7/31/2019 Introduction to Batteries and Fuel Cells

http://slidepdf.com/reader/full/introduction-to-batteries-and-fuel-cells 1/2

Introduction: Batteries and Fuel Cells

This special issue of C hemi cal R evi ew s covers th eelectrochemical storage an d generat ion of energy inbatter ies and fuel cells. This area is gaining tremen-dous import an ce for powering h igh techn ology devicesand for enabling a greener a nd less energy-intensivetransportation industry. Whether the demand is froma cell phone, a compu ter, or an iPOD, consumers ar edemanding a longer life in a smaller package and at

a lower cost with minimal if any wired connection.The consumer generally does not care whether thepower source is a battery, a fuel cell, or somethinge ls e, a s l on g a s i t w o r k s. I n t h e a r e a of g r e en e rtran sportat ion, th ere has been a surge of interest invehicles th at ar e electrically powered, either totally,as plann ed for th e green Beijing Olympic Games, orpart ially, as in h ybrid electric vehicles. The presentgeneration of such vehicles uses a combination of ani n t er n a l com b u s t ion e n gi n e a n d a b a t t e r y, t od a yn i c k e l m e t a l h y d r i d e , a s i n t h e T o y o t a P r i u s , a n dtomorrow lithium; a fut ure generat ion is likely to bea hybrid of a fuel cell an d a battery.

Both batteries and fuel cells uti l ize contr olled

chemical reactions in which the desired processoccurs electrochemically and all other reactions in-cluding corr osion ar e h opefully a bsent or severelykinetically suppressed. This desired selectivity de-man ds careful selection of the chemical componentsincluding their morphology and structure. Nanosizeis not necessarily good, and in present commerciallithium batteries, part icle sizes are intentionallylarge. All batt eries an d fuel cells cont ain an electr o-positive electrode (the anode or fuel) and an electro-negative electrode (the cathode or oxidant ) betweenw h ich r e s id e s t h e e le ct r ol yt e . T o e n s u r e t h a t t h ea n od e a n d ca t h o de d o n o t con t a c t e a ch ot h e r a n dshort out the cell, a separator is placed between the

two electr odes. Most of th ese critical component s a rediscussed in this thematic issue.

T h e i s s u e s t a r t s w i t h a g e n e r a l i n t r o d u c t i o n b yBrodd and Winter to batteries and fuel cells and theassociated electrochemistry. It then continues firstwith several papers discussing batteries and thenwith papers discussing fuel cells.

Batteries 

O u t s id e of t h e a b ov e i n t r od u ct i on , t h e b a t t e r ypapers describe lithium batteries, where most chemi-

cal a nd materials research h as been focused dur ingthe past three decades. The second paper, by Whit-tingham, begins with a general historical backgroundt o l i t h i u m b a t t e r i e s a n d t h e n f o c u s e s o n t h e n e x tgeneration of cathodes. The third, by Xu, gives ani n -d e pt h r e vi ew of t h e p r e se n t ly u s e d a n d fu t u r eelectrolytes; this is followed by an extensive reviewby Arora a nd Zhan g of the separa tors used in lithium

an d relat ed bat teries. The following paper, by Long,D u n n , R ol is on , a n d W h it e , a d d r e ss es n e w t h r e e -dimensional concepts for increasing the storage ca-pacity. Critical t o the development of new m ater ialsare advanced characterization and modeling tech-niques, an d some of these ar e described by Grey andDupre and by Reed and Ceder in the last two papersof the battery group. Several papers covering anodes,p h os p h a t e a n d n i ck e l ox id e ca t h o de s, a n d n i ck e lmeta l hydride batter ies did not meet t he pu blicationd e a d l i n e , a n d i t i s h o p e d t h a t t h e y w i l l a p p e a r i nfutu re issues.

Fuel Cells 

Although fuel cells were invented in th e middle of th e 19th centu ry, they didn’t find th e first applicat ionuntil space exploration in the 1960s. Since then, thedevelopmen t of fuel cell technology ha s gone t hr oughseveral cycles of intense activity, each followed by aperiod of reduced inter est. However, du ring t he pa stt w o d e ca d e s, a con fl u en ce of d r iv in g for ce s h a screated a sustained and significant world-wide effortto develop fuel cell materials and fuel cell systems.These driving needs include the demand for efficiente n er g y s y s t em s for t r a n s p or t a t i on , t h e d e si r e t oreduce CO2 emissions and other negative environ-m e n t a l i m p a c t s , a n d t h e d e m a n d f o r h i g h e n e r g ydensity power sources for portable electr onic applica-tions. Due to the high level of interest in fuel cellsduring th e last decade or so, there ha ve been n umer-ous summary articles and symposia focused on thetechnology state of the art . In this thematic issue,w e p r e s e n t a s e r i e s o f s u m m a r y a r t i c l e s t h a t d e a lwith some of the fundam enta l scientific issues relat edto fuel cell development.

