Fuel Cell Systems: an Introduction for the Engineer (and others) Professor Donald J. Chmielewski Center for Electrochemical Science and Engineering Illinois Institute of Technology Presented to the E 3 Class March 16 th, 010 Illinois Institute of Technology
What is a Fuel Cell???? Illinois Institute of Technology
Applications Stationary (00 kw) Mobile (50 kw) International Fuel Cells Toyota Illinois Institute of Technology 3
What is a Fuel Cell? Fuel Cell Air O Answer: An electrochemical device that converts a fuel directly to electrical power Electric Power Illinois Institute of Technology 4
Where Does the Energy Come From? Air Fuel Cell O Electric Power Illinois Institute of Technology 5
Where Does the Energy Come From? Fuel Cell Air O Answer: The enthalpy released by the reaction: + ½ O O Electric Power ( H ~ 58 kcal/mole ) Illinois Institute of Technology 6
The Fuel Cell Reactor? Air Fuel Cell O??? Illinois Institute of Technology 7
The Fuel Cell Reactor? Fuel Cell Air O Problem: Heat is released but not electric power Heat Illinois Institute of Technology 8
The Fuel Cell Reactor Air Fuel Cell O Solution: Two reactors separated by an electrolyte membrane. Illinois Institute of Technology 9
The Fuel Cell Reactor Air Fuel Cell E cell Current Voltage * Current = Electric Power O Solution: Two reactors separated by an electrolyte membrane. This allows for manipulation of electrons Illinois Institute of Technology 10
Electrolyte Types Polymer Membrane: Solid Oxide Membrane: e - e - e - e - H + O N O - O N H + N O O N O - N O O N N O N O H + O N O - O N H + O O - O Anode Electrolyte Cathode Anode Electrolyte Cathode Illinois Institute of Technology 11
Polymer Electrolyte Membrane Fuel Cell (PEMFC) e - e - Electrolyte conducts ions (H + ), but not electrons (e - ). H + O N Anode H + H + H + Electrolyte N O N O O Cathode O N N O Electrodes (Anode and Cathode) conduct electrons (e - ), but not ions (H + ). Illinois Institute of Technology 1
Solid Oxide Fuel Cell (SOFC) e - e - Electrolyte conducts ions (O = ), but not electrons (e - ). O - O N Anode O - O - O - Electrolyte N O N O O Cathode O N N O Electrodes (Anode and Cathode) conduct electrons (e - ), but not ions (O = ). Illinois Institute of Technology 13
Where Does the Water Go? Polymer Membrane: Solid Oxide Membrane: e - e - e - e - H + O N O - O N H + N O O N O - N O O N N O N O H + O N O - O N H + O O - O Anode Electrolyte Cathode Anode Electrolyte Cathode Illinois Institute of Technology 14
Where Does the Water Go? Polymer Membrane: Solid Oxide Membrane: e - e - e - e - O H + H + H + H + O N O N O O O O O O O N N O N O O O O O O O O O - O - O - O - O N O N O O N O N N O Anode Electrolyte Cathode Anode Electrolyte Cathode Illinois Institute of Technology 15
Where Do the Electrons Go? Illinois Institute of Technology 16
Where Do the Electrons Go? SOFC Configuration: Fuel Interconnect/Bipolar plate: (La,Sr)CrO 3 or High Temp Alloy Anode: Ni - (Zr,Y)O - cermet Electrolyte: (Zr,Y)O - Air Cathode: (La,Sr)MnO 3 Illinois Institute of Technology 17
Fuel Cell Stack Illinois Institute of Technology 18
Current Collectors SOFC: O Anode Electrolyte Cathode e - e - e - O = e - O Illinois Institute of Technology 19
The Electrode Electrolyte Assembly O Anode Electrolyte Cathode e - e - O = O Anode Grains e - e - Electrolyte O= e - O Illinois Institute of Technology 0
The Three Phase Region Anode Grains e - O Electrolyte O= Ni YSZ YSZ O YSZ YSZ Ni Ni Ni YSZ Ni Ni Ni Ni YSZ YSZ Ni O = e - Illinois Institute of Technology 1
Design Issues SOFC: O Anode Electrolyte Cathode e - e - e - O = e - O Illinois Institute of Technology
How Much Fuel Does a Fuel Cell Use? Air Fuel Cell O E cell Current Voltage * Current = Electric Power Illinois Institute of Technology 3
How Much Fuel Does a Fuel Cell Use? Air Fuel Cell E cell Current Voltage * Current = Electric Power O Reaction rate is proportional to current density r H j n F Current j* Area Illinois Institute of Technology 4
