New Developments in Electrochemical Cells Science Update
Programme Education Bureau, HKSAR & Department of Chemistry The
University of Hong Kong June 2002 Slide 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 Slide 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 Slide 4 June
2002Electrochemical Cells, K.Y. Chan, HKU4 1.Fundamental Theories
and Concepts 2.Batteries 3.Fuel Cells 4.Applications Slide 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 Slide 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 Slide 7 June 2002Electrochemical
Cells, K.Y. Chan, HKU7 Fundamentals Kinetics Current Rate of
reaction (Faradays law) Rate (current) described by Tafel Equation
or Butler-Volmer Equation (Bard and Faulkner, Wiley 2001) Slide 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 Slide 9 June 2002Electrochemical
Cells, K.Y. Chan, HKU9 Current into electrolyte Electrons out of
electrode Slide 10 June 2002Electrochemical Cells, K.Y. Chan, HKU10
Concentration or pH effect i E Slide 11 June 2002Electrochemical
Cells, K.Y. Chan, HKU11 E cell Cathode Anode E Slide 12 June
2002Electrochemical Cells, K.Y. Chan, HKU12 E cell Cathode Anode E
Ref. electrode E-E ref Slide 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 Slide 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 Slide 15 June
2002Electrochemical Cells, K.Y. Chan, HKU15 Slide 16 June
2002Electrochemical Cells, K.Y. Chan, HKU16 Ideal Voltage
Activation Ohmic Mass-Transfer Current Density Cell Voltage Slide
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
Slide 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 Slide 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 Slide 20 Batteries A. Volta, 1880
Slide 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) Slide 22 June
2002Electrochemical Cells, K.Y. Chan, HKU22 Batteries Zinc/Carbon
(Leclanch 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 Slide 23 June
2002Electrochemical Cells, K.Y. Chan, HKU23 Batteries Zinc/Carbon
(Leclanch 1880s) Zinc can anode (-ve) Carbon rod current collector
(+ve) MnO 2 based positive paste separator Slide 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 Slide 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? Slide 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 Slide 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 Slide 28
June 2002Electrochemical Cells, K.Y. Chan, HKU28 Batteries
Nickel/Metal Hydride Overcharging Cathode: 2 OH - H 2 O + O 2 + 2e
- Anode: charge reserve M + H 2 O + 2e - MH + OH - Oxygen dissolves
to Anode: 2MH + O 2 2M + H 2 O Prevent gassing and build up of
pressure Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 34 June
2002Electrochemical Cells, K.Y. Chan, HKU34 ( ) ( ) C x H y O z
===> CO 2 + H 2 O + e - O 2 + e - ===> H 2 O Slide 35 June
2002Electrochemical Cells, K.Y. Chan, HKU35 Fuel Cells Chemical
Energy Electrical Energy Slide 36 June 2002Electrochemical Cells,
K.Y. Chan, HKU36 Ideal Voltage Activation Ohmic Mass-Transfer
Current Density Cell Voltage Slide 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 Slide 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 Slide 39 June
2002Electrochemical Cells, K.Y. Chan, HKU39 Fuels n Hydrogen H 2
+2OH - 2H 2 O +2e - 2e - + O 2 +H 2 O 2 OH - n Methanol CH 3 OH + H
2 O CO 2 + 6H + +6e - 6e - +1 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 Slide 40 June 2002Electrochemical
Cells, K.Y. Chan, HKU40 Thermochemistry Slide 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 Slide 42 June
2002Electrochemical Cells, K.Y. Chan, HKU42 Scanning Tunneling
Spectroscopy Slide 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 Slide 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. Slide 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 Slide 46 June
2002Electrochemical Cells, K.Y. Chan, HKU46 Performances of
different air cathode Slide 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 Slide 48 June 2002Electrochemical
Cells, K.Y. Chan, HKU48 Single air cathode Slide 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 Slide 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
Slide 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 Slide 52 June 2002Electrochemical Cells, K.Y.
Chan, HKU52 H+H+ e-e- Slide 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 Slide 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 Slide 55 Stationery Power
Utilities 10~100 kW 100~500 kWhr ONSY (IFC), Fiji SOFC (Westing
House, Honey Well) Load Levelling Power Distribution Life Slide 56
June 2002Electrochemical Cells, K.Y. Chan, HKU56 Slide 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 Slide 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" Slide 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 Slide 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 Slide 61 June 2002Electrochemical Cells,
K.Y. Chan, HKU61 Slide 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
Slide 63 Special Applications Space/Defence Communication Energy
Storage for Solar Energy Vector Biomedical Enery Recovery from
Waste Marine and Remote Power Sources Slide 64 June
2002Electrochemical Cells, K.Y. Chan, HKU64 Energy Vector Slide 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 Slide 66 June 2002Electrochemical Cells, K.Y. Chan, HKU66
Slide 67 Demo Fuel Cells 0.02 ~ 10 W H 2, MeOH, Glucose, alcohols,
NaBH 4 PEM, Alkaline Slide 68 June 2002Electrochemical Cells, K.Y.
Chan, HKU68 Worlds first glucose FC Demonstration Kit (HKU-002,
Version 3) Slide 69 June 2002Electrochemical Cells, K.Y. Chan,
HKU69 Typical Performance of HKU-001
