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Solid Oxide Fuel Cells Rodger McKain, PhD. Ion transport observed by William Grove in 1839…Based on hydrogen-oxygen, sulfuric acid electrolyte, and platinum.

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Presentation on theme: "Solid Oxide Fuel Cells Rodger McKain, PhD. Ion transport observed by William Grove in 1839…Based on hydrogen-oxygen, sulfuric acid electrolyte, and platinum."— Presentation transcript:

1 Solid Oxide Fuel Cells Rodger McKain, PhD

2 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, H 2 O

4 Fuel Cell Types Source: U.S. Fuel Cell Council Increasing Temperature

5 Attributes of Fuel Cells AFC PACF PEM MCFC SOFC ElectrolyteKOH PhosphoricSulfonic MoltenY 2 O 3 -ZrO 2 Acid Acid CarbonateCeramic Acid Acid CarbonateCeramic Polymer Salt Temperature100 0 C C C C C Fuel H 2 H 2 H 2 H 2 /CO H 2 /CO Efficiency (H 2 fuel) 60% 55% 60% 55% 55% (NG fuel) -- 40% 35% 50% 50% (NG fuel) -- 40% 35% 50% 50% PollutionVery low Very lowVery 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: Source: U.S. Fuel Cell Council

7 Fuel Cell Power System Fuel cell Stack Sub Assembly Useful heatAirAir FuelFuel 10 kW HeatManagement Power Conditioner Fuel Processor Controls

8 High Efficiency

9 High Efficiency at Part Load

10 Contaminant Average U.S. Utility Emissions (lbs per megawatt-hour) ONSI PC kW NG Fuel Cell (lbs per megawatt-hour) Nitrogen Oxides Carbon monoxide Reactive organic gases Sulfur oxides16.10 Particulates (PM10)0.460 Low Emissions

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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 Pt Ink Fuel/CH 4 Effluent CH 4 + CO 2 2CO + 2H 2 CH 4 + H 2 OCO 2 + 3H 2 CO + H 2 OCO 2 + H 2 CH O 2 CO + 2H 2 O 2- CH 4 + 3O 2- CO 2 + H 2 O + 2e - Electrolyte Disc Cathode catalyst layer Anode catalyst layer Pt Wire Yttrium-stablized Zirconia (>950 °C) Galladium-doped Ceria (>600°C) O 2 + 4e - 2O 2- AO ad ProductsT (°C) CH 4 O ad CO, H 2, CO 2, H 2 O C n H 2n O ad C n H 2n O, CO 2, H 2 O CO ad CO v A RLRL

15 Relationship between fuel processing and fuel cells

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 Current is the flow of electrons Electric terms Volts 6,240,000,000,000,000,000 electrons / sec = 1 amp 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. Fuel Cell Stack Low resistance High resistance

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

19 Energy flow Same story for electric system Food  anode, Air  cathode Stack produces power and 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. Food Air Work, power Heat All the energy in the food eventually appears as heat.

20 V-I scan Balls lifted per hour, or amps (I) Height lifted or volts (V) ASR is the slope of the dashed red line

21 V-I scan Balls lifted per hour, or amps (I) Height lifted or volts (V) 1 of these = 2 of these!

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

23 Complete micro view Air Flow, O 2 + N 2 N2N2N2N2 Via Anode Electrolyte Cathode e - O=O=O=O= O=O=O=O= O=O=O=O= Air layer #1 Fuel layer #1 Fuel Flow, H 2 O+CO  H 2 +CO 2 N2N2N2N2 N2N2N2N2 N2N2N2N2 N2N2N2N2 N2N2N2N2 N2N2N2N2 N2N2N2N2 N2N2N2N2 N2N2N2N2 N2N2N2N2 N2N2N2N2 N2N2N2N2 N2N2N2N2 N2N2N2N2 N2N2N2N2 N2N2N2N2 N2N2N2N2 N2N2N2N2 O2O2O2O2 O2O2O2O2 Porous ½ O 2 + 2e - = O = O = + H 2 = 2e - +H 2 O e - H2H2H2H2 H2OH2OH2OH2O CO 2 CO CO CO CO CO CO + - CO O=O=O=O= O=O=O=O= Icon Bond Layer

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

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

27 Add a cell Thermocouples, Voltage taps

28 Manifold arrangement Fuel inlets Air inlets Gasket Manifold

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

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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