| 1. |
- Folkesson, Anders, et al.
(författare)
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Real life testing of a hybrid PEM fuel cell bus
- 2003
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Ingår i: Journal of Power Sources. - 0378-7753 .- 1873-2755. ; 118:1-2, s. 349-357
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Tidskriftsartikel (refereegranskat)abstract
- Fuel cells produce low quantities of local emissions, if any, and are therefore one of the most promising alternatives to internal combustion engines as the main power source in future vehicles. It is likely that urban buses will be among the first commercial applications for fuel cells in vehicles. This is due to the fact that urban buses are highly visible for the public, they contribute significantly to air pollution in urban areas, they have small limitations in weight and volume and fuelling is handled via a centralised infrastructure. Results and experiences from real life measurements of energy flows in a Scania Hybrid PEM Fuel Cell Concept Bus are presented in this paper. The tests consist of measurements during several standard duty cycles. The efficiency of the fuel cell system and of the complete vehicle are presented and discussed. The net efficiency of the fuel cell system was approximately 40% and the fuel consumption of the concept bus is between 42 and 48% lower compared to a standard Scania bus. Energy recovery by regenerative braking saves up 28% energy. Bus subsystems such as the pneumatic system for door opening, suspension and brakes, the hydraulic power steering, the 24 V grid, the water pump and the cooling fans consume approximately 7% of the energy in the fuel input or 17% of the net power output from the fuel cell system. The bus was built by a number of companies in a project partly financed by the European Commission's Joule programme. The comprehensive testing is partly financed by the Swedish programme "Den Grona Bilen" (The Green Car). A 50 kW(el) fuel cell system is the power source and a high voltage battery pack works as an energy buffer and power booster. The fuel, compressed hydrogen, is stored in two high-pressure stainless steel vessels mounted on the roof of the bus. The bus has a series hybrid electric driveline with wheel hub motors with a maximum power of 100 kW. Hybrid Fuel Cell Buses have a big potential, but there are still many issues to consider prior to full-scale commercialisation of the technology. These are related to durability, lifetime, costs, vehicle and system optimisation and subsystem design. A very important factor is to implement an automotive design policy in the design and construction of all components, both in the propulsion system as well as in the subsystems.
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| 2. |
- Selimovic, Azra, et al.
(författare)
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Networked solid oxide fuel cell stacks combined with a gas turbine cycle
- 2002
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Ingår i: Journal of Power Sources. - 0378-7753 .- 1873-2755. ; 106:1-2, s. 76-82
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Konferensbidrag (refereegranskat)abstract
- An improved design of fuel cells stacks arrangement has been suggested before for MCFC where reactant streams are ducted such that they are fed and recycled among multiple MCFC stacks in series. By networking fuel cell stacks, increased efficiency, improved thermal balance, and higher total reactant utilisation can be achieved. In this study, a combination of networked solid oxide fuel cell (SOFC) stacks and a gas turbine (GT) has been modelled and analysed. In such a combination, the stacks are operating in series with respect to the fuel flow. In previous studies conducted on hybrid SOFC/GT cycles by the authors, it was shown that the major part of the output of such cycles can be addressed to the fuel cell, In those studies, a single SOFC with parallel gas flows to individual cells were assumed. It can be expected that if the performance of the fuel cell is enhanced by networking, the overall system performance will improve. In the first part of this paper, the benefit of the networked stacks is demonstrated for a stand alone stack while the second part analyses and discusses the impact networking of the stacks has on the SOFC/GT system performance and design. For stacks with both reactant streams in series, a significant increase of system efficiency was found (almost 5% points), which, however, can be explained mainly by an improved thermal management.
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| 3. |
- Agrell, J., et al.
(författare)
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Steam reforming of methanol over a Cu/ZnO/Al2O3 catalyst : a kinetic analysis and strategies for suppression of CO formation
- 2002
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Ingår i: Journal of Power Sources. - 0378-7753 .- 1873-2755. ; 106:1-2, s. 249-257
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Konferensbidrag (refereegranskat)abstract
- Steam reforming of methanol (CH3OH + H2O --> CO2 + 3H(2)) was studied over a commercial Cu/ZnO/Al2O3 catalyst for production of hydrogen onboard proton exchange membrane (PEM) fuel cell vehicles. A simple power-law rate expression was fitted to experimental data in order to predict the rates Of CO2 and H-2 formation under various reaction conditions. The apparent activation energy (E-a) was estimated to be 100.9 kJ mol(-1), in good agreement with values reported in the literature. Appreciable amounts of CO by-product were formed in the reforming process at low contact times and high methanol conversions. Being a catalyst poison that deactivates the electrocatalyst at the fuel cell anode at concentrations exceeding a few ppm, special attention was paid to the pathways for CO formation and strategies for its suppression. It was found that increasing the steam-methanol ratio effectively decreases CO formation. Likewise, addition of oxygen or air to the steam-methanol mixture minimises the production of CO. By shortening the contact time and lowering the maximum temperature in the reactor, CO production can be further decreased by suppressing the reverse water-gas shift reaction.
