Pd Anode Research Articles

Preparation of CO-tolerant Pt and Pd Anodes Modified with SnO2 Nanoparticles for PEFC

Preparation of CO-tolerant Pt and Pd Anodes Modified with SnO2 Nanoparticles for PEFC

Construction of fuel cells based on thin proton conducting oxide electrolyte and hydrogen-permeable metal membrane electrode

This work aims to construct the hydrogen-air fuel cells, which operate at intermediate temperature. In order to reduce the operation temperature, the fuel cells are constructed from a thin proton conducting oxide electrolyte and a hydrogen-permeable membrane anode. In this work, we examine at first the applicability of the hydrogen-permeable metal membrane for the anode in the fuel cell. Then, we evaluated the performance of the fuel cells consisting of the thin electrolyte supported by the metal membrane anode. It is recognized that the hydrogen-permeable metal membrane anode works well similar to the porous Ni anode except the voltage loss. The voltage loss for the fuel cell with the Pd anode is lower than that for the fuel cell with the porous Ni anode. BaCe 0.9Y 0.1O 2.95 films, which are used for the electrolyte in the fuel cells, are prepared by the pulsed laser ablation method on the hydrogen-permeable metal substrates used as the anode. The fuel cells with the BaCe 0.9Y 0.1O 2.95 electrolyte of 1.5–2.0 μm thickness and the hydrogen-permeable Pd anode of 25 μm thickness operate stably giving an open circuit voltage of 0.86 V at 400 °C and the power density of 0.52 mW/cm 2 is derived.

Electrochemical Studies of the Alkene- NO x Fuel Cell for Organic Synthesis

Electrochemical studies of the [alkene, anode/silica-wool|VGCF-cathode NO] cell were carried out at 373 K (VGCF, vapor-grown carbon fiber). The oxidation rates of and i.e., current densities, were increased more than ten times by the addition of NO to the stream in the cathode. A carbon electrode (VGCF-electrode) without precious metals could function as the cathode for the reduction of the mixture of and NO as well as a Pt cathode. The cyclic voltammetry and electrode potential studies over the VGCF-cathode in NO, and suggested that produced from and NO in the gas phase worked as a strong oxidant. easily reduced to and NO that was re-oxidized to by in the cathode. NO functioned as a catalyst for the electrochemical reduction of to The electrochemical studies over a Pd electrode suggested that the oxidation state of the Pd anode changed from to under short-circuit conditions. The dramatic changes in product selectivities and formation rates in the oxidation were due to the change of the oxidation state of the Pd anode by the addition of NO to the stream. The electrochemical oxidation of alkene proceeded over the anode, but not through a stoichiometric oxidation with by (the Wacker oxidation mechanism). © 2003 The Electrochemical Society. All rights reserved.

Solid oxide fuel cells that enable the detection of CO in reformed gases

Solid oxide fuel cells (SOFCs) using Pd metal as the anode were fabricated for detection of CO in a flowing mixture of 0–4000 ppm CO, 50% H 2, 10% CO 2 and 6% H 2O vapor between 300 and 400 °C. When 20 mol% Sm 3+-doped CeO 2 (SDC) was used as the electrolyte, the Pd anode was subjected to a large and reversible change in the anodic-reaction resistance with the CO concentration. This behavior brought about an almost linear relationship between the electromotive force (EMF) generated from the cell or the short-circuit current through the cell and the logarithm of the CO concentration. In both signals, the minimum detectable CO concentration was 50 ppm, and the 90% response and 90% recovery times were about 60 s. However, the EMF of the cell at a CO concentration of 0 ppm significantly deviated from the theoretical value, which made it difficult to obtain reproducible data. In addition, the current signal of a few μA at a CO concentration of 4000 ppm was not large enough to monitor the CO concentration exactly. The improvement of these problems could be achieved by using 25 mol% Y 3+-doped BaCeO 3 (BCY25) with higher ionic conduction as the electrolyte: the EMF of the cell at a CO concentration of 0 ppm was near the theoretical value; the current signal reached 66 μA at a CO concentration of 4000 ppm.

