     

High catalytic activity of chemically activated gold electrodes towards electro-oxidation of methanol

Electro-oxidation of methanol has been investigated on activated, rough gold electrodes in alkaline solutions. The electrodes were activated by formation and decomposition of gold amalgam. The oxidation of methanol starts at potentials about 400 mV less positive as compared with smooth poly and single crystal gold electrodes and the oxidation current is much higher. For freshly prepared, activated gold electrodes the oxidation current is similar to that obtained on smooth platinum, however it diminishes with time. The formation of small crystallites, which could trap OH⁻ anions, seems to be the most important factor for this unusual catalytic activity. The dependence of the oxidation process on electrode topography is discussed.     

Comparative voltammetric study of methanol oxidation and adsorption on noble metal electrodes in perchloric acid solutions

Periodic current/potential curves were measured potentiostatically on smooth electrodes of platinum, iridium, rhodium, and gold at 30 mV/s in perchloric acid solutions with different additions of methanol (10⁻³ M to 1 M). Information on methanol adsorption was obtained from impedance measurements at 1000 c/s by volcammetry with superimposed a.c. voltage. The current/potential curves look similar on Pt and Pd on the one hand, and on Ir and Rh on the other hand. There is no noticeable methanol oxidation on gold. The peak current of the first wave during the anodic sweep decreases considerably in the order Pt> Pd> Rh> Ir. The capacitive component of the impedance shows methanol adsorption in the hydrogen and double layer region. The shape of the current/potential curves and the methanol adsorption are strongly influenced on platinum metals by oxygen layers which are formed or reduced electrochemically during the sweeps in different potential ranges.     

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.     

Electrocatalytic oxidation of methanol and C1 molecules on highly dispersed electrodes Part II: Platinum-ruthenium in polyaniline

The oxidation of methanol and C1 molecules at electrodes modified with polyaniline and particles of platinum and ruthenium has been studied in aqueous HClO₄ electrolyte. The platinum and ruthenium particles were incorporated into the polyaniline film by electrochemical reduction. The activity for the oxidation of C1 molecules is higher for bimetallic electrodes than for polyaniline-coated electrodes modified with platinum alone. Indeed, a negative shift of more than 100 mV is observed as compared to the potential obtained with a polyaniline film modified by pure platinum. Moreover, the oxidation of methanol is faster and more complete on the Pt-Ru modified polyaniline electrode, since carbon dioxide is the main reaction product.     

载铂聚苯胺/聚砜复合膜修饰电极对甲醇的电催化氧化行为研究

采用循环伏安法制备聚苯胺(PAN)/聚砜(PSF)复合膜修饰电极,在其上电沉积铂粒子,制得载铂聚苯胺/聚砜复合膜修饰电极,用循环伏安法和交流阻抗法研究它对甲醇的电催化氧化行为。复合膜的化学组分用FTIR进行表征,复合膜内层载铂后的表面形态用SEM进行表征。结果表明,复合膜的内层(与工作电极接触的一面)是聚苯胺,外层(与溶液接触的一面)是聚砜,铂粒子在复合膜内层的多孔聚苯胺上均匀沉积,从而使载铂聚苯胺/聚砜复合膜修饰电极对甲醇有好的电催化氧化性能。     

The oxidation of carbon monoxide at platinum and gold metallized membrane electrodes

The oxidation of carbon monoxide at gold platinum membrane electrodes is discussed and it is shown that the electrochemical characteristics of these electrodes are similar to massive electrodes. At platinum the short time response is determined by the oxidation of a surface monolayer of carbon monoxide by a reactant pair mechanism occuring at the edges of growing islands of an oxidised platinum species whilst at gold, the process is diffusion controlled. On both metals the longer timescale response is complicated by poisoning of the surface by a reaction intermediate but it is also shown that a gold anode may be reactivated by potential cycling. The relevance of these results to the construction of an analytical device is discussed.     

Structural effects in electrocatalysis: oxidation of formaldehyde on gold and platinum single crystal electrodes in alkaline solution

The oxidation of formaldehyde in sodium hydroxide solution has been studied on platinum and gold single crystal electrodes with the (111), (110) and (100) orientations. There is apparently no structural sensitivity of this reaction, since minor differences have been found between the three low index faces. This is valid for both platinum and gold electrodes. The hydrogen adsorption on platinum and the AuOH formation on gold electrodes exhibit structural sensitivity in the same solution. Similar activity of platinum and gold electrodes is noteworthy. A weak adsorption of gem-diol, formed in the interaction of formaldehyde with H₂O or OH^? appears as the origin of the structural insensitivity of this reaction.     

