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New Developments in Electrochemical Cells Science Update Programme Education Bureau, HKSAR & Department of Chemistry The University of Hong Kong June 2002.

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Presentation on theme: "New Developments in Electrochemical Cells Science Update Programme Education Bureau, HKSAR & Department of Chemistry The University of Hong Kong June 2002."— Presentation transcript:

1 New Developments in Electrochemical Cells Science Update Programme Education Bureau, HKSAR & Department of Chemistry The University of Hong Kong June 2002

2 Electrochemical Cells, K.Y. Chan, HKU2 References Batteries www.nec-tokin.net www.duracell.com Fuel Cells www.fuelcells.com chem..hku.hk/~fuelcell Books: A.J. Bard, L. Faulkner, “Electrochemical Methods”, 2001, Wiley. Derek Pletcher and Frank C. Walsh, “Industrial Electrochemistry”, Chapman and Hall, 1990. C.A. Vincent and B. Scrosati, “Modern Batteries : An Introduction to Electrochemical Power Sources”, Butterworth- Heinemann, 1998. James Larminie and Andrew Dicks, “Fuel Cell Systems Explained”, Wiley, 2000. Utilities www.ifc.com www.gepower.com Portable Power Sources www.nokia.com www.motorola.com Capacitors www.nec-tokin.net www.faradnet.com Green Energy www.greenenergy.org.uk www.greenenergyohio.org Electric Vehicles Evworld.com

3 June 2002Electrochemical Cells, K.Y. Chan, HKU3 Electrochemistry, General Chemistry Physical Chemistry:Thermodynamics, Kinetics, Transport Organic Chemistry Inorganic, Solid State Chemistry Materials Science Basics Physics, Energy, Electricity Environmental Science and Ecological/Biological Issues Can be discussed with different emphasis, at different levels, and platforms. Multidisciplinary and Integrated Science

4 June 2002Electrochemical Cells, K.Y. Chan, HKU4 1.Fundamental Theories and Concepts 2.Batteries 3.Fuel Cells 4.Applications

5 June 2002Electrochemical Cells, K.Y. Chan, HKU5 Fundamentals Thermodynamics Relate Reactivity to Electrode Potential Nernst Equation accounts for concentration(activity) effects Calculate Electrode Potential from Free Energy

6 June 2002Electrochemical Cells, K.Y. Chan, HKU6 -1.66 -0.76 0.0 0.52 1.23 V Al/Al +3 Zn/Zn +2 H 2 /H + Cu/Cu 2+ H 2 O/O 2 Electrochemical Activity Series

7 June 2002Electrochemical Cells, K.Y. Chan, HKU7 Fundamentals Kinetics Current  Rate of reaction (Faraday’s law) Rate (current) described by Tafel Equation or Butler-Volmer Equation (Bard and Faulkner, Wiley 2001)

8 June 2002Electrochemical Cells, K.Y. Chan, HKU8 Fundamentals Kinetics n F E Free energy G Reaction co-ordinate  nF E R O + n e - O* from Absolute Rate Theory

9 June 2002Electrochemical Cells, K.Y. Chan, HKU9 Current into electrolyte Electrons out of electrode

10 June 2002Electrochemical Cells, K.Y. Chan, HKU10 Concentration or pH effect i E

11 June 2002Electrochemical Cells, K.Y. Chan, HKU11 E cell Cathode Anode E

12 June 2002Electrochemical Cells, K.Y. Chan, HKU12 E cell Cathode Anode E Ref. electrode E-E ref

13 June 2002Electrochemical Cells, K.Y. Chan, HKU13 Fundamentals Transport and Interfaces Rate of supply of raw materials : diffusion of active materials Rate of removal of: products including ions, electrons ionic vs ohmic resistance Change of solid interfaces: dentritic growth Wetting/non-wetting affects gas transport into electrolyte Selectivity of transport, e.g. cationic membrane

14 June 2002Electrochemical Cells, K.Y. Chan, HKU14 concentration  10 M KOH H 2 SO 4 0.6 ohm -1 cm -1 CH 3 COOH KCl

15 June 2002Electrochemical Cells, K.Y. Chan, HKU15

16 June 2002Electrochemical Cells, K.Y. Chan, HKU16 Ideal Voltage Activation Ohmic Mass-Transfer Current Density Cell Voltage

