PEFC & DMFC: materials, experiences, challenges

Transcription

1 Mitglied der Helmholtz-Gemeinschaft PEFC & DMFC: materials, experiences, challenges Joint European Summer School for Fuel Cell and Hydrogen Technology Institute of Energy and Climate Research IEK-3: Fuel Cells 29 August 2011 Jürgen Mergel

2 Outline Introduction PEFC & DMFC PEFC - Materials, experiences, challenges DMFC - Materials, experiences, challenges Summary Institute of Energy and Climate Research Fuel Cells (IEK-3) 2

3 Fuel Cells: Addressing Economic, Energy and Environmental Challenges Institute of Energy and Climate Research Fuel Cells (IEK-3) Source: U.S. Department of Energy 3

4 Fuel Cells: Goal and Objectives Source: U.S. Department of Energy Institute of Energy and Climate Research Fuel Cells (IEK-3) 4

5 Comparison of Targets and 2009 Status Laboratory Cell Stack targets 2010 Target 2009 Status > 60 Not applicable > 7300 with cycling Institute of Energy and Climate Research Fuel Cells (IEK-3) Source: U.S. Department of Energy 5

6 PEFC Polymer Electrolyte Fuel Cell - Stack components Components of a fuel cell stack Endplate Electrode Catalyst Single cell Electrode - bipolar plates & flow-fields - endplates - membrane electrode assembly diffusion layer catalyst layer membrane - gaskets Membrane Bipolar plate & Flow-fields Institute of Energy and Climate Research Fuel Cells (IEK-3) 6

7 PEFC Polymer Electrolyte Fuel Cell - Stack components Endplate Bipolare plate (Graphite) Electrode Single cell Membrane Electrode Assembly Catalyst Electrode Components of a fuel cell stack - bipolar plates & flow-fields - endplates - membrane electrode assembly diffusion layer catalyst layer membrane - gaskets Bipolar plate & Flow-fields Membrane Bipolare plate (Graphite) Institute of Energy and Climate Research Fuel Cells (IEK-3) 7

8 PEFC Polymer Electrolyte Fuel Cell Challenges: - Platinum cost is ~34% of total stack cost - Catalyst durability needs improvement Endplate Electrode $ 8.5/kW Single cell Catalyst Electrode Membrane Bipolar plate & Flow-fields 1 troy ounce = grams Source: U.S. Department of Energy Institute of Energy and Climate Research Fuel Cells (IEK-3) 8

9 PEFC Polymer Electrolyte Fuel Cell Challenges: - Platinum cost is ~34% of total stack cost - Catalyst durability needs improvement Catalyst cost 80 kw car: Currently: 0.5 g Pt /kw at $ 35/g Pt-as-catalyst 40 g Pt /car $ 18/kW $ 1.400/car $ 8.5/kW Target 2015: 0.2 g Pt /kw at $ 35/g Pt-as-catalyst 16 g Pt /car $ 7/kW $ 560/car Catalyst durability: Currently: < 2000 hours vs hours target carbon support corrosion & Pt dissolution 1 troy ounce = grams $ 35/g Pt Source: U.S. Department of Energy Institute of Energy and Climate Research Fuel Cells (IEK-3) 9

10 Platinum price 2006 bis 2011 $ 72,2 /g $ 55,9/g g Pt / System $ 894 Pt Institute of Energy and Climate Research Fuel Cells (IEK-3) 10

11 DMFC Direct Methanol Fuel Cells - Applications Portable 50 W Replacement of Li battery Source: TOSHIBA Source: Samsung Source: MTI Micro Fuel Cells Transportable 50 W - 1 kw Replacement of Diesel generator Source: SFC Source: Mitsubishi Gas Chemicals Source: IRD Light traction kw Replacement of battery Source: ProPower Source: Suzuki Motors Source: SFC Source: Oorja Protonics Institute of Energy and Climate Research Fuel Cells (IEK-3) 11

12 DMFC Direct Methanol Fuel Cell Challenges: - Durability - Cost - Performance Institute of Energy and Climate Research Fuel Cells (IEK-3) 12

