NPRENPRE--470470 FuelFuel CellCell TypesTypes Chapter 8 of Fuel Cell Fundamentals Dr. Kyu-Jung Kim Department of Nuclear, Plasma and Radiology Engineering University of Illinois BasicBasic FuelFuel CellCell OperationOperation

 PEM FC

+ - • Anode : 2H2  4H + 4e

+ - • Cathode : O2 + 4H + 4e  2H2O

• Cell : 2H2 + O2  2H2O

• Eo = 1.23 V

2 OxidationOxidation vs.vs. ReductionReduction

. Oxidation • Electrons removed from species • Electrons liberated by reaction • Anode half reaction (Hydrogen Oxidation Reaction: HOR) + - • 2H2  4H + 4e

. Reduction • Electrons added to species • Electrons consumed by reaction • Cathode half reaction (Oxygen Reduction Reaction: ORR) + - • O2 + 4H + 4e  2H2O

3 LowLow TempTemp FuelFuel CellsCells

180 ~ 210 oC

60 ~ 250 oC

90 oC

90 oC

4 HighHigh TempTemp FuelFuel CellsCells

600 ~ 1,000 oC

650 oC

5 PEMFCPEMFC – Polymer Electrolyte Membrane Fuel Cell

90 oC Porous Pt/C PEM Pt/C Porous Carbon Carbon • PEM – 20~200 μm • Advantages Highest power density as 500 ~ 2500 mW/cm2 Fast start-stop, Low temperature operation • Disadvantages Platinum catalyst, active water management, poor CO and S tolerance 6 Pt/CPt/C catalystcatalyst

*

* Transmission Electron Microscopy 7 PEMFCPEMFC – Typical PEMFC MEA fabrication process

8 PEMFCPEMFC – Polymer Electrolyte Membrane Fuel Cell

15%

37.8%

= 1.36 million Btu/hr

47.2%

= 498 kW

9 PEMFCPEMFC – Polymer Electrolyte Membrane Fuel Cell

Backup Water Heater

Ene-Farm Home Fuel Cell TM

• 700 W maximum • Combined Heat and Power generation (CHP) • Tokyo Gas and Panasonic

Fuel Cell Unit Hot Water Unit

10 PEMFCPEMFC – Polymer Electrolyte Membrane Fuel Cell

• System Schematics

11 PEMFCPEMFC – Polymer Electrolyte Membrane Fuel Cell

95 % co-gen

= 6.8 years

Price 12 DMFCDMFC – Direct Methanol Fuel Cell

90 oC Porous Pt/C PEM Pt/C Porous Carbon Ru, Sn, W, Re Carbon • Advantages Direct use of liquid fuel Suitable for potable application • Disadvantages Low power density as 30 ~ 100 mW/cm2 Undesirable intermediates formation such as CO Methanol cross-over through PEM

13 DMFCDMFC – Direct Methanol Fuel Cell

14 DMFCDMFC – Direct Methanol Fuel Cell

1 month of operation with 650 Whr/ℓ of power density and 1,200 Whr of energy storage

1 month = 8 hrs/day and 5 days/week 30 W of average power

Methanol DMFC Extended Tank (100cc) Methanol 1.1 Whr/cc Tank (1,000cc)

15 DirectDirect MethanolMethanol FuelFuel CellCell

Specification

Type DMFC`

For use in Lap-top computer

Power 25 W

Nominal Voltage 8 ~ 10 Volt

Typical capacity 250 Whr 1.25 Whr/cc Fuel capacity 200 cc

Fuel type 100 % Methanol

Nominal weight 1.7 kg (3.75 lbs)

Size 232 x 106 x 54 mm

Lifetime 4,000 hr

16 DirectDirect MethanolMethanol FuelFuel CellCell

Control circuit board

Display

Switch

Battery & power converter

Stack Fuel manifold

Methanol fuel canister

17 DirectDirect MethanolMethanol FuelFuel CellCell

18 AFCAFC – Alkaline Fuel Cell

60 ~ 250 oC Porous Pt/C KOH Pt/C Porous Carbon or Ni aqueous or Ni Carbon solution • Advantages Non-precious catalyst due to higher cathode performance Low-cost electrolyte • Disadvantages - 2- Pure H2 and O2 only due to 2OH + CO2 → CO3 + H2 O and K2CO 3 precipitation Occasional replenishment of KOH electrolyte Water removal from anode is critical 19 AFCAFC – Alkaline Fuel Cell

20 PAFCPAFC – Phosphoric Acid Fuel Cell

o 180~210 C Porous Pt/C H3 PO4 in Pt/C Porous Graphite SiC matrix Graphite • Phosphoric acid under 42 oC  solidifies, over 210 oC  phase transition loosing ability as an electrolyte.

