Dynamics of Electrocatalytic Oxidation of Ethylene Glycol,Methanol and Formic Acid at MWCNT Platform Electrochemically Modified with Pt/Ru Nanoparticles

Comparative electrocatalytic behavior of functionalized multiwalled carbon nanotubes (fMWCNTs) electrodecorated with Pt/Ru nanoparticles towards the oxidation of methanol (MeOH), ethylene glycol (EG) and formic acid (FA) has been investigated. The catalytic current density decreased approximately as MeOH≈EG>FA. Result revealed that BPPGE‐fMWCNT‐Pt/Ru tolerates CO poisoning for FA electrooxidation than when used for the oxidation of the EG or MeOH. Electrochemical impedance spectra are dependent on the oxidation potentials, with equivalent circuit models characteristic of adsorption‐controlled charge transfer kinetics. The results provide important insights into the electrochemical response of these small organic molecules useful in fuel cell technology.     

A Revisit to the Role of Bridge-adsorbed Formate in the Electrocatalytic Oxidation of Formic Acid at Pt Electrodes (cited: 2)

The mechanism and kinetics of electrocatalytic oxidation of formic acid at Pt electrodes is discussed in detail based on previous electrochemical in-situ ATR-FTIRS data [Langmuir 22, 10399 (2006) and Angewa. Chem. Int. Ed. 50, 1159 (2011)]. A kinetic model withformic acid adsorption (and probably the simultaneous C-H bond activation) as the rate determining step, which contributes to the majority of reaction current for formic acid oxi-dation, was proposed for the direct pathway. The model simulates well the IR spectroscopic results obtained under conditions where the poisoning effect of carbon monoxide (CO) is negligible and formic acid concentration is below 0.1 mol/L. The kinetic simulation predicts that in the direct pathway formic acid oxidation probably only needs one Pt atom as active site, formate is the site blocking species instead of being the active intermediate. We review in detail the conclusion that formate pathway (with either 1st or 2nd order reaction kinetics) is the direct pathway, possible origins for the discrepancies are pointed out.     

Mechanistic study of the deactivation of carbon supported Pd during formic acid oxidation

Palladium is an attractive anode catalyst for direct formic acid fuel cells (DFAFC) because of its high activity relative to Pt, but it suffers significant activity losses during operation of the DFAFC. The deactivation mechanism of a Pd/C catalyst during oxidation of formic acid has been studied by means of electrochemical stripping voltammetry. The stripping characteristics of the anode poison are virtually the same as those of adsorbed CO, and adsorbed CO has a similar poisoning effect. It is therefore proposed that a gradual build-up of adsorbed CO causes the deactivation of Pd in DFAFCs.     

Electrochemical oxidation of carbon monoxide, methanol, formic acid, ethanol, and acetic acid on a platinum electrode under hot aqueous conditions

Using a pressure cell equipped with an Ag AgCl 0.1 M KCl external pressure-balanced reference electrode (EPBRE), hydrogen, methanol, formic acid, carbon monoxide, ethanol, acetic acid, and glucose were electrochemically oxidized on a Pt electrode under hot aqueous conditions (365−525 K), and the polarization curves were obtained at a sweep rate of 1 or 10 mV s⁻¹. The potential measured versus EPBRE was corrected to the RHE scale based on the experimentally or theoretically calculated pH of the solution at high temperature. During methanol and carbon monoxide oxidation, a strongly adsorbed intermediate presumably CO, was formed but it was oxidized at a lower potential than under ambient temperature. Formic acid was rapidly oxidized around 0 V versus RHE without formation of this adsorbed intermediate. Using a gas mixture of hydrogen and carbon monoxide, it was confirmed that the surface coverage by CO was decreased dramatically with a temperature increase from 425 to 475 K under hot aqueous conditions. Ethanol and acetic acid were also satisfactorily oxidized, but the trial to measure the electrochemical oxidation behavior of glucose was not successful due to the adhesion of char-like compounds to the electrode.     

