Showing papers by "Edson A. Ticianelli published in 2015"

Pt modified tungsten carbide as anode electrocatalyst for hydrogen oxidation in proton exchange membrane fuel cell: CO tolerance and stability

Abstract: Pt supported on tungsten carbide-impregnated carbon (Pt/WC/C) is evaluated for hydrogen oxidation reaction in hydrogen/oxygen polymer electrolyte fuel cell at two different temperatures (85 and 105 °C), in absence and presence of 100 ppm CO. Carbon supported PtW, prepared by a formic acid reduction method is also evaluated for comparison. At 85 °C, the initial hydrogen oxidation activity in the presence of 100 ppm CO is higher for Pt/WC/C, showing a CO induced overpotential of 364 mV for 1 A cm −2 of current density as compared to an overpotential of 398 mV for PtW/C. As expected, an increase in CO tolerance is observed with the increase in cell temperature for both the catalysts. The increased CO tolerance of Pt/WC/C catalyst is in agreement with CO stripping experiments, for which the CO oxidation potentials occurred at lower potentials at three different temperatures (25, 85 and 105 °C) in comparison to PtW/C. The stability of both electrocatalysts is evaluated by an accelerated stress test and the results show a better stability for Pt/WC/C catalyst. On the basis of cyclic voltammograms and polarization curves, it is concluded that Pt/WC/C is more stable than PtW/C and can be used as alternative anode catalyst in PEMFC, especially at high temperatures.

Accelerated degradation of Pt3Co/C and Pt/C electrocatalysts studied by identical-location transmission electron microscopy in polymer electrolyte environment

Abstract: Identical-location transmission electron microscopy (ILTEM) coupled with X-ray energy dispersive spectroscopy (X-EDS) analyses were used to characterize the changes in the morphology and composition of Pt and Pt3Co nanoparticles deposited on high surface area carbon (Vulcan XC72) before and after electrochemical ageing tests performed in polymer electrolyte environment, using a “dry cell” The Pt/C and Pt3Co/C electrocatalysts are modified upon electrochemical ageing, following changes in particle size, geometry, and composition; these changes are however milder to what happens upon aging in H2SO4 electrolyte, because of the lack of liquid water, a reactant in both carbon corrosion and Pt (Pt3Co) corrosion/dissolution reactions The negative vertex potential of the ageing procedure also matters: Pt redeposition occurs at 01 V vs RHE and not at 06 V vs RHE, while carbon corrosion is emphasized after incursions at the lower vertex potential, in agreement to what demonstrated in liquid electrolyte Besides, the presence of Co in Pt3Co alloys enables to somewhat slow-down the Pt corrosion from Pt3Co/C electrocatalysts, since cobalt acts as a sacrificial anode, which also lowers carbon corrosion These morphology and composition changes were further used to explain the changes in ORR intrinsic activity of the electrocatalysts upon electrochemical aging; the ORR activity and the accelerated stress tests (AST) were measured/performed in a similar setup (at the interface with a polymer electrolyte) using an ultramicroelectrode with cavity The ORR activity only improved for Pt/C nanoparticles when the AST contained the lower vertex potential (01 V vs RHE), thanks to the favorable increase of the particle sizes, favored because the Ptz+ ions released by the corrosion of the Pt/C nanoparticles at 09 V vs RHE remains trapped in the Nafion®, thereby easing its redeposition in the subsequent step at 01 V vs RHE In all the other cases, the ORR activity decreased upon the AST On Pt3Co/C the positive effect of Pt redeposition in the 01–09 V vs RHE ageing procedure is counterbalanced by a detrimental (and large) effect of Co dissolution, which adversely affects the nanoparticles composition for the ORR and pollutes the polymer electrolyte membrane (the Coy+ cations hinder O2 and H+ transport in the electrolyte membrane) After the 06–09 V vs RHE ageing procedure, the ORR activity always decreases, because the redeposition of Pt is not likely, therefore suppressing the positive effect of particle size increase monitored in the 01–09 V vs RHE ageing procedure, and because Co dissolution and adverse effect is maintained

Investigation of Ni-based alloy/CGO electro-catalysts as protective layer for a solid oxide fuel cell anode fed with ethanol

Abstract: Ni-based alloys were prepared by using the oxalate method and subsequent in-situ reduction. The crystallographic phase and microstructure of the catalysts were investigated. These bimetallic alloys were mixed with gadolinium-doped ceria in order to obtain a composite material with mixed electronic-ionic conductivity. Catalytic and electrocatalytic properties of the composite materials for the conversion of ethanol were investigated. Electrochemical tests were carried out by utilizing the Ni-based alloy/CGO cermet as a barrier layer in a conventional anode-supported solid oxide fuel cell (SOFC). A comparative study between the modified cells and a conventional anode-supported SOFC without the protective layer was made. The aim was to efficiently convert the fuel directly into electricity or syngas (H2 and CO) just before the conventional anode support. In accordance with the ex-situ catalytic tests, the SOFC anode modified with Ni–Co/CGO showed superior performance towards the direct utilization of dry ethanol than the bare anode and that modified with Ni–Cu/CGO. A peak power of 550 mW cm−2 was achieved with the dry ethanol-fed Ni–Co/CGO pre-layer modified-cell at 800 °C. A total low frequency resistance of <0.5 Ω cm2 at 0.8 V of cell voltage was recorded in the presence of ethanol directly fed to the SOFC.

