| 1. |
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| 2. |
- Carlson, Annika, et al.
(författare)
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Kinetic parameters in anion-exchange membrane fuel cells
- 2019
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Ingår i: ECS Transactions. - : Electrochemical Society Inc.. - 1938-6737 .- 1938-5862. - 9781607685395 ; , s. 649-659
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Konferensbidrag (refereegranskat)abstract
- Understanding limitations in an operating AEMFC is essential to .enhance the technology. Here the electrode processes are studied experimentally as well as by two physics-based models taking the porosity of the electrodes into account. The aim is to use the models to determine kinetic parameters specific for in-situ operation. The models can also be used to explain the experimental .behavior. From the impedance model of a symmetric H2/H2 cell it is shown that the hydrogen oxidation reaction (HOR) proceeds through the Tafel-Volmer reaction pathway, with the hydrogen adsorption as the slower reaction step. Based on the HOR model a •steady-state model of an O2/H2 cell is used to evaluate data from 14 experimental I-V curves, obtained for different gas partial pressures and catalyst loadings, in order to study the effects of the oxygen reduction reaction and overall cell limitations. The results show that the oxygen reduction reaction kinetics limit the cell performance for low current densities. However, at higher currents the uneven current distribution and locally low hydrogen adsorption at the anode increasingly affect the overall performance. Uneven current distribution is also observed at the cathode and likely caused by insufficient effective ionomer conductivity.
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| 3. |
- Carlson, Annika, et al.
(författare)
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The Hydrogen Electrode Reaction in the Anion Exchange Membrane Fuel Cell
- 2021
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 168:3
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Tidskriftsartikel (refereegranskat)abstract
- The hydrogen electrode in the anion-exchange membrane fuel cell needs further attention to understand the overall cell limitations. In this study, electrochemical impedance spectroscopy and galvanodynamic measurements in combination with a physics-based model are used to determine the kinetic parameters of the hydrogen oxidation reaction and hydrogen evolution reaction on Pt/C porous gas-diffusion electrodes in an AEMFC. Two semicircles are observed in the Nyquist plot of a symmetrical AEM hydrogen cell, indicating a two-step reaction pathway. The fit of the model shows that the Tafel-Volmer pathway describes the kinetics better than the Heyrovsky-Volmer pathway. The reaction rates of the adsorption and charge transfer steps are similar in magnitude implying that both need consideration during modeling and evaluation of the hydrogen electrode. Furthermore, the performance is limited also by the ionic conductivity in the electrode. Comparison of the impedance of the HOR and a hydrogen/oxygen AEMFC indicates that the low-frequency semicircle is mainly associated with the oxygen reduction reaction and the cathode, while the high-frequency semicircle is likely related to a combination of the anode and the cathode. Based on this work, a platform for further studies of losses and total impedance of operating AEMFC has been created.
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| 4. |
- Eriksson, Björn, et al.
(författare)
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Quantifying water transport in anion exchange membrane fuel cells
- 2019
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Ingår i: International journal of hydrogen energy. - : Elsevier. - 0360-3199 .- 1879-3487. ; 44:10, s. 4930-4939
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Tidskriftsartikel (refereegranskat)abstract
- Sufficient water transport through the membrane is necessary for a well-performing anion exchange membrane fuel cell (AEMFC). In this study, the water flux through a membrane electrode assembly (MEA), using a Tokuyama A201 membrane, is quantified using humidity sensors at the in- and outlet on both sides of the MEA. Experiments performed in humidified inert gas at both sides of the MEA or with liquid water at one side shows that the aggregation state of water has a large impact on the transport properties. The water fluxes are shown to be approximately three times larger for a membrane in contact with liquid water compared to vaporous. Further, the flux during fuel cell operation is investigated and shows that the transport rate of water in the membrane is affected by an applied current. The water vapor content increases on both the anode and cathode side of the AEMFC for all investigated current densities. Through modeling, an apparent water drag coefficient is determined to −0.64, indicating that the current-induced transport of water occurs in the opposite direction to the transport of hydroxide ions. These results implicate that flooding, on one or both electrodes, is a larger concern than dry-out in an AEMFC.
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| 5. |
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| 6. |
- Grimler, Henrik, et al.
(författare)
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Determination of Kinetic Parameters for the Oxygen Reduction Reaction on Platinum in an AEMFC
- 2021
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 168:12, s. 124501-
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Tidskriftsartikel (refereegranskat)abstract
- To promote the development of anion exchange membrane fuel cells (AEMFC), an understanding of the oxygen reduction reaction (ORR) kinetics in porous gas diffusion electrodes is essential. In this work, experimental polarisation curves for electrodes with different platinum catalyst loadings and oxygen partial pressures at the cathode are fitted to a physics-based porous electrode model in the voltage range from open circuit voltage (OCV) to 0.7 V. Polarisation curves measured with different anode catalyst loadings, and hydrogen partial pressures, were used to verify the model. The reactions are described using a two-step Tafel-Volmer pathway at the anode and concentration-dependent Butler-Volmer kinetics at the cathode. A good fit to experimental data in the kinetic region is obtained with an exchange current density of 1.0.10(-8)Acm(-2), a first order dependency on oxygen partial pressure, and a charge transfer coefficient of 0.8 for the ORR. For lower oxygen partial pressure, hydrogen crossover is needed to explain the downward shift of the polarisation curves in the kinetic region. In the experimental data, the polarisation curves show an apparent limiting current density at lower hydrogen partial pressures, explained by the lower rate of the Tafel step at these conditions.