Electrocatalytic mechanism and kinetics of SOMs oxidation on ordered PtPb and PtBi intermetallic compounds: DEMS and FTIRS study

The electrocatalytic activities and mechanisms of PtPb and PtBi ordered intermetallic phases towards formic acid, formaldehyde and methanol oxidation have been studied by DEMS and FTIRS, and the results compared to those for a pure polycrystalline platinum electrode. While PtPb exhibits an enhanced electrocatalytic activity for the oxidation of all three organic molecules when compared to a Pt electrode, PtBi exhibits an enhanced catalytic activity towards formic acid and formaldehyde oxidation, but not methanol. FTIRS data indicate that adsorbed CO does not form on PtPb or PtBi intermetallic compounds during the oxidation of formic acid, formaldehyde and methanol, and therefore their oxidation on both PtPb and PtBi intermetallic compounds proceeds via a non-CO(ads) pathway. Quantitative DEMS measurements indicate that only CO(2) was detected as a final product during formic acid oxidation on Pt, PtPb and PtBi electrodes. At a smooth polycrystalline platinum electrode, the oxidation of formaldehyde and methanol produces mainly intermediates (formaldehyde and formic acid), while CO(2) is a minor product. In contrast, CO(2) is the major product for formaldehyde and methanol oxidation at a PtPb electrode. The high current efficiency of CO(2) formation for methanol and formaldehyde oxidation at a PtPb electrode can be ascribed to the complete dehydrogenation of formaldehyde and formic acid due to electronic effects. The low onset potential, high current density and high CO(2) yield make PtPb one of the most promising electrocatalysts for fuel cell applications using small organic molecules as fuels.     

可见光诱导提升Pt/g-C3N4纳米片甲酸氧化性能的研究

以半导体材料类石墨氮化碳纳米片(g-C₃N₄纳米片)为载体,通过微波-多元醇法构筑了Pt/g-C₃N₄纳米片催化剂. 通过TEM、XRD、XPS、紫外-可见吸收光谱等方法对Pt/g-C₃N₄纳米片催化剂的粒径尺寸、组成、结构、光学等性质进行分析. 通过对比可见光照和暗室条件下的甲酸电氧化活性,Pt/g-C₃N₄纳米片催化剂在可见光照射下展现出良好的催化性能. 该性能的提高一方面可能是由于g-C₃N₄纳米片在可见光照射下加速了电子从Pt转移给g-C₃N₄纳米片,Pt处于“电子匮乏”状态,可削弱CO与Pt之间的化学键能,减弱CO在Pt表面的吸附能力,促进了CO的氧化,提高了催化剂抗中毒能力;另一方面,g-C₃N₄纳米片在光照条件下分离出的空穴可有效氧化甲酸分子,提高甲酸氧化活性. 因此,可见光条件下可有效提高Pt/g-C₃N₄纳米片催化剂甲酸催化氧化活性,这为直接甲酸燃料电池的发展提供了新思路.     

一种提高铂电催化氧化甲酸性能的简单方法

在离子液体1-乙基咪唑三氟乙酸盐(HElmTfa)中,采用循环伏安法在铂电极表面修饰聚吡咯(PPY),制得PPy-HEImTfa/Pt,并研究了其对甲酸的电催化氧化性能.与相同条件下的铂基底电极相比,PPy-HEImTfa/Pt对甲酸的电催化氧化性能有很大的提高.原位红外光谱表明,PPy-HElmTfa能降低中间体CO等对铂电极的毒化作用,促进甲酸直接氧化生成CO_2.     

High activity of Pt(4)Mo alloy for the electrochemical oxidation of formic acid

Surface processes on Pt4Mo alloy well-defined by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) were studied in acid solution by cyclic voltammetry. It was established that Mo in the alloy is much more resistant toward electrochemical dissolution than pure Mo. During the potential cycling of Pt4Mo surfaces in completely quiescent electrolyte, hydrous Mo-oxide could be generated on Mo sites. Investigation of the formic acid oxidation revealed that this type of Mo-oxide enhances the reaction rate by more than 1 order of magnitude with respect to pure Pt. Surface poisoning by CO(ads) is significantly lower on Pt4Mo alloy than on pure Pt. The effect of hydrous Mo-oxide on the HCOOH oxidation rate was explained through the facilitated removal of the poisoning species and through its possible influence on the intrinsic rate of the direct reaction path.     

