Exploration of electrodeposited platinum alloy catalysts for methanol electro-oxidation in 0.5 M H<Subscript>2</Subscript>SO<Subscript>4</Subscript>: Pt-Ni system

In this work, we examine the electrocatalytic activity of electrodeposited Platinum (Pt)-Nickel (Ni) alloy layers on an inert substrate electrode for methanol oxidation reaction. Analyses using energy-dispersive fluorescent X-ray analysis and powder X-ray diffractometry confirm alloying of Pt with Ni in a range of compositions. Steady-state polarisation measurements in 0.5 M methanol+0.5 M H₂SO₄ solutions clearly show that the onset of electro-oxidation shifts to less anodic potential values (approximately 160 mV), while also exhibiting current enhancements up to ~15 times the currents obtained for the pure Pt electrodeposit. A linear relationship between the cyclic voltammetric peak (oxidation) current and [MeOH] is observed at a scan rate of 50 mVs^–1, thus indicating reduced influence of adsorbed CO (CO_ads) surface poison. A critical composition, Pt (92%)/Ni (8%) [denoted Pt-Ni(3) alloy] is found to exhibit maximum electrocatalytic activity, beyond which the activity drops, whereas pure Ni does not catalyse the reaction. While the promotion of electro-oxidation is understood to be largely due to the alloy catalyst, surface redox species of Ni oxide formed during the electro-oxidation process may also contribute to the oxygenation of CO_ads, thereby enhancing the oxidation current. Plausible mechanisms of methanol oxidation on Pt/ transition metal alloy electrocatalysts are discussed in terms of electron transfer (in the alloy) and the role of Ni oxide species.     

Hydrogen evolution and oxidation—a prototype for an electrocatalytic reaction

Due to progress in the theory of electrocatalysis and in quantum chemistry, it has become possible to investigate the hydrogen reaction and perform quantitative calculations for the reaction rate. First, we demonstrate this with model calculations for the adsorption of hydrogen on Pt(111). In accordance with experimental data, we find hydrogen adsorption at a potential above the equilibrium potential and with an almost vanishing energy of activation. As a second example, we explain trends in the catalytic activity of palladium overlayers and clusters on Au(111) electrodes. Dedicated to J.O’M. Bockris on the occasion of his 85th birthday and in recognition of his contributions to electrochemistry.

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On the open-circuit interaction between methanol and oxidized platinum electrodes

In the present work, results of the interaction between methanol and oxidized platinum surfaces as studied via transients of open-circuit potentials are presented. The surface oxidation before the exposure to interaction with 0.5 M methanol was performed at different polarization times at 1.4 V vs reversible hydrogen electrode (RHE). In spite of the small changes in the initial oxide content, the increase of the pre-polarization time induces a considerable increase of the time needed for the oxide consumption during its interaction with methanol. The influence of the identity of the chemisorbing anion on the transients was also investigated in the following media: 0.1 M HClO₄, 0.5 M H₂SO₄, and 0.5 M H₂SO₄ + 0.1 mM Cl⁻. It was observed that the transient time increases with the energy of anion chemisorption and, more importantly, without a change in the shape of the transient, meaning that free platinum sites are available at the topmost layer all over the transient and not only in the potential region of small oxide ‘coverage’. The impact of the pre-polarization time and the effect of anion chemisorption on the transients are rationalized in terms of the presence of surface and subsurface oxygen driven by place exchange.

Pt–Ru electrocatalysts for fuel cells: a representative review

Three periods of Pt–Ru research are considered step-by-step: the initial period after discovery (1963–1970); observation and classification of basic tendencies (like the effects of composition, segregation, structural features on the activity; up to 1990); nanostructural studies and molecular level consideration of electrocatalytic phenomena in combination with advanced applied studies of materials, mechanistic, and applied aspects (after 1990). The main idea of this review is to balance various aspects of Pt–Ru electrochemistry related to material science and electrocatalysis as well as to remember the early basic results being of importance for future understanding of Pt–Ru functional properties. Dedicated to Professor Teresa Iwasita, as a token of her remarkable contribution to electrocatalysis.

