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 experimentas an important one…”William Grove to Michael FaradayOctober 22, 1842
3 Fuel CellAn 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 TypesIncreasing Temperaturepolytetrafluoroethylene and perfluorosulfonyl-ethoxyvinyletherNafionSource: U.S. Fuel Cell Council
5 Attributes of Fuel Cells AFC PACF PEM MCFC SOFCElectrolyte KOH Phosphoric Sulfonic Molten Y2O3-ZrO2Acid Acid Carbonate CeramicPolymer SaltTemperature 1000C C C C CFuel H H H H2/CO H2/COEfficiency (H2 fuel) 60% % % % %(NG fuel) % % % %Pollution Very low Very low Very low Low LowHydrocarbon No Difficult Difficult Yes YesFuel UseStart-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 heatAirFuel10 kWHeatManagementPower ConditionerFuel ProcessorControls
10 Average U.S. Utility Emissions (lbs per megawatt-hour) Low EmissionsContaminantAverage U.S. Utility Emissions(lbs per megawatt-hour)ONSI PC kW NG Fuel CellNitrogen Oxides7.650.016Carbon monoxide0.340.023Reactive organic gases0.0004Sulfur oxides16.1Particulates (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 IndependenceLow regulated emissionsQuietFuel flexibilityHigh quality powerHigh reliability Energy SecurityWidespread applications: (transportation, power, medical, communications, military, aerospace, electronics)IF: <$400/kW stationary power<$35/kW automotiveNew industry ($250 billion per year)
13 Solid Oxide Fuel CellsBased upon ion conductivity of certain ceramic materials at elevated temperatures (>600 C)First observed by Nernst in 1890’sFluorite Structures (e.g. yttria stabilized zirconia)Face Centered cubic arrangementTransport through crystal lattice vacancies and oxide ions located between crystal facesFirst SOFC constructed in 1937 by Baur and PreisRequires porous electrodes and dense electrolyte, low electronic conductivity, and high strength
14 Cathode catalyst layer vRLAAnode catalyst layerCH4 + 3O2- CO2 + H2O + 2e-O2 + 4e O2-Pt InkO2-EffluentPt WireFuel/CH4Cathode catalyst layerCH4 + CO2 2CO + 2H2CH4 + H2O CO2 + 3H2CO + H2O CO2 + H2CH O2 CO + 2H2Electrolyte DiscYttrium-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 isA Oad Products T (°C)CH4 Oad CO, H2, CO2, H2OCnH2n Oad CnH2nO, CO2, H2OC 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 reactionVoltage determined by difference in chemical potential of fuel and oxygenCurrent determined by area of cellCatalyzed conversion of oxygen and hydrogen into reactive species O= and HH2 + O2 = H2O + 2 electrons + heatElectrons are separated from reactants by circuitNeed 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 electronsFuel CellStackLow resistanceHigh resistanceVoltsResistanceIf h is 1 volt and current is 1 ampResistance is 1 ohmCopper wire, 1/16” diameter,10 amps, electrons travel 1 cmIn 28 seconds.
18 What’s a watt? Power = (height lifted times weight Work involves height liftedand weight of ball, ft-lbsPower = (height lifted times weightof ball) times (balls per second), orPower = voltage times current,Watts = volts times ampsWork has no time limit, power does550 ft-lbs/sec = 1 horsepower= 746 watts
19 Energy flow Same story for electric system Work,powerHeatFoodAirSame story for electric systemFood anode, Air cathodeStack produces power and heatHeatAll the energy in the food eventually appears as heat.In a perfect system all the energy inthe food would be converted to power.Actually, only part is converted whichdefines the efficiency.
20 Balls lifted per hour, or amps (I) V-I scanBalls lifted per hour, or amps (I)10203040502468Height liftedor volts (V)ASR is the slopeof the dashed red line
21 Balls lifted per hour, or amps (I) V-I scan1086Height liftedor volts (V)1 of these = 2 of these!42510152025Balls lifted per hour, or amps (I)
22 Micro view - Electric - O= + Icon Via Anode Fuel layer #1 Electrolyte* Cathodee -O=Air layer #1Fuel layer #1Porous½ O2 + 2e- = O=O= + H2 = 2e- +H2O-IconBond Layer*A nonmetallic electric conductor in whichcurrent is carried by the movement of ions.Fuel utilizationAir Stoics
29 Vehicle ICE vs. Fuel Cell Direct Drive Efficiency Comparison 40100Energy UnitsIC Engine40%Power Train37.5%156020Idling5Friction2040Energy UnitsFuel Cell50%Direct Drive75%1520Idling5Friction
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 energySolid oxide fuel cells are based upon ion conducting properties of ceramic materials like doped zirconiaTemperatures above 600 C are required for operationTo be viable fuel cells must have high power per area, and operate with low cost materials