Studies of carbon monoxide oxidation on carbon-supported platinum-osmium electrocatalysts

The electrocatalytic oxidation of hydrogen in the presence of carbon monoxide was studied on PtOs/C electrocatalysts prepared by the formic acid method and heat-treated under several temperatures and atmospheres. The physical properties of the metallic phase were evaluated by X-ray diffraction (XRD), energy dispersive X-ray (EDX) analysis, and in situ X-ray absorption spectroscopy (XAS). The electrochemical performance of these materials was evaluated by single-cell polarization measurements, cyclic voltammetry, and linear sweep CO stripping voltammetry. The results have shown an enhancement of the CO oxidation process for the as-prepared PtOs/C and for a material heat-treated in a reducing atmosphere (hydrogen at 500 °C), compared to Pt/C. The electrochemical data also showed that the as-prepared and hydrogen-treated PtOs/C catalysts present CO tolerance higher than Pt/C. This has been associated with the occurrence of a surface reaction of CO adsorbed on Pt and oxygenated Os sites, favored by an intimate physical contact between segregated Os and Pt phases.Dedicated to Prof. Wolf Vielstich on the occasion of his 80th birthday in recognition of his numerous contributions to interfacial electrochemistry     

A combination of SERS and electrochemistry in Pt nanoparticle electrocatalysis: Promotion of formic acid oxidation by ethylidyne

In this paper, formic acid electrooxidation on ethylidyne modified Pt nanoparticles is reported. The formation as well as the stability electrochemical range of the ethylidyne adlayers was studied by surface enhanced Raman spectroscopy (SERS) and cyclic voltammetry. The presence of adsorbed ethylidyne on platinum nanoparticles improved their electrocatalytic activity towards formic acid oxidation, which could be attributed to an instabilization of the carbon monoxide poisonous species as evidenced by SERS. The use of in situ spectroscopic measurements with electrocatalysts similar to those applied in practice is highlighted.     

A high dispersed Pt0.35Pd0.35Co0.30/C as superior catalyst for methanol and formic acid electro-oxidation

Pt：Pd：Co ternary alloy nanoparticles were synthesized by sodium borohydride reduction under nitrogen, and were supported on carbon black as catalysts for methanol and formic acid electro-oxidation. Compared with Pt0.65C00.35/C, Pt/C, Pd0.65C00.35/C, and Pd/C catalyst, Pt0.35Pd0.35Co0.30/C exhibited relatively high durability and strong poisoning resistance, and the Pt-mass activity was 3.6 times higher than that of Pt/C in methanol oxidation reaction. Meanwhile, the Pt0.35Pd0.35Co0.30/C exhibited excellent activity with higher current density and higher CO tolerance than that of Pt0.6sCo0.35/C, Pt/C, Pd0.65C00.35/ C, and Pd/C in formic acid electro-oxidation.     

促进型PtMoSi/C催化剂的制备、表征及电催化活性

采用甲醛还原、H2还原、肼还原三种方法制备了添加硅钼酸的PtMoSi/C阳极催化剂, 并用XRD、XPS和TEM技术对催化剂进行了表征. XRD表明Pt粒子呈立方面心晶态结构, TEM显示PtMoSi/C催化剂粒径小(3−4 nm), 分布窄, 分散性好. XPS分析可知Pt主要以0价, Mo主要以6价, Si主要以4价形态存在于催化剂中. 同时通过循环伏安法和线性扫描法考察了制备方法和添加硅钼酸对催化剂电化学活性的影响. 结果表明, 甲醛还原法制备的PtMoSi/C催化剂(Pt、Mo的原子比为3:1)对甲醇氧化的电化学性能和抗中毒性能优于自制的PtRu/C和E-TEK PtRu/C催化剂, 可能是因为添加硅钼酸可以使活性组分的分散度提高, 从而提高了催化剂的活性和抗毒性能.     