17 June 2002Electrochemical Cells, K.Y. Chan, HKU17 Open Circuit Voltage Equilibrium potential, Standard Potential Overpotential, underpotential Polarization (activation, ohmic, concentration) Capacity mA hr Energy Density W hr kg -1, W hr l -1 Power Density W kg -1, W l -1, W cm -2 Current Density mA cm -2 Some Terminologies

18 June 2002Electrochemical Cells, K.Y. Chan, HKU18 Anode: Oxidation reaction, release electrons to external circuit, negative terminal (galvanic cell) Cathode: Reduction reaction, receive electrons from external circuit, positive terminal (galnanic cell) Current Collector: continuous electronic conducting solid phase to collect electrons (in anode) and to distribute electrons (in cathode) Electrolyte: ionic conducting but electronic insulating, transfer ions from/to electrodes Separator: hydrophilic porous sheet material to hold a thin layer of electrolyte, electronic insulation

19 June 2002Electrochemical Cells, K.Y. Chan, HKU19 Polymer Electrolyte: polymeric backbone with fixed charge to allow transport of either cation or anion Porous Matrix to hold electrolyte: Ceramic, asbestos, “polymers”. Gel/Paste electrolyte: immobilize electrolyte but allow ionic transport Molten Salt Electrolyte:e.g. Carbonates Solid Oxide Electrolyte: oxide ion mobiliity at elevated temperature

20 Batteries A. Volta, 1880

21 June 2002Electrochemical Cells, K.Y. Chan, HKU21 Primary Batteries:Zn/C Alkaline Zn/HgO Li metal Secondary Batteries:Lead Acid (Rechargeable)Ni-Cd Ni-MH Li ion Hybrid of Battery and Fuel Cell:Zn-Air Al-Air (Regenerative Fuel Cells)

22 June 2002Electrochemical Cells, K.Y. Chan, HKU22 Batteries Zinc/Carbon (Leclanché 1880s) Cathode: 2 MnO 2 + H 2 O + 2e -  Mn 2 O 3 + 2OH - Anode: Zn  Zn 2+ + 2e - Overall: 2 MnO 2 + Zn + H 2 O  Mn 2 O 3 + Zn 2+ + 2OH -  G=-257 kJ mol -1, E o = 1.55 V electrolyte: moist NH 4 Cl/ZnCl 2 /MnO 2 /C powder current collectors: graphite rod and zinc Capacity 6 A hr, energy density 80 Whr kg -1

23 June 2002Electrochemical Cells, K.Y. Chan, HKU23 Batteries Zinc/Carbon (Leclanché 1880s) Zinc can anode (-ve) Carbon rod current collector (+ve) MnO 2 based positive paste separator

24 June 2002Electrochemical Cells, K.Y. Chan, HKU24 Batteries Lead/Acid Cathode: PbO 2 + 4H + +SO 4 2- + 2e -  2H 2 O + PbSO 4 Anode: Pb + SO 4 2-  PbSO 4 + 2e - Overall: PbO 2 + Pb + 4H + + 2SO 4 2-  2PbSO 4 + 2H 2 O  G= -394 kJ mol -1, E o = 2.05 V electrolyte: aqueous H 2 SO 4 current collectors: both Pb Capacity: 2.7 Ahr, Energy density 30 Whr kg -1 cell voltage> 1.23 V, Electrolysis of water kinetically hindered Discharge reactions

25 June 2002Electrochemical Cells, K.Y. Chan, HKU25 -0.3505 0.0 1.23 V 1.698 Pb/PbSO 4 H 2 /H + H 2 O/O 2 PbSO 4 /PbO 2 Possible Electrode Pairs?