• Advantages – Reliability, long-term performance, low-cost electrolyte.

• Disadvantages – Platinum catalyst, CO and S poisoning, replenishment of corrosive electrolyte.

21 PAFCPAFC – Phosphoric Acid Fuel Cell

22 MCFCMCFC – Molten Carbonate Fuel Cell

650 oC Porous Porous Li2CO 3 Nickel / Chrome Nickel Oxide K2CO 3

In LiOAlO2

23 MCFCMCFC – Molten Carbonate Fuel Cell

• Suitable for stationary continuous power application

• Advantages

Fuel flexibility – H2, CO, CnH m (Methane, alcohols) Non-precious metal catalyst

High quality of waste heat for cogeneration application

• Disadvantages

CO2 recycling complexity Corrosive molten carbonate electrolyte

Degradation / Life-time issues

24 MCFCMCFC – Molten Carbonate Fuel Cell

(a) (b)

25 MCFCMCFC – Molten Carbonate Fuel Cell

26 MCFCMCFC – Molten Carbonate Fuel Cell

84 % co-gen

27 MCFCMCFC – Molten Carbonate Fuel Cell

21 units

28 SOFCSOFC – Solid Oxide Fuel Cell

YSZ 600 ~ 1000 oC Porous Solid Porous Nickel / YSZ* cermet ceramic Conducting oxide * Yttria-Stabilized Zirconia 29 SOFCSOFC – Solid Oxide Fuel Cell

• High temperature environment of operation

• Anode – durable against highly reducing environment

Nickel : catalytic activity, conductivity

YSZ cermet : ion conductivity, thermal expansion compatibility, mechanical stability, maintain high porosity & surface area

• Cathode – durable against highly oxidizing environment

MIEC : Mixed Ion-Electron Conducting ceramic material

LSM : Strontium-doped Lanthanum Manganite

LSF : Lanthanum Strontium Ferrite

LSC : Lanthanum Strontium Cobaltite

LSCF : Lanthanum Strontium Cobaltite Ferrite

30 SOFCSOFC – Solid Oxide Fuel Cell

• Advantages

Fuel flexibility – H2, CO, CnH m Non-precious metal catalyst

High quality of waste heat for cogeneration application

Solid electrolyte

• Disadvantages

High temperature materials issues

Sealing issues

Expensive components and fabrication

Fuel dilution problem because H2O generation from anode

31 SOFCSOFC – Solid Oxide Fuel Cell

32 SOFCSOFC – Solid Oxide Fuel Cell

33 SOFCSOFC – Solid Oxide Fuel Cell

34 SOFCSOFC – Solid Oxide Fuel Cell

. SOFC and Gas Turbine Combined Cycle for 1 MW Power Plant

35 SOFCSOFC – Solid Oxide Fuel Cell

. Triple Combined Cycle ( SOFC + Gas Turbine + Steam Turbine )

55% 45% 1200 oC

Turbocharger

Mitsubishi Heavy Industries

36 SOFCSOFC – Solid Oxide Fuel Cell

. Energy Balance of Triple Combined Cycle for 400 MW Plant

Mitsubishi Heavy Industries

37 SingleSingle--ChamberChamber SOFCSOFC Ni–GDC (Gadolinium-Doped Ceria) cermets

Sm0.5Sr 0.5CoO 3-x (SSC)

38 SingleSingle--ChamberChamber SOFCSOFC

 Advantages • Simple design structure • Require no high-temperature seals • The electrolyte no longer needs to be gastight, significantly relaxing electrolyte fabrication requirements. • Size reduction/miniaturization is facilitated by the intrinsic simplicity of single-chamber design and reduced gas manifolding requirements.

 Disadvantages • The risk of fuel–air mixture explosions. • Operation on very dilute (typically < 4%*) fuel mixtures, decreasing performance. • Electrode materials are never 100% selective, and parasitic non- electrochemical reactions result reducing of fuel utilization and decrease efficiency.

* Flammability of H2 = 4.1~72.5 vol. % 39 DirectDirect FlameFlame SOFCSOFC

40 DirectDirect FlameFlame SOFCSOFC

 Advantages • The fuel flexible system - intermediate flame species are similar for all kinds of hydrocarbons, the cell can be operated on virtually any carbon- based fuel. • Remarkably simple structure - The anode is simply held in the exhaust gases close to a fuel-rich flame, while the cathode breathes ambient air. • The system is thermally self-sustained and there are no sealing requirements. • System start-up is rapid - typically within seconds depending on the thermal mass of the fuel cell.

