MINATEC 2003 Development of Micro Fuel Cells with help of MEMS Technologies, Stefan Wagner, Herbert Reichl, Fraunhofer IZM, 13355 Berlin, Germany, Tel. +49 30 314 72 833, hahn@izm.fhg.de Michael Krumm, Krystan Marquardt, TU-Berlin, 13355 Berlin, Germany 1
Content Introduction, Fraunhofer State of the art PEM-micro fuel cell development Conclusions and outlook 2
Fraunhofer IZM Laboratory Sources Micro- Solarcells MEMs Fuel Cell Verkapselung, Hermetisierung MEMs Elektrolyt, Separator Batteries Anode und Kathode The Group at Fraunhofer IZM addresses packaging and system integration related topics concerning the energy supply of portable and miniaturized future electronic products and is involved in novel battery and alternative energy developments. Batteriezuleitungen Stromableiter Substrat: Trägerfolie oder IC 3
Energy density potential of fuel cells as power supply for portable electronics DMFC H2-FC-Stack* Alkalin Zink-Luft NiMH NiCd Li-Polymer 2005 0 200 400 600 800 1000 1200 1400 1600 1800 2000 Wh/l DMFC H2-FC-Stack* Alkalin Zink-Luft NiMH NiCd Li-Polymer 2005 0 200 400 600 800 1000 1200 1400 1600 1800 2000 Wh/kg 4
Our Roadmap since 1997 evaluation of prototypes 1998-2000 Planar PEM Test, Design 1999-2002 Materials and Design of PCB-PEM 2000-2003 Development and Thermal Management of PEM micro stacks 2001- FC peripheral micro components 1999- planar PEM micro fuel cell development 2002- micro DMFC activities 2003- product development PEM-stacks 2008 mass market for micro fuel cells 5
Camcorder PEM-Miniature Stack Demonstration 6
IZM - micro fuel cell partnership Simulation TUB, WIAS, ISE Materials ICT, ISC, TU-HH IZM SME-cooperation Heliocentris, h2-interpower micro peripherals IZM-M, IMM, microsensys, ETH-Z component supply Fumatec, Gore, Freudenberg 7
Why MEMS fuel cells?? Improve fuel cell performance by exploiting micro-scale phenomena. Solve problems which are critical in the conventional stack technology. --> fabrication of micro-porous membranes optimized for two phase transport --> plasma polymerisation of ion conducting polymers --> transport optimized micro flowfields Miniaturization, micro-power applications. Miniaturization of the conventional fuel cell stack technology is not achievable down to the dimensions of handheld electronics, autonomous sensors, medical electronics... 8
International Competition Source Design Fuels Density S.C. Kelley Univ. of Minnesota Front and back KOH etched Si wafer, Nafion Membrane with custom Pt, Pt-Ru catalysts coatings 0.2 L/min. hydrated neat hydrogen 0.2 L/min ambient air 130 mw/cm 2 J.P. Meyers Bell Labs Porus Si etching, Electropolished channels, Nafion membrane, Pt/C catalyst Hydrogen and oxygen at 1 atm 60 mw/cm 2 S.J. Lee Stanford Univ. Front and back RIE Si wafer, Nafion membrane, carbon cloth and platinum, series connected Compressed hydrogen and oxygen 40 mw/cm 2 R. Hahn Fraunhofer, GER Wafer level and foil processes, screen printing. 0.5 sccm hydrogen (DMFC) NO AIR PUMPING 80 mw/cm 2 S.C. Kelley Univ. of Minnesota Front and back KOH etched Si wafer, Nafion Membrane with custom Pt, Pt-Ru catalysts coatings 0.2 L/min. 0.5M Methanol, H 2 O 0.2 L/min ambient air 15 mw/cm 2 Y.H. Seo KAIST, Korea Front and back KOH and RIE Si Wafer, Nafion membrane Pt catalyst Methanol and ambient air NO FUEL OR AIR PUMPING 0.1 mw/cm 2 Source: Lyndermann, ETH-Zürich 9
State-of-the-art µ-fuel Cell Designs Stanford University, California 10
State-of-the-art µ-fuel Cell Designs Bell Laboratories Porous Si etching, Electropolished channels, Nafion membrane, Pt/C catalyst Hydrogen and oxygen at 1 atm density: 60 mw/cm² Manhattan Scientifics Inc., R. G. Hockaday 11
µ-fuel Cell Designs State-of-the-art RIE Chanels on Si Wafer Anodic Collector PVD Insulator Layer Diffusion Layer Pt Catalyst Ink Nafion Cathodic catalyst PVD cathodic Collector + - µ-fc flow chart CEA - Small Sources Laboratory 12
Fraunhofer IZM µ-fuel Cell Design Breakthrough s System consists of 3 foils in a planar configuration (independent of the number of cells), use of commercial MEA Integrated planar sealing Serial interconnection of individual cells in a planar configuration Natural air convection at the cathode side Mechanically flexible 13
Fraunhofer IZM µ-fuel Cell: Core Technologies Sandwich laminate of Polymer-Stainless steel foils Lithography of free standing grid microstructures Micro patterning of flow fields Subtractive patterning of MEA-electrodes Adhesive sealing and electrical interconnection 14
Fraunhofer IZM µ-fuel Cell µ-fuel Cell Demonstrator Design single cell Dreizeller AF 54,72 mm² 18,24 mm² A1 400 µm 400 µm A2 400 µm 400 µm A4-200 µm L3 10 mm 10 mm B 10 mm 10 mm 15
Assembly sealing current collector cathode MEA current collector anode electrical contacts simultaneous processing of numerous cells dispensing or screen printing of gaskets screen printing of contacts 16
Technology Patterning of micro flow field Lamination Kapton foil and substrate on a wafer metalization hardmask RIE channel in Kapton layer Removing hardmask Au metalization anodic current collector 17
SEM: anode side width 35-25 µm 10-3,5 µm 15 µm 30 µm 18
