1. ELECTROCHEMICAL SYSTEMS FOR ELECTRIC POWER GENERATION
Dzmitry Malevich
Depatrment of Chemistry and Biochemistry
University of Guelph

2. Electric power conversion in electrochemistry
Electrolysis / Power consumption
Electric Power
Chemical Reactions
Electrochemical battery / Power generation

3. Volta’s battery (1800) Paper moisturized with NaCl solution Cu Zn
Alessandro Volta
Paper moisturized with NaCl solution Cu Zn

4. Principles of power generation in the electrochemical systems
Me2n+ - ne- = Me20
CATHODE
Me20 - ne- = Me2n+
ANODE
Me2
Me1
Salt Bridge
Me1n+
SO42-
Me2n+
SO42-

5. IMPORTANT NOTICE ! Electrolysis ANODE + CATHODE - Battery ANODE -
System consumes energy
G>0
ANODE +
CATHODE -
Battery
System releases energy
G<0
ANODE -
CATHODE +
(oxidation process)
(oxidation process)
(reduction process)
(reduction process)

6. Principles of power generation in the electrochemical systems
Me2n+ - ne- = Me20
CATHODE
Me20 - ne- = Me2n+
ANODE
Me2
Me1
Diaphragm
Membrane or
Me1n+
SO42-
Me2n+
SO42-

7. Primary batteries Modern Zinc-Manganese battery
Zn-container
Carbon rod
MnO2 paste (cathode)
Gas space
Gel electrolyte
Leclanché’s battery (1866)
Anode: Zn  Zn2+ + 2e-
Cathode: 2MnO2 + 2H2O +2e-  2MnOOH + 2OH-
Electrolyte: Zn2+ 2NH4Cl +2OH-  Zn(NH3)Cl2 + 2H2O
2MnO2 + Zn + 2NH4Cl  2MnOOH + Zn(NH3)Cl2
Georges Leclanché ( )
Seal
Zn-container
MnO2 paste (cathode)
Carbon rod
NH4OH electrolyte

8. Primary batteries Zinc-Manganese alkaline battery
MnO2 paste (cathode)
Gel electrolyte
Porous Zn (anode)
Zinc-Manganese alkaline battery
Anode: Zn + 2OH- - 2e-  Zn(OH)2
Cathode: MnO2 + H2O +1e-  MnOOH + OH- aaaaaaaaa MnOOH + H2O +e-  Mn(OH)2 + OH-
Zinc-Air battery
Anode: Zn + 2OH- - 2e-  Zn(OH)2
Cathode: 1/2 O2 + H2O + 2e-  Zn(OH)2

9. Secondary (rechargeable) batteries
Lead-acid battery
Lead paste in Pb-mesh (anode)
Lead dioxide paste in Pb-mesh (cathode)
Porous separator
Safety valve
Lead-acid battery Pb
PbO2
E=2.06 V
36% H2SO4
discharge
charge
PbSO4+H2O
PbO2+(2H++SO42-)+2H++2e-
PbSO4+ 2H+
Pb+(2H++SO42-)-2e-
PbSO4
PbO2 + Pb + H2SO PbSO4 + 2H2O
discharge

10. Secondary (rechargeable) batteries
Lithium-ion battery
Cathode:
LiMeO2 - xe Li1-xMeO2 + xLi+
Anode:
C + xLi+ + xe CLix
CHARGE
DISCHARGE
Discharge
Charge
Anode (CLix)
Cathode (LiMexOy)
LiCoO2 -utilized for commercial batteries
LiNiO2, LiMn2O4-prospective
Separator
Aluminum can
Positive terminal
Negative terminal

11. Secondary (rechargeable) batteries
Nickel-Metal Hydride battery
Cathode:
NiOOH + H2O - e Ni(OH)2 + OH-
Anode:
Me + OH- + e Me + H2O
CHARGE
DISCHARGE
CHARGE
DISCHARGE
Picture from: T. Takamura / Solid State Ionics (2002)19

12. Types of the electrochemical system for electric power generation
Fuel cells
Reaction products (exhaust)
Reductant (fuel)
Oxidant
POWER
Primary batteries
POWER
Secondary batteries
Recharge
POWER

13. Grove’s fuel cell (1839) O2 H2 4H+ + 4e- 2H2 2H2O - 4e- O2 + 4H+
Sir William Grove 1811–1896
4H+ + 4e- 2H2
2H2O - 4e- O2 + 4H+

14. Fuel Cells performance improving
Raising the voltage:
Raising the current:
• Increasing the temperature
• Increasing the area of eelectrode electrolyte interface
• The use of catalyst
Cell stack
ANODE
CATHODE
ELECTROLYTE
Bipolar electrode
ANODE
CATHODE
ELECTROLYTE
Connection of cells in series
Anode catalyst
Cathode catalyst
Electrolyte frame
Bipolar plate H2 O2
Stack of several hundred

15. Phosphoric Acid Fuel Cell (PAFC)
Electrolyte in SiC porous matrix O2
Pt-particles catalysts (anode or cathode)
Gas (H2 or O2)
PACF parameters:
current density mA cm-2
single cell voltage mV
temperature oC
At atmospheric pressure H2

