Solid Oxide Fuel Cells for Undersea Naval Applications

Solid Oxide Fuel Cells for
Undersea Naval Applications
10 th Electrochemical Power Sources R&D Symposium
August 20-23, 2007
A. Alan Burke, Ph.D.
Louis G. Carreiro, Ph.D.
Naval Undersea Warfare Center (NUWC),
Division Newport

SOFC Construction
Ceramic electrolyte (yttria-stabilized zirconia,
YSZ) sandwiched between two electrodes
The electrolyte’s function:
(1) acts as a diffusion barrier between
the fuel and oxidizer and
(2) serves as an ionic conductor for the
transport of oxide ions from the cathode
to the anode.
The anode is a cermet of metallic nickel
and YSZ, while the cathode is a p-type
semiconductor such as La 0.7 Sr 0.3 MnO 3 .
Cathode
Electrolyte
Anode
The interconnect is a necessary component of
the stack. It must have high electrical conductivity
while being inert in oxidizing and reducing
environments. It provides electrical connection and
gas flow channel separation between cells.
Operation below 750°C allows the use of stainless
steel interconnects, which are cost effective.
Fuel
Channel
Cathode:
O 2 + 2e - → 2O 2-
Anode:
Bipolar Plate
Interconnect
H 2 + O 2- → H 2 O + 2e -
CO + O 2- → CO 2 + 2e -
Oxidant

Voltage vs. Efficiency Plots
R.W. Sidwell, W.G. Coors / Journal of Power Sources
143 (2005) 166-172
Operation at lower current
density allows for higher
voltage and higher efficiency,
but stack size must be larger
to reach desired power level.
(Operation at lower stack
power density can result in a
higher system energy density
and efficiency.)

Proposed System Design
with Anode Recycle
Pre-
Reformer
Fuel
Water
Heat to
Reformer
CO2
Adsorber
Adsorber
Cooler
Recycle
Stream
Reformate
Stream
ANODE
Hot
Exhaust
SOFC
Condenser
CATHODE
Cooled
Exhaust
Water
Recovery
Oxygen
Cathode
Cooler

Autonomous Undersea Vehicles

Conceptual 21” Diameter
Mission Reconfigurable UUV
Propulsion Section: Trust Vectored Pumpjet, Control Surfaces, Recovery and
Handling System, Future Integrated Motor Propulsor
Ballast and Trim Section: Pump, Valves,
Aft Tank
Electronics and Control Section: Power
Distribution, Vehicle Computer, Navigation
System, Communications System,
Payload/Vehicle Integration Computer
Nose Section: FLS, Acoustic
Communications System
� 20.95 Inch OD, 240 Inches Long
� Weight = About 2800 lbs
� Speed = 3 to 8 knots
� Sortie Reliability Ps = 0.953
� Sortie Duration = up to 40 Hours
� Sortie Reach = 75 - 120 NM
� Full Impulse Launch Capable
Energy Section: -- Lithium
Battery, AgZn Battery,
Future Fuel Cell
Mission Payload Section: 5 Cubic
Feet with Standard Interfaces
Forward Auxiliary Section: SATCOM & GPS
Antennas, Antenna Mast, Anchor, Forward
Ballast Tank

Force Net
�� ISR
�� Oceanography
�� Communication
Navigation Network
Nodes (CN3)
HWV
~21”
Large
>36”
Class
Diameter
Man Portable
3-9”
LWV
~12.75”
UUVMP SeaPower21
Sub-Pillar Capabilities
Sea Shield
�� Littoral Sea Control
• ASW
• MCM
�� HLD - AT/FP
Inspect/ID
Displacement
(lbs)

Torpedo & UUV Power
& Energy Needs
Specific energy, Wh/kg
UUV, Long Term Goal
Torpedo, Long Term
Goal
* David Linden
Handbook of
Batteries, 2nd
ed, 1995
Commercial Sector and Conventional Energy sources will not meet
the Navy Torpedo and UUV Future Requirements

Broad Fuel Comparisons
Energy Content (LHV)
� Fuel Flashpoint, ºC MP, ºC MJ/L MJ/kg
� Methanol 12 -98 15-18 19-22
� Ethanol 13 -114 18 23
� Gasoline -7.2 -58 (aviation) 31-34 42-46
� Diesel 40-50 -20 to 5 (cloud) ~36-40 42-47
� Liquid H 2 (no tank) -252 (BP) 8 121
� LNG (no tank) -164(BP) 21 51
� 2015 H 2 Storage Goal (9wt% systems basis) 10-15 10
� Glycerin 176 ~ 17 22 18

