Electrochemical Behavior Of Pt Research Articles

Controlled synthesis of reduced graphene oxide-supported bimetallic Pt–Au nanoparticles for enhanced electrooxidation of methanol

Controlled construction of bimetallic interfaces on conductive carbon supports is extremely important for achieving better synergistic effect required for electrooxidation of small organic molecules for energy applications. Herein, controlled synthesis of reduced graphene oxide (RGO)-supported bimetallic Pt–Au nanoparticles (Pt–Au/RGO) for electrooxidation of methanol using a facile and practical approach was described. By carefully adapting sequential and simultaneous reduction steps H2PtCl6 and AuCl3were reduced on RGO support using ammonia borane (AB) and ascorbic acid (AA) as reducing agents. Three types of Pt–Au/RGO catalysts were prepared and labeled as PtAu/RGO-AB1, PtAu/RGO-AB, and PtAu/RGO-AA. The reduction process was carried at ambient conditions, without the use of surfactants, and the catalysts obtained were analyzed through various techniques, including X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), selected area electron diffraction (SAED), and energy dispersive X-ray spectroscopy (EDS). The PtAu/RGO-AB1 catalyst showed remarkable uniformity on the RGO sheets, with an average particle size of 2–3 nm. The electrochemical behavior of Pt–Au catalysts supported on reduced graphene oxide (RGO) for methanol oxidation was systematically investigated via cyclic voltammetry and chronoamperometry techniques. Among the studied catalysts, PtAu/RGO-AB1 exhibited high electrochemical active surface area (ECSA) of 92.47 m2/g, along with the highest mass and ECSA-normalized activities for the electrooxidation of methanol. PtAu/RGO-AB1 manifested exceptional resistance to accumulated CO-like species, as evidenced by its higher forward peak current density to reverse peak current density ratio (If/Ib) of 2.20. The facile and effective synthesis strategy described here provides a promising method for fabricating well-defined multi-component nanostructured electrocatalysts with potential applications for various fuel cell reactions.

Influence of the Sn-Oxide-Carbon Carrier Composition on the Functional Characteristics of Deposited Platinum Electrocatalysts

The effect of the SnO2 nanoparticles content on the structure and electrochemical behavior of Pt/(SnO2/C) catalysts containing about 20 wt% Pt was studied. In this case, SnO2/C nanostructured materials were obtained by tin electrodeposition on the carbon particles in suspension. It was found that the optimal combination of stability and activity in the oxygen electroreduction reaction is demonstrated by materials containing 25–30% wt. SnO2. A comparative assessment of the durability and activity of Pt/(SnO2/C) catalysts and a commercial Pt/C catalyst with 20% Pt-loading has been carried out.

HOR Activity of Pt-TiO2-Y at Unconventionally High Potentials Explained: The Influence of SMSI on the Electrochemical Behavior of Pt

The formation of strong metal support interactions (SMSI) is known for many metal/metal oxide systems and its consequences are well established in the field of heterogeneous catalysis, but this knowledge has only been recently transferred to the field of electrocatalysis. In this study, Pt was deposited via atomic layer deposition (ALD) onto TiO2−Y, which allowed a good control of the particle size through the number of ALD cycles. During the ALD process, a thin-film of reduced titania is formed on the Pt surface, which leads to SMSI effects. With increasing Pt particle size, the fraction of the titania-covered Pt surface decreases. As a result, the extent of platinum oxide formation in cyclic voltammetry (CV) measurements scales with the size of the Pt particles. The influence of these thin titanium oxide films, which cover the Pt surface, on the catalytic behavior with respect to oxygen reduction reaction (ORR), hydrogen oxidation reaction (HOR), CO oxidation and oxygen evolution reaction (OER) is investigated by using an RDE setup. The covering TiOX thin-films reduce the ability to catalyze ORR, OER and CO oxidation, while it does not influence the HOR and Pt H-UPD formation. These findings indicate that proton and hydrogen transport are possible through the thin TiOX film, while oxygenated species suffer from transport limitations through the thin-film. Due to this selective permeability, these materials are able to oxidize hydrogen well beyond 1.2 VRHE.

