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Solid Oxide Fuel Cells Rodger McKain, PhD.

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Presentation on theme: "Solid Oxide Fuel Cells Rodger McKain, PhD."— Presentation transcript:

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 layer
v 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 Comparison
40 100 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

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