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FUEL CELL

 A SPECIAL FOCUS TO BIOFUEL

CELL

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INTRODUCTION

• One very promising technology which is compact !le"i#le an$e"ceptionally clean an$ receiving increasing attention #eca%se o! itsa#ility to increase overall energy e!!iciency is !%el cells&

•  A !%el cell is an electrochemical $evice that converts hy$rogen an$

o"ygen into electricity witho%t com#%stion&

• F%el cells have #een aro%n$ since the mi$ '(th cent%ry an$ thespace program has %se$ them since the early '()*s&

•  A !%el cell operates m%ch li+e a #attery t%rning o"ygen an$hy$rogen into electricity in the presence o! an electrically con$%ctivematerial calle$ an electrolyte& B%t %nli+e a #attery it never loses itscharge an$ will generate electricity as long as there is a so%rce o!hy$rogen an$ o"ygen&

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 A schematic representation o! a FC 

 All !%el cells create electricity thro%gh a electrochemical reaction o! hy$rogen an$

o"ygen& The only #y,pro$%cts o! a hy$rogen !%ele$ !%el cell is p%re water an$ heat&

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TYPES OF FUEL CELL

The most common classi!ication o! !%el cells is #y the

type o! electrolyte %se$ in the cells&

• Proton e"change mem#rane -polymer. electrolyte

!%el cell -PEFC.•  Al+aline !%el cell -AFC.

• Phosphoric aci$ !%el cell -PAFC.

• /olten car#onate !%el cell -/CFC.• Soli$ o"i$e !%el cell -SOFC. an$

• 0irect methanol !%el cell -0/FC.&

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PROTON EXCHANGE MEMBRANE FUEL CELLS

(PEMFCS)

  Polymer electrolyte mem#ranesometimes calle$ protone"change mem#rane soli$polymer electrolyte 1 !%el cells

%se thin polymer sheets as anelectrolyte&

It is now the !%el cell type most!avore$ #y a%to companies asthe replacement !or the internalcom#%stion engine&

 As with many o! the lower temperat%re !%el cells PE/FCs re2%ire ap%re hy$rogen so%rce !or operation&

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PROTON EXCHANGE MEMBRANE FUEL

CELLS (PEMFCS)

• In the PE/ !%el cell the electrolyte is a thin polymermem#rane s%ch as poly 3per!l%oros%lphonic4 aci$ 5a!ionwhich is permea#le to protons #%t $oes not con$%ctelectrons an$ the electro$es are typically ma$e !romcar#on&

• 6y$rogen !lows into the !%el cell on to the ano$e an$ issplit into hy$rogen ions -protons. an$ electrons&

• The hy$rogen ions permeate across the electrolyte tothe catho$e while the electrons !low thro%gh an e"ternalcirc%it an$ provi$e power&

• O"ygen in the !orm o! air is s%pplie$ to the catho$e an$this com#ines with the electrons an$ the hy$rogen ionsto pro$%ce water&

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ALKALINE FUEL CELLS 

• The $esign o! an al+ali !%el cell issimilar to that o! a PE/ cell&

• These !%el cells %se a sol%tion o!potassi%m hy$ro"i$e in water asthe electrolyte an$ can %se a

variety o! non, precio%s metals as acatalyst at the ano$e an$ catho$e&

• The hy$ro"yl ions -O6,. migrate!rom the catho$e to the ano$ewhere they react with hy$rogen to

pro$%ce water an$ electrons&

The $isa$vantage o! this !%el cell type is that it is easily poisone$# car#on $io"i$e CO7 &

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BIOFUEL CELLS

• The #io!%el cells o! twocompartments an ano$ecompartment an$ a catho$ecompartment separate$ #y a

proton e"change mem#rane-PE/.&

• 5a!ion !ilm %se as the PE/which allows hy$rogen ionsgenerate$ in the ano$e

compartment to #etrans!erre$ across themem#rane into the catho$ecompartment&

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ANODE COMPARTMENT OF BIOFUEL CELLS

 Ano$e compartment o!

#io!%el cell8

• The ano$e compartment

wo%l$ consist o! the

!ollowing8 

Bacteria

-E&Coli. 9l%cose

Electron me$iator

-methylene #l%e.

Potassi%m Phosphate#%!!er -p6 :&*. 9raphite

or ;oven graphite !elt

electro$e&

• For long,term e"periments

gl%cose wo%l$ nee$ to #e

p%mpe$ into the ano$e

compartment as a constant

so%rce o! !%el !or #acterialmeta#olism& Over time

o"i$ative meta#olism wo%l$

gra$%ally $ecrease i! there is

a limite$ availa#ility o!gl%cose which wo%l$ #e

re!lecte$ in a $ecreasing

c%rrent o%tp%t&

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CATHODE COMPARTMENT OF BIOFUEL CELLS

Catho$e compartment o!

#io!%el cell8

• The catho$e

compartment o! the

micro#ial !%el cell wo%l$

comprise o! the !ollowing8

Potassi%m !erricyani$e

Potassi%m Phosphate

#%!!er -p6 :&*. 9raphiteor ;oven graphite !elt

electro$e&

• Potassi%m !erricyani$e is an

important component o! the

catho$e compartment&

• The !erricyani$e reaction is

attractive !or %se at thecatho$e since it has a rapi$

electron %pta+e&

• 6y$rogen ions -6<. migrate

across the proton e"changemem#rane -PE/.&

• The en$ pro$%ct at the

catho$e is water& 

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WORKING OF BIOFUEL CELL

• 0%ring the electron transport process electrons !rom the #acterialplasma mem#rane passes to the ano$e -negative electro$e.&• These electrons travel thro%gh an electric circ%it an$ s%#se2%ently

re$%ce !erricyani$e to !errocyani$e at the catho$e -positiveelectro$e.&

• Protons p%mpe$ !rom the #acteria into the ano$e environment

traverse the PE/ into the catho$e compartment& Ferrocyani$e isreo"i$i=e$ to !erricyani$e while the hy$rogen ions com#ine witho"ygen to !orm water&

 At the ano$e8 C)6'7O) < )67O   )CO7 < 7>e, < 7>6<

 At the catho$e8 >Fe -C5.)?,< >e, >Fe -C5.)

>, 

>Fe -C5.)>,< >6< < O7  >Fe -C5.)?, < 767O

• Complete o"i$ation o! gl%cose $oes not always occ%r&

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WORKING OF BIOFUEL CELL