 Disadvantages • Low-efficiency, low-power density • Issues with coking depending on the flame chemistry and thermal shock due to rapid thermal cycles.

41 LiquidLiquid--TinTin AnodeAnode SOFCSOFC

42 LiquidLiquid--TinTin AnodeAnode SOFCSOFC

 Advantages • Uses conventional SOFC electrolytes and cathodes but employs an anode based on liquid tin. • The liquid-tin anode allows direct oxidation of almost any carbon- containing fuel (including biomass, JP8 - a sulfur-rich military logistics fuel, coal, woodchips, even plastic bags) without reforming or other fuel processing. • The liquid-tin anode is surprisingly durable, it is not harmed by coking, and it is not poisoned by sulfur but can be used as a fuel.

 Disadvantages • The required operation temperature is quite high (> 900∘C). • Power densities remain low. • Lifetime/durability issues must be investigated further.

43 MembranelessMembraneless FuelFuel CellsCells

44 MetalMetal--AirAir CellsCells

- - • Anode Reaction: Zn + 2OH  ZnO + H2O + 2e

- - • Cathode Reaction: ½ O2 + H2O + 2e  2OH

• Overall Reaction: ½ O2 + Zn  ZnO

45 ProtonicProtonic CeramicCeramic FuelFuel CellsCells ((PCFCsPCFCs))

• PCFCs are based on proton-conducting capable of solid-state oxide

electrolytes include acceptor-doped perovskite (CaTiO3) compositions based on o BaZrO3 and BaCeO3 with operation temp 350 ~ 500 C

• Advantages - PCFCs share many characteristics in common with SOFCs. - Enable operation on non-hydrogen fuels - Relatively inexpensive oxide materials requiring little or no precious metal catalysts - Like PEMFCs produce water at the cathode. Therefore the anode fuel is not diluted by product water gas, enabling potential gains in cell operating voltage and efficiency.

• Disadvantage - Poor performance unless the new electrode materials (especially new cathode materials) that work at lower temperatures and are compatible with PCFC electrolytes are developed

46 SolidSolid--AcidAcid FuelFuel CellsCells

• SAFCs use a solid proton-conducting electrolyte based on an inorganic acid salt (“a solid acid”) which is thought to be of as in-between normal salts and normal acids.

• For example, if sulfuric acid (H2SO 4 ) is reacted with cesium sulfate (Cs2SO 4 ) salt, the solid acid CsHSO4 is produced: ½ H2 SO4 + ½ Cs2SO 4 → CsHSO4

• The structure of most solid acids like CsHSO4 is highly ordered and crystalline at room temperature and therefore it is poor ionic conductors. • Temperatures typically between 50 and 150∘C it becomes a “superprotonic phase transition” where the onset of structural disorder enables a dramatic increase in the proton conductivity by two to three orders of magnitude. • Most solid acids do not decompose until temperatures > 250∘C. • SAFCs enable operation of high-performance PEM-like fuel cells at temperatures greater than 100∘C. Haile et al. at the California Institute of Technology have largely been responsible for the development of SAFC technology over the last 15 years. • Combine the advantages of thin and relatively mechanically strong structure of MEA as of PEMFCs and somewhat greater tolerance for CO and other fuel-stream impurities as of PAFCs. • The main issues associated with the SAFC include preventing degradation of the solid- acid electrolyte during long-term operation and decreasing the amount of precious metal catalyst needed in the electrodes.

47 RedoxRedox FlowFlow BatteriesBatteries • Reduction–Oxidation Flow Battery is a rechargeable battery that uses liquid fuel and liquid oxidant very similar to a fuel cell; it stores the fuel and oxidant in separate tanks outside of reaction cells then they are pumped to the anode for oxidation and reduction at the cathode. • A key feature of the redox flow battery is the reversibility of the reaction, which enables these systems to be rechargeable. During charging, depleted fuel (or oxidant) can be reconverted to fresh fuel (or oxidant).