13 Outline Introduction PEFC & DMFC PEFC - Materials, experiences, challenges DMFC - Materials, experiences, challenges Summary Institute of Energy and Climate Research Fuel Cells (IEK-3) 13

14 PEFC Polymer Electrolyte Fuel Cell PEFC - e- R + Endplate Electrode H + O 2 (Air) H 2 Anode Pt H 2 O Cathode Pt Catalyst Single cell Electrode MEA H 2 2H + + 2e - (anode) 1 / 2 O 2 + 2H + + 2e - H 2 O (cathode) H / 2 O 2 H 2 O (overall) Bipolar plate & Flow-fields Membrane Institute of Energy and Climate Research Fuel Cells (IEK-3) 14

15 PEFC Polymer Electrolyte Fuel Cell Source: Institute of Energy and Climate Research Fuel Cells (IEK-3) 15

16 PEFC Polymer Electrolyte Fuel Cell PEFC - e- R + (ƞ HOR < 5 mv) H + O 2 (Air) ( 60 mv R contact ) H 2 H 2 O Anode Pt Cathode Pt MEA H 2 2H + + 2e - (anode) 1 / 2 O 2 + 2H + + 2e - H 2 O (cathode) anode membrane cathode H / 2 O 2 H 2 O (overall) Source: Gasteiger, WHEC 2010 Institute of Energy and Climate Research Fuel Cells (IEK-3) 16

17 PEFC Polymer Electrolyte Fuel Cell PEFC - e- R + (ƞ HOR < 5 mv) H + O 2 (Air) ( 60 mv R contact ) H 2 H 2 O Anode Pt Cathode Pt 60 % void volume / pore nm Source: Gasteiger, WHEC 2010 Institute of Energy and Climate Research Fuel Cells (IEK-3) 17

18 PEFC Polymer Electrolyte Fuel Cell - MEA Performance Analysis (ƞ HOR < 5 mv) ( 60 mv R contact ) MEA: 0.05 / 0.40 mg Pt /cm² MEA DOE Target 2015: 0.2 g Pt /kw MEA 0.05 / 0.10 mg Pt /cm² MEA 4 x better ORR catalyst!!! Source: Gasteiger, WHEC 2010 Institute of Energy and Climate Research Fuel Cells (IEK-3) 18

19 MEA Performance Catalyst development Source: Gasteiger, WHEC 2010 Institute of Energy and Climate Research Fuel Cells (IEK-3) 19

20 MEA Performance Catalyst development Institute of Energy and Climate Research Fuel Cells (IEK-3) 20

21 Catalyst development - Core shell catalysts Source: AMR 2011, Brookhaven National Laboratory Institute of Energy and Climate Research Fuel Cells (IEK-3) 21

22 Catalyst development NSTF catalysts NanoStructured Thin Film (NSTF) catalysts, Pt 3 Ni 7 & PtCoMn Institute of Energy and Climate Research Fuel Cells (IEK-3) 22 Source: AMR 2011, 3M

23 MEA Performance Catalyst durability Carbon corrosion High cathode potentials cause electrochemical oxidation of carbon supports High cathode potentials can be induced by Start-up shut down (E cathode V) Local H 2 starvation (E cathode V) Operation at OCV (E cathode 0.95 V) Loss of catalyst mass activity Voltage cycling can cause loss of catalyst surface area Institute of Energy and Climate Research Fuel Cells (IEK-3) 23 Source: GM

24 MEA Performance Catalyst durability - Carbon corrosion (start-up shut-down) air reduction ~ 1,0 V O 2 + 4H + + 2e - 2 H 2 O air cathode membrane anode H + oxidation H 2 2 H + + 2e - H 2 hydrogen Institute of Energy and Climate Research Fuel Cells (IEK-3) Quelle: H. Tang et al. J. Power Sources 158, 2006,

25 MEA Performance Catalyst durability - Carbon corrosion (start-up shut-down) air (B) air (D) ~ 1,0 1.0 V ~ V reduction O 2 + 4H + + 2e - 2 H 2 O C + 2 H 2 O CO 2 + 4H + + 4e - 2 H 2 O O 2 + 4H + + 4e - oxidation cathode membrane anode e - H + H + e - oxidation H 2 2 H + + 2e - O 2 + 4H + + 2e - 2 H 2 O reduction hydrogen (A) air (C) shutdown Start-up Institute of Energy and Climate Research Fuel Cells (IEK-3) Quelle: H. Tang et al. J. Power Sources 158, 2006,