Fuel
Type
Diesel
Appropriate Fuel Selection
FT-diesel
(S-8)
JP-8
Biodiesel
Sulfur?
Aromatics?
< 5 ppm
< 1%
~ 500 ppm
~ 20%
~ 10 ppm
~ none
10-500ppm
10-25%
Flash &
Cloud Pt.
40 - 50 C
-47 C
> 38 C
-47 C
> 130 C
~ 0 C
40 - 50 C
-20 - 5 C
Others: Dodecane, JP-10 are > $25/gallon**
Cost
$/gal
20-
30?
~3
3-5
(sub)
~3
Energy
Density,
MJ/L
~37
34
33
35-40
Shelf life
8 yrs *
1 yr
6 months
2 yrs
Max
* FT Diesel specs from www.rentechinc.com &
www.syntroleum.com, Energy & Fuels 1991,5, 2- 21
** Missile Fuel Prices FY07

OSD Sponsored SBIR
� OSD07-ES5
� Focuses on mobile synthetic fuel plant
� 50-500 barrels per day
� Lightweight, ~ 3 tons per barrel-day of output
� This would be suitable platform for remote or
shipboard fuel generation for Navy UUVs &
portable generators
� Safety is the major issue—high pressure
reactors must be able to flash & vent

Fuel Processing (Reformers)
Catalytic Partial Oxidation (CPOX )
CmHn + m/2 O2 n/2 H2 + mCO + heat
• Exothermic reaction - no additional heating required for heating inlet
• Fast kinetics - reformer starts and achieves operating temperature quickly
• Air-dependent operation; further studies needed to consider pure O 2 feed
Steam Reforming
C mH n + mH 2O + heat (m+n/2) H 2 + mCO
• Endothermic reaction - requires heat for reaction and evaporation of
fuel/water feed
- Heat is supplied from fuel cell exhaust gases and CO 2 scrubber
- Steam can be recycled from SOFC product gases
• More hydrogen produced per mole of fuel
• Air-independent operation

Delphi Inc.
Solid Oxide Fuel Cell Stack
SOFC Stack Testing
and System Design
Versa Power Systems (VPS)
Solid Oxide Fuel Cell Stack

Furnace
SOFC
Stack
Reformer
Furnace
SOFC Test Stand
Compression
System
Furnace
Controller
1 kW Load
Bank
Gas Handler
Humidifier

Efficiency, %;
Utilization, %
100
90
80
70
60
50
40
30
20
10
0
VPS Stack Performance Using
Dodecane with S/C = 3.63
Dodecane Feed = 0.779 mL/min
Water Feed = 2.68 mL/min
Cathode Gas: 6 L/min O 2
efficiency
utilization
Power
0 100 200 300 400 500
Current Density, mA/cm 2
200
150
100
50
0
Power, W
20 Liters
would provide
~ 100 kW-hrs
However...
Single Pass
needs water
separation
& steam
generation

V, V
Modeling SOFC Cell
Performance
1.2
1
0.8
0.6
0.4
0.2
0
IV & Pd curves for 6-cell VPS Stack single cell average
0
0 0.2 0.4 0.6 0.8
i, A/cm2
Model was first adjusted to fit the published standard operating
curves for the VPS cell, and then the projected performance was
modeled for operation under expected under high utilization of
reformate and pure oxygen feed streams seen in the UUV. A slight
voltage boost from higher operating pressure is also modeled.
0.6
0.5
0.4
0.3
0.2
0.1
Pd, W/cm2
V,std
Vmodel
1 atm, V
3 atm, V
P,std
Pmodel
1 atm,Pd
3 atm, P

Stack Voltage, V;
Efficiency, %
Modeling Projected SOFC
Stack Performance
120
100
80
60
40
20
0
T = 725º C, P = 3 atm
Inlet Gases:
V, P curves, from model
0 10 20 30 40 50
Stack Current, A
Anode: 54% H 2 , 24% H 2 O, 9% CO 2 , 13% CO at total flow of 50 SLPM
Cathode: Pure oxygen dead ended, readily available (no mass transfer limitations)
V
Eff
P
4000
3500
3000
2500
2000
1500
1000
500
0
Stack Power, W

Average Cell Voltage, V
SOFC Stack Peformance Under
Simulated UUV Operating
Conditions (1 atm, 725º C)
1.2
1
0.8
0.6
0.4
0.2
0
0
0 0.2 0.4 0.6 0.8 1 1.2
Current Density, A/cm2
Model, V
Delphi, V
Model,P
Delphi, P
Targeted Steady State operating point: 0.8 V/cell at 0.3 A/cm 2
For a 100-cell stack, this results in 80 V at 35 Amps = 2800 W
Model does not consider methane reformation at the cell surface, localized cooling from methane
reforming could explain higher OCV & lower voltage at low current density
0.6
0.5
0.4
0.3
0.2
0.1
Average Cell Power Density,
W/cm2

Preliminary Energy Section for
21” UUV Platform
Scaling:
Suitable for 21” and
Larger UUVs
(> 1 kW systems)
System Level
Performance:
350-450 W-hr/L
350-450 W-hr/kg
System Demo of all
components except
LOX expected in
Winter 2007
Liquid
Oxygen
Storage
(LOX) SOFC
21” UUV Platform
1-3 kW, ~75 kW-hr
Diesel
Fuel
Storage
Fuel
Processor &
CO 2
Scrubber