A Fuel-Cell-Type Sensor for Detection of Carbon Monoxide in Reformed Gases

A solid oxide fuel cell using a samaria-doped ceria electrolyte with a Pd anode was fabricated for detecting carbon monoxide (CO) in reformed gases at 300°C. The CO concentration in a flowing mixture of 0-4000 ppm CO, 50% hydrogen, 10% carbon dioxide, and 6% water vapor was related to a decrease in both the electromotive force generated from the cell and the short-circuit current through the cell due to a reversible change in the anodic reaction resistance with the CO concentration. In both signals, the minimum detectable concentration was 50 ppm, and the 90% response and 90% recovery times were as short as 20 s. © 2001 The Electrochemical Society. All rights reserved.

Design of alkenes–(O 2+NO) cell system for the selective partial oxidation of alkenes

Wacker type oxidations of alkenes were performed using an [alkene |Pd-black (anode)| H 3PO 4 |graphite (cathode)| O 2+NO] gas-cell at 353 K. The addition of NO to O 2 in the cathode led to a dramatic enhancement of the oxidation rate of ethylene to MeCHO more than 10 times. The kinetic experiments were studied to get information on reaction mechanisms and the optimum conditions for MeCHO synthesis. The enhancement was ascribed to the acceleration in the rate of electrochemical oxidation of Pd(0) to Pd(II) due to the formation of NO 2 at the cathode. The formation of NO 2 led to an increase in the electromotive force of the cell and the over potential at the Pd anode. The graphite without precious metals was sufficient as the cathode for the reduction of NO 2 into NO and H 2O. The electrochemical reduction of O 2 to H 2O was catalyzed by NO. In the case of propene oxidation, the formation of acrolein, the major product for the [C 3H 6–O 2] cell, was remarkably decelerated and acetone was the major product when NO had been added to O 2. These observations may be ascribed to changes in the concentrations of Pd(0) and Pd(II) which are responsible for the π-allyl and Wacker type oxidations, respectively.

An Alkene- NO x Cell for the Wacker-Type Oxidation of Alkenes

Oxidations of and were performed using an gas cell at 353 K. The cofeed of NO with at the cathode dramatically enhanced the Wacker-type oxidations of the alkenes. The enhancement was ascribed to the acceleration in the rate of electrochemical oxidation of Pd(0) to Pd(II) due to the formation of at the cathode. The formation of increased the electromotive force of the cell and the polarization at the Pd anode. The graphite without precious metals was sufficient as the cathode for the reduction of into NO under the reaction conditions in this work. The NO cofed with works as a mediator for the electrochemical reduction of In the case of propene oxidation, acetone was the major product for the cell. The formation of acrolein, the major product for the cell, was decreased markedly when NO had been cofed with These observations could be ascribed to the changes in the concentrations of Pd(0) and Pd(II) responsible for the π-allyl and Wacker type oxidations, respectively. © 2001 The Electrochemical Society. All right reserved.

A portable apparatus for energy-dispersive X-ray fluorescence analysis of sulfur and chlorine in frescoes and stone monuments

A simple and portable equipment was constructed, based on the energy dispersive X-ray fluorescence. It is composed of a small size X-ray tube, a thermoelectrically cooled Si-PIN detector, and a multi channel analyzer. The tube has a Pd anode, and works at 3–30 kV, 0.1 mA. At 3–5 kV, it emits Pd-L lines and bremsstrahlung radiation, and therefore is suited to the analysis of low atomic number elements, such as P, S, Cl. Working at 30 kV the tube emits Pd-K lines and bremsstrahlung radiation, and is able to excite medium atomic number elements up to tin (K-lines) and high atomic number elements (L-lines). The Si-PIN detector has a 25 μm Bc-window and energy resolution of about 190 eV at 5.9 keV. It has a thickness of about 300 μm and thus an efficiency rapidly decreases at energies larger than about 20 keV. The equipment is completed by a portable multi channel analyzer. The described system was first tested in Laboratory and then employed to analyze mainly sulfur and chlorine in the follwoing frescoes and monuments: • frescoes of Piero della Francesca (church of S. Francesco, Arezzo) • frescoes of Domenichino (cathedral of Fano) • Roman frescoes (church of S. Clemente, Rome) • lapideous altars (church of S. Croce, Lecce).