The electrooxidation of small organic molecules on platinum nanoparticles supported on gold: influence of platinum deposition procedure

The electrocatalytic properties of small platinum nanoparticles were investigated for the oxidation of CO, methanol, and formic acid using voltammetry, chronoamperometry, and surface-enhanced Raman spectroscopy. The particles were generated by galvanostatic deposition of platinum on a polished gold surface from an H₂PtCl₆ containing electrolyte and ranged between 10 and 20 nm in diameter for low platinum surface concentrations, 10 and 120 nm for medium concentrations, and full Pt monolayers for high concentrations. CO stripping and bulk CO oxidation experiments on the particles up to 120 nm in diameter displayed pronounced structural effects. The CO oxidation current-time transients show a current decay for low platinum coverages and a current maximum for medium and high coverages. These results were also observed in the literature for particles of 2- to 5-nm size and agglomerates of these particles. The similarities between the literature and our results, despite large differences in particle size and morphology, suggest that particle structure and morphology are also very important catalytic parameters. Surface-enhanced Raman spectroscopy data obtained for the oxidation of CO on the Pt-modified Au electrodes corroborate this conclusion. A difference in the ratio between CO adsorbed in linear- and bridge-bonded positions on the Pt nanoparticles of different sizes demonstrates the influence of the surface morphology. The oxidation activity of methanol was found to decrease with the particle size, while the formic acid oxidation rate increases. Again, a structural effect is observed for particles of up to ca. 120 nm in diameter, which is much larger than the particles for which a particle size effect was reported in the literature. The particle shape effect for the methanol oxidation reaction can be explained by a reduction in available “ensemble sites” and a reduction in the mobility of CO formed by decomposition of methanol. As formic acid does not require Pt ensemble sites, decreasing the particle size, and thus, the relative number of defects, increases the reaction rate. Dedicated to Prof. Dr. Teresa Iwasita on the occasion of her 65th birthday in recognition of her numerous contributions to interfacial electrochemistry.     

Mass-transport-limited oxidation of formic acid on a PdMLPt(100) electrode in perchloric acid

In this communication, we study the electrocatalytic formic acid oxidation process on an epitaxially grown Pd monolayer on a Pt(100) single crystal in perchloric acid. The formic acid oxidation activity on this Pd_MLPt(100) electrode in perchloric acid is significantly enhanced compared to the same electrode in sulfuric acid and compared to unmodified Pt(100), with a low onset potential of around 0.14 V_RHE. The absence of hysteresis between the positive and negative scan during formic acid oxidation indicates the remarkable resistance to CO poisoning of the Pd monolayer surface. Most importantly, we report, for the first time, a mass-transport-limited formic acid oxidation rate on the Pd_MLPt(100) rotating electrode in perchlorate acid, setting a catalytic benchmark for future electrocatalysts for formic acid oxidation.     

Composition effects of FePt alloy nanoparticles on the electro-oxidation of formic acid

The catalytic activities of FexPt100-x alloy nanoparticles at different compositions (x=10, 15, 42, 54, 58, and 63) in the electro-oxidation of formic acid have been investigated by using cyclic voltammetry (CV), chronoamperometry, and electrochemical impedance spectroscopy (EIS). It was observed that the electrocatalytic performance was strongly dependent on the FePt particle composition. In chronoamperometric measurements, the alloy particles at x approximately 50 showed the highest steady-state current density among the catalysts under study and maintained the best long-term stability. In addition, on the basis of the anodic peak current density, onset potentials, and the ratios of the anodic peak current density to the cathodic peak current density in CV studies, the catalytic activity for HCOOH oxidation was found to decrease in the order of Fe42Pt58>Fe54Pt46 approximately Fe58Pt42>Fe15Pt85>Fe10Pt90>Fe63Pt37. That is, within the present experimental context, the alloy nanoparticles at x approximately 50 appeared to exhibit the maximum electrocatalytic activity and stability with optimal tolerance to CO poisoning. Consistent responses were also observed in electrochemical impedance spectroscopic measurements. For the alloy nanoparticles that showed excellent tolerance to CO poisoning, the impedance in the Nyquist plots was found to change sign from positive to negative with increasing electrode potential, suggesting that the electron-transfer kinetics evolved from resistive to pseudoinductive and then to inductive characters. However, for the nanoparticles that were heavily poisoned by adsorbed CO species during formic acid oxidation, the impedance was found to be confined to the first quadrant at all electrode potentials. The present work highlights the influence of the molecular composition of Pt-based alloy electrocatalysts on the performance of formic acid electro-oxidation, an important aspect in the design of bimetal electrocatalysts in fuel cell applications.     