How Do We Calculate Current Density? Illinois Institute of Technology 5
Load How Do We Calculate Current Density? Fuel Cell DC R int E o I=j*A cell E cell A fuel cell looks like a battery to the electrical world. Current output depends on the load. Illinois Institute of Technology 6
Review of Circuits 101 Battery I R int E load R load DC E o Illinois Institute of Technology 7
Review of Circuits 101 Battery R int I Equation #1: E load = E o - I*R int E load R load Equation #: DC E o E load = I*R load Illinois Institute of Technology 8
Review of Circuits 101 E load E o E load = E o - R int *I Equation #1: E load = E o - I*R int -R int I Illinois Institute of Technology 9
Review of Circuits 101 E load E o E load = E o - R int *I Equation #1: E load = E o - I*R int -R int Equation #: E load = R load *I R load I E load = I*R load Illinois Institute of Technology 30
Review of Circuits 101 E load E o E load = E o - R int *I Equation #1: E load = E o - I*R int -R int Equation #: E load = R load *I R load I E load = I*R load Illinois Institute of Technology 31
How Much Fuel Does a Fuel Cell Use? r H n I / A F E load E o E load = E o - R int *I -R int moles of H sec m E load = R load *I R load I Illinois Institute of Technology 3
Fuel Used is Proportional to Current r H I / n moles of A F sec m cell H Air Fuel Cell E cell Current Voltage * Current = Electric Power O Illinois Institute of Technology 33
Changing the Reaction Rate E load E load = E o - R int *I r H n I / A F E o Battery I -R int R int E load R load E load = R load *I I DC E o Illinois Institute of Technology 34
Load Circuit Perspective of the SOFC Solid Oxide Fuel Cell I=j*A cell R int E cell DC E o Illinois Institute of Technology 35
Load Circuit Perspective of the SOFC Solid Oxide Fuel Cell I=j*A cell R int (T cell ) E cell DC E o (P H,P O, P HO ) Illinois Institute of Technology 36
Resistance in the SOFC Zirconia Electrolyte Fuel Air Cathode (~30 μm) Electrolyte (10-00 μm) Anode ( up to 1 mm) Bipolar Plate (3-10 mm) R int = r (T ) * ( thickness / Area ) Illinois Institute of Technology 37
Circuit Perspective of the SOFC E load E load = E o - R int *I E o Lower T R load I Illinois Institute of Technology 38
Load Circuit Perspective of the SOFC Solid Oxide Fuel Cell I=j*A cell R int (T cell ) E cell DC E o (P H,P O, P HO ) Illinois Institute of Technology 39
Equilibrium Voltage Air O Fuel Cell E o E o g RT F F m log P H P H P 1/ O O Illinois Institute of Technology 40
Circuit Perspective of the SOFC E load E load = E o - R int *I E o Lower P R load I Illinois Institute of Technology 41
Load Circuit Perspective of the PEMFC PEM Fuel Cell I=j*A cell R int (T cell, j ) E cell DC E o (P H,P O, P HO, j ) Illinois Institute of Technology 4
PEMFC Polarization Curve 0 000 Illinois Institute of Technology 43
PEMFC Polarization Curve 0 000 Illinois Institute of Technology 44
How Much Heat Does a FC Generate? Q gen ( H ) r f, H O HO P e Illinois Institute of Technology 45
Cell Voltage (V) Power Density (watts/cm ) How Much Heat Does a FC Generate? Q gen ( H ) r f, H O HO P e 1.4 0.35 1. 0.3 r H j n F 1 0.8 0.6 E P e cell 0.5 0. 0.15 P j * V e cell 0.4 0.1 0. 0.05 0 0 00 400 600 Current Density (ma/cm 800 1000 ) Illinois Institute of Technology 46
Cell Voltage (V) Power Density (watts/cm ) How Much Heat Does a FC Generate? 1.4 1. 1 0.8 0.6 0.4 0. E P e 0.35 0.3 0.5 0. 0.15 0.1 0.05 0 0 00 400 600 Current Density (ma/cm 800 1000 0 ) cell Q gen P e H 0.5 w/ cm f, H O r H 0.4 w/ cm O P e r H 0.4A / cm F n H f, H OrH O 0.49 w/ cm Illinois Institute of Technology 47
Applications Stationary (00 kw) Mobile (50 kw) International Fuel Cells Toyota Illinois Institute of Technology 48
The Fuel Cell System Electric Power Conditioner Air Fuel Air Fuel Processor Fuel Cell Stack Spent-Fuel Burner Exhaust O CO Thermal & Water Management Illinois Institute of Technology 49
Stationary Applications International Fuel Cells Illinois Institute of Technology 50
