This paper presents the results of an assessment of the requirements and technology for the Proton Exchange Membrane (PEM) fuel cell as the electric power source for next-generation spacecraft, and particularly as an accepted upgrade to replace the current Orbiter alkaline fuel cell. As part of the technology assessment, a commercially available 4-kW PEM fuel cell was tested for over 400 hours at NASA-Johnson Space Center using hydrogen and oxygen as reactants. The findings of this evaluation, as well as a short summary of some test facility improvements and accomplishments as they relate to fuel cell testing in general, are presented. A short status of other items in the Orbiter PEM Fuel Cell Upgrade effort is also presented

Le, Michael

Vasquez, Arthuros

English

Embry-Riddle Aeronautical University

The Space Congress® Proceedings 1997 (34th) Our Space Future - Uniting For Success May 1st, 1:00 PM Paper Session III-C - Proton Exchange Membrane Fuel Cells for the Next Generation Spacecraft Applications Arthuros Vasquez NASA Johnson Space Center Michael Le NASA Johnson Space Center Follow this and additional works at: https://commons.erau.edu/space-congress-proceedings Scholarly Commons Citation Vasquez, Arthuros and Le, Michael, "Paper Session III-C - Proton Exchange Membrane Fuel Cells for the Next Generation Spacecraft Applications" (1997). The Space Congress® Proceedings. 15. https://commons.erau.edu/space-congress-proceedings/proceedings-1997-34th/may-1-1997/15 This Event is brought to you for free and open access by the Conferences at Scholarly Commons. It has been accepted for inclusion in The Space Congress® Proceedings by an authorized administrator of Scholarly Commons. For more information, please contact commons@erau.edu. Proton Exchange Membrane Fuel Cellsfor the Next GenerationSpacecraft ApplicationsbyArturo Vasquez and Michael LeNASA Johnson Space CenterAbstractThis paper presents the results of an assessment of the requirements and technology for theProton Exchange Membrane (PEM) fuel cell as the electric power source for next-generationspacecraft, and particularly as an accepted upgrade to replace the current Orbiter alkaline fuelcell.  As part of the technology assessment, a commercially available 4-kW PEM fuel cell wastested for over 400 hours at NASA-Johnson Space Center using hydrogen and oxygen asreactants.  The findings of this evaluation, as well as a short summary of some test facilityimprovements and accomplishments as they relate to fuel cell testing in general, are presented.A short status of other items in the Orbiter PEM Fuel Cell Upgrade effort is also presented.Proton Exchange Membrane Fuel Cellsfor the Next Generation Spacecraft ApplicationsIntroductionAn in-house review of the requirements and technology for, and demonstration of, a ProtonExchange Membrane (PEM) fuel cell as the next generation electric power source for theOrbiter and future spacecraft applications has been completed and will be discussed in thispaper.  A need exists to replace the current Orbiter fuel cell with a new low cost, high powerdensity fuel cell while maintaining the excellent reliability and safety record of the current sys-tem.  PEM fuel cells offer the potential for significant long term cost savings, safety and reliabil-ity improvements, and a much greater assurance of continued technology readiness that wouldnot be offered by continuing with the current alkaline fuel cell powerplant.  Also, the alkaline fuelcell has lost to other types of fuel cells (PEM in particular) technology development supportedby government and private industry funds.  The electric car fuel cell development is almostexclusively in the hydrogen / air / PEM arena.  To achieve low cost, service life beyond thecurrent 2400 hours specification, and higher power density, a system employing simple designand low cost materials will be needed.  All of these attributes can be found in a PEM fuel cell.Advances made in research, development, and even commercial market readiness, for the  fuelcell powered electric car and related industry programs have significantly expanded the technol-ogy base.  Other areas that the PEM fuel cell is being considered for use with are: (1) theReuseable Launch Vehicle, (2) battery replacement for an advanced space suit for Lunar orMars exploration, (3) ground based power systems for the Mars surface, and (4) electric powersource for a possible upgrade of the Orbiter’s APU/hydraulic actuator system with electrome-chanical actuators.  The project cost for the spacecraft applications, if achieved, will be substan-tially low compared to what NASA pays for the current fuel cell today.  The PEM stack powerdensity obtained to date has been comparable to, if not better than, the current alkaline fuel cell.The primary issue identified in this review was fuel cell powerplant compatibility with micro-gravity and launch environment.  Technology maturity and readiness for space application mustbe proven through extensive test evaluation.  A program has been initiated to address thetechnical issues and provide data to support management decisions.  One of the first taskscompleted for this effort was the test of a 4-kW demonstrator unit for over 400 hours at theJohnson Space Center.  