• Example is the all-vanadium redox flow battery system which is using vanadium oxide V2 O5 5+ 4+ 3+ 2+ dissolved in sulfuric acid H2 SO4 . When all four vanadium oxidation states V , V , V , V + 2+ 3+ 2+ can exist in the aqueous electrolyte in the form of VO2 , VO , V and V . • Anode: V2+ → V3+ + e− + + − 2+ • Cathode: VO2 + 2H + e → VO + H2 O 2+ + + 3+ 2+ • Overall reaction: V + VO2 + 2H → V + VO + H2 O

• Proton Exchange Membrane is placed between the anode and the cathode. This makes the redox flow battery very similar to a PEMFC in principle even though the cell structure and materials are different. • Challenges associated with redox flow batteries include system complexity as well as low energy density and power density. • Large-scale energy storage systems and back-up power supply systems with sizes up to 1MW in power and several MWh in energy storage due to cheap price of redox flow batteries compared to common solid-state secondary batteries such as lithium-ion batteries.

48 ElectrolysisElectrolysis && ReversibleReversible FuelFuel CellCell––ElectrolyzersElectrolyzers

49 FormicFormic AcidAcid FuelFuel CellsCells

+ - Anode: HCOOH → CO2 + 2H + 2e

+ - Cathode: ½ O2 + 2H + 2e → H2 O

Overall: HCOOH + ½ O2 → CO2 + H2 O

50 DAAAEMFCDAAAEMFC Direct Ammonia Alkaline Anion-Exchange Membrane Fuel Cells

− − O2 + 2H2 O + 4e  4 OH Cathode reaction E0 = + 0.40 V − − − 2NH3 + 6 OH  N2 + 6H 2 O + 6 e Anode reaction E0 = 0.77 V 4NH3 + 3 O2  2 N2 + 6 H2 O Overall reaction E0 = + 1.17 V Rong Lan and Shanwen Tao Department of Chemistry, Heriot-Watt University, Edinburgh, United Kingdom Electrochemical and Solid-State Letters, 13 [8] B83-B86, 2010 51 DirectDirect UreaUrea FuelFuel CellCell

Anion Exchange Resin Rohm and Haas

Rong Lan, Shanwen Tao and John T. S. Irvine Department of Chemistry, Heriot-Watt University, Edinburgh, United Kingdom Energy Environ. Sci,, 2010, [3], 438-441 The Royal Society of Chemistry 52 DirectDirect UreaUrea FuelFuel CellCell

at Room temperature at 50 oC

o Ni/C – MnO2/C Fuel cell performance, 50 C, O2

Rong Lan, Shanwen Tao and John T. S. Irvine Department of Chemistry, Heriot-Watt University, Edinburgh, United Kingdom Energy Environ. Sci,, 2010, [3], 438-441 The Royal Society of Chemistry 53 DirectDirect BorohydrideBorohydride FuelFuel CellsCells Na+ cation

 PEM using Na+ cation of mobile charge carrier

1.64 V

Cheolhwan Kim, Kyu-Jung Kim, Man Yeong Ha Performance enhancement of a direct borohydride fuel cell in practical running conditions Journal of Power Sources 180 (2008) 154–161 54 DirectDirect BorohydrideBorohydride FuelFuel CellsCells Na+ cation

 PEM using Na+ cation of mobile charge carrier

1.5 250 SUS single cell SUS single cell SUS 5 cell SUS 5 cell 1.2 Graphite 5 cell 200 Graphite 5 cell 2 V

0.9 150

0.6 100 Average voltage, voltage, Average

0.3 mW/cm density, Power 50

0.0 0 0 100 200 300 400 500 0 100 200 300 400 500 Current density, mA/cm2 Current density, mA/cm2

Stack Bi-polar plate material : SUS vs Graphite

Cheolhwan Kim, Kyu-Jung Kim, Man Yeong Ha Performance enhancement of a direct borohydride fuel cell in practical running conditions Journal of Power Sources 180 (2008) 154–161 55 DirectDirect BorohydrideBorohydride FuelFuel CellsCells Na+ cation

 PEM using Na+ cation of mobile charge carrier

1.5 200 250 20 cells stack 5 cells stack 1.2 160 200 2

0.9 mW/cm 120 150 W

0.6 80 100 Power, Average voltage, V voltage, Average

0.3 density, Power 40 50 Power density Power 0.0 0 0 0 100 200 300 400 500 0 100 200 300 400 500 Current density, mA/cm2 Current density, mA/cm2

Multi-cell Performance : 5 cell stack vs 20 cell stack

Cheolhwan Kim, Kyu-Jung Kim, Man Yeong Ha Performance enhancement of a direct borohydride fuel cell in practical running conditions Journal of Power Sources 180 (2008) 154–161 56 DirectDirect BorohydrideBorohydride FuelFuel CellsCells H+ proton

