Innovations in fuel cell technologies

367 Pages·2010·40.29 MB·English

by  Robert Steinberger-Wilckens, Werner Lehnert

RSC Energy and Environment Series
Edited by Robert Steinberger-Wilckens and Werner Lehnert
Innovations in Fuel Cell
Technologies
I
n
n
o
v
a
t
i
o
n
s

i
n

F
u
e
l

C
e
l
l

T
e
c
h
n
o
l
o
g
i
e
s
S
t
e
in
b
e
r
g
e
& r-
L W
eh ilc
nert kens
Innovations in Fuel Cell Technologies
RSC Energy and Environment Series
Editor-in-Chief:
Professor Laurence Peter, University of Bath, UK
Series Editors:
Professor Heinz Frei, Lawrence Berkeley National Laboratory, USA
Professor Ferdi Schu¨th, Max Planck Institute for Coal Research, Germany
ProfessorTimS.Zhao,TheHongKongUniversityofScienceandTechnology,
Hong Kong
Titles in the Series:
1: Thermochemical Conversion of Biomass to Liquid Fuels and Chemicals
2: Innovations in Fuel Cell Technologies
How to obtain future titles on publication:
A standing order plan is available for this series. A standing order will bring
delivery of each new volume immediately on publication.
For further information please contact:
BookSalesDepartment,RoyalSocietyofChemistry,ThomasGrahamHouse,
Science Park, Milton Road, Cambridge, CB4 0WF, UK
Telephone:[phone],Fax:[phone],Email:[email protected]
Visit our website athttp://www.rsc.org/Shop/Books/
Innovations in Fuel Cell
Technologies
Edited by
Robert Steinberger-Wilckens and Werner Lehnert
Forschungszentrum Ju¨lich, Ju¨lich, Germany
RSCEnergyandEnvironmentSeriesNo.2
ISBN:978-1-84973-033-4
ISSN:2044-0774
AcataloguerecordforthisbookisavailablefromtheBritishLibrary
rRoyalSocietyofChemistry2010
Allrightsreserved
Apartfromfairdealingforthepurposesofresearchfornon-commercialpurposesorfor
privatestudy,criticismorreview,aspermittedundertheCopyright,DesignsandPatents
Act1988andtheCopyrightandRelatedRightsRegulations2003,thispublicationmaynot
bereproduced,storedortransmitted,inanyformorbyanymeans,withouttheprior
permissioninwritingofTheRoyalSocietyofChemistryorthecopyrightowner,orinthe
caseofreproductioninaccordancewiththetermsoflicencesissuedbytheCopyright
LicensingAgencyintheUK,orinaccordancewiththetermsofthelicencesissuedbythe
appropriateReproductionRightsOrganizationoutsidetheUK. Enquiriesconcerning
reproductionoutsidethetermsstatedhereshouldbesenttoTheRoyalSocietyof
Chemistryattheaddressprintedonthispage.
TheRSCisnotresponsibleforindividualopinionsexpressedinthiswork.
PublishedbyTheRoyalSocietyofChemistry,
ThomasGrahamHouse,SciencePark,MiltonRoad,
CambridgeCB40WF,UK
RegisteredCharityNumber207890
Forfurtherinformationseeourwebsiteatwww.rsc.org
Preface
Fuel cells have evolved from an exotic technology only feasible under the
constraints of space flight into a product addressing the ‘everyman’ con-
sumer, although, at first, in niche markets only. The considerable level of
technological readiness that has been reached today finally gives rise to
hopes that fuel cells will eventually make it to larger markets within the dec-
ade leading up to the year 2020. Their high potential for emission-free energy
supply, high electrical efficiency, modularity, low maintenance requirements
and almost noiseless operation have encouraged researchers and developers
worldwide to stubbornly and gradually improve performance, robustness and
cost effectiveness, inching their way towards eventually technically realising
the potential dormant in the concept. Many companies have been seen to
invest in fuel cell technology, lose a lot of money and leave again, whereas
the number of firms with commercially successful operations is small but – in
more recent times – constantly growing.
Different fuel cell types are being discussed for different applications: sta-
tionary,mobileandportable.Therequirementsonthefuelcellsystemsdifferin
each application not only from the point of view of lifetime but also with
respect to dynamic or stationary application and to power range. In the mil-
liwattrangetheefficiencyisoftennotthemaindriverforfuelcelldevelopment
whereasinthekilowattrangeandinthefutureinthemegawattpowerrangethe
use of fuel cells is mainly driven by the high efficiency of the evolving fuel cell
technology.
Thealkalinefuelcell(AFC) proveditsreliabilityindemanding applications
like space flight. Cost issues and the requirement for pure gases at both elec-