The results of this effort are discussed below, as well as the status ofthe in-house design definition and technology programs.Energy Partners 4-kW Fuel Cell EvaluationThe program initially began with the integration of a leased 15-cell, 4-kW Proton ExchangeMembrane (PEM) Fuel Cell system manufactured by Energy Partners , Inc. (EPI), of West PalmBeach, Florida, into the Fuel Cell Test Bed at the Power Generation Test Facility (Building 354)of the Energy Systems Test Area (ESTA) at NASA, Johnson Space Center.  This fuel cell wasattractive to NASA as a candidate for shuttle upgrade because of its technology readiness andcommercial availability.  This test program was effectively the first part of a larger effort toevaluate PEM fuel cells for this upgrade effort.  In an effort to eliminate the increasing costs tothe government associated with on-going monthly lease extensions, the fuel cell system waspurchased from the vendor during the test program.  Each cell’s active area was 0.75 squarefeet.  Included in the fuel cell stack were pre-humidifying assemblies that provided a means of“passively” pre-humidifying the reactant inlet streams on their way to the reaction sites of thefuel cell.  The manufacturer rated the fuel cell as capable of providing 4 kW when operating onhydrogen and oxygen and 2 kW when operating on hydrogen and air.  The stack weighed 120lbs with the end plates both weighing ~40 lbs each.  This left the cell stack and internal pre-humidifier assembly at 40 lbs.On reactant tests were performed in three phases from 5/96 to 10/96.  The first phase (Phase 0)was structured primarily to become familiar with the operation and performance of both the fuelcell system and ESTA supplied support stand.  Approximately 60 hours of operational time wasaccumulated over 14 days of testing during this phase.  During this phase, a water separatorchilling bath, automatic computer control of the electrical load profiles, user control of reactantdelta pressures, and automatic control of the water separator drain valves were added to thestand as improvements to the as-delivered test system.  The second phase (Phase 1) wasstructured to evaluate the effectiveness of the water separator chilling bath and the effect ofreactant-to-reactant delta pressure.  One week of round-the-clock testing was accumulatedduring this phase.  The third phase (Phase 2) was structured to evaluate the effect of coolantloop temperature control and stack reactant absolute pressure on fuel cell performance.  Threeweeks of round-the-clock testing were accumulated during this phase.In all, 440 hours of operational time was accumulated.  The full manufacturer’s (>4kW) ratedperformance was met with the ESTA testing.  The test system operated continuously for ~110hours during the last week of testing; no shutdowns occurred during that week.  Average cellvoltage degradation was  3 microV / hr , which compares very favorably over the 21 microV / hraverage cell voltage degradation for the current alkaline fuel cell.  The PEM fuel cell has toler-ance for water removal system failures and flooding in that no permanent damage will haveoccurred after water is removed.  Alkaline fuel cell flooding is almost always permanently dam-aging.  There is not a requirement for precise reactant pressure control, and related expense,that is absolutely required for the alkaline fuel cell.  Start up and shut down of the system in-volved providing reactants to the stack and starting the cooling water loop and oxygen circula-tion loop; there were no electrolyte concentration / flooding concerns that are inherent with thecurrent alkaline fuel cell.  The EPI fuel cell power production was ~80 % of the current alkalinefuel cell’s power production at the point shown in Figure 1.  It is important to note that twofactors which affected the performance of the EPI stack were present.  The first was the rela-tively low temperature of the stack during tests at ESTA.  The second was the presence of inertsin the gas stream from two sources; these were: (1) definite high concentrations of argon (1900ppm by volume) in the oxygen supply from the tube trailer supply and (2) a suspect 3-waysolenoid valve (which was part of the vendor supplied fuel cell system) which exhibited a ten-dency to leak inerting nitrogen into the oxygen stream whenever oxygen pressure dropped dueto increased supply demands from the fuel cell.  The internal pre-humidifier supplied from themanufacturer caused performance shortcomings that have also been recognized by the manu-facturer.  The manufacturer of this fuel cell has moved towards external pre-humidification(separating the cooling and pre-humidification) as a means of increasing performance in generaland offering greater operational control.  The gravity-dependent water separator was anothercomponent of the fuel cell system which exhibited less than ideal operation.  This was primarilydue to the fact that the separator was designed for service in higher pressure (100-250 psig)compressed-air fluid systems.  With the relatively low pressures (20-35 psig) involved with thissystem, the device’s float-controlled, automatic drain did not always re-seat properly at thecompletion of a drain cycle.  In an attempt to “fix” this problem, the JSC test team added a timer-controlled 2-way valve at the water outlet of the water separator.  