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| 2. |
- Eiler, Konrad, et al.
(author)
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Oxygen reduction reaction and proton exchange membrane fuel cell performance of pulse electrodeposited Pt–Ni and Pt–Ni–Mo(O) nanoparticles
- 2022
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In: Materials Today Energy. - : Elsevier Ltd. - 2468-6069. ; 27
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Journal article (peer-reviewed)abstract
- Proton exchange membrane fuel cells (PEMFCs) are an important alternative to fossil fuels and a complement to batteries for the electrification of vehicles. However, their high cost obstructs commercialization, and the catalyst material, including its synthesis, constitutes one of the major cost components. In this work, Pt–Ni and Pt–Ni–Mo(O) nanoparticles (NPs) of varying composition have been synthesized in a single step by pulse electrodeposition onto a PEMFC's gas diffusion layer. The proposed synthesis route combines NP synthesis and their fixation onto the microporous carbon layer in a single step. Both Pt–Ni and Pt–Ni–Mo(O) catalysts exhibit extremely high mass activities at oxygen reduction reaction (ORR) with very low Pt loadings of around 4 μg/cm2 due to the favorable distribution of NPs in contact with the proton exchange membrane. Particle sizes of 40–50 nm and 40–80 nm were obtained for Pt–Ni and Pt–Ni–Mo(O) systems, respectively. The highest ORR mass activities were found for Pt67Ni33 and Pt66Ni32–MoOx NPs. The feasibility of a single-step electrodeposition of Pt–Ni–Mo(O) NPs was successfully demonstrated; however, the ternary NPs are of more amorphous nature in contrast to the crystalline, binary Pt–Ni particles, due to the oxidized state of Mo. Nevertheless, despite their heterogeneous nature, the ternary NPs show homogeneous behavior even on a microscopic scale. © 2022 The Author(s)
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| 4. |
- Mölmen, Live, et al.
(author)
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Contact resistance measurement methods for PEM fuel cell bipolar plates and power terminals
- 2023
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In: Journal of Power Sources. - : Elsevier B.V.. - 0378-7753 .- 1873-2755. ; 555
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Journal article (peer-reviewed)abstract
- The electrical contact resistance is a key parameter for optimising both the bipolar plate of the polymer electrolyte membrane fuel cell (PEMFC) and the electrical contact of the power terminal of the stack. The contact resistance is affected by the conductivity, roughness, and hardness of the two contacting surfaces. Here, new, application-specific contact resistance measurement methods are proposed for both the stack power terminal, and the bipolar plate. The proposed methods are compared to methods from references as well as standards, and it is concluded that the uncertainty of the measurements can be reduced by changing the measurement setup, and that the influence of probe resistance on measurement results can be eliminated. Furthermore, the effect of different accelerated durability tests on the contact resistance of the power terminal is examined both on test coupons and on a prototype screw connection with an electroless NiP and an electroplated NiSn coatings. As expected, the NiSn coupons gives lower contact resistance after ageing as compared to the NiP. However, the increase in contact resistance seen on coupons after ageing is not observed on the prototype screw connection. © 2022 The Author(s)
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| 8. |
- Mølmen, Live
(author)
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Durability evaluation of PEM fuel cell components
- 2023
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Doctoral thesis (other academic/artistic)abstract
- Proton exchange membrane fuel cells (PEMFCs) are used to convert hydrogen and oxygen to electricity, heat, and water. There are no greenhouse gas emissions, given that the hydrogen is produced from renewable sources, such as water electrolysis from wind, hydro or solar energy. PEMFCs can be found on the commercial market today, predominantly in applications such as forklifts, passenger cars and combined heat and power units. The PEMFC is a new technology, and there are hurdles to overcome, mainly with regard to price and durability.In this work, two PEMFC components are the main focus: the bipolar plate and the catalyst. For the bipolar plate, the effect of defects from fabrication is investigated to further understand the critical factors for corrosion and how to avoid it. Droplets from laser cutting and cracks in the coating due to the forming of pre-coated plates are both identified as possible sources of corrosion. However, by correct design, both can be avoided or made less critical. Laser welding stainless steel 304 is, on the other hand, found not to be a source of corrosion under simulated PEMFC bipolar plate conditions. Furthermore, tailoring the properties of a multicomponent alloy coating by additions of Ta and W is explored to stabilise the coating at higher potentials in the acidic environment of the PEMFC. Ta is found to achieve a protective passive layer at a lower concentration than W. However, it does significantly increase the interfacial contact resistance. One-step synthesis of a ternary alloy by electrodeposition is studied for the catalyst to allow for facile screening of new alloy compositions, both in- and ex-situ. The ternary alloy gives comparable results to the binary alloy even at lower Pt content.As the PEMFC has entered the commercial market relatively quickly, there is a lack of standardised tests, both on the component and system level. The procedure for testing the interfacial contact resistance of the bipolar plate is studied in detail, and the methodology is further developed to ensure reliable and comparable results.