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| 4. |
- Andersson, Anna M, et al.
(författare)
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Electrochemically lithiated graphite characterised by photoelectron spectroscopy
- 2003
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Ingår i: Journal of Power Sources. - 0378-7753 .- 1873-2755. ; 119-121, s. 522-527
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Tidskriftsartikel (refereegranskat)abstract
- X-ray photoelectron spectroscopy (XPS) has been used to study the depth profile of the solid–electrolyte interphase (SEI) formed on a graphite powder electrode in a Li-ion battery. The morphology of the SEI-layer, formed in a 1 M LiBF4 EC/DMC 2:1 solution, consists of a 900 Å porous layer of polymers (polyethylene oxide) and a 15–20 Å thin layer of Li2CO3 and LiBF4 reduction–decomposition products. Embedded LiF crystals as large as 0.2 μm were found in the polymer matrix. LiOH and Li2O are not major components on the surface but rather found as a consequence of sputter-related reactions. Monochromatised Al Kα XPS-analysis based on the calibration of Ar+ ion sputtering of model compounds combined with a depth profile analysis based on energy tuning of synchrotron XPS can describe the highly complex composition and morphology of the SEI-layer.
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| 5. |
- Dissanayake, M. A K L, et al.
(författare)
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Effect of concentration and grain size of alumina filler on the ionic conductivity enhancement of the (PEO)9LiCF3SO3:Al2O3 composite polymer electrolyte
- 2003
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Ingår i: Journal of Power Sources. - 0378-7753.
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Konferensbidrag (refereegranskat)abstract
- Nano-composite polymer electrolytes are receiving attention as potential candidates to be used as electrolyte membranes in lithium polymer batteries and other devices. However, a survey of literature reveals that a systematic study of the effect of concentration and surface area of ceramic fillers on the conductivity enhancement of micro- and nano-composite polymer electrolytes is lacking. In this work, we have studied the thermal and electrical properties of the composite polymer electrolyte (PEO)9LiCF3SO3 + Al2O3 incorporating alumina filler grains of four different sizes with different specific surface areas. The results show that the PEO crystallite melting temperature decreased by a few degrees in samples with fillers exhibiting a minimum for samples with high conductivity. The presence of the filler enhanced the ionic conductivity substantially above as well as below 60 °C, and the nano-porous alumina grains with 5.8 nm pore size and 150 m2/g specific area and 15 wt.% filler concentration exhibited the maximum enhancement. The observed conductivity enhancement has been attributed to Lewis acid-base type surface interactions of ionic species with O/OH groups on the filler surface, with an additional contribution below 60 °C coming from the retention of an increased fraction of the amorphous phase due to the presence of the filler. The conductivity versus filler concentration curves exhibit two conductivity maxima which has been explained in terms of the surface interactions, blocking effect and grain consolidation. The conductivity enhancement appears to saturate beyond 100 m2/g grain surface area. © 2003 Elsevier Science B.V. All rights reserved.
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| 6. |
- Escudero, M. J., et al.
(författare)
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Development and performance characterisation of new electrocatalysts for PEMFC
- 2002
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Ingår i: Journal of Power Sources. - 0378-7753 .- 1873-2755. ; 106:1-2, s. 206-214
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Konferensbidrag (refereegranskat)abstract
- New electrocatalysts based on Pt, Pt-Ru and Pt-Pd have been prepared by the microemulsion method. This method allows the production of a very narrow size distribution of metal particles, with an average size smaller than that of conventional electrocatalysts prepared by impregnation. Eight membrane electrode assemblies (MEAs) with an active surface area of 50 cm(2) were characterised in a single fuel cell. The MEAs consist of Nation 117 as membrane and a commercial electrocatalyst (40% Pt/C from E-TEK) on the cathode side, Four MEAs have electrocatalysts prepared by the microemulsion technique and the other four have commercial electrocatalysts on the anode side. The performance of the eight MEAs was evaluated by measuring the fuel cell polarisation curves and the internal resistance with H-2/O-2 and H-2/air, at 60 T and pressure in the range from I to 3 bar. The MEAs with the electrocatalysts prepared by microemulsion showed a performance comparable to that of the MEAs with commercial electrocatalysts. The satisfactory results obtained show that microemulsion is a promising method for the preparation of electrocatalysts for fuel cells. Further effort will be devoted to the optimisation of the method, mainly, the deposition of the metal particles on the carbon support, which it is expected to enhance the fuel cell performance.