26 June 2002Electrochemical Cells, K.Y. Chan, HKU26 Batteries Nickel/Cadmium Cathode: 2NiO(OH) + 2H 2 O + 2e -  2Ni(OH) 2 + 2OH - Anode: Cd + 2OH -  Cd(OH) 2 + 2e - Overall: 2NiO(OH) + Cd + 2H 2 O  2Ni(OH) 2 + Cd(OH) 2  G= -283 kJ mol -1, E o = 1.48 V electrolyte: aqueous KOH current collectors: Ni foam and peforated nickel sheet Capacity: 4 Ahr, energy density: 33 Whr kg -1

27 June 2002Electrochemical Cells, K.Y. Chan, HKU27 Batteries Nickel/Metal hydride Cathode: NiO(OH) + H 2 O + e -  Ni(OH) 2 + OH - Anode: MH + OH -  M + H 2 O + 2e - Overall: MH + NiO(OH)  M + Ni(OH) 2 Metal hydride: AB 5 e.g. LaNi 5 or AB 2, e.g. TiMn 2, ZnMn 2 electrolyte: aqueous KOH current collectors: Ni foam and peforated nickel sheet Capacity: 4 Ahr, energy density: 80 Whr kg -1

28 June 2002Electrochemical Cells, K.Y. Chan, HKU28 Batteries Nickel/Metal Hydride Overcharging Cathode: 2 OH -  H 2 O + ½O 2 + 2e - Anode: charge reserve M + H 2 O + 2e -  MH + OH - Oxygen dissolves to Anode: 2MH + ½ O 2  2M + H 2 O Prevent gassing and build up of pressure

29 June 2002Electrochemical Cells, K.Y. Chan, HKU29 Batteries Lithium Ion Cathode: xLi + + LiM 2 O 4 + xe -  Li 1+x M 2 O 4 M=Mn,Ti xLi + + LiMO 2 + xe -  Li 1+x MO 2 M=Co, Ni Anode: LiC 6  x Li + + x e - + Li 1-x C 6 Overall: C 6 + LiMO 2  Li x C 6 + Li 1-x MO 2 LiMn 2 O 4  G= -287 kJ mol -1, E o = 2.97 V Energy density > 100 Whr/kg

30 June 2002Electrochemical Cells, K.Y. Chan, HKU30 Batteries Lithium Ion Aprotic Solvent Gel Polymer (lower weight) Electrolyte Li in graphite lattice Lower activity but safer than Li metal Anode Solid Structures for storing Li Spinels, Olivines, rhombohedral NASICON Cathode

31 June 2002Electrochemical Cells, K.Y. Chan, HKU31 Batteries and Fuel Cells Batteries n Recharge n Intermittent n Closed system n Mostly solid n High power density Fuel Cells n ReFuel n Continuous n Open system n Mostly Gas/Liquid Fuel n High energy density n Micro to Mega Watts

32 June 2002Electrochemical Cells, K.Y. Chan, HKU32 Fuel Cells n Efficient conversion of Chemical Energy to useful energy (without losing to heat, mechanical linkages) n Environmentally friendly n Flexible: from micro to mega n Materials and Nanotechnology

33 June 2002Electrochemical Cells, K.Y. Chan, HKU33 Fuel Cells Classification according to electrolyte n Alkaline Fue Cells n Proton Exchange Membrane (PEM) n Phosphoric Acid n Molten Carbonate n Solid Oxide Electrolyte

34 June 2002Electrochemical Cells, K.Y. Chan, HKU34 燃料電池發電的原理 正極 ﹕氧氣 ( 氧化劑 ) 負極﹕燃料 ( 氫氣﹐酒精﹐ 葡萄糖等 ) 電能 C x H y O z ===> CO 2 + H 2 O + e - O 2 + e - ===> H 2 O 負極 電解液 正極

35 June 2002Electrochemical Cells, K.Y. Chan, HKU35 Fuel Cells Chemical Energy Electrical Energy

36 June 2002Electrochemical Cells, K.Y. Chan, HKU36 Ideal Voltage Activation Ohmic Mass-Transfer Current Density Cell Voltage

37 June 2002Electrochemical Cells, K.Y. Chan, HKU37 Diversity of Technology and Materials Problems in Fuel Cells n Fuel n Oxidant n Catalyst n Container n Control n Transport n Storage

38 June 2002Electrochemical Cells, K.Y. Chan, HKU38 Fuels:Hydrogen Metals Natural Gas Small Hydrocarbons (methanol, glucose) Oxidant: air oxygen halides oxides Catalysts: platinum metals metal oxides macrocycles Catalyst Support: Porous Carbon Ceramic Matrix Molecular Sieves Polymer Container and Movable Parts: Alloys Ceramic Polymers Transport/Electrolyte: Proton Exchange Membranes PTFE (Teflon) Solid Electrolyte Storage: Metal Hydride

