Supported platinum electrocatalysts are generally used in low temperature fuel cells to enhance the rates of the hydrogen oxidation and oxygen reduction reactions. In such catalysts, the high surface ...to volume ratios of the platinum particles maximize the area of the surfaces available for reaction. It is the structure and proper dispersal of these platinum particles that make low-loading catalysts feasible for fuel cell operation, lowering the cost of the system. If the platinum particles cannot maintain their structure over the lifetime of the fuel cell, change in the morphology of the catalyst layer from the initial state will result in a loss of electrochemical activity. This loss of activity in the platinum/carbon catalysts due to the agglomeration of platinum particles is considered to be a major cause of the decrease in cell performance, especially in the case of the cathode. In the light of the latest advances on this field, this paper reviews the preparation methods of these catalysts, their microstructural characteristic and their effect on both thermal and in cell conditions stability.
The performance and durability of low-temperature fuel cells seriously depend on catalyst support materials. Catalysts supported on high surface area carbons are widely used in low temperature fuel ...cells. However, the corrosion of carbonaceous catalyst-support materials such as carbon black has been recognized as one of the causes of performance degradation of low-temperature fuel cells, in particular under repeated start-stop cycles or high-potential conditions. To improve the stability of the carbon support, materials with a higher graphitic character such as carbon nanotubes and carbon nanofibers have been tested in fuel cell conditions. These nanostructured carbons show a several-fold lower intrinsic corrosion rate, however, do not prevent carbon oxidation, but rather simply decrease the rate. Due their high stability in fuel cell environment, ceramic materials (oxides and carbides) have been investigated as carbon-substitute supports for fuel cell catalysts. Moreover, the higher specific electrocatalytic activity of some ceramic supported metals than unsupported and carbon supported ones, suggests the possibility of a synergistic effect by supporting metal catalyst on ceramic supports. This paper presents an overview of ceramic materials tested as a support for fuel cell catalysts, with particular attention addressed to the electrochemical activity and stability of the supported catalysts.
Alkaline direct alcohol fuel cells Antolini, E.; Gonzalez, E.R.
Journal of power sources,
06/2010, Letnik:
195, Številka:
11
Journal Article
Recenzirano
Odprti dostop
The faster kinetics of the alcohol oxidation and oxygen reduction reactions in alkaline direct alcohol fuel cells (ADAFCs), opening up the possibility of using less expensive metal catalysts, as ...silver, nickel and palladium, makes the alkaline direct alcohol fuel cell a potentially low cost technology compared to acid direct alcohol fuel cell technology, which employs platinum catalysts. A boost in the research regarding alkaline fuel cells, fuelled with hydrogen or alcohols, was due to the development of alkaline anion-exchange membranes, which allows the overcoming of the problem of the progressive carbonation of the alkaline electrolyte. This paper presents an overview of catalysts and membranes for ADAFCs, and of testing of ADAFCs, fuelled with methanol, ethanol and ethylene glycol, formed by these materials.
Context. The Cherenkov Telescope Array (CTA) represents the most advanced facility designed for Cherenkov Astronomy. ASTRI SST-2M has been developed as a demonstrator for the Small Size Telescope in ...the context of the upcoming CTA. Its main innovation consists in the optical layout which implements the Schwarzschild-Couder configuration and is fully validated for the first time. The ASTRI SST-2M optical system represents the first qualified example of a two-mirror telescope for Cherenkov Astronomy. This configuration permits us to (i) maintain high optical quality across a large field of view; (ii) demagnify the plate scale; and (iii) exploit new technological solutions for focal plane sensors. Aims. The goal of the paper is to present the optical qualification of the ASTRI SST-2M telescope. The qualification has been obtained measuring the point spread function (PSF) sizes generated in the focal plane at various distances from the optical axis. These values have been compared with the performances expected by design. Methods. After an introduction on Gamma-ray Astronomy from the ground, the optical design of ASTRI SST-2M and how it has been implemented is discussed. Moreover, the description of the set-up used to qualify the telescope over the full field of view is shown. Results. We report the results of the first–light optical qualification. The required specification of a flat PSF of ~ 10 arcmin in a large field of view (~ 10°) has been demonstrated. These results validate the design specifications, opening a new scenario for Cherenkov Gamma-ray Astronomy and, in particular, for the detection of high-energy (5–300 TeV) gamma rays and wide-field observations with CTA.