A fuel cell that has desirable features for trans-portation an d porta ble power is th e polymer electro-lyt e m e m br a n e (P E M ) s y st e m . T h e cor e of t h istechnology is a polymer membrane that conducts

Volume 104, Number 10

10.1021/cr020705e CCC: $48.50 © 2004 American Chemical SocietyPublished on Web 10/13/2004

7/31/2019 Introduction to Batteries and Fuel Cells

http://slidepdf.com/reader/full/introduction-to-batteries-and-fuel-cells 2/2

protons but separates the fuel from the oxidant. Thematerial used historically a nd most frequently inPE M fuel systems is N afion, a perfluorocarbon-basedpolymer car rying su lfonic acid r esidues. Nafion is acom m e r ci a l m a t e r ia l a n d h a s r e ce iv ed t h e m os textensive study of any PEM fuel cell membranes.M a u ri tz a n d M oor e p r ep a r ed a s u m m a r y o f t h ecu r r e n t u n d e r s t a n d in g of t h e l a r ge v ol u m e o f r e -search that has gone into optimizing and understand-

ing this m embrane system. Oth er polymer systemsthat would have even better performance than Nafionand /or ha ve lower costs are being sought by research-e r s a r o u n d t h e w or l d. H i ck n e r , G h a s s em i , K i m ,Einsla, and McGrath summarize work on such al-ternative polymer systems for proton exchange mem-branes. These types of materials have complex trans-port properties th at involve not just proton movementbut also the movement of water. Theoretical treat-ments of the transport mechanisms and processes inthese proton conductors are given by Kreuer, Pad-dison, Spohr, and Schuster and by Weber an d New-m a n .

In PEM fuel cells, catalyst activity and catalyst

efficiency are still significant issues. Russell and Rosesummarize fundamental work involving X-ray ab-sorption sp ectr oscopy on catalysts in low tem perat ur efuel cell systems. These types of studies are veryuseful for developing a detailed understanding of themechan isms of reactions at catalyst surfaces a ndcou l d l ea d t o t h e d e ve lop m e n t of n e w i m pr ov edefficient catalysts. Important in the development of fuel cell technology are math ematical models of  engineering aspects of a fuel cell system. Wan g writesabout studies related to this topic.

Finally, in order for PEM fuel cell systems to beaffordable for portable power applications, a source

of high energy density fuel must be considered. Tothis end, Holladay, Wang, and Jones present a reviewof the developments of using m icroreactor t echn ologyto convert l iquid fuels into hydrogen for directlyfeeding into a PE M fuel cell.

Another fuel cell system undergoing intense re-search is th e solid oxide type. Adler presents thefactors th at govern t he r at e limiting oxygen r eductionreaction within the solid oxide fuel cell cath odes.

M c I n t o s h a n d G o r t e , o n t h e o t h e r h a n d , t r e a t t h ea n od e i n t h e s ol id ox id e fu e l ce ll b y e xa m i n in gcata lytic direct hydrocarbon oxidation. Finally,Calabrese Bar ton, Gallaway, an d Atanossov ta ke al o o k a t t h e f u t u r e . I n t h e i r a r t i c l e , t h e y p r e s e n t asummary of some of the enzymatic biological fuelcells that are being developed as implantable devicesan d also to power microscale devices.

We hope this collection of papers will provide newr e s ea r ch e r s i n t h e fi el d w i t h a s t a r t i n g p oi n t fora d va n c in g r e s ea r ch . F u r t h e r m o r e, ou r h op e i s t ostimulate the next generation of breakthroughs thatwill lead to t he success of fuel cell development .

M. Stan ley WhittinghamChemistry a nd Materials,

State University of New York at Binghamton

Robert F. SavinellChemical Engineering,

Case Western Reserve University

Thomas ZawodzinskiChemical Engineering,

Case Western Reserve University

CR020705E

4244 Chemical Reviews, 2004, Vol. 104, No. 10 Editorial