Dissolution Of Pd Research Articles

Effect of Pd ions in electrolyte on electrocatalytic performance of carbon supported Pd catalyst for oxidation of formic acid

One problem of carbon supported Pd (Pd/C) anodic catalyst in direct formic acid fuel cell (DFAFC) is the poor electrocatalytic stability. Considering Pd metal can be dissolved in the acidic electrolyte, the effect of the addition of Pd2+ ions in the electrolyte on the electrocatalytic stability of Pd/C catalyst for formic acid oxidation was investigated. It was found that after the Pd/C catalyst is immersed in the electrolytes with 1.0×10−4M Pd2+ for 8 days, the electrocatalytic activity and stability of the Pd/C catalyst are higher than that of the Pd/C catalyst without immersing and with immersing in the electrolyte without Pd2+ ions. There are four reasons for obtaining high electrocatalytic performance of the Pd/C catalyst by Pd2+. (1) The existence of Pd2+ ions in the electrolyte could effectively inhibit the dissolution of Pd in the Pd/C catalyst. (2) Some Pd2+ ions would be adsorbed on the surface of Pd particles and then increase the roughness of the Pd particles. (3) Pd2+ ions adsorbed on Pd particles can make the intermediate of formic acid oxidation easy to be oxidized to CO2. (4) Pd2+ could be reduced to Pd under −0.2V and 0.8V electrode potential. Then, the new active sites are generated constantly in the process of potential scanning. Therefore, this investigation suggested a new method to improve the performance of the Pd/C anodic catalyst in DFAFC.

Performance Enhancement by Adaptation of Long Term Chronoamperometry in Direct Formic Acid Fuel Cell using Palladium Anode Catalyst

In the present study, we suggest a new way to reactivate performance of direct formic acid fuel cell (DFAFC) and explain its mechanism by employing electrochemical analyses like chronoamperometry (CA) and cyclic voltammogram (CV). For the evaluation of DFAFC performance, palladium (Pd) and platinum (Pt) are used as anode and cathode catalysts, respectively, and are applied to a Nafion membrane by catalyst-coated membrane spraying. After long DFAFC operation performed at 0.2 and 0.4 V and then CV test, DFAFC performance is better than its initial performance. It is attributed to dissolution of anode Pd into . By characterizations like TEM, Z-potential, CV and electrochemical impedance spectroscopy, it is evaluated that such dissolved ions lead to (1) increase in the electrochemically active surface by reduction in Pd particle size and its improved redistribution and (2) increment in the total oxidation charge by fast reaction rate of the Pd dissolution reaction.

High Electrochemical Performance and Stability of Co-Deposited Pd–Au on Phase-Pure Tungsten Carbide for Hydrogen Oxidation

Co-deposited Pd and Au nanoparticles were loaded on phase-pure tungsten mono-carbide (WC) prepared by a polymer-induced carburization method. Among the electrocatalysts, Pd3Au/WC displayed an excellent electrochemical activity for the hydrogen oxidation reaction comparable to the state-of-the-art Pt/C catalyst both in half-cell tests and single cell tests under proton exchange membrane fuel cell (PEMFC) conditions. This unique and strong synergistic effect was not observed on the carbon support, and thus the crucial role of WC was demonstrated as a strongly interacting support as well as an active component of the electrocatalyst. Dissolution of Pd observed on the carbon support was suppressed in this Pd3Au/WC electrocatalyst, which showed good stability in a continuous operation for 3,000 min. Thus the proposed electrocatalyst could be a potential alternative anode catalyst of lower cost for PEMFC replacing Pt/C.

