Energy storage systems with extremely high specific energy (>400 Wh/kg) have been designed that use lightweight pressure vessels to contain the gases generated by reversible (unitized) regenerative fuel cells (URFCs).[1] URFC systems are being designed and developed for a variety of applications, including high altitude long endurance (HALE) solar rechargeable aircraft (SRA), zero emission vehicles (ZEVs), hybrid energy storage/propulsion systems for spacecraft, energy storage for remote (off-grid) power sources, and peak shaving for on-grid applications.[1-10] Energy storage for HALE SRA was the original application for this set of innovations, and a prototype solar powered aircraft (Pathfinder-Plus) recently set another altitude record for all propeller-driven aircraft on August 6, 1998, when it flew to 80,285 feet (24.47 km).[11

Mitlitsky, F

Molter, T M

Myers, B

Weisberg, A H

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September 10, 1998This is a preprint of a paper intended for publication in a journal or proceedings.  Sincechanges may be made before publication, this preprint is made available with theunderstanding that it will not be cited or reproduced without the permission of theauthor.LawrenceLivermoreNationalLaboratoryUCRL-JC-130198PREPRINTUnitized Regenerative Fuel Cell SystemsThis paper was prepared for submittal to the1998 Fuel Cell SeminarPalm Springs, CANovember 16-19, 1998F. MitlitskyB. MyersA. H. WeisbergT. M. MolterDISCLAIMERThis document was prepared as an account of work sponsored by an agency ofthe United States Government.  Neither the United States Government nor theUniversity of California nor any of their employees, makes any warranty, expressor implied, or assumes any legal liability or responsibility for the accuracy,completeness, or usefulness of any information, apparatus, product, or processdisclosed, or represents that its use would not infringe privately owned rights.Reference herein to any specific commercial product, process, or service by tradename, trademark, manufacturer, or otherwise, does not necessarily constitute orimply its endorsement, recommendation, or favoring by the United StatesGovernment or the University of California.  The views and opinions of authorsexpressed herein do not necessarily state or reflect those of the United StatesGovernment or the University of California, and shall not be used for advertisingor product endorsement purposes.UNITIZED REGENERATIVE FUEL CELL SYSTEMSF. Mitlitsky, B. Myers, and A.H. Weisberg Trent M. MolterLawrence Livermore National Laboratory Proton Energy Systems, Inc.7000 East Avenue, L-174 50 Inwood DriveLivermore, CA 94551-0808 Rocky Hill, CT 06067Energy storage systems with extremely high specific energy (>400 Wh/kg) have been designedthat use lightweight pressure vessels to contain the gases generated by reversible (unitized)regenerative fuel cells (URFCs).[1] URFC systems are being designed and developed for a varietyof applications, including high altitude long endurance (HALE) solar rechargeable aircraft (SRA),zero emission vehicles (ZEVs), hybrid energy storage/propulsion systems for spacecraft, energystorage for remote (off-grid) power sources, and peak shaving for on-grid applications.[1-10]Energy storage for HALE SRA was the original application for this set of innovations, and aprototype solar powered aircraft (Pathfinder-Plus) recently set another altitude record for allpropeller-driven aircraft on August 6, 1998, when it flew to 80,285 feet (24.47 km).[11]Progress is reported on the development, integration, and operation of rechargeable energy storagesystems with such high specific energy. A primary fuel cell test rig with a single cell (46 cm2active area) has been modified and operated reversibly as a URFC for thousands of cycles atLLNL.