39 June 2002Electrochemical Cells, K.Y. Chan, HKU39 Fuels n Hydrogen H 2 +2OH -  2H 2 O +2e - 2e - +½ O 2 +H 2 O  2 OH - n Methanol CH 3 OH + H 2 O  CO 2 + 6H + +6e - 6e - +1½ O 2 +6H +  3H 2 O n Aluminium Al + 4OH -  Al(OH) 4 - +3e - 4e - +O 2 +2H 2 O  4 OH - n Borohydride NaBH 4 + 8 OH -  NaBO 2 + 6H 2 O + 8e - n Methane (natural gas) n Octane : demonstrated in SOFC half cell

40 June 2002Electrochemical Cells, K.Y. Chan, HKU40 Thermochemistry

41 June 2002Electrochemical Cells, K.Y. Chan, HKU41 Micro and Nanostructured Electrodes: n Catalyst Support: High Surface Carbon n Size Effects of Catalysts n Controlled Porosity n Controlled Wetting n Maxinum Gas-Liquid-Solid Interface n Minimize ohmic resistance n Minimize ionic resistance

42 June 2002Electrochemical Cells, K.Y. Chan, HKU42 Scanning Tunneling Spectroscopy

43 June 2002Electrochemical Cells, K.Y. Chan, HKU43 Catalysts n Platinum is the most important for both anode and cathode n Platinum can be replaced by Ag, Mn, Co, only for oxygen reduction in alkaline medium n Platinum subject to CO poisoning (impure H 2 ) n Binary/Ternary system, macrocycle, bifunctional n Stability/Life of nanometals

44 June 2002Electrochemical Cells, K.Y. Chan, HKU44 Maximum peak current density at 52.5~77.6% Co, one order of magnitude higher than that of pure Pt particles. One possible role of cobalt in promoting the catalysis of platinum, is the removal of CO ad COOH ad intermediates. Chi et al., Catalysis Letters, 71 (2001) 21.

45 June 2002Electrochemical Cells, K.Y. Chan, HKU45 Catalysts n Oxygen Cathode is most limiting and is present in most fuel cells n Non-platinum cathode catalyst can tolerant cross over effect. n At high temperature, no precious metal or no catalysts is needed in MCFC and SOFC

46 June 2002Electrochemical Cells, K.Y. Chan, HKU46 Performances of different air cathode

47 June 2002Electrochemical Cells, K.Y. Chan, HKU47 Gas Diffusion Electrodes H2H2 H+H+ e-e- Chan et al., Electrochimica Acta, 32 (1987), 1227;33 (1988) 1767. Tang and Chan, Electroanal. Chem. 334 (1992) 65. Electronic circuit: continuous solid phase Ionic circuit: Continuous electrolyte phase Materials flow circuit: feed of reactancts

48 June 2002Electrochemical Cells, K.Y. Chan, HKU48 Single air cathode

49 June 2002Electrochemical Cells, K.Y. Chan, HKU49 Electrolyte n Alkaline electrolyte (first deployed for Apollo mission) n Phosphoric Acid 180 C n Polymer Electrolyte n Cross Over n Stability (CO 2 removal in alkaline) n Solid Oxide (YSZ, doped Ceria) n Shunt Current / Leak Current

50 June 2002Electrochemical Cells, K.Y. Chan, HKU50 SOFC Electrolyte n Ytrium Stabilized Zirconia n Doped Ceria (Cerium Oxide) n O 2- conductivity at 600~800  C Zr Ce YY O 2- Ce

51 June 2002Electrochemical Cells, K.Y. Chan, HKU51 Stack Design n Manifold for fuel feed n Manifold for oxidant feed n Electronic circuit n Ionic circuit n Water transport n Temperature, humidity control

52 June 2002Electrochemical Cells, K.Y. Chan, HKU52 H+H+ e-e-

53 June 2002Electrochemical Cells, K.Y. Chan, HKU53 Product Name: Fuel Cell Stack Fuels usable: Glucose, methanol, ethanol,NaBH 4 No. of Fuel Cells: 10 in Serial Open Circuit Voltage: 4.0-9.0V Power Output: 0.5-1.0W Application: Stationary or Portable ( Mobile phone or toy cars ) Applications Demonstrated: Radio(Voice of Glucose); Portable CD player; Mobile Phone(GSM). Stack Design

