1. Solid Oxide Fuel Cells
Rodger McKain, PhD

2. “I cannot but regard the experiment as an important one…”
Ion transport observed by William Grove in 1839…Based on hydrogen-oxygen, sulfuric acid electrolyte, and platinum electrodes
“I cannot but regard the experiment
as an important one…”
William Grove to Michael Faraday
October 22, 1842

3. Fuel Cell
An energy conversion device that directly converts chemical energy into electrical energy (dc power).
Analogous operation to a natural gas fueled electric generator: energy in fuel and oxygen are converted to electric power as long as fuel and air are supplied.
Six types, each suited for specific applications +
Heat, H2O

4. Increasing Temperature
Fuel Cell Types
Increasing Temperature
polytetrafluoroethylene and perfluorosulfonyl-ethoxyvinylether
Nafion
Source: U.S. Fuel Cell Council

5. Attributes of Fuel Cells
AFC PACF PEM MCFC SOFC
Electrolyte KOH Phosphoric Sulfonic Molten Y2O3-ZrO2
Acid Acid Carbonate Ceramic
Polymer Salt
Temperature 1000C C C C C
Fuel H H H H2/CO H2/CO
Efficiency (H2 fuel) 60% % % % %
(NG fuel) % % % %
Pollution Very low Very low Very low Low Low
Hydrocarbon No Difficult Difficult Yes Yes
Fuel Use
Start-Up Fast Moderate Fast Slow Slow

6. Fuel Cell Stacks Operating voltage of a single cell is ~0.7 volts
Cells are “stacked” in series to increase voltage to useful levels:
Individual fuel cells are “stacked” together to increase the voltage to meet whatever the demand is for your application. It can be a few watts to run a cellular phone; 5 kilowatts to power a house; 50 kilowatts to operate a car; or 200 kilowatts to provide electricity for a hospital.
Source: U.S. Fuel Cell Council

7. Fuel Cell Power System Fuel cell Stack Sub Assembly Air Fuel 10 kW
Useful heat
Air
Fuel
10 kW
Heat
Management
Power Conditioner
Fuel Processor
Controls

8. High Efficiency

9. High Efficiency at Part Load

10. Average U.S. Utility Emissions (lbs per megawatt-hour)
Low Emissions
Contaminant
Average U.S. Utility Emissions
(lbs per megawatt-hour)
ONSI PC kW NG Fuel Cell
Nitrogen Oxides
7.65
0.016
Carbon monoxide
0.34
0.023
Reactive organic gases
0.0004
Sulfur oxides
16.1
Particulates (PM10)
0.46

11. Fuel cell is an electrochemical device that allows the direct conversion of chemical energy to electric energy. Fuel cell can operates at high efficiency with low pollutant emission. Various type of fuel cells have been under development for a wide range of applications. Solid oxide fuel cells have been commercialized with synthesis gas as the fuel.

12. The Fuel Cell Opportunity
High efficiency Energy Independence
Low regulated emissions
Quiet
Fuel flexibility
High quality power
High reliability Energy Security
Widespread applications: (transportation, power, medical, communications, military, aerospace, electronics)
IF: <$400/kW stationary power
<$35/kW automotive
New industry ($250 billion per year)

13. Solid Oxide Fuel Cells
Based upon ion conductivity of certain ceramic materials at elevated temperatures (>600 C)
First observed by Nernst in 1890’s
Fluorite Structures (e.g. yttria stabilized zirconia)
Face Centered cubic arrangement
Transport through crystal lattice vacancies and oxide ions located between crystal faces
First SOFC constructed in 1937 by Baur and Preis
Requires porous electrodes and dense electrolyte, low electronic conductivity, and high strength

14. Cathode catalyst layerv RL A
Anode catalyst layer
CH4 + 3O2- CO2 + H2O + 2e-
O2 + 4e O2-
Pt Ink
O2-
Effluent
Pt Wire
Fuel/CH4
Cathode catalyst layer
CH4 + CO2 2CO + 2H2
CH4 + H2O CO2 + 3H2
CO + H2O CO2 + H2
CH O2 CO + 2H2
Electrolyte Disc
Yttrium-stablized Zirconia (>950 °C)
Galladium-doped Ceria (>600°C)
It is my pleasure to discuss with you our recent study on the solid oxide fuel cell.
This morning I would like discuss with you how we build the SOFC and the approach we used to study the reaction on the surface of the anode catalyst.
SOFC consists of three key components: cathode catalyst layer, O2- anion conducting electrolyte, and an anode catalyst layer. The schematic I am showing here is a reactor chamber where fuel such as methane enter to the anode side. Cathode is open and exposed to the ambient air. CH4 reacts on the surface of the anode catalyst producing CO2, CO, and H2O. Anode catalyst can also catalyze the reaction of CH4 with H2O and CO2 which are the combustion product to produce syngas such as CO and H2.
The function of the cathode catalyst is
A Oad Products T (°C)
CH4 Oad CO, H2, CO2, H2O
CnH2n Oad CnH2nO, CO2, H2O
C Oad CO