26 MEA Performance Catalyst durability - Carbon corrosion (start-up shut-down) H 2 -zone air-zone Quelle: C.A. Reiser et al., Electrochem. and Solid-State Letters, Institute of Energy and Climate Research Fuel Cells (IEK-3) 8 (6) A273-A276 (2005) 26

27 MEA Performance Catalyst durability - Carbon corrosion (start-up shut-down) Electrochemical oxidation of carbon: C + H 2 O CO 2 + 4H + + 4e - Large performance losses at 5 8 %wt. C-loss Gaphitized Carbon support improves durability Institute of Energy and Climate Research Fuel Cells (IEK-3) Source: Gasteiger, WHEC

28 MEA Performance Catalyst durability - Carbon corrosion (Local H 2 starvation) Anode flow field with one-third missing Limiting current density distribution map Institute of Energy and Climate Research Fuel Cells (IEK-3) 28 Source: Z.Y. Liu et al., J. Electrochem. Soc., 155 (10) B979-B984 (2008)

29 MEA Performance Catalyst durability - Carbon corrosion (Local H 2 starvation) Limiting current density distribution map Institute of Energy and Climate Research Fuel Cells (IEK-3) 29 Source: Z.Y. Liu et al., J. Electrochem. Soc., 155 (10) B979-B984 (2008)

30 MEA Performance Catalyst durability - Carbon corrosion Conventional approaches used to reduce/avoid carbon corrosion Graphite supports, CNTs Graphitization of carbon blacks Non-carbon supports - Nitrides, carbides or metal oxides Institute of Energy and Climate Research Fuel Cells (IEK-3) 30

31 MEA Performance Catalyst durability - Platin surface area loss Voltage cycling can cause loss of catalyst surface area Pt dissolution by two different processes: Diffusion of dissolved Pt species towards membrane phase Ostwald ripening of Pt inside the cathode electrode The Pt particle size rate of growth increases with increasing temperature The rate of Pt particle growth decreases with decreasing relative humidity Institute of Energy and Climate Research Fuel Cells (IEK-3) R.L. Borup et al. / Journal of Power Sources 163 (2006)

32 Fuel Cells: Goal and Objectives - Progress Fuel Cells for transportation Institute of Energy and Climate Research Fuel Cells (IEK-3) Source: AMR 2011, DOE 32

33 Introduction Polymer Membranes PEFC - e- + R Polymer Membrane H + O 2 (Air) H 2 H 2 O Anode Pt MEA Cathode Pt H 2 2H + + 2e - (anode) 1 / 2 O 2 + 2H + + 2e - H 2 O (cathode) H / 2 O 2 H 2 O (overall) carbon fluorine oxygen hydrogen sulphur sulfonic acidgroup, SO 3- H + Nafion (CF 2 CF 2 ) x (CRFCF 2 ) y R O(CF 2 )(CF 3 CF)O(CF 2 ) 2 (SO 3 H) Institute of Energy and Climate Research Fuel Cells (IEK-3) 33

34 Nafion State of the Art Nafion NR 211 Dispersion-cast Non-reinforced Thickness: 1 mil = 25 µm Equivalent weight: 1100 g // ion exchange capacity: 0.9 meq/g Extrapolated net sales price: /kw (Gebert, Jülich 2004) anode membrane cathode Source: Gasteiger, WHEC 2010 Only 30 mv voltage loss due to ohmic membrane resistance smaller than contact resistances Institute of Energy and Climate Research Fuel Cells (IEK-3) 34