Flat-Plate Hydrogen Fed SOFC Fuel Cell Stack O H - + O = O +4 e - Anode 4 e - HEAT Solid O = RELEASED Electrolyte V O + 4 e - O = Cathode 4 e - + Anode Flow Cathode Flow O Illinois Institute of Technology 51
Plug Flow Reactor Analogy Feed Exhaust Conventional Design Reaction Rate Illinois Institute of Technology 5
Thermal Stresses in the Literature Peters et al., state that Large temperature gradients in either direction can cause damage to one or more of the components or interfaces due to thermal stresses Yakabe et al., state that the internal stress would cause cracks or destruction of the electrolytes Figure taken from Selimovic Dissertation, Lund University, (00). Illinois Institute of Technology 53
Internal Reforming SOFC CH 4 O CO O Fuel Flow O = Fuel Cell Stack O Air Flow Air Channel Cathode Electrolyte Anode Interconnect Fuel Channel Illinois Institute of Technology 54
Internal Reforming H r 1 + O H HO Exothermic CH kref 4 + HO CO + 3H rch kref CCH k ref is very large Endothermic 4 4 CO + H k, f O CO + H r CO k shift, f C H OC Exothermic shift k shift, f is also large CO C H K C eq CO Illinois Institute of Technology 55
Plug Flow Reactor Analogy (Internal Reforming) Reforming Reaction Rate Electrochemical Reaction Rate Reforming Heat Generation Electrochemical Heat Generation Combined Heat Generation Illinois Institute of Technology 56
Impact of Internal Reforming Figure taken from Selimovic Dissertation, Lund University, (00). Illinois Institute of Technology 57
Effective Structure of IR SOFC Methane Steam Pre-Heater CH 4 + H O 3 CO + H O Reforming Section H H + CO + CO H + O H O Electrochemical Section Heat and steam produced not used by reforming. Pre-heating steam is expensive. Steam in the feed lowers hydrogen utilization (reaction rate is a function of hydrogen to steam ratio). Illinois Institute of Technology 58
Distributed Feed Plug Flow Reactors Feed Feed Exhaust Distributed Feed Design Makes PFR act like a CSTR. Improves Yield and Selectivity. Improves Thermal Management. Illinois Institute of Technology 59
Hydrogen Fed Simulations Solid Temperature Profile Illinois Institute of Technology 60
Simulation of the Internal Reforming Case Illinois Institute of Technology 61
-D Distributed Feed Design Active Area Inactive Area Wall Side Feed Channels x z z 1 z z 3 z 4 z 5 Section of a stack layer Illinois Institute of Technology 6
Internal Reforming SOFC CH 4 O CO O Fuel Flow O = Fuel Cell Stack O Air Flow Air Channel Cathode Electrolyte Anode Interconnect Fuel Channel Illinois Institute of Technology 63
Mobile Applications Toyota Illinois Institute of Technology 64
The Fuel Cell System Electric Power Conditioner Air Fuel Air Fuel Processor Fuel Cell Stack Spent-Fuel Burner Exhaust O CO Thermal & Water Management Illinois Institute of Technology 65
Hydration Model for MEA Anode Solid Material Current Collector In Cathode (, O) H Air in O H + H + O H + H + H + N Anode Exhaust H + H + H + O Cathode Exhaust MEA Illinois Institute of Technology 66
Hydration Model for MEA Anode Solid Material Current Collector In Cathode (, O) H Air in O H + H + O H + H + H + N Anode Exhaust H + H + H + O Cathode Exhaust MEA Illinois Institute of Technology 67
Water Transport in the Membrane ELECTRO-OSMOTIC DRAG DIFFUSION Illinois Institute of Technology 68
Concentration Profiles ( mem C ) ( ) H O m ( an) C HO ˆ ( mem ) C o ( mem) C H O ( 0) ( ca) ˆ ( mem) C C HO m ( mem C ) ( z) HO Anode Gas GDL Membrane GDL Cathode Gas δ a δ m δ c Illinois Institute of Technology 69
The Fuel Cell System Electric Power Conditioner Air Fuel Air Fuel Processor Fuel Cell Stack Spent-Fuel Burner Exhaust O CO Thermal & Water Management Illinois Institute of Technology 70
Why On Board Fuel Processing? Transportation Applications Hydrogen Storage Tank PEMFC Liquid Fuel Storage Tank C m H n CO Fuel Processors O CO PEMFC Illinois Institute of Technology 71
CO Poisoning Illinois Institute of Technology 7