This greatly improved theoverall reliability of the water separator process, but there was still  a significant amount ofexcess oxygen flow carried with the out going water stream.  Ideally, only bulk product waterwould be drained from the separator with very little extra oxygen gas being carried out with theexiting water stream.4003002001000Average Individual Cell Power Density (Watts / Square Foot)5004003002001000Current Density (Amps / Square Foot)1.00.80.60.40.20.0Average Individual Cell Voltage (Volts)4003002001000Total Stack Current (Amps)EPI Average Individual Cell Voltage ----> <---- Orbiter Average Cell Power DensityOrbiter Average Individual Cell Voltage ----> <---- EPI Average Cell Power DensityFigure 1.  Average Cell Voltage and Average Cell Power Density vs. Total Stack Cur-rent and Cell Current Density for both the current Orbiter Alkaline Fuel Cell and theEnergy Partners, Inc. Fuel Cell evaluated as part of the test program.General Fuel Cell Test ImprovementsDuring the planning phase of the test described above, the responsible parties of NASA-JSChave continued working in the area of equipment procurements and test facility modifications forthe improved ability of the ESTA to support fuel cell testing for NASA and other governmentagencies, and also for possible outside organizations.  These efforts have been focused prima-rily at Building 354 of the ESTA.  Significant accomplishments are summarized as follows.Designs, supporting documentation, procedures, fabrication, functional check out, and safe useof the Fuel Cell Test Bed was completed to support the Energy Partners Fuel Cell Test.  Threeof the several available electronic load banks (with a combined power handling capability andcurrent handing capability of 32000 watts and 2600 amps, respectively) have been used todirectly support the fuel cell test mentioned above.  These load banks were: (1) electricallyconnected in parallel to dissipate the fuel cell’s electric load current, (2) controlled from their rearpanel analog control input from the test computer’s analog output ports, and (3) modified toallow remote control of their main load connection relays from dry contact relays controlled bythe test computer.  Equipment that was procured in fiscal year 1995 in anticipation of developingan Orbiter Improved Cell Performance Monitor breadboard development project was evaluatedwith its use as the individual cell and stack voltage measurement system for the fuel cell testmentioned above.  Electronic pressure regulators procured in fiscal year 1995 were successfullyused to control the reactant pressures to the fuel cell stack during the test discussed above.Sufficient experience was gained and some small procurements were completed that shouldallow for complete automation and unattended continuous operation of the test system forplanned fuel cell test programs; this should result in significant labor cost savings in the longterm.Technology Development StatusThe effort to characterize the state of technology readiness of PEM fuel cells for next generationspacecraft has resulted in the following set of indicators.The primary development emphasis for terrestrial PEM fuel cells has been with the hydrogen /air systems.  A few of the developers of these fuel cell systems have also produced hydrogen /oxygen systems for special purpose operating environments; the majority of these have pro-vided a recirculating oxygen stream with the retention of their basic air planform.  The recirculat-ing oxygen stream replaces the excess air flow stream in order to effect water removal from thestack by entrainment.  Since this could be considered the most common of the stack productwater removal methods, the development of a launch-environment (high g’s and vibration) andmicro-gravity compatible water separator to use with the typical recirculating-oxygen stack hasbeen recognized as a development item.  Two areas of investigation and evaluation have beenentered into by a team consisting of persons from several NASA centers.  These are: (1) dy-namic water phase separators much like the current Orbiter fuel cell powerplant’s, and (2)passive (probably membrane-based) water separators.  Related to this effort is a requirement todevelop a reactant gas pre-humidifying system that is compatible with the gravity and vibrationenvironments just mentioned.Two additional fuel cell vendor’s stacks are planned for testing at JSC in the next year.  The firstof these is one that was developed by International Fuel Cells as part of a DARPA fundedprogram to develop a fuel cell replacement for the existing battery power source on an Un-manned Underwater Vehicle (UUV).  The second is a stack from Ballard Power Systems,although the particular model had not been determined at the time of this writing.  The team hasinitiated a NASA Cooperative Agreement Notice (CAN) effort for joint industry / NASA develop-ment of flight prototype hardware demonstrations including a sub-scale powerplant and potentialflight experiment.

Paper Session III-C - Proton Exchange Membrane Fuel Cells for the Next Generation Spacecraft Applications

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Paper Session III-C - Proton Exchange Membrane Fuel Cells for the Next Generation Spacecraft Applications

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