35 Increased Lifetime of Nafion Membranes Membrane degradation - Due to an attack of H 2 O 2 / OH radicals - Depolymerizazion at reactive polymer endgroups and scission of side chains - Monitored by fluorine release rate Curtin et al. (DuPont Fuel Cells), J. Power Sources 131 (2004) 41 Mitigation strategies Treatment of the polymer during membrane production with elemental fluorine reduction of the number of reactive endgroups Protection of the endgroups by chemical reactions Use of redox-active additives such as e.g. Cerium(III) as regenerative free-radical scavengers Trogadas et al., Electrochem. Solid-State Lett. 11 (2008) B113 Institute of Energy and Climate Research Fuel Cells (IEK-3) Danilczuk et al., Macromolecules 42 (2009)

36 Motivation for High Temperature PEM Fuel Cells Comparison cooling circuit heat load ICE and FC at full power Thermal management: Small differential between operating and ambient temperatures Large heat exchanger necessary Source: Daimler AG Institute of Energy and Climate Research Fuel Cells (IEK-3) 36

37 Motivation for High Temperature PEM Fuel Cells Automotive FC System must be designed for their peak power operating point The hottest (& driest) conditions will exist at peak power > 90 % of the time system will run colder & thus, wetter Stack humidity will depend on system temperature & pressure US OEMs currently focusing on 95 C peak power system, where RH could range from 40 - >100% RH depending on pressure Q/ITD target: < kw/k (80 kw, 40 C ambient temperature) Q/ITD is proportional to radiator size T system > 95 C Requirements: Membranes with high 120 C and low RH Institute of Energy and Climate Research Fuel Cells (IEK-3) Source: US DOE Fuel Cell Pre-Solicitation Workshop,

38 Approaches to Increase the Operating Temperature Short side-chain PFSAs Multi-acid side-chain PFSAs Extremely thin membranes (5 µm; autohydration) Inorganic additives Oxides (mechanical stabilization) Layered zirconium phosphates Heteropolyacids (e.g. H 4 SiW 12 O H 2 O) as additional intrinsic proton conductors) Highly sulfonated linear hydrocarbons Polymers with angled / bulky side groups (= frozen-in free volume) 2-D and 3-D matrix polymers NanoCapillary networks (ionomeric nanofibers in an inert matrix) P. Pintauro, DOE Merit Review Meeting 2010 Institute of Energy and Climate Research Fuel Cells (IEK-3) 38

39 Short Side-Chain PFSAs Flexible side chains counteract close packing of polymer backbones Shorter side chains Increased degree of crystallinity Higher glass transition temperature (e.g. Nafion: > 100 C, 3M ionomer: >125 C) Better mechanical properties at same ion exchange capacity (IEC) Higher IEC possible without loss of mechanical stability Long side-chain Ionomers Short side-chain Ionomers Source: M. Gebert, Fuel Cell Seminar 2009 Institute of Energy and Climate Research Fuel Cells (IEK-3) 39

40 PEFC Membranes for Automotive Applications Stabilization of Nafion durabilities > 5,000 h (single cell) / 2,400 h (stack) achieved Membranes with a continuous operating temperature ~ 95 C needed Short-term operation at 120 C must be possible (at full load of the fuel cell) All developmental membranes still rely on proton transport in liquid water Most approaches for C membranes aim to increase the mechanical stability of a polymer backbone / matrix and to use low-ew ionomer Source: J. Healy, GM Institute of Energy and Climate Research Fuel Cells (IEK-3) 40

41 Outline Introduction PEFC & DMFC PEFC - Materials, experiences, challenges DMFC - Materials, experiences, challenges Summary Institute of Energy and Climate Research Fuel Cells (IEK-3) 41

42 Introduction - Direct Methanol Fuel Cell (DMFC) PEFC DMFC - e- R + - e- R + H + O 2 (Air) CO 2 H + O 2 (Air) H 2 Anode Pt H 2 O Cathode Pt CH 3 OH +H 2 O Anode PtRu H 2 O Cathode Pt MEA MEA H 2 2H + + 2e - (anode) 1 / 2 O 2 + 2H + + 2e - H 2 O (cathode) H / 2 O 2 H 2 O (overall) CH 3 OH + H 2 O CO 2 + 6H + + 6e - (anode) 3 / 2 O 2 + 6H + + 6e - 3H 2 O (cathode) CH 3 OH + 3 / 2 O 2 CO 2 + 2H 2 O (overall) Institute of Energy and Climate Research Fuel Cells (IEK-3) 42

