| 1. |
- Lindberg, Jonas, et al.
(författare)
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The effect of O2 concentration on the reaction mechanism in Li-O2 batteries
- 2017
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Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657 .- 0022-0728 .- 1873-2569. ; 797, s. 1-7
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Tidskriftsartikel (refereegranskat)abstract
- The promising lithium-oxygen battery chemistry presents a set of challenges that need to be solved if commercialization is ever to be realized. This study focuses on how the O2 reaction path is effected by the O2 concentration in the electrolyte. An electrochemical quartz crystal microbalance system was used to measure current, potential, and change in electrode mass simultaneously. It is concluded that the mass reversibility is O2 concentration dependent while the coulombic efficiency is not. The mass reversibility is higher at low O2 concentration meaning that more of the deposited Li2O2 is removed during oxidation in relation to the amount deposited during reduction. The first step of the reduction is the formation of soluble LiO2, which is then either reacting further at the electrode or being transported away from the electrode resulting in low current efficiency and low deposited mass per electrons transferred. During the oxidation, the first step involves de-lithiation of Li2O2 at low potential followed by bulk oxidation. The oxidation behavior is O2 concentration dependent, and this dependence is likely indirect as the O2 concentration effects the amount of discharge product formed during the reduction. The O2 concentration at different saturation pressures was determined using a mass spectrometer. It was found that the electrolyte follows Henry's law at the pressures used in the study. In conclusion, this study provides insight to the O2 concentration dependence and the preferred path of the O2 electrochemical reactions in lithium-oxygen batteries.
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| 2. |
- Marra, Eva, et al.
(författare)
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Oxygen reduction reaction kinetics on a Pt thin layer electrode in AEMFC
- 2022
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 435, s. 141376-141376
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Tidskriftsartikel (refereegranskat)abstract
- The study of the catalytic activity in a fuel cell is challenging, as mass transport, gas crossover and the counterelectrode are generally interfering. In this study, a Pt electrode consisting of a thin film deposited on the gasdiffusion layer was employed to study the oxygen reduction reaction (ORR) in an operating Anion Exchange Membrane Fuel Cell (AEMFC). The 2D Pt electrode was assembled together with a conventional porous Pt/Ccounter electrode and an extra Pt/C layer and membrane to reduce the H2 crossover. Polarization curves atdifferent O2 partial pressures were recorded and the resulting reproducible ORR activities were normalized withrespect to the active surface area (ECSA), obtained by CO stripping. As expected, decreasing the O2 partialpressure results in a negative shift in open circuit voltage (OCV), cell voltage and maximum attainable currentdensity. For cell voltages above 0.8 V a fairly constant Tafel slope of 60 mV dec−1 was recorded but at lowervoltages the slope increases rapidly. The observed Tafel slope can be explained by a theoretical model with anassociative mechanism where charge- and proton-transfer steps are decoupled, and the proton transfer is the rate-determining step. A reaction order of 1 with respect to O2 was obtained at 0.65 V which corresponds well withthe mechanism suggested above. Based on the obtained catalyst activities, the electrode performance is comparable to good porous electrodes found in the field. The methodology presented in this study is expected to beuseful in future kinetic studies of other catalysts for AEMFC.
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| 3. |
- Lindahl, Niklas, 1981, et al.
(författare)
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Fuel Cell Measurements with Cathode Catalysts of Sputtered Pt3Y Thin Films
- 2018
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Ingår i: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 11:9, s. 1438-1445
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Tidskriftsartikel (refereegranskat)abstract
- Fuel cells are foreseen to have an important role in sustainable energy systems, provided that catalysts with higher activity and stability are developed. In this study, highly active sputtered thin films of platinum alloyed with yttrium (Pt 3 Y) are deposited on commercial gas diffusion layers and their performance in a proton exchange membrane fuel cell is measured. After acid pretreatment, the alloy is found to have up to 2.5 times higher specific activity than pure platinum. The performance of Pt 3 Y is much higher than that of pure Pt, even if all of the alloying element was leached out from parts of the thin metal film on the porous support. This indicates that an even higher performance is expected if the structure of the Pt 3 Y catalyst or the support could be further improved. The results show that platinum alloyed with rare earth metals can be used as highly active cathode catalyst materials, and significantly reduce the amount of platinum needed, in real fuel cells.
