solid oxide fuel cells: cell and stack technology

Mitg

lied

der H

elm

holtz

-Gem

eins

chaf

t

Solid Oxide Fuel Cells:cell and stack technology

August 23, 2011

1st Joint European Summer School on Fuel Cell and Hydrogen TechnologyAug 22 – Sep 2, 2011, Viterbo, Italy

Institute of Energy and Climate Research:Fundamentals of Electrochemistry (IEF-9)


SOFC: cell and stack technology

Solid Oxide Fuel Cells:cell and stack technology

contents

requirementsapplicationsstack design

cell configurationscharge transportmass transportheat management

some examplestubularplanarindustrial developments




SOFC: cell and stack requirements

are governed by the system requirements,which, in turn, are governed by the application:

size demand for kWeoperation dynamic load-following vs. stationary base-load

operation time vs. degradation ratefuel availability

in the end, however, it will all come down to

cost of investmentcost of operation




SOFC: systems applications and sizes

mobilehand held < 1kWpersonal power e.g. military applicationμ-CHP 1-5 kWrecreational, camper

APUcars 5-10 kWstationary heating, onboard electronicstrucks 5-50 kWidling reduction, refrigerationplanes 50 kWnoise reduction, water generatorships 10-250 kWport power

stationaryμ-CHP 1-5 kWsingle housesCHP 10-250 kWhospitals, distributed power power plant > 1 MWcentralized power production




SOFC: systems applications and operation

stationary μ-CHP for single housing

(1-5 kW)

APUfor cars

(5-10 kW)

operation time 40.000 hours 5.000 hours

degradation < 1% in 1000 hours

< 10% in 1000 hours

cycling > 50 (thermal) > 250 (thermal)> 250 (red-ox)

start up 4-5 hours < 10 minutes

cost $ 100/kW for stack $ 50/kW for stack




+

-

SOFC: stack design

fuelH2, CO, CH4, CO2, H2O

coolantwarm

oxidantO2

exhaustH2, CO2, H2O

coolanthot




+

-

SOFC: stack design

fuelH2, CO, CH4, CO2, H2O

coolantwarm

oxidantO2

exhaustH2, CO2, H2O

coolanthot

anode inter-connect

electrolyte

cathode sealing

distributorfuel gas

distri-butoroxidant

heatexchanger

collectorexhaust

is solving the puzzle




SOFC: stack design

taking into accountthe materials used for the componentsthe manufacturing technologies usedthe cell configuration selectedthe processes for

charge transport short current paths, no short-circuiting good electrical contacts and sufficient contact area

mass transport no gas leakages, no cross-leakages uniform distribution of reactants, not only across thearea of each cell but also to each cell of the stack

heat transport appropriate gas flow configurations for stack cooling,more uniform temperature distribution during operation

mechanical/structural integrity adequate mechanical strength for assembly, handling and during operationminimise mechanical and thermal stresses

is solving the puzzle




SOFC: cell configurations

electrolyte =

supporting component

tubular

planar

electrolyte anode

cathode

high mechanical strengthno high-temperature seals

low(er) power densityhigh(er) manufacturing costs

limited mechanical strengthhigh-temperature seals require

high(er) power densitylow(er) manufacturing costs

advantages disadvantages





electrolyte anode

cathode

inertceramic

tubular

planar





electrolyte anode

cathode

inertceramic

metal

tubular

planar





electrolyte anode

cathode

inertceramic

metal

tubular

planar





planar

flattenedtubular

tubular




SOFC: stack design and charge transport

electrical connection of cells:

in series and in series in parallel

A

A'

A - A'

interconnectorinterconnector




SOFC: stack design and charge transport

electrical connection of cells:

in series

interconnector

contact elementsmaller conducting cross sectionlonger distance between contact pointssmaller contact area

larger conducting cross sectionshorter distance between contact pointslarger contact area




SOFC: stack design and mass transport

fuel and air supply:to all cells in a stack manifolding (Z- or U-type)

externalinternal (integrated)

over the cell (electrode) area flow fieldparallelserpentine (meander)radialspiral

in the (porous) electrode tothe electrode/electrolyte interfacee.g. the reaction sites not directly relevant for stack design

fuel vs. air flow configurationco-flow in same directioncounter-flow in opposite directionscross-flow in directions usually differing 90°