Electrodeposited platinum catalysts over hierarchical carbon monolithic support

Mesoporous deposits of platinum catalysts were electrodeposited over monolith carbon with hierarchical porous structure. The liquid crystal used as a template allowed the electrodeposition of the catalyst on the outer region of the carbon with low penetration in the porous structure. The platinum hexagonal mesostructured deposits exhibits an excellent stability enhanced by the roughness of the carbon support. The mass activity for the electrooxidation of methanol of the mesoporous Pt catalyst supported on the hierarchical carbon is similar to that observed on gold and to that reported for commercial Pt nanoparticulated catalysts, even when this catalyst has a smaller Pt load than the commercial one. Also, the poisoning rate of the mesoporous catalyst is lower than that observed for the commercial catalyst. The integrated system of structured materials could be suitable for the fabrication of modified electrodes in small scale applications.     

Electrocatalytic oxidation of methanol and C1 molecules on highly dispersed electrodes Part 1: Platinum in polyaniline

The oxidation of methanol and C1 molecules was investigated on platinum-modified polyaniline electrodes. It was found that such electrodes are conducting even at 0.0 V vs RHE. They were found to have a higher electrocatalytic activity than bulk platinum electrodes. Moreover, the poisoning effect is drastically decreased as proved by in situ EMIRS studies which show no significant CO_ads signal. Finally, kinetic results show that the methanol electrooxidation is first order with respect to methanol and that the main oxidation product is formaldehyde.     

用磷钼酸修饰甲醇燃料电池的铂电极

近年来以杂多化合物为基础的催化体系受到广泛的关注.为了研究杂多酸与铂电极对甲醇电催化氧化的协同效应,通过循环伏安扫描法制备了磷钼酸（H3PMo12O40）修饰铂电极.通过循环伏安和计时电流法研究了该修饰电极对甲醇氧化的电催化活性和抗中间产物的毒化作用,并比较了该修饰电极与其单酸盐（Na2MoO4）修饰铂电极的性能,测试结果表明：磷钼酸修饰铂电极能够提高对甲醇氧化反应的催化活性,基本上同其单酸盐Na2MoO4修饰铂电极的催化活性相当,并且这种促进作用主要是由Mo原子价态变化引起的.同时计时电流曲线测试结果表明,该修饰电极具有一定的抗毒化作用,但不如钼酸钠好.     

Oxydation electrocatalitique du glycerol sur electrodes d'or et de platine en milieu aqueux

The electrocatalytic oxidation of glycerol has been investigated at platinum and gold electrodes, both in acid and in alkaline medium. In acid medium only platinum electrodes are electroactive, whereas in alkaline medium both electrodes, particularly gold electrodes, give relatively high current densities (about 20 mA cm^?2 for 0.1 M glycerol at 25°C).By varying the reaction parameters (electrode potential, concentrations of glycerol and of hydroxylions), it is possible to determine the transfer coefficient and the reaction orders. The fractional values obtained may be interpreted by formulating a reaction mechanism involving adsorbed intermediates.     

Graphite Electrodes Modified with Platinum‐Nickel Nano‐Particles for Methanol Oxidation

Methanol electro‐oxidation is investigated at graphite electrodes modified with various platinum and nickel nano‐particle deposits using cyclic voltammetry. The modified electrodes are prepared by the simultaneous electrodeposition of metals from their salt solutions using potentiostatic and galvanostatic techniques. They show enhanced catalytic activity towards methanol oxidation in KOH solution. The catalytic activity of platinum nano‐particles is found to be significantly affected by the presence of relatively small amounts of nickel deposits. A comparison is made between the electrocatalytic activity of Pt/C and (Pt‐Ni)/C electrodes. The results show that the methanol electro‐oxidation current increases with an increase in the nickel content. In particular, the highest catalytic activity is achieved for platinum to nickel deposits of 95%:5% (wt.‐%), in other cases the catalytic activity decreases. It is found that Ni enhances the catalytic activity of Pt by increasing the number of active sites, as well as through an electron donation process from Ni to Pt. This process takes place once the nickel hydroxide (Ni(OH)₂)/nickel oxy‐hydroxide (NiOOH) transformation begins. The effect of the methanol concentration on the methanol oxidation reaction is investigated. The order of reaction, with respect to methanol, at the modified (Pt‐Ni)/C electrode is found to be 0.5.     

Platinum—tin catalysts for methanol fuel cells prepared by a novel immersion technique,by electrocodeposition and by alloying

A novel technique has been developed for the preparation of platinum—tin electrodes. In essence, it consists in covering a properly pretreated platinum surface with a fraction of a monolayer of tin without the use of electrical current. Best results are achieved by immersing a hydrogen-covered platinum electrode into an aqueous tin solution. High surface tin coverages lead to passivation at low potentials in methanol oxidation. The optimal activity per unit of real surface area is about the same platinum—tin electrodes prepared by the immersion technique as for those obtained by conventional electrodeposition and by partial corrosion of PtSn alloys, which indicates that conventional PtSn electrodes can only be improved by using higher dispersions.     