 PEM using H+ proton of mobile charge carrier

NaBH4 + NaOH 4H2 O2 or 2O2 from Air

+ H2 O

+ NaBH + 2H O 8H 4H O + 8H+ + 8e- 2O + 8H+ + 8e- 4 2 2 2 or 2 + -  8H2 O  4H2 O  NaBO2 + 8H + 8e

NaBO2

+ NaOH 8H2 O

+ H2 O

+ - • Anode: NaBH4 + 2H2O  NaBO2 + 8 H + 8 e + - • Cathode (H2O 2): 4H2O 2 + 8 H + 8 e  8H2O E0 = 1.62 V + - • Cathode (Air): 2O2 + 8 H + 8 e  4H2O

Nie Luoa, G.H. Miley, Kyu-Jung Kim, Rodney Burton, Xinyu Huang NaBH4/H2O 2 fuel cells for air independent power systems Journal of Power Sources 185 (2008) 685–690 57 DirectDirect BorohydrideBorohydride FuelFuel CellsCells H+ proton  DBFC Test Cell Design Performance

 Maximum 14 W with 2”x2” active area of MEA

 543 mW/cm2

 Actual OCV (Open Cell Voltage)

DBFC = 1.62 V PEM = 1.23 V DMFC = 0.8 V DMFC PEMFC

2 2 x 2 in DBFC Test Cell using H2 O2 oxidizer

Nie Luoa, G.H. Miley, Kyu-Jung Kim, Rodney Burton, Xinyu Huang NaBH4/H2O2 fuel cells for air independent power systems Journal of Power Sources 185 (2008) 685–690 58 kWkW LevelLevel DBFCDBFC StackStack

MEA

Stainless steel Bi-polar plate (Coolant circulating)

Graphite Bi-polar plate (Fuel and oxidizer flow channel)

24 Cell Stack 4”x4” of active MEA area Fuel and oxidizer manifolds operation

59 DirectDirect BorohydrideBorohydride FuelFuel CellsCells H+ proton  Modular Type Gelled Mini DBFC

Epoxy Bipolar Plate Cathode Membrane Anode

Cover Frame End Plate Cover

20 W Mini DBFC, 2W x 10 cell modular type 1” x 5.5” x 1.5” chocolate bar size 60 DirectDirect BorohydrideBorohydride FuelFuel CellsCells H+ proton  Modular Type Gelled Mini DBFC

Modular Type FC for the Sandia Hopper Robot Hopper Robot

. Energy density: ~ 300 Wh/kg . Weight: less than 126 g . Max power: 45 W 2 sec. of pulse . Rated Power: more than 22 W

61 DirectDirect BorohydrideBorohydride FuelFuel CellsCells H+ proton  Composite Cell Design

62 DirectDirect BorohydrideBorohydride FuelFuel CellsCells H+ proton  Composite Cell Stack Design

63 DirectDirect BorohydrideBorohydride FuelFuel CellsCells H+ proton

64 DirectDirect BorohydrideBorohydride FuelFuel CellsCells H+ proton

12 cell DBFC stack performance

25 180

160

20 140 12 cell DBFC Stack 120 15 100 168 W 80

10 Power (W) Potential (V) Potential 14 W/Cell 60

2 5 40 140 mW/cm I-V I-P 20

OCV = 1.75 V 0 0 0 5 10 15 20 25 30 Current (A)

65 BOPBOP; Balance of Plant

 The fuel cell stack doesn’t work alone !

Hybrid power source using 1.5 KW PEM fuel cell. Metal hydride hydrogen storage

66 DBFCDBFC SystemSystem ConceptConcept

Battery DC/DC Converter & Control DBFC Stack DC Fuel Pump Fuel Tank (Main) Fuel Tank (auxiliary)

Fuel Heat Exchanger

Fuel Manifold

H2O 2 Manifold

DC H2O 2 Pump

Dilutor Circulation Pump

H2O 2 Tank

H2O 2 Heat Exchanger

67 DirectDirect BorohydrideBorohydride FuelFuel CellsCells H+ proton  BOP Schematic

68 DirectDirect BorohydrideBorohydride FuelFuel CellsCells H+ proton  Controller

69 DirectDirect BorohydrideBorohydride FuelFuel CellsCells H+ proton

DBFC Stack DC/DC Converter NaBH4 Storage Water storage H2O2 Storage

Battery Battery Charge Fuel cell and Pump Controller power distribution controller

70 ThankThank youyou

71