Electrocatalytic Activity and Stability of Platinum Nanoparticles Supported on Carbon–Molybdenum Oxides for the Oxygen Reduction Reaction

Abstract: The degradation of Pt-based electrocatalysts used in proton-exchange membrane fuel cell (PEMFC) cathodes is one of the main issues restricting the widespread application of PEMFCs as energy converters. This work aims to contribute to the improvement of the stability of platinum nanoparticles (Pt NPs) by modifying the support to which they are anchored. Thus, syntheses of catalyst supports based on molybdenum oxides and carbon are carried out, followed by impregnation of the supports with Pt NPs. The Pt/MoO3–C catalyst shows the highest specific activity in the oxygen reduction reaction (ORR), and this must be because of synergistic metal–support effects. Regarding the electrochemical stability of the materials, it is observed that, in principle, none of the Mo oxides decrease the extent of Pt degradation. However, after comparing the specific ORR activities before and after electrochemical ageing, it is concluded that Pt/MoO2*–C is a more stable material compared to Pt/C and Pt/MoO3–C.

Effect of Addition of Ru and/or Fe in the Stability of PtMo/C Electrocatalysts in Proton Exchange Membrane Fuel Cells

Abstract: In this work, the activity, stability, and CO tolerance of ternary and quaternary electrocatalysts formed by PtMo/C-PtFe/C, PtMo/C-PtRu/C, and PtMo/C-PtRuC-PtFe/C were studied in the anodes of proton exchange membrane fuel cells (PEMFCs). Cyclic voltammetry (CV) was used to study the surface characteristics and stability of the electrocatalysts and polarization curves were used to investigate the performance of PEMFC anodes supplied with pure hydrogen and hydrogen containing 100 ppm CO. Online mass spectrometry (OLMS) and CO stripping experiments were conducted to investigate the CO tolerance mechanism. The PtMo/C-PtRu/C-PtFe/C, PtMo/C-PtFe/C, and PtMo/C-PtRu/C electrocatalysts showed better performance for the oxidation of hydrogen in the presence of hydrogen containing 100 ppm CO as compared to the PtMo/C electrocatalyst. It was found that the partial dissolution of Mo, Ru, and Fe, and their migration/diffusion from the anode to the cathode occur during a CV cycling from 0.1 to 0.7 V vs. RHE at a scan rate of 50 mVs-1 up to total of 5,000 cycles. The results also showed that the stability of PtMo/C-PtRu/C-PtFe/C, PtMo/C-PtFe/C, and PtMo/C-PtRu/C are better than that of PtMo/C.

Activity and Stability of Molybdenum-Containing Dispersed Pt Catalysts for CO Tolerance in Proton Exchange Membrane Fuel Cell Anodes

Abstract: In this work, results of attempts to improve the activity and stability of Mo-containing dispersed Pt catalysts for the CO tolerance in proton exchange membrane fuel cell (PEMFC) anodes are revised for the following approaches: (1) application of a heat treatment at various temperatures ranging from 400 to 700 °C on carbon supported PtMo (60:40, Pt:Mo) electrocatalyst; (2) deposition of Pt and PtMo nanoparticles on carbon-supported molybdenum carbides (Mo2C/C) and; (3) employing ternary and quaternary materials formed by PtMoFe/C, PtMoRu/C and PtMoRuFe/C. The Pt-Mo/C catalyst heat-treated at 600 °C showed higher hydrogen oxidation activity in the absence and in the presence of CO and better stability, compared to all other Mo-containing catalysts. Similar CO tolerances were observed for PtMoRuFe, PtMoFe, PtMoRu supported on carbon, and for Pt supported on Mo2C/C, which also presented better stability, as compared to as-prepared PtMo supported on carbon. However, partial dissolution of Mo, Ru, and Fe from the anodes and their migration toward cathodes during the cell operation was observed.

Ni-based Alloys as Protective Layer for a Conventional Solid Oxide Fuel Cell Fed with Biofuels

Abstract: A possible scenario for the future is the utilization of alternative fuels especially those obtained from renewable sources including those derived from biomass. One of the main implications is regarding the consumer's ability to use an increasingly diverse selection of energy sources. Small fuel cells systems, typically less than 10kW, are under consideration for many applications that traditional electric utilities have not supplied widely. In this area, solid oxide fuel cells (SOFCs) may enable new companies to enter the power-generation business as equipment providers or heat and electricity providers. The most common type of SOFC is based on Ni-YSZ as anode and operates at temperatures above 700 °C using H2 or syngas (H2 + CO) produced from a reforming process (internal or external). In this communication, we report the preparation and electrochemical characterization of catalysts having proper behaviour for the utilization as protective layer for the anode.