High Temperature Membranes RH x w P P (T) sat ElectricalConductivity,, Increases with Humidity x w = 0.35 Illinois Institute of Technology 73
Fuel Processing Reactors Reformer Water- Gas Shift (WGS) Preferential Oxidation (PrOx) PEMFC Hydrocarbon Feed Large Hydrocarbons Cracked: CO levels down to ~ 10 ppm / CO ratio ~ Most CO converted to CO : ~ 1% CO remaining Illinois Institute of Technology 74
Reforming Reactors Steam Reforming Partial Oxidation Autothermal Reforming Illinois Institute of Technology 75
Steam Reforming Steam Fuel C m H n + mh O mco + m + n / ) CO + H + O CO H ( H Heat Illinois Institute of Technology 76
Catalytic Partial Oxidation (CPOX) Air C H + ( m + n / ) O mco + n / H m n O C m H n + mh O mco + m + n / ) ( H Fuel CO + H + O CO H Illinois Institute of Technology 77
Autothermal Reforming (ATR) Steam Air Fuel C C H + ( m + n / ) O mco + n / H m n m H n + mh O mco + m + n / ) CO + H + O CO H ( H O Illinois Institute of Technology 78
Start-up and Regulation of an ATR Water Flow In Air Flow In Fuel Flow In ATR Reformat Flow Out TT TC Illinois Institute of Technology 79
The Effect of Water Injection Illinois Institute of Technology 80
Closed-loop Water Injection Illinois Institute of Technology 81
Slower Water Injection Rate Illinois Institute of Technology 8
Fuel Processing Reactors Reformer Water- Gas Shift (WGS) Preferential Oxidation (PrOx) PEMFC Hydrocarbon Feed Large Hydrocarbons Cracked: CO levels down to ~ 10 ppm / CO ratio ~ Most CO converted to CO : ~ 1% CO remaining Illinois Institute of Technology 83
Water Gas Shift Reactors CO + H + r O CO H ( ( s) ( s) ( s) ( s) y y y y K ) 3 k3 CO O CO eq High Temp WGS Medium Temp WGS Low Temp WGS Illinois Institute of Technology 84
Preferential Oxidation Reactors CO + 1 O CO 1 H + O HO Reformat Air PrOx Illinois Institute of Technology 85
Preferential Oxidation Reactors CO 1 1 + O CO H O H O + Reformate Air Air Air Prox Stage 1 100 o C 100 o C Prox Stage Intercooler Intercooler Prox Stage 3 Illinois Institute of Technology 86
Hydrogen Convereted (%) Preferential Oxidation Reactors.5 1.5 1 0.5 1-Stage -Stage 3-Stage 0 0 0.5 1 1.5.5 3 3.5 Inlet CO Concentration (%) Illinois Institute of Technology 87
The Fuel Cell System Electric Power Conditioner Air Fuel Air Fuel Processor Fuel Cell Stack Spent-Fuel Burner Exhaust O CO Thermal & Water Management Illinois Institute of Technology 88
Hybrid Fuel Cell Vehicle i a i fc i afc i b i ab R a R b L a V fc FC K fc V b K b V a E b Illinois Institute of Technology 89
Separation of Time-Scales i fc i afc i b R b i ab i a R a L a 1000 800 Armature Power Profles [W] Fuel Cell V fc FC K fc V b E b K b V a 600 400 00 (sp) P load P mot (sp) - + PI V fc (sp) x P fc FUEL CELL VOLTAGE CONTROLLER V fc 0 Battery P bat (sp) + - x PI P bat k fc k bat Vehicle P mot -00 5 10 15 0 5 30 35 time, sec Illinois Institute of Technology 90
Hybrid Fuel Cell Vehicle (Double Storage Configuration) Power Bus i arm i fc i afc i bat i abat i scap i ascap R arm Fuel Cell E fc DC-DC Converter R bat E bat DC-DC Converter R scap E scap DC-DC Converter E arm L arm w arm k fc k bat k scap Illinois Institute of Technology 91
Supervisory Control P motor PI k fc Supervisory Controller P (sp) fc + - PI P (sp) bat + - PI P fc k bat P bat k scap Vehicle Power System P (sp) scap + - P scap Illinois Institute of Technology 9
The Fuel Cell System Electric Power Conditioner Air Fuel Air Fuel Processor Fuel Cell Stack Spent-Fuel Burner Exhaust O CO Thermal & Water Management Illinois Institute of Technology 93
Acknowledgements IIT Collaborators: Said Al-Hallaj Ali Emadi Herek Clack Argonne National Laboratory: Shabbir Ahmed Rajesh Ahluwalia Students: Kevin Lauzze J. Robert Selman Satish Parulekar Jai Prakash Dennis Papadias Qizhi Zhang Ayman Al-Qattan Funding: Kuwait Institute for Scientific Research Graduate College and Armour College, IIT Argonne National Laboratory Illinois Institute of Technology 94