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| 7. |
- Fu, Q. X., et al.
(författare)
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Intermediate temperature fuel cells based on doped ceria-LiCl-SrCl2 composite electrolyte
- 2002
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Ingår i: Journal of Power Sources. - 0378-7753 .- 1873-2755. ; 104:1, s. 73-78
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Tidskriftsartikel (refereegranskat)abstract
- A new type of oxide-salt composite electrolyte, gadolinium-doped ceria (GDC)-LiCl-SrCl2, was developed and demonstrated its promising use for intermediate temperature (400-700 degreesC) fuel cells (ITFCs). The dc electrical conductivity of this composite electrolyte (0.09-0.13 S cm(-1) at 500-650 degreesC) was 3-10 times higher than that of the pure GDC electrolyte, indicating remarkable proton or oxygen ion conduction existing in the LiCl-SrCl2 chloride salts or at the interface between GDC and the chloride salts. Using this composite electrolyte, peak power densities of 260 and 510 mW cm(-2), with current densities of 650 and 1250 mA cm(-2) were achieved at 550 and 625 degreesC, respectively. This makes the new material a good candidate electrolyte for future low-cost ITFCs.
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| 8. |
- Georen, P., et al.
(författare)
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On the use of voltammetric methods to determine electrochemical stability limits for lithium battery electrolytes
- 2003
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 124:1, s. 213-220
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Tidskriftsartikel (refereegranskat)abstract
- In previous studies a novel amphiphilic co-polymer was developed for use in lithium-ion batteries. In order to evaluate the electrochemical stability of that electrolyte and compare it with others, a voltammetric method was applied on a set of electrolytes with different salts, solvents and polymers. However, initially the voltammetric methodology was studied. Platinum was found to be the most suited electrode material, experiencing no significant interfering reactions and a proper diffusion-controlled kinetic behaviour when sweep rate was varied. Furthermore, the influence on the voltammograms of adding water traces to the electrolytes was studied. It could be established that the oxidation peak around 3.8 V versus Li was related to water reactions. It was concluded that quantitative voltage values of the stability limits were difficult to assess using voltammetry. On the other hand, the method seemed well suited for comparison of electrolytes and to investigate the influences of electrolyte components on the stability. The voltammetric results varied little between the different electrolytes evaluated and the anodic and cathodic limits, as defined here, were in the range of I and 4.5 V vs. Li, respectively. Although the novel polymer did not affect the stability limit significantly it seemed to promote the breakdown reaction rate in all electrolytes tested. Furthermore, the use of LiTFSI salt reduced the stability window.
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| 9. |
- Herstedt, Marie, et al.
(författare)
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Rate capability of natural graphite as anode material in Li-ion batteries
- 2003
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Ingår i: Journal of Power Sources. - 0378-7753 .- 1873-2755. ; 124:1, s. 191-196
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Tidskriftsartikel (refereegranskat)abstract
- Jet-milled natural Swedish graphite has been evaluated as an anode material for Li-ion battery applications, with a focus on rate capability of the material. The material was found to have a superior rate capability compared to other carbon materials with similar particle sizes. It could also intercalate and deintercalate lithium reversibly in an electrolyte based on propylene carbonate:ethylene carbonate (1:1). Jet-milling was found to increase the amount of rhombohedral phase (3R) in the material from 15 to 40%. However, after repeated electrochemical intercalation and deintercalation of lithium, the amount of 3R phase decreases to ~5%. Neither rate capability nor PC-tolerance can therefore be correlated to the amount of 3R phase.
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| 10. |
- Kiros, Yohannes, 1956-, et al.
(författare)
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Cobalt and cobalt-based macrocycle blacks as oxygen-reduction catalysts in alkaline fuel cells
- 1993
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Ingår i: Journal of Power Sources. - 0378-7753 .- 1873-2755. ; 45:2, s. 219-227
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Tidskriftsartikel (refereegranskat)abstract
- The electrochemical reduction of oxygen on high surface are carbons catalyzed by cobalt and pyrolyzed macrocycles has been studied in alkaline fuel cells. Tests were also carried out with 'green black', i.e., pyrolyzed phyto-biomass. Galvanostatic polarization curves show that cobalt from cobalt acetate and fine cobalt metal power exhibit a high catalytic activity. The activity of pyrolyzed cobalt tetraphenylporphyrin (CoTPP) is due to the combined effects of the cobalt additive and the charred residue of the macrocycle. 'Green black', with chlorophyll as macrocycle black precursor, has a similar effect. The dissolution of cobalt from the electrode surface has been established. Life tests with these electrodes are reported. © 1993.
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