trodespreventabroadapplicationoutsidesomenichemarkets.Consequently,
despite the proven technological readiness, most activities in the field of R&D
were stopped, especially after Nafion was shown to be a good electrolyte for
low temperature fuel cells. Now, worldwide R&D activities on Nafion-based
fuel cells have shown a sharp rise in research activities and also in industry.
Several automotive companieswhohavethevisionofbringingfuel celldriven
RSCEnergyandEnvironmentSeriesNo.2
InnovationsinFuelCellTechnologies
EditedbyRobertSteinberger-WilckensandWernerLehnert
rRoyalSocietyofChemistry2010
PublishedbytheRoyalSocietyofChemistry,www.rsc.org
v
vi Preface
cars into the market focus on these polymer electrolyte membrane fuel cells
(PEFCs). The effort of the industry to develop a reliable and competitive
product led to advanced fuel cell systems which were proven to fulfil the
requirements of cars in daily use. The necessary hydrogen infrastructure and
costissuesarethemainreasonsthatthemarketentryisfurtherdelayed.Inthe
slipstream of the automotive industry the development of PEFCs for other
applications, especially for stationary power generation has increased. Based
on natural gas, several companies started a development of PEFC combined
heatandpowersystems.Thereformingofthenaturalgas,thetreatmentofthe
reformate gas in order to remove the resulting CO from the fuel gas and the
water management lead to complex system architectures and it seems to be
difficult to reach the desired cost goals.
Afew years agohigh-temperature polymer electrolytefuel cells(HT-PEFC)
cameintothefocusofthefuelcellcommunity.Thisfuelcelltypeisbasedona
phosphoric acid-doped polybenzimidazol-type electrolyte. The advantage of
theoperatingtemperatureofabout1601CisthehighCO toleranceofabout1
to2%.Furthermore,thedifficultwatermanagementisnotamajor issue asin
classical PEFCs. This opened up the option to simplify the complex system
when using natural gas as fuel. In addition, reformate gas from middle dis-
tillates like diesel or jet fuel can be used without the necessity of employing a
selectiveoxidationormethanationstepaftertheshiftreactors.Atthemoment
HT-PEFC auxiliary power unit (APU) systems are within the focus of devel-
opers. One drawback is the missing cold start capability of a HT-PEFC, the
stack has tobe heated to atleast 1201Cbefore current can bedelivered bythe
system. Compared to classical PEFCs the development of HT-PEFCs is at
an early stage but many improvements have been made in the last few years.
The latest research activities focus on the oxygen reduction reaction (ORR)
which is a major reason for the low power density. While lifetime is high
at steady state operation, dynamic operation and thermal cycling leads to
increased degradation.
Thesearealsomajorissuesforphosphoricacidfuelcells(PAFCs)whichuse
thesameelectrolyteasHT-PEFCs.Industrialcompanieshaveinvestedagreat
dealoftimeandmoneyinordertodevelopstationaryPAFCsystems.Despite
thehighcostsofsuchsystemsitcanbesaidthatthePAFCisaproductwhich
has proven its functionality especially in the 200 kW range for stationary
applications. Until the 1980s there were many publications concerning phos-
phoric acid fuel cells but in the last few years research and development has
been performed mainly within industry and few results have been published.
Due to the high interest in HT-PEFCs, research activities worldwide on fuel
cells with phosphoric acid as electrolyte are growing again.
Inthefieldofhigh-temperaturefuelcellsthetechnologyofmoltencarbonate
fuelcells(MCFCs)liesinthehandsoffewindustrialcompanies.Systemsof250
kW capacity for stationary applications are state of the art. Much experience
has been gained during the last few years in field tests. These fuel cell stacks
have been operated for some tens of thousands of hours without failure in
various system environments. The future transition to an automated assembly
Preface vii
may lead to decreasing costs. As a result, the MCFC may also become
attractive outside the niche markets where they are located today.
The solid oxide fuel cell (SOFC) also has a long tradition. The main
advantage of the SOFC over other fuel cells is the ability of internally
reformingmethane,themainconstituentofnaturalgaswhichresultsinavery