Electrochemical Behavior of Pt–Ru Catalysts Supported on Graphitized Ordered Mesoporous Carbons toward CO and Methanol Oxidation

In this work, graphitized ordered mesoporous carbons (gCMK-3) were employed as support for Pt and Pt–Ru nanoparticles synthesized by different reduction methods. The catalysts displayed metal contents and Pt:Ru atomic ratios close to 20 wt % and 1:1, respectively. A comparison of the physical parameters of Pt and Pt–Ru catalysts demonstrated that Ru enters into the Pt crystal structure, with well-dispersed nanoparticles on the carbon support. The Pt catalysts exhibited similar surface oxide composition, whereas a variable content of surface Pt and Ru oxides was found for the Pt–Ru catalysts. As expected, the Pt–Ru catalysts showed low CO oxidation onset and peak potentials, which were attributed to the high relative abundances of both metallic Pt and Ru oxides. All the studied catalysts exhibited higher maximum current densities than those observed for the commercial Pt and Pt–Ru catalysts, although the current–time curves at 0.6 V vs. reversible hydrogen electrode (RHE) demonstrated a slightly higher stationary current density in the case of the Pt/C commercial catalyst compared with Pt nanoparticles supported on gCMK-3s. However, the stationary currents obtained from the Pt–Ru/gCMK-3 catalysts surpassed those of the commercial Pt–Ru material, suggesting the suitability of the prepared catalysts as anodes for these devices.

In Situ Electrochemical AFM Imaging of a Pt Electrode in Sulfuric Acid under Potential Cycling Conditions.

Understanding the electrochemical behavior of Pt at the solid/liquid interface is of significant importance for the development of efficient electrochemical devices, such as fuel cells and water electrolyzers. In this work, the evolution of the surface morphology of a polycrystalline platinum under potential cycling conditions was investigated by in situ electrochemical atomic force microscopy (EC-AFM). After 50 cycles between 0.05 and 1.8 V in 0.1 M H2SO4, the Pt surface is coarsened and nanoparticles of several nanometers appear on the surface. The critical upper and lower potentials for the formation of nanoparticles are found to be 1.8 and 0.8 V, respectively. The in situ AFM observation coupled with Cyclic Voltammerty reveals the periodic disappearance and reappearance of the nanoparticles, based on which the formation of nanoparticles is attributed to the deposition of dissolved Pt from solution, and a model for the nanoparticle formation is proposed. While the formation of a thick oxide layer is a prerequisite, the reduction process is found to have a strong influence on Pt nanoparticle formation as well. This investigation provides a visualization of the Pt electrode surface under electrochemical control in a large potential window, enabling a broader understanding of the Pt electrode roughening mechanisms.

Pt(Cu)/C Electrocatalysts with Low Platinum Content

The structure characteristics and the electrochemical behavior of Pt(Cu)/C electrocatalysts synthesized by consecutive deposition of copper and platinum on carbon-support microparticles is studied. The stability and catalytic activity of Pt(Cu)/C materials in reactions of oxygen electroreduction and methanol electrooxidation are assessed and compared with analogous characteristics of a commercial Pt/C material. It is shown that combining the method of galvanic displacement of Cu by Pt with the additional chemical deposition of Pt favors optimization of the structure and functional characteristics of Pt(Cu)/C electrocatalysts. The effect of thermal treatment on the characteristics and properties of electrocatalysts is studied and the optimal conditions of such pretreatment are revealed.

Catalytic Duality of Platinum Surface Oxides in the Oxygen Reduction and Hydrogen Oxidation Reactions