On the Microstructure, Chemical Composition, and Porosity Evolution of Nanoporous Alloy through Successive Dealloying of Ternary Al–Pd–Au Precursor

In the present Article, we have investigated the microstructure, composition, and porosity evolution of nanoporous alloy during successive dealloying of ternary Al75Pd17.5Au7.5 precursor in NaOH/HCl and HNO3 aqueous solutions. The results show that the selective dissolution of Al through the first-step dealloying contributes to the formation of Pd–Au nanoporous composites, which are composed of two distinct structures: the finer nanoporous AuPd dendrites derived from the dealloying of Al2(Au,Pd) and the coarser nanoporous Pd(Au) derived from the dealloying of Al3(Pd,Au). Moreover, compared with those dealloyed in the 20 wt % NaOH solution, the Pd–Au nanocomposites exhibit a coarser length scale of ligaments/channels in the 5 wt % HCl solution. After the second-step dealloying in the 65 wt % HNO3 solution, the nanoporous Pd(Au) dissolves away, and the Pd dissolution results in the formation of Au-rich nanoporous alloy with bimodal channel size distributions. Nanoporous alloys with unique structures and com...

Channel flow double electrode study on palladium dissolution during potential cycling in sulfuric acid solution

Abstract Channel flow double electrode (CFDE) was applied to study palladium dissolution during potential cycling in 0.5 M H 2 SO 4 solution at 25 °C. In the CFDE, Pd ions (Pd n + ) dissolved from a Pd working electrode were detected by reducing them to Pd on a gold collector electrode, which was placed at the downstream. The detection of the Pd dissolution by the collector current was confirmed by (Electron Probe Micro Analyzer) EPMA analysis of the collector electrode surface. In anodic scan, gradual rise of the collector current till 0.7 V indicated Pd dissolution. The dissolution was confirmed by EPMA. Anodic as well as cathodic dissolution was confirmed when potential cycling was done till 0.8 V. Dissolution of palladium was found to increase anodically as well as cathodically when upper limit of polarization was increased. From collector current and the results of EPMA, the dissolution mechanism is proposed.

Effects of the PdO nanoflake support on electrocatalytic activity of Pt nanoparticles toward methanol oxidation in acidic solutions

We prepared PdO nanoflake thin films on carbon cloths by reactive sputtering deposition, and studied electrocatalytic performance of Pt nanoparticles electrodeposited on the PdO thin film in methanol oxidation reaction (MOR) in acidic media. The PdO nanoflake thin film exhibits a cyclic voltamperometric (CV) behavior similar to metallic Pd electrodes because a metallic Pd surface layer is formed on the PdO thin film electrode under the CV measurement condition. The nanoflake morphology of the PdO electrode provides a large surface area for Pt nanoparticle loading, resulting in a large electrochemical active surface area (ESA). The Pt/PdO electrode has a high electrocatalytic activity toward MOR, and the good electrocatalytic performance of the Pt/PdO electrode is ascribed to a high CO tolerance and the large ESA. We suggest that the high CO tolerance of the catalyst on the Pt/PdO electrode is a result of the synergism of the bifunctional mechanism and the electronic effect. XPS analyses indicate that negative charge transfer occurs from the PdO support to the Pt nanoparticles, indicating the presence of the electronic effect. Pt nanoparticles on the PdO support can greatly alleviate the nanoflake damage during the CV measurement, which results from anodic dissolution of metal Pd from the PdO support in acidic media.

Structure evolution of nanocrystalline Ce1−xPdxO2−y mixed oxide in oxidizing and reducing atmosphere: Reduction-induced activity in low-temperature CO oxidation