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| 4. |
- Acevedo Gomez, Yasna, et al.
(författare)
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Effect of nitrogen dioxide impurities on PEM fuel cell performance
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Air is the most practical and economical oxidant to feed to the cathode in a proton exchange membrane fuel cell (PEMFC). However, the air is accompanied by small amounts of impurities that affect the performance of the fuel cell. Among these, nitrogen dioxide is the impurity that has been least investigated, and its effect is not fully understood. In this study, a possible mechanism is proposed based on the contamination of the fuel cell at different concentrations and adsorption potentials, and by employing stripping cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The results at different concentrations showed that the catalyst sites are blocked by the adsorption of NO2, and that there is a non-linear relationship between the concentration and degradation. The degradation is suggested to be related to the formation of intermediate species, as also shown by the pseudo-inductive impedance at the concentration of 100 and 200 ppm. Furthermore, the cyclic voltammetry showed that there is an oxidation to NO3- at 1.05 V, followed by the reduction of this specie to NO2- at 0.68 V, and a subsequent reduction of NO2- to N2O and/or NH2OH.
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| 5. |
- Acevedo Gomez, Yasna
(författare)
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On Gas Contaminants, and Bipolar Plates in Proton Exchange Membrane Fuel Cells
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The proton exchange membrane (PEM) fuel cell is an electrochemical device that converts chemical energy into electrical energy through two electrocatalytic reactions. The most common catalyst used is platinum on carbon (Pt/C), which has shown the best performance in the fuel cell until now. However, the drawback of this catalyst is that it does not tolerate impurities, and both hydrogen and oxygen may carry small amounts of impurities depending on the production sources. The purpose of this thesis is to understand the effect of two impurities that are less investigated, i.e., ammonia, which may accompany the hydrogen rich reformates from renewable sources, and nitrogen dioxide, which may come from air pollution. The mechanism of contamination and an adequate recovery method for the respective contaminant are studied. Additionally, electroplated bipolar plates with Ni-Mo and Ni-Mo-P coatings were tested as alternatives to stainless steel and carbon materials.The results show that ammonia not only provokes changes in the polymer membrane but also in the oxygen reduction reaction (ORR), hydrogen oxidation reaction (HOR) and catalyst ionomer in both electrodes. The extent of performance recovery after the contamination depends on the concentration used and the exposure time. In contrast, nitrogen dioxide affects the catalyst in the electrode directly; the contamination is related to side reactions that are produced on the catalyst’s surface. However, NO2 is not attached strongly to the catalyst and it is possible to restore the performance by using clean air. The time the recovery process takes depends on the potential applied and the air flow.Finally, the evaluation of electroplated Ni-Mo and Ni-Mo-P on stainless steel by ex situ and in situ studies shows that these coatings reduce the internal contact resistance (ICR) and the corrosion rate of the stainless steel considerably. However, the in situ experiments show that phosphorus addition to the coating does not improve the fuel cell performance; thus, the Ni-Mo alloy is found to be a promising choice for electroplating stainless steel bipolar plates.
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| 6. |
- Acevedo Gomez, Yasna, et al.
(författare)
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Performance recovery after contamination with nitrogen dioxide in a PEM fuel cell
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- While the market of fuel cell vehicles is increasing, these vehicles will still coexist with combustion engine vehicles on the roads and will be exposed to an environment with significant amounts of contaminants that will decrease the durability of the fuel cell. In order to investigate different recovery methods, a PEM fuel cell is in this study contaminated with 100 ppm of NO2 at the cathode side. The possibility to recover the cell performance is studied by using different airflow rates, different current densities, and by subjecting the cell to successive polarization curves. The results show that the successive polarization curves are the best choice for recovery; it took 35 min to reach full recovery of cell performance, compared to 4.5 hours of recovery with pure air at 0.5 A cm-2 and 110 ml min-1. However, the performance recovery at a current density of 0.2 A cm-2 and air flow 275 ml min-1 was done in 66 min, which is also a possible alternative. Additionally, two operation techniques are suggested and compared during 7 h of operation; air recovery and air depletion. The air recovery technique shows to be a better choice than the air depletion technique.