In polymer electrolyte membrane fuel cells (PEMFCs), the hydrogen oxidation reaction (HOR) and the oxygen reduction reaction (ORR) take place on the surface of platinum nanoparticles (Pt-NPs) residing on carbon support. Polycrystalline platinum (Pt(poly)) serves as a model polyoriented system due to its randomly oriented grains separated by grain boundaries, and research using Pt(poly) creates important background knowledge that is used to identify and understand electrochemical phenomena occurring in fuel cells. In this study, we report new results on the electrochemical behavior of Pt(poly) in 0.50 M H2SO4 aqueous solution saturated with reactive gases, namely O2(g) and H2(g). We analyze the influence of the potential scan rate over a broad range of values (1.00–50.0 mV s−1) on the cyclic voltammetry (CV) behavior of Pt(poly). A comparative analysis of the impact of dissolved O2 and H2 on the electrochemical behavior of Pt(poly) is performed using CV profiles and capacitance transients. Their analysis reveals the existence of new features that are observed in the potential range corresponding to the Pt surface oxide formation and reduction. The results indicate that the Pt surface oxide reveals catalytic duality because it acts both as an inhibitor and a catalyst in both the ORR and HOR. In the case of the ORR, the anodic-going transients reveal that the process becomes inhibited as the Pt surface oxide develops, while in the cathodic-going transients, the reduction of Pt surface oxide significantly (ca. 65%) increases the reaction rate. In the case of the HOR, the anodic-going transients also reveal that the process becomes inhibited as the Pt surface oxide develops, while in the cathodic-going transients, the reduction of Pt surface oxide increases (ca. 15%) the reaction rate. The catalytic effect can be attributed either to changes in the surface electronic structure that accompanies the surface oxide reduction or to short-lived increase in the electrochemically active surface area.

Growth of epitaxial Pt1-xPbx alloys by surface limited redox replacement and study of their adsorption properties.

The surface limited redox replacement (SLRR) method has been used to design two-dimensional Pt-Pb nanoalloys with controlled thickness, composition, and structure. The electrochemical behavior of these alloys has been systematically studied as a function of alloy composition. A single-cell, two-step SLRR protocol based on the galvanic replacement of underpotentially deposited monolayers of Pb with Pt was used to grow epitaxial Pt1-xPbx (x < 0.1) alloys of up to 10 ML thickness on Au substrates. It is shown that by varying the terminating potential of the galvanic replacement step, the Pb atomic content can be controlled in the films. Electrochemical analysis of the alloys showed that the adsorption of both H and CO exhibits similar, and systematic, decreases with small increases in the Pb content. These measurements, commonly used in electrocatalysis for the determination of active surface areas of Pt, suggested area values much lower than those expected based on the net Pt composition in the alloy as measured by XPS. These results show that Pb has a strong screening effect on the adsorption of both H and CO. Moreover, changes in alloy composition result in a negative shift in the potential of the peaks of CO oxidation that scales with the increase of Pb content. The results suggest electronic and bifunctional effects of incorporated Pb on the electrochemical behavior of Pt. The study illustrates the potential of the SLRR methodology, which could be employed in the design of 2-dimensional bimetallic Pt nanoalloys for fundamental studies of electrocatalytic behavior in fuel cell reactions dependent on the nature of alloying metal and its composition.

Extensive Studies of the Electrochemical Behavior of Pt Ni/MWCNT Catalysts in Alkaline Media

Multi-walled carbon nanotubes (MWCNT) enclose properties and characteristics that are interesting and suitable for electrochemical applications. In this way, the deposition of metallic particle in the surface of MWCNT has been a topic of intense study. It is well know that bimetallic systems of Pt with other metal are of great interest due to the possibility of reduce the costs by decreasing the metal loading, and at the same time increase the properties of the electrocatalyst. In specific, PtNi/MCNT systems have proven to have high activity in different electrochemical reactions in acid media, along with good tolerance to CO poisoning. However, the main drawback is the poor stability in acidic environments. Thus, the electrochemical evaluation of these materials in alkaline media becomes an interesting field of study. Previous investigations of the research group performed in alkaline media showed that the system PtNi/MWCNT exhibited activity towards the hydrogen oxidation reaction as well as the oxidation of methanol. As a continuation, in this work a more detailed study was performed including the evaluation of different materials PtNi/MWCNT in the oxygen reduction reaction. The experimental matrix was designed to evaluate the influence of PtNi structure on the electrochemical behavior, interesting results were found. The materials were characterized by microscopy as well as x-ray diffraction. The electrochemical tests were done in a conventional three electrodes cell, using a glassy carbon rod as working electrode, a Pt wire as counter electrode, a Ag/AgCl (KCl Sat) electrode as reference, and 1M NaOH solution as electrolyte. The results as well as the discussion will be presented at the conference. Authors acknowledge the support to CONACyT under grant No. 213373