Nanocrystalline (4–8nm) Ce1−xPdxO2−y mixed oxide (0<x<0.3), active in low temperature CO oxidation, has been prepared by microemulsion method. Thorough XRD, TEM, SEM-EDS, BET and FT Raman studies revealed that the oxide with x<0.2 is a homogeneous solid solution structurally stable up to 800°C in oxidizing atmosphere. In hydrogen, already at 500°C segregation of Pd particles occurs, which exhibit preferential Pd (111)∥CeO2 (111) orientation, preserved even after reduction at 800°C. Ce0.89Pd0.11O2−y oxide showed reversible extraction–dissolution of Pd upon successive reduction–oxidation cycles at 500°C, which is an example of “self-regenerative” property important for potential catalytic applications. Doping with Pd strongly hinders the sintering of ceria at high temperatures and enhances its reducibility at low temperatures (below 500°C).“As prepared”, oxidized Ce0.89Pd0.11O2−y sample demonstrates moderate activity in CO oxidation (reaching 85% conversion at ∼250°C) similar to that of 3% Pd/CeO2 prepared by impregnation. The activity improves dramatically (measurable CO conversion below room temperature and 100% conversion at ∼120°C) after pre-reduction at 400°C in H2. It appears that partially reduced Pd species, or extremely small particles (<1nm) at the surface of ceria are responsible for the low temperature activity in CO oxidation. Such Pd species could be strongly bonded to the surface, e.g., exhibiting a special epitaxial orientation observed for larger Pd crystallites (∼2nm) formed during reduction at higher temperatures.

Performance and stability of Pd–Pt–Ni nanoalloy electrocatalysts in proton exchange membrane fuel cells

Pd–Pt–Ni nanoalloy catalysts have been synthesized by a polyol reduction method and characterized for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). The performance of the membrane-electrode assembly (MEA) fabricated with the Pd–Pt–Ni catalysts is found to increase continuously in the entire current density range with the operation time in the PEMFC until it becomes comparable to that of commercial Pt. The Pt-based mass activity of Pd–Pt–Ni exceeds that of commercial Pt by a factor of 2, and its long-term durability is comparable to that of commercial Pt within the 200h of operation. Compositional characterizations by energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) suggest a dealloyed active catalyst phase consisting of Pd-rich core and Pt-rich shell, formed by dissolution of Pd and Ni under the testing conditions. The surface catalytic activity of nanoparticles can be modified by the strain effect caused by lattice mismatch between the surface and core components. Transmission electron microscopy (TEM) observation of the MEA cross-section reveals that the Pd ions move into the Nafion membrane and even to the anode side and redeposit on reduction by hydrogen crossover. The deposition of Pd-rich PdPt particles mainly forms a band at the center of the membrane and along the cathode/membrane interface. On the other hand, the Ni ions ion-exchange with the protons in the Nafion membrane.

ChemInform Abstract: Adsorbate-Catalyzed Corrosion. Anodic Dissolution of Palladium Catalyzed by Chemisorbed Iodine in Halide-Free Acid Solutions.

In the course of our investigations, we have discovered that the anodic dissolution of Pd in 1Mh 2 SO 4 solution is actually catalyzed by the presence of a single layer of chemisorbed iodine atoms even if the sulfuric acid solution does not contain halide anions. The results which demonstrate the adsorbate-catalyzed corrosion in halide-free acid solutions are the subject of this communication

Asymmetric CC Bond‐Formation Reaction with Pd: How to Favor Heterogeneous or Homogeneous Catalysis?

The enantioselective allylic alkylation of (E)-1,3-diphenylallyl acetate was studied to clarify the heterogeneous or homogeneous character of the Pd/Al(2)O(3)-(R)-BINAP catalyst system. A combined approach was applied: the catalytic tests were completed with in situ XANES measurements to follow the oxidation state of Pd as a function of the reaction conditions. The study revealed that the oxidized Pd (after exposure to ambient air) is efficiently reduced by the solvents THF and dioxane, and by the nucleophile sodium dimethyl malonate, and thus these conditions prevent Pd leaching. The chiral modifier BINAP plays a dual role: a considerable coverage of the Pd surface by the bulky compound slows down the initial reduction of the surface oxides but BINAP itself may consume surface oxygen (through its conversion to BINAPO and BINAPO(2)) and contribute to the maintenance of the active metal surface during the reaction. Carrying out the reaction under pressure in an inert gas atmosphere is important to minimize the oxygen diffusion into the reaction mixture and to avoid leaching. The (known) effect of temperature is critical as well: our catalyst system is inactive at room temperature, which is a clear deviation from the behavior of the corresponding homogeneous system. In contrast, halogenated solvents are easily dehalogenated on Pd/Al(2)O(3) and thus they favor leaching of the metal and formation of soluble compounds, analogous to classical metal corrosion in the presence of halide ions. The frequently observed dissolution of Pd in the presence of halogenated substrates may be explained similarly.