highelectricefficiencywhenoperatedwithnaturalgas.Furthermore,theSOFC
providesahighoff-gastemperaturewhichcanbeusedforalargerangeofheat
applications.AnSOFCcanalsobecoupledwithsteamandgasturbineswhich
further increases the overall efficiency of the system. Intensive industrial and
institutional research and development resulted in long-term stable materials
and highly efficient systems. Operating times of 40000h were demonstrated
under steady-state conditions. As with the MCFC, thermal cycles will induce
stress and microcracking in the ceramic materials. Therefore applications are
preferred wherethermalcycling can beavoided orkepttoa minimum. This is
typical for stationary applications in the high-power range. In the low power
range of about 1kW SOFCs will be used as residential combined heat and
power systems. In this application the main goal of the system is heating. The
electricity is more or less a by-product. Nevertheless, the high electrical effi-
ciencyofupto60%offersahighpotentialinde-central electricity generation.
Major issues for further development are redox stability of the anode and the
ability to withstand hundreds of thermal cycles. Furthermore, the sealing
between the cells inside a stack has to be improved.
Lastbutnotleastthedirectmethanolfuelcellhastobementioned.Thislow-
temperature fuel cell can be operated with a mixture of methanol and water.
The advantages are (1) the simple system layout, and (2) methanol can be
converted in the fuel cell directly without a preceding reforming step. The
disadvantages of the DMFC are the low efficiency and the limited lifetime of
typically a few thousand hours. Typical applications are in the 100W region,
e.g. in recreational applications. Fuel cell systems in this power range can be
purchased from the company Smart Fuel Cells. Instead of using a battery
whichhastoberechargedafterawhile,theDMFCofferstheabilitytooperate
as long as methanol is present or can be refilled. Therefore continuous opera-
tion of electric devices is possible even when no electricity for recharging of a
battery is available. Another typical application can be found in the kilowatt
power range. In pallet trucks a DMFC can replace the battery pack. The
advantageisthecontinuousoperationwithonlyshortrefuellingbreaks.Atthe
moment the research effort is focusing on new membrane materials and long-
term stable catalysts.
Seeing this overview, it can well be stated that fuel cells areevolvingto bea
well developed technology with far-reaching R&D expertise. When and how
the‘real’marketswith‘real’,‘typical’customerscanbeenterednowremainsto
beseen.Thiswillnotonlybeaquestionofattractivenessofthetechnologyand
the products that are made thereof, but also of a variety of societal and eco-
nomical conditions, regulations, political decisions on emission control etc.
Generally, in technology development three phases can be discerned, and fuel
cellsarenoexceptiontothisrule:first,thetechnologyisbroughtfromscientific
viii Preface
principle to laboratory demonstration, then first demonstration and niche
market items arebroughttothe public, and,finally,thetechnologyachievesa
break-through and wins a reasonable share in markets or at least firmly
establishesitselfinnicheareas.Thethirdphasewouldespeciallybedominated
byconsiderationsthathavenothingmuchtodowiththetechnologyassuch–
althoughcustomerswouldstilltendtodiscusssuchtopicsastheprosandcons
of diesel versus petrol vehicles – but rather with aspects like usefulness, dur-
ability, cost, added value etc. According to our assessment, fuel cells stand at
thebeginningofphase2.Thisisagoodpointintimetoleavethemajorpartof
further developments to the engineers and company laboratories and scienti-
fically venture out to new shores!
In the volume you are just holding we therefore have attempted to look
beyond our own noses and try to identify new fields of high potential and
interest to the fuel cell community. This includes many fields where success is
still fragile or technical solutions are at a laboratory level, and in some cases
alsotheoreticalconceptsthatsoundworthwhilebutstilllackpracticalproof.In
allchaptersofthisbook,though,wehavetriedtoencourageauthorstoextend
today’s knowledge to new concepts and ideas. Innovations in Fuel Cell Tech-
