| 1. |
- Acevedo Gomez, Yasna, et al.
(författare)
-
Effect of nitrogen dioxide impurities on PEM fuel cell performance
-
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.
|
|
| 2. |
- Acevedo Gomez, Yasna
(författare)
-
On Gas Contaminants, and Bipolar Plates in Proton Exchange Membrane Fuel Cells
- 2019
-
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.
|
|
| 3. |
- Acevedo Gomez, Yasna, et al.
(författare)
-
Performance recovery after contamination with nitrogen dioxide in a PEM fuel cell
-
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.
|
|
| 4. |
- Acevedo Gomez, Yasna, et al.
(författare)
-
Performance Recovery after Contamination with Nitrogen Dioxide in a PEM Fuel Cell
- 2020
-
Ingår i: Molecules. - : MDPI. - 1431-5157 .- 1420-3049. ; 25:5
-
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.
|
|
| 5. |
- Acevedo Gomez, Yasna, et al.
(författare)
-
Reformate from biogas used as fuel in a PEM fuel cell
- 2013
-
Ingår i: EFC 2013 - Proceedings of the 5th European Fuel Cell Piero Lunghi Conference. ; , s. 163-164
-
Konferensbidrag (refereegranskat)abstract
- The performance of a PEM fuel cell can be easily degraded by introducing impurities in the fuel gas. Since reformate of biogas from olive mill wastes will contain at least one third of carbon dioxide, its influence was studied on a PtRu catalyst. A clean reformate gas for the anode (67% H2 and 33% CO2) without any traces of other compounds was used and electrochemical measurements showed that the performance of the fuel cell was hardly affected. However, diluting the hydrogen with higher amounts of CO2 will reduce the performance remarkably.
|
|
| 6. |
- Benamira, M., et al.
(författare)
-
Behaviour of Gadolinia-doped ceria mixed with alkali carbonates in view of SOFC applications
- 2009
-
Ingår i: EFC 2009 - Piero Lunghi Conference, Proceedings of the 3rd European Fuel Cell Technology and Applications Conference. - 9788882862114 ; , s. 197-198
-
Konferensbidrag (refereegranskat)abstract
- Composite materials based on mixtures of gadolinia-doped ceria and alkali carbonate salts were developed and analyzed for their use as electrolyte materials in low-temperature solid oxide fuel cells (LT-SOFCs). Cycling and ageing studies showed a good chemical stability of the composite material. A high and stable conductivity value (0,66 S.cm-1) was obtained all over a test of about 1600 hours at 600°C.
|
|
| 7. |
- Benamira, M., et al.
(författare)
-
Gadolinia-doped ceria mixed with alkali carbonates for SOFC applications : II - An electrochemical insight
- 2012
-
Ingår i: International journal of hydrogen energy. - : Elsevier BV. - 0360-3199 .- 1879-3487. ; 37:24, s. 19371-19379
-
Tidskriftsartikel (refereegranskat)abstract
- Composite materials based on gadolinia-doped ceria (GDC) and alkali carbonates (Li2CO3-K2CO3 or Li2CO3-Na2CO3) are potential electrolytes for low temperature solid oxide fuel cell applications (LTSOFC). This paper completes a first one dedicated to the thermal, structural and morphological study of such compounds; it is fully focussed on their electrical/electrochemical properties in different conditions, temperature, composition and gaseous atmosphere (oxidative or reductive). The influence of the gaseous composition on the Arrhenius conductivity plots is evidenced, in particular under hydrogen atmosphere. Finally, electrical conductivity determined by impedance spectroscopy is presented as a function of time to highlight the stability of such composites over 6000 h. First results on single cells showed performance at 600 degrees C of 60 mW cm(-2).
|
|
| 8. |
- Benamira, M., et al.
(författare)
-
Gadolinia-doped ceria mixed with alkali carbonates for solid oxide fuel cell applications : I. A thermal, structural and morphological insight
- 2011
-
Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 196:13, s. 5546-5554
-
Tidskriftsartikel (refereegranskat)abstract
- Ceria-based composites are developed and considered as potential electrolytes for intermediate solid oxide fuel cell applications (ITSOFC). After giving a survey of the most relevant results in the literature, the structural, thermal and morphological properties of composite materials based on gadolinia-doped ceria (GDC) and alkali carbonates (Li2CO3-K2CO3 or Li2CO3-Na2CO3) are carefully examined. Thermal analyses demonstrate the stability of the composite with very low weight losses of both water and CO2 during thermal cycling and after 168 h ageing. High-temperature and room-temperature X-ray diffraction allowed determining the precise structure of the composite and its regular and reversible evolution with the temperature. The microstructure and morphology of electrolyte pellets, as observed by scanning electron microscopy (SEM), show two-well separated phases: nanocrystals of GDC and a well-distributed carbonate phase. Finally, electrical conductivity determined by impedance spectroscopy is presented as a function of time to highlight the stability of such composites over 1500h.
|
|
| 9. |
- Benamira, M., et al.
(författare)
-
Structural and Electrical Properties of Gadolinia-doped Ceria Mixed with Alkali Earth Carbonates for SOFC Applications
- 2007
-
Ingår i: SOLID OXIDE FUEL CELLS 10 (SOFC-X), PTS 1 AND 2. - : The Electrochemical Society. - 9781566775540 ; , s. 2261-2268
-
Konferensbidrag (refereegranskat)abstract
- The properties of composite materials based on mixtures of gadolinium-doped ceria (GDC) and Li(2)CO(3)-K(2)CO(3) are analyzed as potential SOFC electrolytes. In a temperature range higher than 500 degrees C, their ionic conductivity is significantly higher than for single GDC. Discontinuities were found in the conductivity Arrhenius diagram (sigma vs. 1/T) around the melting point of the carbonate mixture (490 degrees C), showing, at least partially, the contribution of molten carbonates. At this stage, precise mechanisms are still under analysis.
|
|
| 10. |
- Bergman, B., et al.
(författare)
-
Contact corrosion resistance between the cathode and current collector plate in the molten carbonate fuel cell
- 2001
-
Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 148:1, s. A38-A43
-
Tidskriftsartikel (refereegranskat)abstract
- The corrosion layer Formed in the contact between the cathode and the current collector is one factor limiting the cathode performance in molten carbonate fuel cells (MCFC). In order to investigate the contribution to the total polarization of the contact resistance, electrochemical experiments were performed in a laboratory-scale fuel cell unit with a specially designed current collector. Two cathode materials, NiO and LiCoO2, were investigated to elucidate the impact of the cathode material on the formed corrosion layer. Polarization measurements as well as electrochemical impedance spectroscopy were used. The method works well for NiO electrodes. However, due to the poor electronic conductivity in the LiCoO2 electrode, the experimental results become difficult to evaluate due to a nonuniform potential distribution. The contact resistance between the cathode and the current collector contributes with a large value to the total cathode polarization. The corrosion layer in case of the LiCoO2 cathode was iron-rich and has a thickness of about 20 mum after 8 weeks operation of the fuel cell. Ln the case of the NiO cathode, a nickel-rich corrosion layer of about 15 mum was formed after 5 weeks operation of the fuel cell.
|
|