Dissolution and Interface Reactions between Palladium and Tin(Sn)-Based Solders: Part II. 63Sn-37Pb Alloy

The interface microstructures as well as the rate kinetics of dissolution and intermetallic compound (IMC) layer formation were investigated for couples formed between molten 63Sn-37Pb (wt pct) solder and 99.9 pct Pd sheet. The solder bath temperatures were 488 K to 593 K (215 °C to 320 °C), and the immersion times were 5, 15, 30, 60, 120, and 240 seconds. The predominant IMC phases were Pd(Sn, Pb)4, PdSn4, and PdSn3. The IMC layer microstructure contained these phases and varying amounts of solder Pb- and Sn-rich phases. Isolated Pd-Sn needles appeared in the solder field at temperatures and times of ≥563 K (290 °C) and ≥30 seconds, respectively. Palladium dissolution was largely monotonic as a function of time and solder temperature, except for a sharp decline at 593 K (320 °C). The dissolution rate kinetics over 488 K to 563 K (215 °C to 290 °C) were represented by the At n exp(−ΔH/RT) equation. The values of n and ΔH were 0.67 ± 0.19 and 48 ± 20 kJ/mol, respectively, suggesting that a combination of interface reaction and solid-state mass transport processes controlled dissolution. The IMC layer grew monotonically with time and solder temperature, except at 593 K (320 °C) where growth dropped off significantly. The IMC growth rate kinetics over 488 K to 563 K (215 °C to 290 °C) exhibited values of n and ΔH equal to 0.88 ± 0.10 and 64 ± 10 kJ/mol, respectively, indicating a combination of interface reaction and solid-state diffusion processes. The extents of Pd dissolution and IMC layer development were significantly greater for molten Sn-Pb solder than the Pb-free Sn-Ag-Cu solder (Part I study) at a given test temperature.

Peculiarities of the behavior of a PdCoPt/C cathodic catalyst in an acidic environment: Formation of core-shell structures

A PdCoPt/C catalytic system is synthesized by modifying a commercial 20% Pd/C (ETEK) catalyst, and its morphology and composition are determined. The stability of the catalyst is estimated by means of accelerated durability testing in a 0.5 M H2SO4 solution either using potential cycling or in the absence of polarization. The partial dissolution of Pd and Co components is shown to result in a restructuring of the catalyst surface and the formation of a core-shell Pt/PdCoPt/C structure with higher catalytic activity and stability compared to a Pt/C system. The results of experiments with a rotating ring disc electrode indicate the change in the reaction path of oxygen reduction after the chemical and electrochemical treatment of the catalyst and confirm the formation of a core-shell structure.

Carbon nanotube‐supported bimetallic palladium–gold electrocatalysts for electro‐oxidation of formic acid

AbstractIt is known that palladium‐based catalysts are initially very active in direct formic acid oxidation but they suffer from fast deactivation caused by a strongly adsorbed CO intermediate. Reactivation of the catalysts involving application of anodic potential may cause palladium dissolution. The aim of the present study is to increase the stability and performance of palladium‐based catalysts in direct formic acid fuel cells (DFAFCs). Preparation and characterization of palladium/multiwalled carbon nanotubes (Pd/MWCNTs) and towards formic acid oxidation via different treatments are described. The catalysts were characterized by thermogravimetric analysis (TGA), X‐ray diffraction (XRD), transmission electron microscopy (TEM) and cyclic voltammetry (CV). It was shown that the Pd and Pd–Au MWCNTs supported catalysts after reduction in H2–Ar at 200 °C (R200 treatment) were highly active in formic acid electro‐oxidation, whereas the catalysts after heating in argon at 250 °C (C250 treatment) were inactive. The catalysts after hydrogen treatment have smaller metal particles and better contact with MWCNTs support. CV, simulating reactivation of the catalysts, showed that the Pd catalyst suffers from severe Pd dissolution, whereas for the Pd–Au selective leaching of Pd is considerably slower.