nologies does not address a single fuel cell technology – many topics covered
here are relevant to several types of fuel cells – but tries to direct the reader’s
attentiontothedevelopmentsoftomorrowandthetechnologyofthedayafter
tomorrow. The chapters may serve as an early warning to technology devel-
opers of the rewarding prospects on the horizon as well as orientation to stu-
dents and young researchers in guiding their studies.
The first group oftwochapters describesthe prospects ofminiaturising fuel
cells. Thistopic hastwo intriguingaspects:first,that ofextreme simplification
and (possibly) low cost; and second, that of integration into everyday life and
equipment. Miniature fuel cells can be part of food wrappings, can act as
environmental and medical sensors, be used as implants etc. In all these ways
theywouldbecomeanintegralpartofourliveswithoutourevennoticingthat
we are using ‘fuel cell technology’.
The second set of two chapters looks at high-temperature polymer mem-
branefuelcellsandtheirapplicationason-boardelectricitysupply,eveninvery
large vehicles, such as aircraft. Although well in development, this membrane
typehasitsintrinsicproblemsandscalinguptolargeunitsisahugechallenge.
The following group of two chapters covers non-standard fuels like pure
carbon,andthehandlingoffuelimpurities.Forverydifferentreasons,theuse
ofcarbonoffersahighpotentialforapplications,althoughlargetechnological
challengesstillexist.Thisfuelisnotconventionallyconsideredfordirectusein
fuel cells, but ridding oneself of excessive fuel processing would bring a high
potentialforsimplificationofsystemsandsubsequentcostreduction.Thesame
goes for a higher tolerance of fuel electrodes towards impurities. Admittedly,
these chapters predominately address SOFC technology, with some relevance
for high temperature fuel cells in general.
The twin set on degradation modelling and accelerated testing looks into a
verycriticalareaoffuelcellresearch.Althoughvehicleapplicationscallforno
Preface ix
more than 5000 to 10000h of operational lifetime, stationary applications for
electricity production require up to 10 years of total component life. It is
obviously impossible to test components for this length of time and there is a
dire need for acceleration in testing lifetime limiting effects. The main pre-
requisiteinaccelerated lifetime testing,though,istheprofoundunderstanding
of degradation issues.
Finally,welookintotheprospectsofreversingthefuelcellreactionstowards
producing instead of consuming hydrogen. This possibility has been under
discussionforsomeyearsandthefirsttechnicalunitsthatcanactually reverse
their principle of operation seem to be under development. In line with the
concept of this book, though, we look a little further at the concept of co-
producinghydrogeninhigh-temperaturefuelcells,atconstructingclosedloops
ofelectrochemicalconversionofchemicalstoenergyandvice-versa,andatthe
useoftheSOFCprincipleto–inreverse–producehydrogenatextremelyhigh
efficiencies.
The concluding chapter then inspects the pitfalls in bringing a technology
from demonstration to technical maturity, including the issues of incumbent
and concurrent technologies and introduction of products to consumer mar-
kets, an issue scientists and laboratory engineers may find strange and irrele-
vanttotheirwork.Nevertheless,theseaspectsshouldbeconsideredatanearly
stage in development and a careful assessment of efficiency, added value and
usefulness aspects may have cut many technology developments short, long
before they failed in the markets.
We do hope that readers will find this volume useful or at least interesting
reading. We are fully aware that developments are not static and that many
topics covered herewill find their technical solution and marketentry. Weare
convinced that the potential in fuel cell technologies is tremendous and that
their commercial success is necessary in tailoring the worldwide energy supply
systems towards efficiencies and emission levels that allow a long-term stable
and sustainable development for the world economy and environment.
Thereforewecanatthispointonlyhopethatourbookwillbeoutdatedsoon!
In which case we will gladly offer an update ...
Robert Steinberger-Wilckens and Werner Lehnert
Forschungszentrum Ju¨lich, Germany