54 June 2002Electrochemical Cells, K.Y. Chan, HKU54 Electronic circuit: continuous solid phase with minimum electrical resistance to electronically connect anode and cathode through external circuit. Ionic circuit: to complete the other half of the “charge circuit”. Continuous electrolyte phase connecting cathode and anode, but electronic insulating. Maintain balance of ions for anodic, cathodic reactions. Materials flow circuit: feed of reactancts to and removal of products from anode/cathode. Avoid shunt current, leak current in multiple cells Avoid short circuit of cathode and anode Avoid breaking electrochemical window of electrolyte

55 Stationery Power Utilities 10~100 kW 100~500 kWhr ONSY (IFC), Fiji SOFC (Westing House, Honey Well) Load Levelling Power Distribution Life

56 June 2002Electrochemical Cells, K.Y. Chan, HKU56

57 Electric Vehicles 10~100 kW 100~500 kWhr Battery vs Fuel Cells Hybrid with ICE and capacitor Costs: 7 times normal costs Startup time Direct/Reformer Fueling Station Infrastructure

58 June 2002Electrochemical Cells, K.Y. Chan, HKU58 Transportation Fuel Cell Ballard Power Systems 1st Generation Fuel Cell Transit Bus 2nd Generation Fuel Cell Transit Bus Chrysler Fuel Cell Vehicle Model. Coval H2 Parteners T-1000 Neighborhood Truck. Daimler-Benz The NECAR 3 Three Generations of NECAR Vehicles The NEBUS DaimlerChrysler Jeep Commander Hybrid Fuel Cell Concept Energy Partners The "Gator" Utility Vehicle The "Genesis" Golf Cart The "Green Car"

59 June 2002Electrochemical Cells, K.Y. Chan, HKU59 Ford Motor Company The P2000 Prodigy Hydrogen Fuel Cell Vehicle The P2000 - Platform for a Fuel Cell Vehicle. General Motors Fuel Cell Engine Model H Power Corporation Fuel Cell Bus 50w PEM Fuel Cell Fuel Cell Bicycle Fuel Cell Wheelchair Humboldt State University's Schatz Energy Research Center The Kewet (Danish 2-Seater) Fuel Cell Golf Carts International Fuel Cells The Georgetown University Fuel Cell Bus

60 June 2002Electrochemical Cells, K.Y. Chan, HKU60 Mazda The Fuel Cell Demio The Demio - On the Road Under the Hood of the Demio Opel The Fuel Cell Sintra The Fuel Cell Zafira Siemens AG PEM Fuel Cell Powered Forklift Toyota The Fuel Cell RAV 4 Volkswagen/Volvo The Fuel Cell Golf (coming soon) Zevco The Fuel Cell Taxi Cab (London) Updated January 8, 1999

61 June 2002Electrochemical Cells, K.Y. Chan, HKU61

62 Portable Power Sources 10~100 kW 100~500 kWhr Battery vs Fuel Cells Safety (H 2, MeOH, caustic electrolyte), Open vs Closed System Volume vs Weight Refueling Vs Recharging

63 Special Applications Space/Defence Communication Energy Storage for Solar Energy Vector Biomedical Enery Recovery from Waste Marine and Remote Power Sources

64 June 2002Electrochemical Cells, K.Y. Chan, HKU64 Energy Vector

65 June 2002Electrochemical Cells, K.Y. Chan, HKU65 Fuel Cells Running on Biogas from Garbage (Kajima Co. Japan) 67% CH 4 33% CO 2 140kg/day

66 June 2002Electrochemical Cells, K.Y. Chan, HKU66

67 Demo Fuel Cells 0.02 ~ 10 W H 2, MeOH, Glucose, alcohols, NaBH 4 PEM, Alkaline

68 June 2002Electrochemical Cells, K.Y. Chan, HKU68 World’s first glucose FC Demonstration Kit (HKU-002, Version 3)

69 June 2002Electrochemical Cells, K.Y. Chan, HKU69 Typical Performance of HKU-001


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