Direct STM Studies of CO Adsorption and Oxidation on Pt(111) Electrodes: (2) Density Functional Theory

The in situ STM technique has been shown to be exceedingly powerful in elucidating the nature of electrode surfaces under potential control, both in the absence and the presence of a reacting species dissolved in solution. Wieckowski and coworkers first observed some of the interesting electrochemical behavior of Pt(111) surfaces in CO-saturated solution, particularly, the decreasing activity for CO oxidation [1]. In Part (1) of the present work, we show that monatomic steps on Pt(111) single crystal surfaces are quite varied, with a range of structures and electrochemical behavior, in contrast to the conventional idea that “steps” in general are active for CO oxidation. The most striking finding was that (111)-type steps, which were initially ragged and highly active, became absolutely straight and nearly inert for CO oxidation after cycling the potential in CO-saturated acid solution [2]. However, (100)-type steps were initially much less active and became even less active, even though the steps developed nanoscale indentations. Density functional theory calculations were carried out to determine, first, why the steps tend to favor the (111) geometry, and second, why certain step geometries are so inert. We have also identified certain candidates for the actual active site for CO oxidation. Specifically, we have found that CO molecules can adsorb in highly ordered, high coverage arrangements, even across steps, if the steps are reasonably ordered, so that there is essentially no access to the Pt surface for water molecules. The only exception appears to be single Pt atoms that are adsorbed at the edge of a (111) step, according to the calculations and also indicated by the experiments. If even a single Pt atom is adsorbed next to a (111) step, there is a disturbance of the protective CO adlayer. Markovic and coworkers had previously concluded that single Pt atoms can be highly active, based on ex situ STM studies and DFT calculations [3], but the present in situ study allows us to achieve a new level of understanding of the structure-activity relationships of various step structures on the Pt(111) surface. It has been realized for a number of years that ordinary DFT calculations have difficulty in correctly identifying the site preference of CO adsorbed on Pt(111), but first Olsen et al. [4] and then Orita et al. [5] showed that high-quality, all-electron, relativistic calculations are able to do so. In the present work, we took advantage of this capability in calculating high-coverage arrangements of CO on the various types of terrace and step structures (Fig. 1). The structures pictured show the highly protective nature of the CO adlayer across steps, if they are straight. There are also microfacetted structures, similar to those obtained experimentally for the cycled (100) steps, for which the CO adlayer is quite protective. As we will show, the correspondence of the calculations and the experimentally observed STM images has been quite satisfactory and convincing [2]. Acknowledgement: The authors gratefully acknowledge support from MEXT and NEDO of Japan.Fig. 1. High coverage CO adsorption across (upper panel) (111) steps on Pt(332), and (lower panel) (100) steps on Pt(322), with atop CO molecules colored yellow, as they appear in corresponding STM images. The steps are located at the vertical white lines. References A. Wieckowski, M. Rubel, and C. Gutierrez, J. Electroanal. Chem., 382, 97-101 (1995).J. Inukai, D. A. Tryk, T. Abe, M. Wakisaka, H. Uchida, and M. Watanabe, J. Amer. Chem. Soc., 135, 1476-1490 (2013).D. S. Strmcnik, D. V. Tripkovic, D. van der Vliet, K.-C. Chang, V. Komanicky, H. You, G. Karapetrov, J. P. Greeley, V. R. Stamenkovic, and N. M. Markovic, J. Amer. Chem. Soc., 130, 15332-15339 (2008).R. A. Olsen, P. H. T. Philipsen, and E. J. Baerends, J. Chem. Phys., 119, 4522-4528 (2003).H. Orita, N. Itoh, and Y. Inada, Chem. Phys. Lett., 384, 271-276 (2004).