16. Gas Diffusion Electrode
Reaction zone
Dry zone (no reaction) H2
Electrode
Gas e- e-
Electrolyte
Reaction zone
Dip zone (reaction is slow because diffusion limitation)

17. Disadvantages of liquid electrolyte fuel cell
Low operation temperature ! (reaction is slow, expensive catalysts are needed to produce valuable current)
Difficulties in three-phase interface maintaining !
Strong fuel crossover!
Recombination (no electron transfer through outer socket - energy loss) H2 O2
Anode Liquid electrolyte Cathode

18. + - Proton Exchange Membrane Fuel Cell (PEMFC) H2 H+ Nafion® membrane
H2O +Air (O2) H+
Nafion®
membrane
Catalyst support (carbon cloth)
Current collector / gas distributor
H2 crossover H2
Air (O2) + -

19. Proton Exchange Membrane (PEM)
Polymerization
Polyethylene
Ethylene C H S F C O
Grafting
Nafion® (DuPont) - H+ C F
Fluorination
Polytetrafluoroethylene (PTFE, Teflon®)

20. Fuel reforming CnHm + nH2O = nCO + (m/2 + n)H2 CH4 + H2O = CO + 3H2
CO + H2O = CO2 + H2
CH3OH + H2O = 3 H2 + CO2
T~ 500 oC, Ni-catalyst
T~ 250 oC, Ni-catalyst
no CO
Stainless still
Catalyst
CH4 + H2O
H2 + COx
CH4 + O2
CO2 + H2O
HEAT

21. + - Direct Methanol Fuel Cell (DMFC) CH3OH + H2O + CO2 H+ Nafion®
H2O +Air (O2) H+
Nafion®
membrane
Catalyst support (carbon cloth)
Current collector / fuel distributor
CH3OH crossover
CH3OH + H2O
Air (O2) + -

22. Methanol oxidation mechanism+ ê + ê + ê + ê + ê + ê
carbon
oxygen
hydrogen Pt Pt

23. Direct Methanol Fuel Cell (DMFC)
Theoretical voltage = V
Real voltage
Current
Potential vs. HRE, V
CH3OH + H2O = CO2 + 6H+ + 6e /2O2 + 6H+ + 6e- = 3H2O

24. Carbon monoxide tolerant anode
oxygen
hydrogen Ru Pt

25. Methanol crossover through Nafion
From M.P. Hogharth and G.A. Hards, Platinum Metals Rev. 40 (1996) 150
Temperature oC Current density, A cm Crossover rate, A cm-2
S. R. Narayanan, DOE/ONR Fuel Cell Workshop, Baltimore, MD, Oct
Number of methanol moles (Nm) transported by crossover can be calculated by Faraday low:
Nm = jc·S·t/n·F, where j - current density(crossover rate) , S - membrane area, t - time, n-number of electrons (n=6 for methanol oxidation), F - Faraday constant

26. Catalysts for fuel cells with polymer electrolyte
PEMFC
DMFC
Anode: Pt or PtRu (~50% Pt) black 1-10 nm Cathode: Pt (~50% Pt) black 1-10 nm
Anode: usually PtRu (~50% Pt) black 1-10 nm Cathode: Pt (~50% Pt) black 1-10 nm
Catalysts are supported on carbon nanoparticles ( nm, for example Vulcan XC72)
Catalysts are usually unsupported
Precious metals load is mg cm-2 for both electrodes
Precious metals load is mg cm-2 for both electrodes
Power density mW cm -2 at cell voltage 0.5 V (t=80 oC, CO-free hydrogen)
Power density mW cm -2 at cell voltage 0.5 V (t=90 oC, CH3OH concentration M)
Catalysts cost ~ 0.8 g per kW ( ~140 CAN$ per kW)
Catalysts cost ~ 10 g per kW ( ~1750 CAN$ per kW)

27. Molten Carbonate Fuel Cell (MCFC)
Anode Porous electrolyte support Cathode
LiNiO2 or LiCoO2
NiCr alloy
Alkali metal carbonates in LiAlO2 matrix
H2 +CO2 + H2O
O2 +CO2
CO32- H2
O2 +CO2
mm mm mm
T= oC
O2 + 2CO2 + 4e - = 2CO32-
2H2 + 2CO e- = 2H2O + 2CO2

28. Solid Oxide Fuel Cell (SOFC)
Anode Electrolyte Cathode
Sr doped La-manganite
H2 + H2O O2
O2- H2 O2
YSZ
2H2 + 2O2- - 4e - = 2H2O
O2 + 4e - = O2-
Ni+YSZ
T= oC
Electrolyte
Anode
Air
Air
Fuel
Cathode

29. Types of Fuel Cells Phosphoric Acid Fuel Cell (PAFC)
Mobile ion
Operating temperature
Power range
Phosphoric Acid Fuel Cell (PAFC)
H ~220 oC kW
H oC kW
H oC kW
CO ~650 oC MW
O oC MW
Proton Exchange Membrane Fuel Cell (PEMFC)
Direct Methanol Fuel Cell (DMFC)
Molten Carbonate Fuel Cell (MCFC)
Solid Oxide Fuel Cell (SOFC)