Low-temperature fuel cells, with either hydrogen or methanol as the fuel, represent an environmentally friendly technology and are attracting considerable interest as a means of producing electricity ...by direct electrochemical conversion of hydrogen/methanol and oxygen into water/water and carbon dioxide. Platinum has the highest catalytic activity for oxygen reduction of any of the pure metals and when supported on a conductive carbon serves as state of the art cathode material in low-temperature fuel cells. Regarding the direct methanol fuel cells (DMFCs), one of the major problems is the methanol crossover through the polymer electrolyte. The mixed potential, which results from the oxygen reduction reaction and the methanol oxidation occurring simultaneously, reduces the cell voltage, generates additional water and increases the required oxygen stoichiometric ratio. This problem could be solved either by using electrolytes with lower methanol permeability or by developing new cathode electrocatalysts with both higher methanol tolerance and higher activity for the oxygen reduction reaction than Pt. Pt alloyed with first-row transition elements is proposed as cathode material with improved methanol tolerance for direct methanol fuel cells. In the light of the latest advances on this field, this paper presents an overview of platinum-based catalysts as methanol-resistant oxygen reduction materials for direct methanol fuel cells.
Due their high accessible surface area, low resistance and high stability, conducting polymers have been investigated as carbon-substitute supports for fuel cell catalysts. This paper provides a ...review of the state-of-the-art in the development of metal/polymer composites as electrode materials for low-temperature fuel cells.
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The dependence of the peak current density on the thickness of PPy film for the oxidation peaks (a) at about 0.62
V in the positive-going sweep and (b) at about 0.43
V in the negative-going sweep in the CV of methanol at the Pt/PPy/GC electrode.
Due to their high accessible surface area, low resistance and high stability, conducting polymers have been investigated as carbon-substitute supports for fuel cell catalysts. The main reason for incorporating metallic particles into porous polymeric matrixes is to increase the specific area of these materials and thereby improve the catalytic efficiency. Polymer-supported metal particles also present higher tolerance to poisoning due to the adsorption of CO species, in comparison to the serious problem of poisoning of bulk and carbon-supported metals. Moreover, conducting polymers are not only electron conducting, but also proton conducting materials, so they can replace Nafion in the catalyst layer of fuel cell electrodes and provide enhanced performance. This paper provides a review of the state-of-the-art in the development of metal/polymer composites as electrode materials for low-temperature fuel cells.
In view of a possible use as anode materials for low-temperature fuel cells, the electro catalytic activity of Pt–Sn catalysts for methanol and ethanol oxidation has been widely investigated. This ...short review examines the effects of Pt–Sn structural characteristics, such as degree of alloying and Sn oxidation state, depending on the synthesis method, on the electro catalytic activity for methanol and ethanol oxidation.
Palladium in fuel cell catalysis Antolini, Ermete
Energy & environmental science,
01/2009, Letnik:
2, Številka:
9
Journal Article
Recenzirano
Carbon supported platinum is commonly used as anode and cathode electrocatalyst in low-temperature fuel cells fuelled with hydrogen or low molecular weight alcohols. The cost of Pt and the limited ...world supply are significant barriers to the widespread use of these types of fuel cells. Moreover, platinum used as anode material is readily poisoned by carbon monoxide, present in the reformate gas used as H sub(2) carrier in the case of polymer electrolyte fuel cells, and a byproduct of alcohol oxidation in the case of direct alcohol fuel cells. In addition, Pt alone does not present satisfactory activity for the oxygen reduction reaction when used as cathode material. For all these reasons, binary and ternary platinum-based catalysts and non-platinum-based catalysts have been tested as electrode materials for low temperature fuel cells. Palladium and platinum have very similar properties because they belong to the same group in the periodic table. The activity for the oxygen reduction reaction (ORR) of Pd is only slightly lower than that of Pt, and by addition of a suitable metal, such as Co or Fe, the ORR activity of Pd can overcome that of Pt. Conversely, the activity for the hydrogen oxidation reaction (HOR) of Pd is considerably lower than that of Pt, but by adding of a very small amount (5 at%) of Pt, the HOR activity of Pd attains that of pure Pt. This paper presents an overview of Pd and Pd-containing catalysts, tested both as anode and cathode materials for low-temperature fuel cells.
A carbon supported Pt–Pd catalyst with a Pt:Pd atomic ratio 77:23 was prepared by reduction of metal precursors with formic acid and characterized by EDX, XRD and XPS techniques. A decrease of the ...lattice parameter compared with that of pure Pt was observed, indicating the formation of a Pt–Pd alloy. Tests in H
2SO
4 solution in the absence of ethanol showed that the Pd-containing is slightly more active than pure Pt for the oxygen reduction reaction (ORR). In the presence of ethanol a larger increase in overpotential of the ORR on pure Pt than that on Pt–Pd was found, indicating a higher ethanol tolerance of the binary catalyst. The enhanced performance at 90
°C of the direct ethanol fuel cell with Pt–Pd/C as cathode material confirmed the results of half cell tests, and was essentially ascribed to a reduced ethanol adsorption on Pt–Pd.
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