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| 9. |
- Mölmen, Live, et al.
(author)
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Investigation of feed water impurities on life-time of PEMWE
- 2019
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Conference paper (other academic/artistic)abstract
- With the introduction of fuel cell electric vehicles (FCEV), hydrogen gas produced without fossil fuels Is requiredto reduce the CO2 emissions. At the same time, the production of renewable energy is increasing. Waterelectrolysis to produce hydrogen with the use of electricity from renewable sources allows for storage of theenergy in the form of hydrogen. The gas can be utilized either back to the electric net or as fuel for FCEVs.However, the cost of water electrolysis systems needs to be reduced while the lifetime must be increased. Oneof the main limitations of the proton exchange membrane water electrolyser (PEMWE) system is the degradationof the membrane1. This limits the lifetime of the system and is expensive to replace. It has been shown thatimpurities from feed water and the degradation products from other component poison the membrane, loweringthe proton conductivity. Furthermore, metal ion impurities catalyse the formation of hydrogen peroxide at thecathode further contributing to irreversible membrane thinning2. In industrial systems, the water circulated tothe cells is purified to minimize the degradation. However, the purification limits the operating temperature ofthe systems and increases the total system cost2.The water quality used in most electrolysis cells today utilises ASTM type II deionized water. However, littleresearch is done on the limitations, and quantifying the reduction in efficiency dependent on the water quality.Dedigama et al.3 calculated the minimum flow needed, and further state that in industry, 5 times the necessaryflow of water is circulated to ensure proper wetting of the membrane. However, in research, an excess of wateris often used, up to 100 times higher flow than required, to exclude mass transport restrictions on thereactions3,4.Increasing temperature decreases the kinetic overpotential and increases the membrane conductivity4.However, also dissolution of the catalyst and degradation of the cell components increase with temperature.Furthermore, in industrial applications the maximum temperature of the water into the purification system is60°C5. Dependent on the aim of the research, experiments at temperatures as low as 25°C are performed to fitwith the industry, while others run at 80 or 90°C to probe the upper limits of current density and efficiency2.In this project we aim to analyse the effect of varying water purity on the membrane degradation in a single PEMelectrolysis cell test setup. Furthermore, the effect of changing temperature from 60 to 80°C on the impuritytolerance will be studied. The circulating feed water will be analysed with respect to conductivity, metal ion andfluorine concentration. A parallel “blank” system with only tubings, fittings etc will be assembled and comparedto the data measured from the electrolyser. Contaminating species will be added to the feed water to study theirimpact.
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| 10. |
- Mølmen, Live
(author)
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Materials Reliability in PEM Fuel Cells
- 2021
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Licentiate thesis (other academic/artistic)abstract
- As part of the global work towards reducing CO2 emissions, all vehicles needs to be electrified, or fueled by green fuels. Batteries have already revolutionised the car market, but fuel cells are believed to be a key energy conversion system to be able to electrify also heavy duty vehicles. The type of fuel cell commercially available for vehicles today is the polymer electrolyte membrane fuel cell (PEMFC), but for it to be able to take a larger market share, the cost must be reduced while sufficient lifetime is ensured.The PEMFC is a system containing several components, made of different materials including the polymer membrane, noble metal catalyst particles, and metallic bipolar plate. The combination of different materials exposed to elevated temperature, high humidity and low pH make the PEMFC components susceptible to corrosion and degradation.The noble metal catalyst is one of the major contributors to the high cost. In this work, the latest research on new catalyst materials for PEMFCs are overviewed. Furthermore, electrodeposition as a simple synthesis route to test different Pt-alloys for the cathode catalyst in the fuel cell is explored by synthesis of PtNi and PtNiMo. The gas diffusion layer of the PEMFC is used as substrate to reduce the number of steps to form the membrane electrode assembly.In addition to cheaper and more durable materials, understanding of how the materials degrade, and how the degradation affects the other components is crucial to ensure a long lifetime. Finding reliable test methods to validate the lifetime of the final system is necessary to make fuel cell a trusted technology for vehicles, with predictable performance.In this work, commercial flow plates are studied, to see the effect of different load cycles and relative humidities on the corrosion of the plate. Defects originating from production is observed, and the effect of these defects on the corrosion is further analysed. Suggestions are given on how the design and production of bipolar plates should be made to reduce the risk of corrosion in the PEMFC.
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