43 DMFC Introduction DMFC U < 0.4 V (vs.rhe) Dehydrogenation: CH - e- 3 OH + Pt Pt-CO ad + 4H e - Adsorption of H 2 O R H 2 O + Ru Ru-OH 2 CO 2 H + O 2 (Air) CH 3 OH +H 2 O Anode PtRu MEA H 2 O Cathode Pt CH 3 OH + H 2 O CO 2 + 6H + + 6e - (anode) 3 / 2 O 2 + 6H + + 6e - 3H 2 O (cathode) CH 3 OH + 3 / 2 O 2 CO 2 + 2H 2 O (overall) Institute of Energy and Climate Research Fuel Cells (IEK-3) Source: T. Yajima, H. Uchida, and M. Watanabe, J. Phys. Chem. B, 108, 2654 (2004) 43

44 DMFC Introduction DMFC U < 0.4 V (vs.rhe) Dehydrogenation: CH - e- 3 OH + Pt Pt-CO ad + 4H e - Adsorption of H 2 O R H 2 O + Ru Ru-OH 2 CO 2 H + O 2 (Air) CH 3 OH +H 2 O Anode PtRu MEA H 2 O Cathode Pt U > 0.4 V (vs.rhe) CH 3 OH + H 2 O CO 2 + 6H + + 6e - (anode) Water discharging 3 / 2 O Ru-OH 2 + 6H + + 6e - 3H 2 O (cathode) 2 Ru-OH + H + + e - CH 3 OH + 3 / 2 O 2 CO 2 + 2H 2 O (overall) Institute of Energy and Climate Research Fuel Cells (IEK-3) Source: T. Yajima, H. Uchida, and M. Watanabe, J. Phys. Chem. B, 108, 2654 (2004) 44

45 DMFC Introduction DMFC U < 0.4 V (vs.rhe) Dehydrogenation: CH - e- 3 OH + Pt Pt-CO ad + 4H e - Adsorption of H 2 O R H 2 O + Ru Ru-OH 2 CO 2 H + O 2 (Air) CH 3 OH +H 2 O Anode PtRu MEA H 2 O Cathode Pt U > 0.4 V (vs.rhe) CH 3 OH + H 2 O CO 2 + 6H + + 6e - (anode) Water discharging 3 / 2 O Ru-OH 2 + 6H + + 6e - 3H 2 O (cathode) 2 Ru-OH + H + + e - CHPt-CO 3 OH + 3 / 2 O 2 CO 2 + 2H O (overall) ad + Ru-OH ad CO 2 + H + + e - Institute of Energy and Climate Research Fuel Cells (IEK-3) Source: T. Yajima, H. Uchida, and M. Watanabe, J. Phys. Chem. B, 108, 2654 (2004) 45

46 DMFC Introduction - Hydrogen versus methanol 1 0, ,8 0.8 H / 2 O 2 H 2 O 0,7 0.7 Cell voltage [V] 0, , , , ,2 0.2 CH 3 OH + 3 / 2 O 2 CO 2 + 2H 2 O 0,1 0.1 DMFC PEFC 0 0, ,1 0, , , , , ,7 0, , ,0 Current density [A/cm²] Institute of Energy and Climate Research Fuel Cells (IEK-3) 46

47 Direct Methanol Fuel Cells - Advantages of DMFCs compared to PEFC High energy density - longer use-time, extended range Quick refueling No high pressure tanks kwh/l Ethanol liquid Methanol liquid kwh/l kwh/l incl. tank Hydrogen gaseous (700 bar) Hydrogen gaseous (300 bar) Lead Acid Battery in rel. to Pb battery gasoline propane Operating Range 700 bar lithium 300 bar Pb battery ICE * DMFC PEFC Battery Institute of Energy and Climate Research Fuel Cells (IEK-3) *ICE: Internal Combustion Engine 47

48 Direct Liquid Fuel Cells - Applications Portable 50 W Replacement of Li battery Source: TOSHIBA Source: Samsung Source: MTI Micro Fuel Cells Transportable 50 W - 1 kw Replacement of Diesel generator Source: SFC Source: Mitsubishi Gas Chemicals Source: IRD Light traction kw Replacement of battery Source: ProPower Source: Suzuki Motors Source: SFC Source: Oorja Protonics Institute of Energy and Climate Research Fuel Cells (IEK-3) 48