[1] This URFC uses bifunctional electrodes (oxidation and reduction electrodes reverseroles when switching from charge to discharge, as with a rechargeable battery) for cathode feedelectrolysis (water is fed from the hydrogen side of the cell) or anode feed electrolysis (water isfed from the oxygen side of the cell). The results of the cycle test are shown in Figure 1, anddemonstrate high cycle life with negligible degradation.[1] Improved URFC cells, with highperformance and reduced catalyst loading were demonstrated at LLNL, as shown in Figure 2.Rapid cycle operation of URFC cells has been demonstrated at LLNL. These results were obtainedon the URFC test rig shown in Figure 3, using the cell in Figure 4. Proton Energy Systems, Inc.has recently built a URFC test rig (Figure 5) for testing and developing URFC cells shown inFigures 6 and 7. These cells are capable of producing up to 400 psi  (2.8 MPa) gas byelectrochemical pressurization. Future designs may be capable of ~3000 psi (21 MPa).LLNL recently started testing URFC cells using Nafion 105 membrane and reduced catalystloading. Cell #9804A uses Nafion 105, Hamilton Standard’s E-5 catalyst, and catalyst loading of 1mg/cm2 per electrode. Figure 2 shows that fuel cell operation on URFCs is feasible at currentdensities >2000 ASF (2.15 A/cm2). Cathode feed electrolysis data was limited to 1200 ASF due tocell dryout. Anode feed electrolysis data was taken at current densities >2000 ASF (2.15 A/cm2),but has not yet been approved for publication. This figure shows that reduced catalyst loadingoperation of PEM electrolyzers and URFCs is feasible, and shows that consumer markets that mayrequire reduced catalyst loading to achieve inexpensive unit costs at high volume may be filled byPEM electrolyzers and URFCs. Experiments with alternate catalyst compositions and furtherreduced catalyst loadings are in progress.LLNL is working with industrial partners to design lightweight pressure vessels for hydrogenpowered vehicles, where the vessels are either conformable to existing rectangular packagingenvelopes, or are cylindrical and incorporated into new “designed from the ground up”vehicle configurations. URFC systems coupled with lightweight pressure vessels have beendesigned for automobiles and are expected to be cost competitive with primary fuel cellpowered vehicles that operate on hydrogen/air.[4] URFC powered vehicles can be safely andrapidly (< 5 minutes) refueled from high pressure hydrogen sources, when available, toachieve driving ranges in excess of 360 miles (600 km). URFC powered systems could savethe consumer the capital cost of a home hydrogen generation unit, since the consumer wouldbe able to electrically recharge at any available electrical source, instead of being tethered to asingle home electrolysis unit. Such URFC systems would be dual-fueled vehicles that can usethe existing electrical infrastructure, or a hydrogen infrastructure when available, for rapidMITLITSKY ET AL-2-refueling. They would enable regenerative braking by electrolysis and power peaking byoxygen supercharging.0.40.50.60.70.80.91.01.11.21.31.41.51.61.71.81.92.02.10 500 1000 1500 2000 2500 3000Cycle Number (600 seconds / cycle)Voltage [V]0.40.50.60.70.80.91.01.11.21.31.41.51.61.71.81.92.02.1320ASF(344mA/cm2)240ASF(258mA/cm2)160ASF(172mA/cm2) 86ASF (80 mA/cm2)Fuel Cell (FC) at: 40ASF (43 mA/cm2)100ASF(108mA/cm2)160ASF(172mA/cm2)220ASF(237mA/cm2)40 psig (0.37 MPa) H2 / H2O50 psig (0.45 MPa) O2 / H2O300 sec FC at 100 ASF (108 mA/cm2)300 sec EC at 240 ASF (258 mA/cm2)Cell ID LLNL01Active Area 0.05 ft2 (46 cm2)Nafion 117, E-5™ (4 mg/cm2/electrode)Inlet Temp 120 °F (49 °C)Cycle number 2010 measured Feb 1997Electrolyzer (EC) at: Figure 1. URFC cycle test at LLNL demonstrated negligible degradation after 2010 cycles.