Energy dispersive x-ray fluorescence analysis of thin and intermediate environmental samples

Energy-dispersive x-ray fluorescence (EDXRF) was applied to the analysis of environmental samples, such as algae, microalgae and marine sediments, prepared as thin samples by mixing powder with two-component epoxy resins, and as intermediate samples in the form of pellets. Further, sulphur, the concentration of which is used as an index of degradation, was analyzed in situ on a 16th century mural painting inside the church of S. Stefano Rotondo in Rome. Finally, lead was monitored in air samples from the city of Lecce and a map of the Pb distribution at various locations in the city was obtained. The equipment for EDXRF analysis is based on miniaturized x-ray tubes (Oxford, 30 kV, 0.1 mA, Mo or Pd anodes; or Hamamatsu, 10 kV, 0.3 mA, Ca anode) and on thermoelectrically cooled Si–PIN detectors, having an energy resolution of 250 eV at 5.9 keV. Lead was excited with a Gilardoni x-ray tube (Radiolight, 80 kV, 5 mA, W anode and Mo secondary target) and x-rays were detected with an HpGe detector with an energy resolution of 160 eV at 5.9 keV. © 1998 John Wiley & Sons, Ltd.

Synthesis gas production in methane conversion using the P|yttria-stabilized zirconia|Ag electrochemical membrane system

The electrochemical membrane reactor of YSZ (yttria-stabilized zirconia) solid electrolyte coated with Pd and Ag as anode and cathode, respectively, has been applied to the partial oxidation of methane to synthesis gas (CO + H2). The Pd|YSZ|Ag catalytic system has shown a remarkable activity for CO production at 773 K, and the selectivity to CO was quite high (96.3%) under oxygen pumping condition at 5 mA. The H2 production strongly depended on the oxidation state of the Pd anode surface. Namely, the H2 treatment of the Pd anode at 773 K for 1 h drastically reduced the rate of H2 production, while air treatment enhanced the H2 production rate. From the results of the partial oxidation of CH4 with molecular oxygen, it is considered that the reaction site of the electrochemical oxidation of CH4 to synthesis gas was the Pd–YSZ–gas-phase boundary (triple-phase boundary). In addition, it is found that the oxygen species pumped electrochemically over the Pd surface demonstrated similar activity to adsorbed oxygen over Pd, PdOad, for the selective oxidation of CH4 to CO, when the Pd supported on YSZ was used as a fixed-bed catalyst for CH4 oxidation with the adsorbed oxygen. The difference with respect to the H2 formation between the electrochemical membrane system and the fixed-bed catalyst reactor results from differences in the average particle size of Pd and the way of the oxygen supply to the Pd surface.

Propylene carbonate stabilized nanostructured palladium clusters as catalysts in Heck reactions

Nanostructured Pd clusters, prepared either electrochemically using a sacrificial Pd anode or by thermolysis of Pd(O2CMe)2, are stable in propylene carbonate even at 140–155 °C; such colloidal solutions catalyse Heck reactions in the absence of phosphine ligands.

Application of the hydrous oxide mediation model of electrocatalysis to reactions at noble metal anodes in base—I. Pt, Pd and Rh

The oxidation of four compounds, hydrazine, the formate anion, formaldhyde and methanol, was investigated, using cyclic voltammetry techniques, at Pt, Pd and Rh anodes in base (the reactivity of three other metals, Au, Ir and Ru is described in Part II of this series). As for the same reactions in acid, whose behaviour was described recently, the results are discussed in terms of the adatom—incipient hydrous oxide mechanism of electrocatalysis. This approach operates quite well in the case of hydrazine oxidation, ie in the case of processes that occur without auto-deactivation of the surface. For most organics, however, more complex behaviour is observed as one of the main products of the oxidation process, CO ads, deactivates the anode surface.