15. Relationship between fuel processing and fuel cells
This complicated slide shows the sophisticated relationship between fuel processing and various types of fuel cell. If we stacked all the different types of fuel cells in one sides; and the various fuels on the other side. H2 is the most expensive fuel; coal and petroleum coke is the cheapest. H2 is considered as a future fuel for H2 economy and it can be directly used to power these 6 different types of fuel cell. In fact H2 has been found to be most effectives fuel for all of these fuel cells. The question is where H2 will come from. None of the fuel cell can effectively take the coal as a fuel. There are molten carbonate fuel cell underdevelopment to take clean coal fuel The current mainstream idea is to gasify the coal, followed by cleaning of syngas, and then send the gases to the SOFC for power generation.

16. Basis for Fuel Cell Operation
Electron transfer – chemical reaction
Voltage determined by difference in chemical potential of fuel and oxygen
Current determined by area of cell
Catalyzed conversion of oxygen and hydrogen into reactive species O= and H
H2 + O2 = H2O + 2 electrons + heat
Electrons are separated from reactants by circuit
Need to understand electrical circuit background as it relates to fuel cell

17. Electric terms 6,240,000,000,000,000,000 electrons / sec = 1 amp
Current is the flow of electrons
Fuel Cell
Stack
Low resistance
High resistance
Volts
Resistance
If h is 1 volt and current is 1 amp
Resistance is 1 ohm
Copper wire, 1/16” diameter,
10 amps, electrons travel 1 cm
In 28 seconds.

18. What’s a watt? Power = (height lifted times weight
Work involves height lifted
and weight of ball, ft-lbs
Power = (height lifted times weight
of ball) times (balls per second), or
Power = voltage times current,
Watts = volts times amps
Work has no time limit, power does
550 ft-lbs/sec = 1 horsepower
= 746 watts

19. Energy flow Same story for electric system
Work,
power
Heat
Food
Air
Same story for electric system
Food  anode, Air  cathode
Stack produces power and heat
Heat
All the energy in the food eventually appears as heat.
In a perfect system all the energy in
the food would be converted to power.
Actually, only part is converted which
defines the efficiency.

20. Balls lifted per hour, or amps (I)
V-I scan
Balls lifted per hour, or amps (I) 10 20 30 40 50 2 4 6 8
Height lifted
or volts (V)
ASR is the slope
of the dashed red line

21. Balls lifted per hour, or amps (I)
V-I scan 10 8 6
Height lifted
or volts (V)
1 of these = 2 of these! 4 2 5 10 15 20 25
Balls lifted per hour, or amps (I)

22. Micro view - Electric - O= + Icon Via Anode Fuel layer #1 Electrolyte*
Cathode
e - O=
Air layer #1
Fuel layer #1
Porous
½ O2 + 2e- = O=
O= + H2 = 2e- +H2O -
Icon
Bond Layer
*A nonmetallic electric conductor in which
current is carried by the movement of ions.
Fuel utilization
Air Stoics

23. Complete micro view - O= O= O= O= O= Fuel Flow, H2O+CO  H2+CO2 O2 O2
Icon
Fuel Flow, H2O+CO  H2+CO2 -
Via H2
Anode
H2O
Bond Layer CO
Fuel layer #1
e -
CO2 CO
Electrolyte CO
CO2
CO2 CO
e -
e -
e -
Cathode
CO2 CO
CO2
CO2 CO CO O= O= O= O= O=
O= + H2 = 2e- +H2O
Porous N2 N2 N2 N2 N2 N2 N2
½ O2 + 2e- = O= N2 N2 N2 N2 N2
e -
e -
e - N2 N2 N2 N2 N2
Bond Layer N2 N2
Air layer #1
e - O2 O2 +
Air Flow, O2 + N2

24. Co-flow Design Concept – Unit Cell
Multi-layer
ceramic construction
Vias carry
current
Cell
Air flow
Fuel flow

26. Interconnect Sealant Ink “bumps” printed on vias Thermocouples,
Voltage taps

27. Add a cell
Thermocouples,
Voltage taps

28. Manifold arrangement
Air inlets
Fuel inlets
Gasket
Manifold

29. Vehicle ICE vs. Fuel Cell Direct Drive Efficiency Comparison40
100
Energy Units
IC Engine
40%
Power Train
37.5% 15 60 20
Idling 5
Friction 20 40
Energy Units
Fuel Cell
50%
Direct Drive
75% 15 20
Idling 5
Friction

30. Summary Fuel Cells have been around a long time
They present the potential to be highly efficient because of direct conversion of chemical energy to electrical energy
Solid oxide fuel cells are based upon ion conducting properties of ceramic materials like doped zirconia
Temperatures above 600 C are required for operation
To be viable fuel cells must have high power per area, and operate with low cost materials