Preparation and characterisation of Pt deposition on ion conducting membrane for direct methanol fuel cell electrodes

Membrane-electrode assemblies (MEAs) for direct methanol fuel cells (DMFC) have been prepared by depositing platinum on the surface of solid polymer electrolytes (SPE). Chemical and electrochemical depositions were used to achieve good adhesion between platinum particles and the SPE and for reducing the contact resistance. Platinum particle structure and composition were investigated by means of SEM and EDX. Cyclic voltammetry (CV) and methanol oxidation tests were used to determine the electrochemical characteristics of the Pt-SPE electrodes which can be applied in DMFC. Overall the electrodes produced by chemical and electrochemical deposition of Pt onto the membranes are not as active as those produced by hot pressing carbon supported Pt catalyst layers onto the membrane.     

Electrocatalytic oxidation of methanol: carbon-supported gold–platinum nanoparticle catalysts prepared by two-phase protocol

This paper describes recent results of an investigation of the electrocatalytic oxidation of methanol at carbon-supported gold and gold–platinum nanoparticle catalysts. The exploration of the bimetallic composition on carbon black support is aimed at modifying the catalytic properties for methanol oxidation reaction (MOR) at the anode in methanol oxidation fuel cells. Gold and gold–platinum nanoparticles of 2–3 nm core sizes with organic monolayer encapsulation were prepared by two-phase protocol. The nanoparticles were assembled on carbon black materials and thermally treated. The electrocatalytic MOR activities were characterized using voltammetric techniques, and were compared with commercial catalysts under several conditions. The results have revealed some initial insights into the catalytic activity of gold–platinum nanoparticle catalysts. Implications of our findings to the design and manipulation of highly-active gold–platinum nanoparticle catalysts for fuel cell applications are also discussed.     

Gold and platinum catalysed oxidation of methanol

A comparative study was made of the vapour phase oxidation of methanol in presence of gold and platinum, using a flow system at temperatures below 500°C. Over gold there is a stoichiometric conversion to formaldehyde and water. In presence of platinum, the reaction is the same up to 200°C, but at higher temperatures other oxidation products appear. Mechanisms are suggested involving interaction between chemisorbed oxygen and methanol fragments.     

Impedance of the oxygen-evolution reaction on noble metal electrodes

The impedances of the oxygen-electrode reaction on platinum, palladium, gold and silver electrodes in acidic and alkaline solutions were measured with an ac bridge in the range of frequency from 10 Hz to 20 kHz, under dc polarization. For these electrodes, plots of impedances on the complex plane give semi-circles whose diameter is proportional to the dc being passed through the cell. By analysing these plots and impedance/dc curves, it is shown that the oxygen-evolution reaction on these electrodes is controlled by a charge-transfer process, except for the case of platinum in perchloric acid solution. In the latter system, a chemical reaction on the electrode surface is rate-determining.     

Electro-oxidation of glycerol on platinum dispersed in polyaniline matrices

Films of polyaniline (PAni) were electrosynthesized on gold and glassy carbon substrates. The morphology of the films was verified using scanning electron microscopy (SEM) and, as expected, the PAni film formed on glassy carbon presented fibrillar morphology, while that formed on gold presented fibrils on top of a more compact structure. Different amounts of platinum were electrodeposited into the polymer matrices at constant potential and the electrocatalytic activities of the electrodes were evaluated for glycerol electro-oxidation in acidic medium. Furthermore, the active areas of such modified electrodes were determined from the charges involved in the electro-oxidation of an adsorbed carbon monoxide monolayer. Considering the real active areas, the modified electrode with the gold substrate presents higher electrocatalytic activity for glycerol oxidation than that with the glassy carbon substrate. This difference is mainly related to their morphological characteristics and platinum particle sizes.     

Electrocatalytic activities of graphite-supported platinum electrodes for methanol electrooxidation

Electrooxidation of methanol in 1 m NaOH at 30°C was studied on graphite-supported platinum electrodes prepared both in hydrogen and in air at various temperatures. Heating in hydrogen always produced higher surface area of Pt, and hence greater mass activity, than in air at a particular temperature. Nevertheless, both the graphite-supported platinum electrodes exhibited almost the same specific activity as a smooth Pt electrode for methanol electrooxidation irrespective of the preparation conditions. This indicates that the difference in mass activity is due to different surface areas produced by the different preparation methods. The Tafel slope of 110 mV decade^–1 on all the electrodes studied indicated that the first charge transfer process was the rate-determining step.