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Nickel foam-based composite electrodes for electrooxidation of methanol

Nickel foam and five nickel foam-based composite electrodes were prepared for being used as anode materials for the electrooxidation of methanol in KOH solution containing 0.1 and 1.0 M of methanol. The layered electrodes composed of nickel foam, platinum nanoparticles, polyaniline (PANI) and/or porous carbon (C) prepared in various assemblies. As shown by SEM analysis, depending on the preparation conditions, the electrodes of different morphologies were obtained. Using the cyclic voltammetry method, the oxidation of methanol on nickel foam electrode was observed in the potential range 0.4 V ↔ 0.7 V, where the Ni(OH)₂/NiOOH transformation occurred. The presence of Pt particles in electrode gave rise to the increase in electrocatalytic activity in this potential range. For electrodes containing dispersed platinum catalyst (Ni/Pt, Ni/PANI/Pt and Ni/C/Pt), the oxidation of methanol was noted also in the potential range −0.5 V ↔ 0.1 V. The electrocatalytic activities of the examined electrodes toward methanol oxidation at low potentials were in order Ni/Pt > Ni/C/Pt > Ni/PANI/Pt, whereas at high potentials in order Ni/PANI/Pt > Ni/Pt> Ni/C/Pt > Ni. Among the examined electrodes, the most resistant to cyclic poisoning appeared to be the Ni/C/Pt electrode. Presented at the 4Th Baltic Conference on Electrochemistry, Greifswald, March 13–16, 2005     

Influence of interface structure on mass transport in phase boundaries between different ionic materials

Abstract  Internal and external interfaces in solids exhibit completely different transport properties compared to the bulk. Transport parallel to grain or phase boundaries is usually strongly enhanced. Transport perpendicular to an interface is usually blocked, i.e., transport across an interface is often much slower. Due to the high density of interfaces in modern micro- and nanoscaled devices, a severe influence on the total transport properties can be expected. In contrast to diffusion in metal grain boundaries, transport phenomena in boundaries of ionic materials are still less understood. The specific transport properties along metal grain boundaries are explained by structural factors like packing densities or dislocation densities in the interface region. In most studies dealing with ionic materials, the interfacial transport properties are merely explained by the influence of space charge regions. In this study the influence of the interface structure on the interfacial transport properties of ionic materials is discussed in analogy to metallic materials. A qualitative model based on the density of misfit dislocations and on interfacial strain is introduced for (untilted and untwisted) phase boundaries. For experimental verification, the interfacial ionic conductivity of different multilayer systems consisting of stabilised ZrO₂ and an insulating oxide is investigated as a funtion of structural mismatch. As predicted by the model, the interfacial conductivity increases when the lattice mismatch is increased. Graphical abstract  

Intermetallic Pt2Si: magnetron-sputtering preparation and electrocatalysis toward ethanol oxidation

Although most transition metals have been tested as the promoter to Pt for electrocatalysis toward fuel cell reactions, semi-conductor elements, such as Si, have hitherto not been examined. Here we report a simple synthesis of intermetallic Pt₂Si electrode using magnetron sputtering and the electrocatalysis toward ethanol oxidation reaction (EOR). In comparison to Pt, the intermetallic Pt₂Si surface turns out to be much more active in catalyzing the EOR: the onset potential shifts negatively by 150 mV, and the current density at 0.6 V increases by a magnitude of one order. Such an enormous enhancement in EOR catalysis is ascribed to the promotion effects of Si, which can not only provide active surface oxygenated species to accelerate the removal of CO_ads, but also strongly alter the electronic property of Pt, as clearly indicated by the core-level shift in XPS spectrum.     

Electrochemical synthesis of a novel platinum nanostructure on a glassy carbon electrode, and its application to the electrooxidation of methanol

We show that the addition of white dextrin during the electrochemical deposition of platinum nanostructures (nano-Pt) on a glassy carbon electrode (GCE) results in an electrochemically active surface that is much larger than that of platinum microparticles prepared by the same procedure but in the absence of dextrin. The nano-Pt deposits are characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy, and electrochemical methods. The SEM images reveal deposits composed of mainly nanoparticles and short nanorods. The GCE was applied as a novel and cost-effective catalyst for methanol oxidation. The use of nano-Pt improves the electrocatalytic activity and the stability of the electrodes.