Oxidative Regeneration of Sulfide-fouled Catalysts for Water Treatment

This study tested the stability, activity, and selectivity of an alumina-supported Pd–In bimetallic catalyst during repetitive sulfide fouling and oxidative regeneration conditions. Nitrate reduction with hydrogen was used as the probe reaction in a continuous-flow packed-bed reactor to assess changes in the catalyst structure as a result of the fouling and regeneration processes. Partial regeneration of a severely sulfide-fouled Pd–In catalyst was achieved with a NaOCl/NaHCO3 solution. However, the regenerated catalyst had a reduced activity for NO3− reduction and increased selectivity towards NH3. Analysis of the catalyst bed after regeneration experiments using XPS, ICP-MS, and BET surface area revealed that bulk structural transformations of the Pd–In bimetallic catalyst occurred, as a result of preferential Pd dissolution near the column influent. The dissolved Pd showed limited mobility in the column, and was re-deposited on the catalyst, resulting in Pd enrichment on the catalyst surface and redistribution of Pd towards the end of the column. These changes along with residual sulfur content on the catalyst surface were likely responsible for the increased selectivity towards NH3. These results indicate the importance of limiting the exposure of reduced sulfur species to Pd-based catalysts, especially when treating contaminants like NO3−, where product selectivity is a priority.

Effects of Aging and Oxidation of Palladized Iron Embedded in Activated Carbon on the Dechlorination of 2-Chlorobiphenyl

Reactive activated carbon (RAC) impregnated with palladized iron has been developed to effectively treat polychlorinated biphenyls (PCBs) in the environment by coupling adsorption and dechlorination of PCBs. In this study, we addressed the dechlorination reactivity and capacity of RAC toward aqueous 2-chlorobiphenyl (2-ClBP), and its aging and longevity under various oxidizing environments. RAC containing 14.4% Fe and 0.68% Pd used in this study could adsorb 122.6 mg 2-ClBP/g RAC, and dechlorinate 56.5 mg 2-ClBP/g RAC which corresponds to 12% (yield) of its estimated dechlorination capacity. Due to Fe0 oxidation to form oxide passivating layers, Fe2O3/Fe3O4 (oxide-water interface) and FeOOH/FeO (oxide-metal interface), RAC reactivity decreased progressively over aging under N2 < H2O + N2 < H2O + 02 conditions. Considering nanoscale Fe/Pd corrosion chemistry, the decline was quite slow at only 5.6%, 19.5%, and 32.5% over one year, respectively. Dissolved oxygen played a crucial role in enhancing 2-ClBP adsorption but inhibiting its dechlorination. The reactivity change could be explained with the properties of the aged RAC including surface area, Fe0 content and Fe species. During the aging and oxidation, the RAC showed limited dissolution of Fe and Pd. Finally, implementation issues regarding application of RAC system to contaminated sites are discussed.

Effect of Impurities of Au and Pd on Tensile Properties of Eutectic Sn-Pb Solder for Aerospace Applications