Dual solution-type HCHO fuel cell systems using an anion exchange resin membrane with electroless-plated Cu or Pd anode

Loading characteristics of a prototype HCHO fuel cell systems with an anion exchange membrane which separates the anolyte from the catholyte were investigated. Electrodes of Cu or Pd, deposited by an electroless-plating technique onto the membrane, showed high electrocatalytic activity to the anodic oxidation of HCHO in 1 M NaOH solution. The system with Cu anode and 1 M NaOH for both anolyte and catholyte showed high loading characteristics but poor durability, whereas that with 1 M K2CO3 showed low characteristics because of lowered pH of the anolyte. It was shown that a dual solution-type cell with 1 M K2CO3 anolyte and 1 M NaOH catholyte yielded improved characteristics as compared with the simple K2CO3 system. The output level was, however, at an unsatisfactory level owing to poor membrane conductance. The temperature dependence of the output performance was studied in the range 7–55°C.

An Investigation of Electrode Materials for the Anodic Oxidation of Sulfur Dioxide in Concentrated Sulfuric Acid

The kinetic studies and electrochemical evaluation of catalysts for the oxidation reaction have been carried out in concentrated (50 weight percent) sulfuric acid solutions using the steady‐state potentiostatic method and cyclic voltammetry. Palladium and palladium oxide have been identified to be better catalysts than platinum for this reaction. The polarization potential for oxidation on a preanodized Pd anode decreases with increasing temperature, while the reaction mechanism is independent of temperature. The electrochemical oxidation of commences at an anodic potential where the formation of adsorbed oxygen‐containing species is initiated. On the Pt, Ru, Ir, and Rh anodes, the chemical transformation of the adsorbed species to metal oxides at higher potentials creates passivated layers which partially cover the electrode surface and inhibit the oxidation reaction.

Oxygen overvoltage on bright iridium

Steady-state oxygen overvoltage measurements were made both galvanostatically and potentiostatically on bright Ir bead anodes and cathodes in O2-saturated sulfuric acid solutions. The mechanism for the reduction of O2 on Ir cathodes is most likely the same as that suggested for Pt cathodes. Although an oxide, IrO2, is formed on Ir anodes, the mechanism for the evolution of oxygen does not take place by an oxide mechanism as for Pd anodes, but by the discharge of H2O as for Pt anodes. From the experimental evidence that a limiting current region appears in the constant potential anodic polarization curve and that the double-layer capacity is increased as oxygen is adsorbed on the Ir surface, it is concluded that the adsorbed oxygen layers on Ir are good electronic conductors. Evidence is presented which supports the contention that the presence of adsorbed oxygen on Ir cathodes hinders the reduction of O2 to H2O2 but promotes the reduction of H2O2 to H2O. A stable intermediate, H2O2, is formed during the oxygen reduction process.

Oxygen overvoltage on bright iridium

Steady-state oxygen overvoltage measurements were made both galvanostatically and potentiostatically on bright Ir bead anodes and cathodes in O2-saturated sulfuric acid solutions. The mechanism for the reduction of O2 on Ir cathodes is most likely the same as that suggested for Pt cathodes. Although an oxide, IrO2, is formed on Ir anodes, the mechanism for the evolution of oxygen does not take place by an oxide mechanism as for Pd anodes, but by the discharge of H2O as for Pt anodes. From the experimental evidence that a limiting current region appears in the constant potential anodic polarization curve and that the double-layer capacity is increased as oxygen is adsorbed on the Ir surface, it is concluded that the adsorbed oxygen layers on Ir are good electronic conductors. Evidence is presented which supports the contention that the presence of adsorbed oxygen on Ir cathodes hinders the reduction of O2 to H2O2 but promotes the reduction of H2O2 to H2O. A stable intermediate, H2O2, is formed during the oxygen reduction process.

Oxygen Overvoltage on Bright Palladium in Acid Solutions

Oxygen overvoltage measurements were made both galvanostatically and potentiostatically on bright Pd electrodes in solutions. The anodic evolution and the cathodic reduction of oxygen were investigated, and, in general, the two measuring techniques gave the same kinetic results. The overvoltage curves exhibited a mixed potential region followed by a Tafel region. In the anodic curves these two regions were separated by a limiting current or passivation region. It was found that Pd is a poorer peroxide‐decomposing catalyst than Pt, that a film of adsorbed is a poor electronic conductor, that oxygen is evolved on a Pd anode through an oxide mechanism, the decomposition of to and O2, and that oxygen is reduced from the adsorbed oxygen molecules on a Pd cathode.