Modification of a Pt surface by spontaneous Sn deposition for electrocatalytic applications. 2. Oxidation of CO,formaldehyde, formic acid,and methanol

The electrocatalytic activity of a spontaneously tin-modified Pt catalyst, fabricated through a simple dip-coating method under open-circuit conditions and characterized using surface analysis methods, was studied in electrooxidation reactions of a preadsorbed CO monolayer and continuous oxidation of methanol, formic acid, and formaldehyde in the potentiodynamic and potentiostatic modes. The catalytic activity of the tin-modified Pt surface is compared with that of a polycrystalline Pt electrode. Spontaneously Sn-modified Pt catalyst shows a superior activity toward adsorbed CO oxidation and thus can be promising for PEFC applications. The methanol oxidation rate is not enhanced on the Sn-modified Pt surface, compared to the Pt electrode. Formic acid oxidation is enhanced in the low potential region on the Sn-modified surface, compared to the Pt electrode. The formaldehyde oxidation rate is dramatically increased by modifying tin species at the most negative potentials, where anodic formaldehyde oxidation is completely suppressed on the pure Pt electrode. The results are discussed in terms of poisoning CO intermediate formation resulting from dehydrogenation of organic molecules on Pt sites, and oxidation of poisoning adsorbed CO species via the surface reaction with OH adsorbed on neighboring Sn sites.     

Electrocatalytic Oxidation of Methanol at Lower Potentials on Glassy Carbon Electrode Modified by Platinum and Platinum Alloys Incorporated in Poly(o‐Aminophenol) Film

The electrocatalytic oxidation of methanol at a glassy carbon electrode modified by a thin film of poly(o‐aminophenol) (PoAP) containing Pt, Pt‐Ru and Pt‐Sn microparticles has been investigated using cyclic voltammetry as analytical technique and 0.10 M perchloric acid as supporting electrolyte. It has been shown that the presence of PoAP film increases considerably the efficiency of deposited Pt microparticles toward the oxidation of methanol. The catalytic activity of Pt particles is further enhanced when Ru or specially Sn is co‐deposited in the polymer film. The effects of various parameters such as the thickness of polymer film, concentration of methanol, medium temperature as well as the long term stability of modified electrodes have also been investigated.     

Pt-Mo电极上CO、甲醛和甲醇的电催化氧化-微分电化学质谱研究

利用微分电化学质谱（DEMS）研究了Mo修饰的Pt电极上CO、甲醛和甲醇的电催 化氧化,证实了Mo(IV)是催化活性样品,而且它只对弱吸附CO的氧化起催化作用, 对强吸附CO的氧化没有催化活性。在低于0.4 V的电位下,吸附在Pt电极上的Mo结 甲醇和甲醛的催化氧化是通过弱吸附CO的氧化路径进行的。     

碱性介质中CO对甲醇在PtAu(111)和Pt(111)表面氧化生成甲酸的影响的第一性原理研究

采用密度泛函理论计算研究了碱性介质中甲醇在清洁的PtAu(111)和Pt(111)表面、及有CO存在的PtAu(111)和Pt(111)表面的氧化。计算结果表明,在碱性介质中,预吸附的CO促进了甲醇在PtAu(111)和Pt(111)表面氧化的每一步反应,这与其在Au(111)表面的作用相似。究其原因,是由于CO的吸附增强了OH的稳定性和碱性,从而增强了OH夺取氢原子的能力。     

Butylphenyl-functionalized Pt nanoparticles as CO-resistant electrocatalysts for formic acid oxidation

Butylphenyl-functionalized Pt nanoparticles (Pt-BP) with an average core diameter of 2.93 ± 0.49 nm were synthesized by the co-reduction of butylphenyl diazonium salt and H(2)PtCl(4). Cyclic voltammetric studies of the Pt-BP nanoparticles showed a much less pronounced hysteresis between the oxidation currents of formic acid in the forward and reverse scans, as compared to that on naked Pt surfaces. Electrochemical in situ FTIR studies confirmed that no adsorbed CO, a poisoning intermediate, was generated on the Pt-BP nanoparticle surface. These results suggest that functionalization of the Pt nanoparticles by butylphenyl fragments effectively blocked the CO poisoning pathway, most probably through third-body effects, and hence led to an apparent improvement of the electrocatalytic activity in formic acid oxidation.