Influence of KOH-activated graphite nanofibers on the electrochemical behavior of Pt–Ru nanoparticle catalysts for fuel cells

Graphite nanofibers (GNFs) were activated chemically by a heat treatment at between 700 and 1000°C. The GNFs were used as carbon supports for Pt–Ru nanoparticles in fuel cells. The surface, structural, and textural characteristics of the carbon supports and Pt–Ru/KOH-activated GNFs catalysts were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, and surface area analyzer, respectively. The electrochemical activity was examined by cyclic voltammetry. The results showed that the concentration of oxygen functional groups and the specific surface area of the carbon supports increased with increasing activation temperature up to 900°C, whereas the mean Pt–Ru nanoparticle size decreased due to an improvement in the dispersibility of the Pt–Ru/KOH-activated GNFs catalysts. From the results, it was found that the electrochemical activities of the Pt–Ru/KOH-activated GNFs catalysts were improved by the larger active surface area available due to an increase in the number of oxygen functional groups and specific surface area, resulting in the enhanced electrochemical activity for use in fuel cells.

Electrochemical behavior of Pt–Co(111), (100) and (110) alloy single-crystal electrodes in 0.1 M HClO4 and 0.05 M H2SO4 solution as a function of Co content

We investigated the electrochemical behavior of Pt–Co(111), (100) and (110) alloy single-crystal electrodes in 0.1M HClO4 and 0.05M H2SO4 solutions as a function of Co composition. Successive changes of cyclic voltammograms at the Pt–Co single-crystal electrodes with increasing Co content revealed alloying effects on the underpotential deposition of hydrogen and the surface oxidation process, with a strong dependence on crystal plane and electrolyte.

Facile preparation and electrochemical behavior of Pt 100−xCo x(111) single-crystal electrodes in 0.1 M HClO 4

We describe the novel and facile preparation of Pt 100 − x Co x alloy single-crystals and preliminary results on the electrochemical behavior of Pt 100 − x Co x(111) surfaces in 0.1 M HClO 4 solution as a function of Co composition. The prepared Pt-Co(111) surfaces were characterized by low energy electron diffraction and scanning tunneling microscopy; the results suggest the thermal formation of a Pt skin layer on the alloy surface. The cyclic voltammograms of the Pt 100 − x Co x(111) electrodes exhibited increasingly negative shifts of the hydrogen adsorption onset potentials and positive shifts of the surface oxidation onset potentials as a function of the Co content due to the modified electronic structure of the Pt skin layer by the underlying Pt–Co alloy.

Mixed solutions of silver cation and chloride anion in acetonitrile: Voltammetric and EQCM study

Electrochemical behavior of Pt and Au electrodes in acetonitrile solutions at different concentration ratios of Cl(-) and Ag(+) ions was studied by cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM). The composition of the mixed silver chloride solutions, i.e. the amount of each component of the system (solid AgCl and solute species: Ag(+), Cl(-), AgCl(2)(-)), is governed by the solubility product of AgCl and the stability constant of AgCl(2)(-)complex and depends strongly on the ratio of the total concentrations of chloride and silver ions. In this work we analyze in detail the influence of the Cl(-)/Ag(+) concentration ratio on the value of equilibrium electrode potential and the shape of cyclic voltammograms. We explain the complicated shapes of the experimental curves observed at different concentration ranges, propose the mechanisms of the processes occurring at the electrode and substantiate them by EQCM data.

Deposition and electrochemical activity of Pt-based bimetallic nanocatalysts on carbon nanotube electrodes

This article reports an approach to prepare bimetallic Pt–M (M = Fe, Co, and Ni) nanoparticles as electrocatalysts and examines their electrochemical activities in 1 M sulfuric acid. The approach consists of chemical oxidation of carbon nanotubes (CNTs), two-step refluxing, and subsequent thermal reduction in hydrogen atmosphere. Three bimetallic pairs of Pt–M catalysts are found to deposit well onto CNT surface, forming Pt–M/CNT composites. The electrochemical behavior of Pt–M/CNT electrodes was investigated in 1 M H 2SO 4 using cyclic voltammetry (CV) and ac electrochemical impedance spectroscopy. The active surface coverage (=electrochemical surface area/geometric surface area) of Pt–M catalysts is significantly enhanced, i.e., Pt–Co (85.1%) > Pt–Ni (80.4%) > Pt–Fe (76.2%) > Pt (26.3%). This enhancement of electrochemical activity can be attributed to the fact that the introduction of Co and Ni may reduce the required potential for water electrolysis and thus the associated carbon oxidation, thereby contributing to hydrogen adsorption. Equivalent circuit analysis indicates that charge transfer resistance accounts for (i) the major proportion of the equivalent serial resistance of Pt–M/CNT electrodes, and (ii) Pt–Co and Pt–Ni catalysts not only improves the electrochemical capacitance but also lowers the equivalent serial resistance. The results shed some light on how use of Pt–M/CNT composite would be a promising electrocatalyst for high-performance fuel cell applications.