49 DMFC - Designs Active DMFC System Passive DMFC System - + CO 2 air cathode anode MeOH tank methanol + water fuel reservoir DMFC stack water + heat Source: SFC Source: Yamaha Source: MTI Micro Fuel Cells Source: ISE Freiburg Institute of Energy and Climate Research Fuel Cells (IEK-3) 49

50 DMFC, Technical Products on the Market - Auxiliary power units for mobile homes As of today, > 20,000 fuel cell systems shipped Fuel Cell System Power Voltage Capacity Cartridges DMFC Watt 12 V Wh/day 5 28 L Methanol Institute of Energy and Climate Research Fuel Cells (IEK-3) Source: SFC 50

51 DMFC, Technical Products on the Market - External charger for cell phone batteries Fuel Cell System Output Size Weight Tank volume Operation temperature DMFC DC 5 V, 400 ma W150 x D21 x H74.5 mm 280 g 14 ml C, %RH Fuel Cartridge Capacity 50 ml, 98 % Methanol Institute of Energy and Climate Research Fuel Cells (IEK-3) Source: TOSHIBA 51

52 DMFC, Technical Products on the Market - Material handling Technical data Drive module Peak power 7 kw (fuel cell battery hybrid system) water 35 C MeOH cartridge 20 L, 32 h operation time battery lithium ion high power (45 Ah, 7s) Stack Nominal power Number of cells 1.3 kw 90 Lifetime 25 % power 5,000 h MEA Power density mv Pt/PtRu-loading 4.5 mg/(cm² cell) Institute of Energy and Climate Research Fuel Cells (IEK-3) 52

53 DMFC System Development - Main problem areas Performance and total system efficiency - Cell voltage - Water & methanol permeation Long-term stability Cost Targets for DMFC system development DMFC overall efficiency 30 % Durability: 25 % power 10,000 h Water autonomous operation up to 35 C ambient temperature Cost competitiveness tot = U x F x S CH 3 OH 3 Stack 0.38 U = voltage efficiency F = fuel utilization level stack System Periph S = system efficiency DC/DC , DMFC system efficiency Pel., net el.. m H Battery Akku Electrical plant efficiency Institute of Energy and Climate Research Fuel Cells (IEK-3) 53

54 DMFC, Performance and total System Efficiency - Cell voltage Cell voltage [V] 1 0, , , , , , , ,2 0.2 CH 3 OH + 3 / 2 O 2 H / 2 O 2 H 2 O CO 2 + 2H 2 O Strategies to improve cell voltage Reduce methanol permeation Methanol tolerant catalysts Anode catalysts New supports for highly active catalysts Example Ternary PtRuCo alloys as anode catalysts 0,1 0.1 DMFC PEFC 0 0, ,1 0, , , , , ,7 0, , ,0 Current density [A/cm²] Cell voltage is lower for DMFC than for PEFC - Slow electrochemical oxidation of methanol - Mixed-potential formation at the cathode Higher catalyst loading in contrast to PEFC - DMFC: 4 mg/(cm² cell) - PEFC: mg/(cm² cell) Addition of Co reduces onset potential of methanol oxidation Source: J.S. Cooper et al. / Journal of Power Sources, 163 (2006) Institute of Energy and Climate Research Fuel Cells (IEK-3) 54

55 DMFC, Performance and total System Efficiency - New supports for highly active catalysts Institute of Energy and Climate Research Fuel Cells (IEK-3) 55 Source: AMR 2011, P.Zelenay

56 DMFC, Performance and total System Efficiency - Permeation of methanol and water Effect of Permeation Water - Cooling of the stack - Water must be returned to the anode - Flooding of cathodic catalyst layer Methanol - Loss of fuel (utilization) - Blocking of cathode catalyst - Reduction of cathode potential Strategies against Permeation Membrane - New membranes with reduced permeability for water and/or methanol MEA-Design - Dense electrodes for reduced diffusion Example Reduction of methanol permeation by different anode catalyst layers Untreated carbon cloth Hydrophobised carbon cloth Source: A. Schröder et al. / Journal of Power Sources 195 (2010) Institute of Energy and Climate Research Fuel Cells (IEK-3) 56 Source: Liu et al. / J. of the Electrochem. Soc., 153 (2006) A543 A553