U-type flow

0 0.25 0.5 0.75 1

rel. position of cell in stack

stat

icpr

essu

re

distributor manifold

collectormanifold

inlet

outlet

Z-type flow

0 0.25 0.5 0.75 1

rel. position of cell in stack

stat

icpr

essu

re

distributor manifold

collectormanifold

inlet

outlet

source: Th. Wüster, Ph.D. Thesis, RWTH Aachen













over the cell (electrode) area flow fieldparallelserpentine (meander)radialspiral





fuel and air supply:fuel vs. air flow configuration

co-flow in same directioncounter-flow in opposite directionscross-flow in directions usually differing 90°

co-flow counter-flow cross-flow

cell length x / cm10 201550

0

5

10

15

20

cell width y / cm


0

5

10

15

20

cell width y / cm


0

5

10

15

20

cell width y / cm

air

fuelfuel fuel

air

air

750 800 850 900 950 1000

temperature / °C

air

has direct effect on current and temperature distribution

heat management




SOFC: stack design and mass and heat transport

heat productionelectrochemical reactions (T S)current (I²R)

coolingair mass flow (stoichiometry > 2)internal reforming of methane (endothermic)

co-flow counter-flow


0

5

10

15

20

cell width y / cm


0

5

10

15

20

cell width y / cmfuel fuel

air

air

750

800

850

900

950

1000

temperature / °C


0

5

10

15

20

cell width y / cm


0

5

10

15

20

cell width y / cmfuel fuel

air

air

30%pre-reformedmethane

100%pre-reformedmethane




SOFC: some examples of stack concepts




SOFC macro tubular cells / stacks

cathode supported tubes with one cell per tubeanode supported tubes with one cell per tubeinert supported tubes with multiple cells

advantages:low degradationrelatively easy sealingpressurized operationfor multiple cells: high output voltage

disadvantages:high temperature 900-1000°Clow power density < 0.3 W/cm²low heating rates




SOFC: micro tubular cells / stacks

electrolyte supported

anode supported

advantages:high heating ratesmoderate power density ~0.5 W/cm²(low degradation?)

disadvantages:high temperature ~900°Clow power per cellcomplex manifolding and sealing

advantages:moderate power density ~0.5 W/cm²medium temperatures 700-800°C

disadvantages:low power per cellcomplex manifolding and sealingredox instable




SOFC: micro tubular cells / stacks

micro tubular anode supported

monolithic

advantages:low temperature 500-600°Chigh power density > 1

W/cm²(high heating rates)

disadvantages:low power per cellcomplex manifolding and sealing cooling problems

advantages:low temperature 600-700°C

disadvantages:low power density < 0.4 W/cm²(complex manifolding and sealing)




SOFC: planar cells / stacks

electrolyte supportedwith ceramic interconnect

advantages:low degradation

disadvantages:high temperature ~900°Clow power density < 0.3 W/cm²complex sealing geometrycomplex manufacturing




SOFC: planar cells / stacks

electrolyte supportedwith metallic interconnect

anode supportedwith metallic interconnect

light-weight APU

advantages:red-ox stable?

round cells: simple sealing geometry

disadvantages:high temperature >900°Clow power density < 0.3 W/cm²degradationcomplex sealing geometrylow heating rates

advantages:high power density 1.0 W/cm²medium temperatures 700-800°C(pressurized operation)

disadvantages:degradationcomplex sealing geometrynot red-ox stable(low heating rates)




SOFC: Siemens Westinghouse Power Co

FuelFlow

Interconnection

FuelElectrode

AirElectrode

ElectrolyteNickel Felt

e-+

e--

AirFlow

FuelFlow

AirElectrode

Electrolyte

Interconnection

FuelElectrode

Nickel-Felt Interconnector

Electrolyte

Anode

Cathode

e-

e-

+

-




SOFC: Siemens Westinghouse Power Co

CHP 125 / SFC-200




SOFC: Rolls Royce Fuel Cell Ltd




SOFC: HEXIS




SOFC: Versa Power Systems




Thanks for your attention

Questions anyone?

solid oxide fuel cells: cell and stack technology

Documents