Steam Reformer
Provided by InnovaTek
Reformer Inlet Streams for
VPS test:
Gas stream: 5.2 L/min H 2 ,
0.27 L/min CO, 0.27 L/min
CO 2 , 2.40 g/min steam
Liquid stream: 0.3 g/min
S-8 fuel from Syntroleum
(Fischer Tropsch diesel)
Reformer Inlet Streams
for Delphi Test:
Gas stream: 6.93 L/min
H 2 , 0.33 L/min CO,
3.09 g/min steam
Liquid stream: 0.45 g/min
S-8 fuel from Syntroleum
Reformer Outlet Stream for
VPS Test:
Dry Flow: 5.96 L/min (82.9%
H 2 , 5.0% CO 2 , 4.5% CO,
7.6% CH 4 )
~2.4 mL/min water
S/C ~ 2.8
Reformer Outlet Stream for
Delphi Test:
Dry Flow: 8.7 L/min (87.4%
H2, 3.4% CO2, 3.9% CO,
5.3% CH4)
~2.6 mL/min water
S/C ~ 2.8

Anode Gas Recycle Blower
Blower Attributes:
• Inlet T = 600-850º C
• Inlet P is atmospheric
• ∆P ~ 4-10” water
• 100 SLPM gas flow
• Nominal composition of 46
slpm H 2 O, 27 slpm CO 2 , 20 slpm
H 2 , and 7 slpm CO
• η > 40%
• Variable speed control with
turn-down ratio of 5 to 2
• 0.5 L, 4.26 kg
Companies Funded under
DoE, Phase II SBIR contracts:
1. R&D Dynamics
2. Phoenix Analysis and Design
Technologies
**Proposed phase II prototypes match
21” UUV design goals
Prototype from R&D to be delivered to
NUWC for testing in November 2007

Conversion, %
� CaO + CO 2 → CaCO 3 + HEAT (17.8 kJ/mol)
� CaCO 3 Decomposes ~ 850º C
80
70
60
50
40
30
20
10
0
Carbon Dioxide Scrubber
0 2 4 6 8 10 12 14
Time, Minutes
8
7
6
5
4
3
2
1
0
CO2 Removal Rate, mmol/min;
Mass CO2 Absorbed, g
-Recently developed sorbent
showed over 70% conversion
of CaO in gas mixture of
21% CO 2 /44% H 2 /35% steam
-Sorbent shows fast kinetics
and stability for repeated
cycles
-Effort in place to scale up
production methods for this
extruded CaO sorbent
* Sorbent provided by TDA Research, Inc.
Sorbent tested at NUWC

Liquid Oxygen (LOX) Storage
German built U212 & U214
submarines already employ
Siemens fuel cell systems,
which store hydrogen via
metal hydrides and oxygen as
LIQUID OXGYEN.
Spanish S-80 goes a step
further, in that it will be
producing LOX on the vehicle
itself. UTC providing fuel cell
system for this submarine.
LOX is becoming standard for
air-independent propulsion
(AIP), and it is an area that the
U.S. Navy cannot afford to
neglect.
Sierra Lobo successfully
demonstrated this technology in a
Phase II STTR funded by ONR

Various Means to Store
30 kg Oxygen
Storage Method
LOX System
(Stainless steel design
from Sierra Lobo),
200 psia
Compressed
(3000 psia)
H 2 O 2 (60 wt.%)
Mass, kg
30 +
dewar (~ 100 kg)
30 + tank (~100)
107 + tank (~10)
Volume, L
30 + dewar (~82)
97 + tank(~70)
90 + tank (~10)
LOX could be lighter with aluminum or composite instead of
steel components, but volume unlikely to change very much.

Conclusions
� Sulfur-free FT-fuels can be used in fuel cells to
obtain higher efficiency, quieter operation, and
lower emissions than combustion engines
� There are niche areas where SOFCs already
look promising; i.e. undersea vehicles
� Oxidant source remains a large obstacle
towards implementation in UUVs
� System Demonstration planned for this fall in
coordination with InnovaTek’s Phase II SBIR

Acknowledgements
� Sponsors
� ONR, Code 33 – Michele Anderson
� DoE, Interagency Agreement – Wayne
Surdoval & Heather Quedenfeld

NiCd
Lead Acid
NiMH
AgO-Zn
Sec. Li Ion
Li-SOCl 2
Comparison of Energy
Sources for 21” UUV
Type of System
Li Polymer *Expected
PEM (NaBH 4 +LOX)
SOFC (S-8 + LOX)
Specific
Energy,
Wh/kg
30
30
95
110
150-200
210
~ 450
300-340
350-400
Energy
Density,
Wh/L
75
65-95
330
240
325
330
900-1000
300-340
400-450
Max Mission
at 2.5 kW, hr
3
3
8
9
11
18
35-38
22-25
30-38
Number of cycles
1500
> 300
500
15
~2000
> 600
1
150
30 (??)
Available Volume: 189 L Available Mass: 209 kg