A pure hydrogen/oxygen polymer electrolyte of 1 kW power fuel cell stack has been designed manufactured and tested in the framework of an European Space Agency (ESA) study, conducted by an Italian consortium (CGS spa and CNR - ITAE). This fuel cell stack has been envisaged to be applied for lunar manned exploration missions as the primary energy source for both Mobile Vehicles (Pressurized Lunar Rovers, PLR) or Power Plants (Lunar Base, LB), and has been bread boarded in order to demonstrate the technology, measure the performance and test under representative power loads. The following constraints have been considered during the study: i) operation with pure hydrogen and oxygen ii) low humidification level (about 50%) iii) use of commercial MEAs. Developed fuel cell breadboard has been made by two module of 500 W nominal power each @ 80A, connected in series electrically but in parallel from the fluidic point of view. Each module is made up of 10 cells with an active area of 160cm2. As regarding the internal distribution of fluids, the gas and coolant fluids are distributes to the single cells by internal manifolds. Z-shape manifolds were used for the reactants and coolant distributions, for a more homogenous distribution of fluids. A parallel serpentine flow path was adopted to distribute the reactants over the electrode surface. The geometrical parameters of the serpentine, were calculated using an own developed worksheet. It can determine the geometry of channels (channels width, channels height, land width, number of parallel serpentines) by respecting some geometrical (such as active area dimensions, electrical/open area ratio) and fluid dynamic constraints (flow path pressure drop and channel to channel crossover ratio). Conventional (polarization curves and time test) and specific electrochemical tests (inclined plane tests and 14 days load cycles) were performed to measure the stack performance, evaluate its robustness and define its operative limits. Regarding the specific tests, they were performed with the aim to verify the compatibility of the developed Breadboard with the reference lunar applications. In particular, the inclined plane tests, were intended to study how the gravity affects the fluid/gases management of the cell. In fact, in a PEM fuel cell, the water is produced at the cathode side and, in a conventional configuration, the water motion direction is perpendicular to the gravity vector. The water, produced on the catalyst surface, that is parallel to the flow field plane, naturally moves towards the flow field channels through the GDL. Depending on the orientation of the flow field plate with respect to the gravity vector, this water motion can be enhanced or inhibited by gravity. Because the designed fuel cell should operate in an environment with a reduced gravity at variable attitudes (due to the terrain slopes and obstacles, which do not allow for an always flat surface where to move on), it is important to measure the fuel cell sensitivity to the gravity orientation. Therefore, a set of tests at four inclinations has been performed (45°, 90°, -45°, -90°). Another set of tests, namely 14 days load cycles, were necessary to demonstrate the ability of the breadboard to operate in accordance with some typical PLR load cycles during a of a 14 days mission. During this test the response of the FC stack, in terms of voltage and power, has been evaluated at sudden current load variations. This test comply with a typical PLR 14 days operative mission, complemented by 2 contingency days performed during night, accounting for a total of 16 days operative plan. Three load profiles have been selected taking into account the time spent during travelling could be longer, without interruption, or even shorter with several "starts and stops". The developed fuel cell breadboard (fig.1) showed good performance along the whole test campaign (0.75V per cell @500 mA/cm2), even if some failure were observed during the inclined plane tests. The Stack operated well at -45/+45° without significant changes in the overall performance, while some failure happened at -90/+90, where the perforation of some MEAs have been recorded. The study has demonstrated the high performances of the developed stack and the potential of fuel cell technology for use in future lunar human exploration missions. At the same time, it has highlighted serious criticalities related to the reliability and robustness against the specific space environment of commercially available MEAs, which need to be further investigated in order to push the current technology level to the next step.
A Polymer Fuel cell stack breadboard development for lunar manned exploration mission
Giacoppo Giosue';Matera Fabio;Passalacqua Enza;
2014
Abstract
A pure hydrogen/oxygen polymer electrolyte of 1 kW power fuel cell stack has been designed manufactured and tested in the framework of an European Space Agency (ESA) study, conducted by an Italian consortium (CGS spa and CNR - ITAE). This fuel cell stack has been envisaged to be applied for lunar manned exploration missions as the primary energy source for both Mobile Vehicles (Pressurized Lunar Rovers, PLR) or Power Plants (Lunar Base, LB), and has been bread boarded in order to demonstrate the technology, measure the performance and test under representative power loads. The following constraints have been considered during the study: i) operation with pure hydrogen and oxygen ii) low humidification level (about 50%) iii) use of commercial MEAs. Developed fuel cell breadboard has been made by two module of 500 W nominal power each @ 80A, connected in series electrically but in parallel from the fluidic point of view. Each module is made up of 10 cells with an active area of 160cm2. As regarding the internal distribution of fluids, the gas and coolant fluids are distributes to the single cells by internal manifolds. Z-shape manifolds were used for the reactants and coolant distributions, for a more homogenous distribution of fluids. A parallel serpentine flow path was adopted to distribute the reactants over the electrode surface. The geometrical parameters of the serpentine, were calculated using an own developed worksheet. It can determine the geometry of channels (channels width, channels height, land width, number of parallel serpentines) by respecting some geometrical (such as active area dimensions, electrical/open area ratio) and fluid dynamic constraints (flow path pressure drop and channel to channel crossover ratio). Conventional (polarization curves and time test) and specific electrochemical tests (inclined plane tests and 14 days load cycles) were performed to measure the stack performance, evaluate its robustness and define its operative limits. Regarding the specific tests, they were performed with the aim to verify the compatibility of the developed Breadboard with the reference lunar applications. In particular, the inclined plane tests, were intended to study how the gravity affects the fluid/gases management of the cell. In fact, in a PEM fuel cell, the water is produced at the cathode side and, in a conventional configuration, the water motion direction is perpendicular to the gravity vector. The water, produced on the catalyst surface, that is parallel to the flow field plane, naturally moves towards the flow field channels through the GDL. Depending on the orientation of the flow field plate with respect to the gravity vector, this water motion can be enhanced or inhibited by gravity. Because the designed fuel cell should operate in an environment with a reduced gravity at variable attitudes (due to the terrain slopes and obstacles, which do not allow for an always flat surface where to move on), it is important to measure the fuel cell sensitivity to the gravity orientation. Therefore, a set of tests at four inclinations has been performed (45°, 90°, -45°, -90°). Another set of tests, namely 14 days load cycles, were necessary to demonstrate the ability of the breadboard to operate in accordance with some typical PLR load cycles during a of a 14 days mission. During this test the response of the FC stack, in terms of voltage and power, has been evaluated at sudden current load variations. This test comply with a typical PLR 14 days operative mission, complemented by 2 contingency days performed during night, accounting for a total of 16 days operative plan. Three load profiles have been selected taking into account the time spent during travelling could be longer, without interruption, or even shorter with several "starts and stops". The developed fuel cell breadboard (fig.1) showed good performance along the whole test campaign (0.75V per cell @500 mA/cm2), even if some failure were observed during the inclined plane tests. The Stack operated well at -45/+45° without significant changes in the overall performance, while some failure happened at -90/+90, where the perforation of some MEAs have been recorded. The study has demonstrated the high performances of the developed stack and the potential of fuel cell technology for use in future lunar human exploration missions. At the same time, it has highlighted serious criticalities related to the reliability and robustness against the specific space environment of commercially available MEAs, which need to be further investigated in order to push the current technology level to the next step.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