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| 7. |
- Acevedo Gomez, Yasna, et al.
(författare)
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Performance Recovery after Contamination with Nitrogen Dioxide in a PEM Fuel Cell
- 2020
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Ingår i: Molecules. - : MDPI. - 1431-5157 .- 1420-3049. ; 25:5
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Tidskriftsartikel (refereegranskat)abstract
- While the market for fuel cell vehicles is increasing, these vehicles will still coexist with combustion engine vehicles on the roads and will be exposed to an environment with significant amounts of contaminants that will decrease the durability of the fuel cell. To investigate different recovery methods, in this study, a PEM fuel cell was contaminated with 100 ppm of NO2 at the cathode side. The possibility to recover the cell performance was studied by using different airflow rates, different current densities, and by subjecting the cell to successive polarization curves. The results show that the successive polarization curves are the best choice for recovery; it took 35 min to reach full recovery of cell performance, compared to 4.5 h of recovery with pure air at 0.5 A cm(-2) and 110 mL min(-1). However, the performance recovery at a current density of 0.2 A cm(-2) and air flow 275 mL min(-1) was done in 66 min, which is also a possible alternative. Additionally, two operation techniques were suggested and compared during 7 h of operation: air recovery and air depletion. The air recovery technique was shown to be a better choice than the air depletion technique.
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| 8. |
- Asp, Leif, 1966, et al.
(författare)
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A structural battery and its multifunctional performance
- 2021
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Ingår i: Advanced Energy and Sustainability Research. - : Wiley. - 2699-9412. ; 2:3
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Tidskriftsartikel (refereegranskat)abstract
- Engineering materials that can store electrical energy in structural load paths can revolutionize lightweight design across transport modes. Stiff and strong batteries that use solid-state electrolytes and resilient electrodes and separators are generally lacking. Herein, a structural battery composite with unprecedented multifunctional performance is demonstrated, featuring an energy density of 24 Wh kg-1 and an elastic modulus of 25 GPa and tensile strength exceeding 300 MPa. The structural battery is made from multifunctional constituents, where reinforcing carbon fibers (CFs) act as electrode and current collector. A structural electrolyte is used for load transfer and ion transport and a glass fiber fabric separates the CF electrode from an aluminum foil-supported lithium–iron–phosphate positive electrode. Equipped with these materials, lighter electrical cars, aircraft, and consumer goods can be pursued.
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| 9. |
- Asp, Leif, 1966, et al.
(författare)
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Structural Battery Composites: A Review, Functional Composites and Structures
- 2019
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Ingår i: Functional Composites and Structures. - : IOP Publishing. - 2631-6331. ; 1
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Forskningsöversikt (refereegranskat)abstract
- This paper presents a comprehensive review of the state-of-the-art in structural battery composites research. Structural battery composites are a class of structural power composites aimed to provide mass-less energy storage for electrically powered structural systems. Structural battery composites are made from carbon fibres in a structural electrolyte matrix material. Neat carbon fibres are used as a structural negative electrode, exploiting their high mechanical properties, excellent lithium insertion capacity and high electrical conductivity. Lithium iron phosphate coated carbon fibres are used as the structural positive electrode. Here, the lithium iron phosphate is the electrochemically active substance and the fibres carry mechanical loads and conduct electrons. The surrounding structural electrolyte is lithium ion conductive and transfers mechanical loads between fibres. With these constituents, structural battery half-cells and full-cells are realised with a variety in device architecture. The paper also presents an overview of material modelling and characterisation performed to date. Particular reference is given to work performed in national and European research projects under the leadership of the authors, who are able to provide a unique insight into this emerging and exciting field of research.
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| 10. |
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