[1]MITLITSKY ET AL-3-0.40.50.60.70.80.91.01.11.21.31.41.51.61.71.81.92.02.12.22.30 200 400 600 800 1000 1200 1400 1600 1800 2000Current Density [ASF]Voltage [V]0.40.50.60.70.80.91.01.11.21.31.41.51.61.71.81.92.02.12.22.3CELL# 9734AActive Area 0.05 ft2 (46 cm2)Nafion 117, E-5™ Catalyst4 mg/cm2/electrode78 PSIG H2/H2O (0.64 MPa)145 PSIG O2/H2O (1.1 MPa)Inlet Temp 195 °F (91 °C)Internal resist 6.3 m Ω at 24 °CMeasured May 1997CELL# 9804AActive Area 0.05 ft2 (46 cm2)Nafion 105, E-5™ Catalyst1 mg/cm2/electrode78 PSIG H2/H2O (0.64 MPa)145 PSIG O2/H2O (1.1 MPa)Inlet Temp 195 °F (91 °C)Internal resist 4.0 m Ω at 24 °CMeasured April 1998Cathode Feed Electrolysis2152 mA/cm2Figure 2. High performance URFCs were demonstrated at LLNL with reduced catalyst loading.MITLITSKY ET AL-4-Figure 3. LLNL URFC test rig.Figure 5. Proton Energy Systems URFC test rig. Figure 4. LLNL URFC 0.05 ft2 (46 cm2) cell. Figure 6. Proton URFC 0.05 ft2 (46 cm2) cell. Figure 7. Proton URFC 0.1 ft2 (93 cm2) cell.MITLITSKY ET AL-5-    ACKNOWLEDGMENTS   A. Baris and P.J. Regna (Aero Tec Laboratories), C.J. Anderson and O.A. Velev(AeroVironment), S.P. Worden (Air Force), S.L. Rodgers and D.G. Talley (Air Force ResearchLaboratory), B.D. James and I.F. Kuhn, Jr. (Directed Technologies), S. Gronich and N.Rossmeissl (DOE), J. O’Sullivan (EPRI), R.I. Sims (Ford Motor Corporation), J.F. McElroy(Hamilton Standard), P.H. Carter II, M.L. Dickerson, M.J. Eckart, and W.A. Jensen (LLNL), J.Baer-Riedhart (NASA Dryden), L. Moulthrop and W. Smith (Proton Energy Systems, Inc.), E.H.Stokes (Southern Research Institute), R.P. Golde and R.K. Kunz (Thiokol Corp.). This work wasperformed under the auspices of the U.S. DOE by LLNL under contract number W-7405-Eng-48.    REFERENCES   1. F. Mitlitsky, A.H. Weisberg, and B. Myers, “Regenerative fuel cell systems,” Energy &Fuels,  12 (1), 56-71, January 12 (1998); UCRL-JC-128267 Rev 1;  http://pubs.acs.org/isubscribe/journals/enfuem/jtext.cgi?enfuem/12/i01/html/ef970151w.html .2. P.H. Carter II, F. Mitlitsky, A.H. Weisberg, J.C. Whitehead, and R.W. Humble, “Designtrade space for a Mars ascent vehicle for a Mars sample return mission,” IAA Conference onLow-Cost Planetary Missions, Pasadena, CA, April 27-May 1 (1998); UCRL-JC-130277.3. W.A. de Groot, L.A. Arrington, J.F. McElroy, F. Mitlitsky, A.H. Weisberg, P.H. Carter II, B.Myers, B.D. Reed, “Electrolysis propulsion for spacecraft applications,” AIAA 97-2948, 33rdAIAA/ASME/SAE/ASEE Joint Propulsion Conf., July 7-9 (1997).4. F. Mitlitsky, B. Myers, and A.H. Weisberg, “Lightweight pressure vessels and unitizedregenerative fuel cells,” 1996 Fuel Cell Seminar, November 17-20 (1996); UCRL-JC-125220 (paper) and UCRL-MI-125220 (viewgraphs).5. F. Mitlitsky, W.A. deGroot, L. Butler, and J.F. McElroy, “Integrated modular propulsion andregenerative electro-energy storage system (IMPRESS) for small satellites,” AIAA SmallSatellite Conference, September 16-20 (1996); UCRL-JC-125242.6. F. Mitlitsky, B. Myers, and F. Magnotta, “Lightweight bladder lined pressure vessels,”Disclosure and Record of Invention, DOE Case No. IL-9722, 1995; U.S. patent no. 5,798,156,August 25, 1998.7. F. Mitlitsky, N.J. Colella, and B. Myers, “Unitized Regenerative Fuel Cells for SolarRechargeable Aircraft and Zero Emission Vehicles,” 1994 Fuel Cell Seminar, pp. 624-627,Nov. 28-Dec. 1, 1994 (UCRL-JC-117130 and UCRL-MI-117130).8. F. Mitlitsky, N.J. Colella, B. Myers, and C.J. Anderson, “Regenerative Fuel Cells for HighAltitude Long Endurance Solar Powered Aircraft,” Proc. 28th IECEC, Vol. 1,. pp. 1255-1262,Aug. 8-13, 1993 (UCRL-JC-113485).9 P.J. Chludzinski, I.F. Danzig, A.P. Fickett, and D.W. Craft, "Regenerative fuel celldevelopment for satellite secondary power," General Electric Company, Technical ReportAFAPL-TR-73-34, Jun. 1973.10. F. Mitlitsky and B. Myers, “Development of an advanced, composite, lightweight, highpressure storage tank for on-board storage of compressed hydrogen,” Fuel Cells forTransportation TOPTEC: Addressing the Fuel Infrastructure Issue, Alexandria, VA, April 1-2, 1996 (UCRL-MI-123802).11. NASA Dryden Press Release 98-64, August 7, 1998;MITLITSKY ET AL-6-http://www.dfrc.nasa.gov/PAO/PressReleases/1998/98-64.html .

Unitized regenerative fuel cell systems

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Unitized regenerative fuel cell systems

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