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| 7. |
- Grimler, Henrik, et al.
(författare)
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Modelling electrode and membrane processes in an anion-exchange membrane fuel cell
- 2017
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Ingår i: EFC 2017 - Proceedings of the 7th European Fuel Cell Piero Lunghi Conference. - : ENEA. ; , s. 127-128
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Konferensbidrag (refereegranskat)abstract
- To better understand which processes that limits the performance in an anion-exchange membrane fuel cell (AEMFC), a physical performance model has been developed. The model considers a tertiary current distribution and is validated against experimental results. The results show that both the anode and the cathode contributes to significant polarisation in the system.
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| 8. |
- Grimler, Henrik, et al.
(författare)
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Water diffusion, drag and absorption in an anion-exchange membrane fuel cell
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Water is a key factor in anion-exchange membrane fuel cells, since it is botha product, reactant, and humidifies the membrane and ionomer phase. Toenable anion-exchange membrane fuel cells, knowledge about the water trans-port properties is needed, so that operating conditions can be optimised toprevent cathode dry-out or anode flooding. In this work, the water trans-port across an AemionTM membrane is quantified for different applied waterpartial pressure differences and current densities, with the help of humiditysensors. Two membrane thicknesses, 25 and 50 μm, are studied, as well astwo gas diffusion layers of different hydrophobicity: Sigracet 25BC which hasbeen PTFE treated to make it more hydrophobic, and Freudenberg H23C2which has not been PTFE treated, and is hence more hydrophilic. The re-sults show that having a hydrophilic GDL on the cathode and a hydrophobicGDL on the anode gives both the highest electrochemical performance, andthe highest water transport, while a hydrophilic GDL on both sides give thelowest electrochemical performance and the lowest water transport. A wa-ter transport model considering absorption/desorption resistance, electroos-motic drag and diffusion was deployed. The best fit was obtained with adrag coefficient close to two and 30 % increased absorption/desorption ratefor a hydrophobic GDL compared to a hydrophilic one.
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| 9. |
- Grimler, Henrik
(författare)
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Limiting processes in anion-exchange membrane fuel cells
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fuel cells allow for converting chemical energy stored in hydrogen into electrical energy, with only heat and water as by-products. In a sustainable energy society, hydrogen may play an important role due to its ability to act both as an energy carrier and as a valuable chemical in the process industry. The main remaining obstacles for widely available commercial fuel cells are durability and cost. One way to potentially decrease the cost is to change the fuel cell environment to an alternative chemistry by replacing the proton-exchange membrane (PEM) with an anion-exchange membrane (AEM). This thesis studies the anode reaction, the cathode reaction and water transport in an anion-exchange membrane fuel cell (AEMFC), to investigate where its performance limitations lies in the system. Electrochemical characterisation techniques together with physics-based modelling have been utilised.The results from the study of the anode, shows that the hydrogen reaction proceeds through the Tafel-Volmer pathway, with the Tafel step starting to limit the reaction as the anode overpotential increases. Combining the anode model with a Butler-Volmer expression for the cathode reaction made it possible to model a H2:O2 fuel cell. Comparing the losses from the different processes in the fuel cell shows that the cathode is still the main contributor, but that the anode contribution cannot be neglected when predicting the fuel cell performance. Low ionic conductivity in the electrode was also identified as responsible for part of the overall resistances, leading to uneven current distribution in the catalyst layers and bad utilisation of the catalytic material.Investigating the water transport properties of AEMs showed that not only electroosmotic drag and diffusion, but also an absorption/desorption step between gas phase and membrane phase, are necessary to get a model that can explain the experimental observations. The choice of gas diffusion layers (GDLs) used on the anode and cathode was found to be of similar importance on the water transport as doubling the membrane thickness, showing that not only the membrane is important for water transport. Under most realistic conditions, the risk of local dry-out in a cell was found to be low, as water readily diffuses from the high humidity side of the membrane to the low humidity side.
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| 10. |
- 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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| 11. |
- Suewatanakul, Siwat, et al.
(författare)
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Conceptual Design of a Hybrid Hydrogen Fuel Cell/Battery Blended-Wing-Body Unmanned Aerial Vehicle—An Overview
- 2022
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Ingår i: Aerospace. - : MDPI AG. - 2226-4310. ; 9:5, s. 275-275
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Tidskriftsartikel (refereegranskat)abstract
- The manuscript presents the conceptual design phase of an unmanned aerial vehicle, withthe objective of a systems approach towards the integration of a hydrogen fuel-cell system and Li-ionbatteries into an aerodynamically efficient platform representative of future aircraft configurations.Using a classical approach to aircraft design and a combination of low- and high-resolution computationalsimulations, a final blended wing body UAV was designed with a maximum take-off weightof 25 kg and 4 m wingspan. Preliminary aerodynamic and propulsion sizing demonstrated that theaircraft is capable of completing a 2 h long mission powered by a 650Wfuel cell, hybridized with a100 Wh battery pack, and with a fuel quantity of 80 g of compressed hydrogen.
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