Investigation of electro-oxidation activity of Pt-CNTs/GC electrodes

The morphology and structure of Pt-CNTs/ GC electrodes were characterized via Transmission Electron Microscopy (TEM) and selected area electron diffraction. The electro-oxidation behavior of CO and methanol on Pt-CNTs/GC electrodes were studied with cyclic voltommograms or chronoamperometry. Three oxidation peaks were observed for CO absorbed on Pt-CNTs/GC electrodes. Methanol was found to be dissociated spontaneously on the electrode to produce a strong absorbed intermediate CO. Among the three oxidation peaks, peak I was presumed to be due to the bridged CO absorption while peaks II and III were attributed to the split in the linear CO which is absorbed on the Pt-CNTs/GC nanocluster with different particle size and Pt film. The oxidation current of methanol on the Pt-CNTs/GC electrode did not always increase with the increase in the amount of Pt loading. The result indicates that there is an optimal Pt loading for methanol oxidation. It is necessary to select the catalyst with proper Pt loading when the anode of a direct-methanol fuel cell is prepared. __________ Translated from Chemical Journal of Chinese Universities, 2007, 28(6): 1135–1138 [译自: 高等学校化学学报]     

Composite electrodes consisting Pt nano-particles and poly (aminophenols) film on pre-treated aluminum substrate as electrocatalysts for methanol oxidation

Electrochemically platinum plated aluminum (Al/Pt) was used as an electrode substrate for the electropolymerization of aminophenols and fabrication of composite electrodes based on platinum nano-particles. The poly(o-aminophenol) (PoAP), poly(m-aminophenol) (PmAP), and poly(p-aminophenol) (PpAP) were synthesized on the Al/Pt electrode, and further modification was performed by deposition of platinum nano-particles onto polymer matrixes. The electrochemical and morphological characteristic of the composed electrodes were carried out by cyclic voltammetry and scanning electron microscopy, respectively. The electrocatalytic oxidation of methanol on the composite electrodes was studied by cyclic voltammetry in 0.1 M sulfuric acid as supporting electrolyte. It was found that the Al/Pt/PoAP electrode incorporated Pt nano-particles (Al/Pt/PoAP/Pt) exhibits a higher electrocatalytic activity for the oxidation of methanol than the Al/Pt/PmAP/Pt and Al/Pt/PpAP/Pt electrodes. On the other hand, a higher catalytic current for methanol oxidation was found on the Al/Pt/PoAP/Pt electrode in comparison to bulk Pt and Al–Pt (Al with 0.2 mg cm⁻² of Pt particles) electrodes. The effects of various parameters such as thickness of the polymer film, concentration of the monomer, Pt loading method and the Pt amounts, concentration of the methanol, and the medium temperature were studied on the electrooxidation of methanol. The long-term stability of the modified electrode has also been investigated.     

Carbon supported electrocatalysts prepared by the sol–gel method and their utilization for the oxidation of methanol in acid media

One of the key objectives in fuel-cell technology is to improve the performance of the anode catalyst for the alcohol oxidation and reduce Pt loading. Here, we show the use of six different electrocatalysts synthesized by the sol–gel method on carbon powder to promote the oxidation of methanol in acid media. The catalysts Pt–PbO _x and Pt–(RuO₂–PbO _x ) with 10% of catalyst load exhibited significantly enhanced catalytic activity toward the methanol oxidation reaction as compared to Pt–(RuO₂)/C and Pt/C electrodes. Cyclic voltammetry studies showed that the electrocatalysts Pt–PbO _x /C and Pt–(RuO₂–PbO _x )/C started the oxidation process at extremely low potentials and that they represent a good novelty to oxidize methanol. Furthermore, quasi-stationary polarization experiments and cronoamperometry studies showed the good performance of the Pt–PbO _x , Pt–(RuO₂–PbO _x )/C and Pt–(RuO₂–IrO₂)/C catalysts during the oxidation process. Thus, the addition of metallic Pt and PbO _x onto high-area carbon powder, by the sol–gel route, constitutes an interesting way to prepare anodes with high catalytic activity for further applications in direct methanol fuel cell systems.     