For aerospace applications, eutectic Sn–Pb solder has been used for soldered joints requiring high reliability. However, the use of lead-free electronic components has been spreading and such components have been required. For lead-free electronic components, electrode materials have been changed from Sn–Pb alloys to lead-free materials. In joints with eutectic Sn–Pb solder and Ni/Pd/Au electrodes, degradation of the mechanical properties of the solder due to the dissolution of Au and Pd into the solder is a concern. In this study, the effect of Au and Pd impurities on the tensile properties of eutectic Sn–Pb solder was examined. In solders with Au ranging from 1 to 5 mass%, the tensile strength is stable at approximately 50 MPa, which is 1.25 times that of Sn–37Pb solder. Elongation decreases with increasing Au content. In solders with Pd ranging from 1 to 5 mass%, the tensile strength increases with increasing Pd content. Elongation decreases with increasing Pd content and is less than half that of Sn–37Pb solder. In the addition range investigated, Pd is more harmful than Au for elongation. In solders with both Au and Pd added, in the range less than 1 mass%, the tensile strength increases and elongation decreases with increasing contents of Au and Pd. It was clarified that the contents of Au and Pd should be less than 0.025 and 0.05 mass%, respectively, to prevent significant decrease in elongation.

Pd/MOx Materials Synthesized by Sol‐Gel Coprecipitation as Catalysts for Carbon–Carbon Coupling Reactions of Aryl Bromides and Chlorides

AbstractIn order to control the interaction of palladium species with oxide supports, a sol‐gel coprecipitation synthesis has been developed for Pd/MOx. The resulting Pd/MOx catalysts are characterized by a rather strong interaction between the highly dispersed Pd2+ species and the alumina and silica lattices. During coupling reactions of the Heck type the catalytically active species is generated by partial dissolution of Pd from the support surface. Due to the strong bonding of Pd to the support this dissolution occurs to significant extent only at comparatively high temperatures (≥160 °C). These temperatures are exactly necessary for the activation of less‐reactive substrates like bromobenzene and aryl chlorides. In this way we are able to synthesize supported catalysts that facilitate a controlled release of soluble Pd species under reaction conditions that are required for the activation of aryl bromides and chlorides. The Pd/MOx catalysts show excellent activity in the Heck reaction of bromobenzene (TON up to 10000; TOF up to 5000 h–1) and 4‐chloroacetophenone (TON up to 9300; TOF up to 1550 h–1).(© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2009)

Inside Cover: Visual Observation of Redistribution and Dissolution of Palladium during the Suzuki–Miyaura Reaction (Angew. Chem. Int. Ed. 17/2008)

Palladium's disappearing (and reappearing) act within a specially designed reactor that heats only a small area of Pd foil during a Suzuki–Miyaura coupling is described by C. M. Crudden et al. in their Communication on page 3279 ff. Dissolution of Pd occurs only in the heated zone (left SEM image), and only in the presence of aryl iodide, whereas deposition of Pd occurs preferentially on the unheated zones adjacent to the reactive zone (right SEM image).

Selected electrochemical properties of Pd–Au alloys: hydrogen absorption and surface oxidation

Hydrogen absorption into and surface oxidation of Pd–Au alloys in acidic solutions were studied by cyclic voltammetry (CV) and chronoamperometry (CA) coupled with the electrochemical quartz crystal microbalance (EQCM). The influence of alloy bulk and surface composition on the process of oxidation of absorbed hydrogen was examined. The stresses induced by hydrogen insertion in Pd–Au alloys were compared with the case of pure Pd. The potential corresponding to the formation of a monolayer of surface oxide was determined for Pd–Au alloys of different surface states. Electrochemical dissolution of Pd–Au alloys was investigated.

On the ratio of processes of adsorbed oxygen layer formation and palladium surface layer dissolution at linear anodic potential sweep

The surface layer dissolution on certain palladium deposits (Pd/Pt) and smooth polycrystalline Pd in sulfuric acid solutions is quantitatively studied at anodic linear potential sweep using atomic absorption analysis. The strong effect of the conditions of Pd/Pt electrolytic generation on the processes of palladium dissolution and oxygen adsorption is shown. The scanning electron microscopy method is used to trace the relationship between the synthesis conditions and the palladium deposit morphology. It is shown that palladium dissolution in the course of the anodic potential sweep is the most active for deposits with the highest specific surfaces. At the oxygen adsorption potentials, the charge value consumed in Pd dissolution decreases as the potential sweep rate increases.