57 DMFC, Performance and total System Efficiency - Permeation of methanol and water Effect of Permeation Water - Cooling of the stack - Water must be returned to the anode - Flooding of cathodic catalyst layer Methanol - Loss of fuel (utilization) - Blocking of cathode catalyst - Reduction of cathode potential Strategies against Permeation Membrane - New membranes with reduced permeability for water and/or methanol MEA-Design - Dense electrodes for reduced diffusion Example Reduction of methanol permeation by different anode catalyst layers 2 M 3 M MeOH CDM CCM Untreated carbon cloth Hydrophobised carbon cloth Source: A. Schröder et al. / Journal of Power Sources 195 (2010) Institute of Energy and Climate Research Fuel Cells (IEK-3) 57 Source: Liu et al. / J. of the Electrochem. Soc., 153 (2006) A543 A553

58 DMFC, Performance and total System Efficiency - Permeation of methanol At a faradaic current density of 150 ma/cm 2, the equivalent of 40 ma/cm 2 is lost by crossover of methanol from anode to cathode without electricity generation. Lower crossover through thicker membranes. Methanol utilization only 75% Institute of Energy and Climate Research Fuel Cells (IEK-3) 58

59 DMFC, Performance and total System Efficiency - Examples of emerging low-crossover membranes Phase-separated block-copolymers Pore-filling membranes with reduced swelling Sulfonated polysulfones Institute of Energy and Climate Research Fuel Cells (IEK-3) 59

60 DMFC, Performance and total System Efficiency - Research on new membranes with lower permeation of methanol Cells with alternative membranes can give the same performance at lower permeation. Methanol utilization increased from 75% to 85-90% Institute of Energy and Climate Research Fuel Cells (IEK-3) 60

61 DMFC, Long-Term Stability - Reasons for performance loss Permanent degradation, unrecoverable performance loss Loss of electrochemically active surface area of electrodes Ruthenium crossover (migration) from the anode to the cathode and its re-deposition at the Pt catalyst surface, Ru corrosion Irreversible loss of cathode hydrophobicity Electrode delamination Poor reagent distribution in individual cells of a fuel cell stack, including cell reversal Temporary degradation, recoverable performance loss Cathode Pt catalyst surface oxidation Membrane dehydration Incipient cathode flooding Source: P. Zelenay, ECS Trans. 1, 8 (2006) 483 Performance loss by metal ions and organic contaminants Degradation is in proportion to the amount of metal ions trapped in the electrolyte membrane Organic contaminants influence cell performance, oxidized products affect the anodic reaction Source: K. Yasuda et al., ECS Trans. 5, 1 (2007) 291 Institute of Energy and Climate Research Fuel Cells (IEK-3) 61

62 DMFC, Long-Term Stability - Reasons for performance loss Unrecoverable performance loss Recoverable performance loss Performance loss by metal ions and organic contaminants Degradation is in proportion to the amount of metal ions trapped in the electrolyte membrane Organic contaminants influence cell performance, oxidized products affect the anodic reaction Source: K. Yasuda et al., ECS Trans. 5, 1 (2007) 291 Institute of Energy and Climate Research Fuel Cells (IEK-3) 62

63 DMFC V3.3-1 hybrid system - Durability test in realistic systems environment (2009/2010) mittlere Zellspannung in mv average cell voltage [mv] ma/cm² 100 ma/cm² Reasons for performance loss: - Ru crossover, Ru corrosion - Trapped metal ions in the electrolyte membrane T Stack = C c MeOH = 0,45 0,95 M VLK = 16,4 26,2 ml/(cm² min) ma/cm²: 41,6 µv/h 100 ma/cm²: 52,0 µv/h Degradation of short stacks ~ 16 0,1 A/cm² Degradation of 90-cell stack ~ 52 0,1 A/cm² time [h] Zeit in h factor ~3 Institute of Energy and Climate Research Fuel Cells (IEK-3) 63