Determination of the potentials of zero total charge of Pt(100) stepped surfaces in the [ [formula omitted]] zone. Effect of the step density and anion adsorption

The electrochemical behavior of Pt(S)[ n(100)×(111)] electrodes is examined in perchloric acid solutions in the absence and in the presence of sodium acetate. Charge densities associated with adsorption processes at step and terrace sites have been analyzed as a function of the step density. The results obtained from CO displacement experiments allow the estimation of, in a first approximation, the corresponding potentials of zero total charge (pztc). The values of the pztc diminish with the step density. In the case of acetate containing solution, the specific adsorption of acetate anions was monitored by means of Fourier transform infrared (FTIR) spectroscopy. The potential and the step density dependence of the corresponding infrared adsorption bands have been found to be in agreement with the electrochemical results.

Erratum to "Electrochemical Behavior of Pt(IV) on Mercury Electrode in the Presence of Dimethylglyoxime"

Erratum to "Electrochemical Behavior of Pt(IV) on Mercury Electrode in the Presence of Dimethylglyoxime"

Structural Change and Electrochemical Behavior of Pt(100)-hex-R0.7° Surfaces in Gases and in Solution

The structural change and electrochemical behavior of a Pt(100) surface in contact with gas, Ar gas, and solution were investigated by cyclic voltammetry in solution and low-energy electron diffraction and scanning tunneling microscopy in ultrahigh vacuum (UHV). The clean and well-defined Pt(100)-hex-R0.7° surface prepared in UHV was transformed into Pt(100)- upon being exposed to gas, whereas the Pt(100)-hex-R0.7° structure remained unchanged when exposed to Ar gas. Electrochemical measurements on both Pt(100)-hex-R0.7° and Pt(100)- electrodes were carried out in 1 mM It was demonstrated that the reconstructed Pt(100)-hex-R0.7° surface was stable in 1 mM in the potential range more anodic than that for hydrogen adsorption. The structural transition from hex-R0.7° to was observed at cathodic potentials where hydrogen atoms are adsorbed on the Pt electrode surface. © 2002 The Electrochemical Society. All rights reserved.

Electrochemical Behavior of Pt(IV) on Mercury Electrode in the Presence of Dimethylglyoxime

The electrochemical behavior of Pt(IV) ions in the presence of dimethylglyoxime has been investigated using adsorptive stripping voltammetric method. The results indicated that the platinum is reduced from its adsorbed state as bis-dimethylglyoxi-mate platinum(IV) complex. The peak current is linearly proportional to the Pt(IV) concentration in the solution, thus representing the basis for a quantitative analysis. Various experimental parameters affecting the stripping response, indicating pH, the ligand concentration or the accumulation time and potential, and the scan rate, were studied to obtain a highly linear response. From the results the scheme for the reduction process of the platinum dimethylglyoximate complex in acidic media is presented.

Simultaneous Potentiostatic Coulometric Determination of Platinum and Palladium

Based on a voltammetric study of the electrochemical behavior of Pt(IV) and Pd(II) in a 1 M HCl + 0.1 M ethylenediamine hydrochloride solution at a carbon–graphite electrode, we have found the optimum conditions for the simultaneous determination of 0.2 to 3 mg of platinum and palladium with a relative standard deviation of less than 0.5%.The oxidation reactions were Pd(0) → Pd(II) and Pt(II) → Pt(IV). Mass excesses of analytes of 3.5- to 4.5-fold with respect to each other did not interfere with the determination of individual elements. With alternate cathodic and anodic polarization of the electrode, these elements can be multiply determined in a single portion of solution. The procedure was used for the simultaneous determination of platinum and palladium in process solutions of KP-1 platinum concentrate after the separation of gold and silver and also in platinum- and palladium-based alloys.