Patterning of the cathodic current collector layer RIE plated conductor lines 19
Segmentation of the Membrane Electrode Assembly (MEA) Segmentation of commercial MEA is necessary to to allow straight forward assembly (all cells simultaneously) Short circuits between adjoining electrodes might occur if the lateral electrical resistance between the cells R L is low. Thus, to secure an appropriate serial connection R L >> R ION + R SI must hold. Fig. a Fig. b + R ION U FC removed catalyst layer R SI R L R L R ION U FC removed catalyst layer R SI R L R L R ION U FC polymer membrane - catalyst layer catalyst layer U FC? cell potential R ION? ionic membrane resistance R SI? resistance of the serial interconnection R L? lateral electrical resistance 20
Segmentation of MEA: RIE Patterning of MEA by reactive ion etching shadow mask Shadow mask for MEA-etching 21
Segmentation of MEA: LASER LASER Ablation Catalyst layer can be removed on both sides at the same time Complete removal of catalyst layer due to ist high absorbance of Laser radiation Distances between the segments less than 200µm are realized Light microscopy image SEM image 22
Electrical characterization of micro fuel cells 23
V/I curve of micro fuel cell voltage [mv] 1000 100 T=25 C design 1 rh=50% design 2 800 600 400 200 80 60 40 20 power density [mw/cm²] 0 0 0 50 100 150 200 250 300 350 400 current density [ma/cm²] 24
Comparison with reference cells at room temperature Voltage [mv] 1000 planar chip sized FC 900 planar PBC-FC reference 800 micro stack (single cell) 700 600 500 400 300 200 100 0-50 0 50 100 150 200 250 300 350 400 450 Current density [ma/cm²] 25
Characterisation in climate chamber, Comparison - with conventional build up, 1 current density [ma/cm²] @ 350mV 300 250 200 150 100 50 0 µfc (Design 1) µfc (Design 2) reference (PBZ) T25 C/HM10% T25 C/HM50% T25 C/HM90% voltage [V] 1,0 0,8 0,6 50% 0,4 10% 0,2 0,0 0 200 400 600 800 1000 1200 1400 time [min] Temp: 60 C 90% 0,25 0,20 0,15 0,10 0,05 0,00 current [A] 26
current density [A/cm 2 ] @ 350mV Charcterisation in climate chamber, Comparison - with conventional build up, 2 0,30 0,25 0,20 0,15 0,10 0,05 E22 10% rh 50% rh 90% rh 0,00 10 20 30 40 50 60 temperature [ C] current density [A/cm 2 ] @ 350mV 0,30 0,25 0,20 0,15 0,10 0,05 PBZ33 10% rh 50% rh 90% rh 0,00 10 20 30 40 50 60 temperature [ C] Micro fuel cell (left) and conventional planar fuel cell using GDLs (right) as function of temperature and relative humidity. Current density at 350 mv is shown. 27
Climate Test summary Behavior of µfc and conventional cells are quite similar. Membrane dries out at lower temperatures and dry ambient conditions. At high humidity and low temperatures the current density drops slightly faster, probably due to flooding of the cell. Best performance at normal ambient conditions. 28
Electrical Characterisation MEA-Segmentation T = 25 C, 50 % RH active area: 0.54 cm 2 29
MEA segmentation, serial interconnection Successful demonstration of planar micro fuel cells with 1.5 V, 40 ma output ( = 120 mw/cm 2, 25 C, 50 %RH. 200 µm gap between adjacent cells; no degradation during patterning process. Still slight reduction of open circuit voltage, probably due to small leakage currents between adjacent cells. 30
Status 2003 Planar micro fuel cell, PEM, dry hydrogen: 80 mw/cm 2 Planar micro fuel cell, DMFC, 2 wt%, 27 C: 5 mw/cm 2 Planar PCB fuel cell, DMFC, 50 C 25 mw/cm 2 Micro DMFC with integrated micro pump will be accomplished until end of 2003 MEMS fuel cell demonstrator: Size: 1 cm 2, thickness: 200 µm, Active membrane area: 0.54 cm 2, dry hydrogen, natural air convection 1.5 V, 20 ma (3 cells serial interconnected), 0.5 V, 60 ma (single cell). 31
Summary 1 Successful demonstration of micro PEM fuel cell technology based on commercially available MEAs and foil processes, Stable long term operation at 80 mw/cm 2 at room temperature, natural air convection, dry hydrogen Test under various climate conditions Future Work Adaption of the technology to micro DMFC 32
Summary 2 Considerable achievements have been made, still a great effort is needed to commercialize micro fuel cells. PEM micro fuel cells are functional and have the potential of low cost mass production. Micro scale hydrogen supply is lacking. We are open to cooperation and technology transfer to commercialize this technology. 33
Fraunhofer Micro Fuel Cell Patents WO030338935 WO0141231A2 WO0005776 WO2002086996A1 DE10155349 DE10224252 DE10217034 DE10306081 DE10309358 DE19833064 Micro fuel cell (Wafer Level, foil) Electrochemical Cell (micro flow field) Proton conducting membrane (micro patterning of MEA) Planar fuel cell (based on printed circuit board) Fuel cell stack with bipolar plates (cooling of microstack) Carrier for semicondictor (flexible micro solar generator) Transverse fuel cell interconnecting structure Hydrogen pressure control (with MEMS valvs) WO9618217 DE4329819 DE 19502391 Planar stripe fuel cell DE4443939 Planar interconnection of stripe membrane fuel cells Fraunhofer Institutes over 30 fuel cell patents 34
Thank you for your attention!!! 35