64 DMFC, Long-Term Stability - Reasons for performance loss Influence of dissolved ions on fuel cell performance Continuous measurement of cell voltage Overlap of irreversible and reversible degradation Discontinuous characterization by polarization plots Irreversible aging voltage Voltage U Cell [A/cm²] [V] 0,6 0,5 0,4 0,3 0,2 0,1 0,0 0,90 mg/l 0,77 mg/l 0,00 mg/l 0,19 mg/l Calcium Voltage U Cell [A/cm²] test Operation duration time t [h] [h] Current density [A/cm²] Institute of Energy and Climate Research Fuel Cells (IEK-3) 64

65 DMFC V3.3-2 hybrid system - Modifications compared to DMFC V3.3-1 Stack 90 cells Expanded graphite purified with oxalic acid (Fe impurities) New optimized wicking port for air low air flows possible (< 10 ml/(cm²*min) Commercial MEA 0341 (Johnson Matthey) with new PtRu catalyst* Anode:TGP-H-060, loading of 3.0 mg Pt/cm², 1.5 mg Ru/cm² Membrane: DuPont Nafion N115 Cathode: TGP-H-060, loading of 1.5 mg Pt/cm² (*see N. Cabello-Moreno et all., ECS Meeting 2009, Vienna, Austria catalyst only available within MEAs) System Condenser/heat exchanger laser welded (Condenser DMFC V3.3-1: bonded with Silane Terminated Prepolymer) Water autonomous 35 C ambient temperature Eliminating critical system parameters, espcially OCV Institute of Energy and Climate Research Fuel Cells (IEK-3) 65

66 DMFC V3.3-2 hybrid system average cell Zellspannung voltage [mv] mittlere in mv - Durability test in realistic systems environment (2010/2011) Tstack= C cmeoh= M VLK= ml/(cm² min) bis 580 Betriebsstunden: 50 ma/cm²: 31,8 µv/h 75 ma/cm²: 56,3 µv/h 100 ma/cm²: 65,7 µv/h ma/cm² 75 ma/cm² 100 ma/cm² ab 580 Betriebsstunden: 50 ma/cm²: 5,1 µv/h 75 ma/cm²: 4,6 µv/h 100 ma/cm²: 8,8 µv/h Betriebs-h time [h] Institute of Energy and Climate Research Fuel Cells (IEK-3) 66

67 DMFC V3.3-2 hybrid system - Cations in anodic H 2 O/MeOH loop (ICP-OES*) Kationen in Anodenflüssigkeit Systembetrieb DMFC V3.3-2 Jul März ,0 Detection limit: Ru 0.1 mg/l Pt 0.2 mg/l 4,5 4,0 3,5 3,0 2,5 mg/l Ru mg/l (after system failures) 2,0 1, Al Ca Ce Cr Fe La Mn Na Pb Ru Sr V Zn B Al Ba Ca Cd Ce Co Cr Cu Fe K La Mg Mn Mo Na Ni Pb Pt Ru Sn Sr Ti V Y Zn Zr B Si Institute of Energy and Climate Research Fuel Cells (IEK-3) *Inductively Coupled Plasma with 67 Optical Emission Spectroscopy 1,0 0,5 0,0 Ru 0.18 mg/l Pt 0.34 mg/l (after interruption)

68 Summary Cost and durability are the major challenges to fuel cell commercialization For transportation applications cathode catalysts with 4x Pt activity or nonpricious metal catalysts are needed Pt-alloys, core-shell structures, dealloyed Pt alloy catalysts, thin Pt (alloy) films on nanostructured supports for higher mass activity cathode catalysts Carbon-support corrosion and Pt-dissolution by start/stop can be mitigated by system controls and advanced support and catalyst materials DMFCs are attractive for different applications as replacement for batteries up to about 5 kw By intensive R&D substantial progress in development of components, stacks and systems was achieved Portable DMFCs have already reached single niche markets DMFC stack durability in real systems has been increased to more than 5,000 h Institute of Energy and Climate Research Fuel Cells (IEK-3) 68