Oxidation of methanol on Pt(Mo) electrodes obtained using galvanic displacement method

The electrocatalytic Pt-Mo system was obtained by formation of platinum particles on the Mo surface under its contact with PtC₆²⁻ (PtCl₄²⁻) under the open circuit conditions. Cyclic voltammograms of the obtained Pt(Mo) electrodes feature well pronounced peaks of hydrogen adsorption and desorption on Pt particles. Nonuniform platinum distribution across the electrode surface was found. Pt(Mo) electrodes showed a higher specific activity in the reaction of methanol oxidation in the potential range of 0.35–0.45 V (RHE) as compared to Pt/Pt.     

Pt纳米粒子修饰的多孔硅电极的制备及其电催化性能

通过循环伏安法电沉积使直径约为7 nm的Pt纳米粒子均匀地分散于多孔硅表面, 拟用作微型质子交换膜燃料电池的催化电极. 与刷涂法相比较, 电沉积Pt纳米粒子的多孔硅电极(Pt/Si)呈现出高的Pt利用率和增强的电催化活性. 当Pt载量为0.38 mg•cm−2时, 其电化学活性比表面积高达148 cm2•mg−1, 是刷涂相近质量的纳米Pt/C催化剂的多孔硅电极Pt-C/Si的2倍多；该修饰电极对甲醇氧化也呈现了增强的催化性能和好的稳定性, 在0.5 V(vs SCE)极化1 h后电流密度为4.52 mA•cm−2, 而刷涂了相近Pt量的Pt-C/Si电极的电流密度只有0.36 mA•cm−2.     

The Interaction of Iodide Film with Platinum Microparticles on Different Electrode Materials for Various Electrocatalytic Reactions

The electrochemical depositions of Pt microparticles and KI film were successfully carried out on glassy carbon electrodes (GCE), gold electrodes (GE), and indium tin oxide electrodes (ITO). The electrochemical studies of Pt micro/KI film on GCE show that the film was stable, active at pH 1.5 electrolyte solutions. The Pt microparticle/KI film modified ITO electrodes were examined by using scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. The SEM and AFM results show that the Pt particle sizes were in the range of 120 nm–1.4 μm, respectively. The proposed film on GCE shows efficient electrocatalysis for oxygen, Cr₂O reduction by using cyclic voltammetry. Further the electrochemical oxidation of sodium meta‐arsenite (As(III)), H₂O₂ were successfully carried out and the detection of H₂O₂ in real samples has been validated.     

Mutual indirect probing of platinized platinum/tungstate nanostructural features

The comparative study of isopolytungstates immobilized on smooth Pt and platinized Pt (Pt/Pt) provides a possibility to separate several specific effects on H- and O-upd at an external platinum surface and inside the pores of Pt/Pt. In the former case, a solid rechargeable product is formed (nonstoichiometric tungsten bronze), which an inherent porous structure allows solution penetration and does not prevent charging of the Pt/solution interface. Electrochemical responses of smooth Pt give more precise information on the film behaviour, when adsorption phenomena are clarified on the basis of data for Pt/Pt. Electrocatalytic tests (nitrate reduction) confirm unambiguously that the major part of the internal Pt/Pt surface area is modified by adsorbed polytungstate. This result gives, in its turn, new understanding of the size of Pt/Pt pores on the nanometre scale.

Oxidation of carbon monoxide and formic acid on bulk and nanosized Pt–Co alloys

Bulk Pt₃Co and nanosized Pt₃Co and PtCo alloys supported on high area carbon were investigated as the electrocatalysts for the CO_ads and HCOOH oxidation. Pt₃Co alloy with Co electrochemically leached from the surface (Pt skeleton) was employed to separate electronic from ensemble and bifunctional effects of Co. Cyclic voltammetry in 0.1 M HClO₄ showed reduced amount of adsorbed hydrogen on Pt sites on Pt₃Co alloy compared to pure Pt. However, no significant difference in hydrogen adsorption/desorption and Pt-oxide reduction features between Pt₃Co with Pt skeleton structure and bulk Pt was observed. The oxidation of CO_ads on Pt₃Co alloy commenced earlier than on Pt, but this effect on Pt₃Co with Pt skeleton structure was minor indicating that bifunctional mechanism is stronger than the electronic modification of Pt by Co. The HCOOH oxidation rate on Pt₃Co alloy was about seven times higher than on bulk Pt when the reaction rates were compared at 0.4 V, i.e., in the middle of the potential range for the HCOOH oxidation. Like in the case of CO_ads oxidation, Pt skeleton showed similar activity as bulk Pt indicating that the ensemble effect is responsible for the enhanced activity of Pt₃Co alloy toward HCOOH oxidation. The comparison of CO_ads and HCOOH oxidation on Pt₃Co/C and PtCo/C with the same reaction on Pt/C were qualitatively the same as on bulk materials.     

Nanocomposite of Platinum Particles Embedded into Nanosheets of Polycarbazole for Methanol Oxidation

Nanoparticles of Pt were successfully electrodeposited onto polycarbazole (PCz) film on a stainless steel (SS‐PCz‐Pt) by chronocoulometry (0.2 C). For comparative purposes, Pt particles were deposited into stainless steel (SS‐Pt) under the same condition. Fourier transform infrared spectroscopy (FT‐IR) results confirmed PCz exists in the SS‐PCz‐Pt composite electrode. X‐ray photoelectron spectroscopy (XPS) results indicated that PCz of SS‐PCz can interact easily with Pt particles. The crystalline behavior and morphology of SS‐PCz‐Pt and SS‐Pt were determined by X‐ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and Transmission Electron Microscopy (TEM). The TEM results indicated that Pt particles disperse more uniformly into the nanosheets of polycarbazole than those of SS film. Catalytic activity and stability for the oxidation of methanol were studied by using cyclic voltammetry and chronoamperometry. A high catalytic current for methanol oxidation (8.04 mA cm^?2 mg^?1) was found for the SS‐PCz‐Pt electrode in comparison to SS‐Pt electrode (5.01 mA cm^?2 mg^?1) at about 0.6 V (vs. Ag/AgCl).     

Pt的氧化状态对甲醇氧化活性的影响

采用NaBH4还原法制备了XC-72碳黑负载的Pt电催化剂,并在化学还原后用H2O2处理部分催化剂以改变Pt的氧化状态,以期改善Pt活性中心上水的离解而提高催化活性.X射线光电子能谱结果表明,经H2O2处理的催化剂含有较多的氧化态Pt.通过循环伏安法和记时电流法考察了经处理和未经处理的催化剂在酸性条件下的甲醇氧化的催化...     

Electrocatalytic and adsorption properties of platinum microparticles electrodeposited onto glassy carbon and into Nafion® films

A comparative investigation of electrocatalytic and adsorption properties of platinum microparticles electrodeposited onto a glassy carbon surface (Pt/GC) and within a thin Nafion® film formed on a GC electrode (Pt/Nf/GC) is described. As test reaction the methanol oxidation in sulfuric acid solutions is used. Dependences of the steady-state specific reaction rates upon potential and methanol concentration were established, as well as those of the platinum surface coverage with methanol chemisorption products upon concentration. It was shown that at higher platinum loadings (above 60 μg cm⁻²) the specific activities of Pt/GC and Pt/Nf/GC are nearly the same and close to that of smooth platinum. At such loadings the surface coverage of the platinum deposit surface with organic particles does not differ from that of smooth platinum. At very low platinum loadings in the polymeric matrix (10–30 μg cm⁻²) a considerable decrease in the adsorption of strongly chemisorbed methanol particles is observed. These deposits are characterized by a low specific activity, which may be caused by the decrease of the platinum particle’s size, leading to a decrease in the amount of weakly bound methanol particles participating in the limiting reaction step.