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Overview of Hydrogen Energy and Fuel Cells

tivation: Sustainable Energy

vising sustainable energy resources that are readily accessible to all nations, environmentally friendly, and cost competitive with fossil fuels (coal, natupetroleum oil) is one of the greatest challenges of the 21 stcentury. As of January 1 !""# $roven world oil reserves were esti%ated at 1!&' billion

( about )1 $ercent located in t(e Middle East or Canada *+nited States Energy ,nfor%ation Ad%inistration http://tonto.eia.doe.gov/country/indw"reserves-. ,n !"") t(e world consu%$tion of $etroleu% was # %illion barrels $er day. /uring t(e sa%e ti%e $eriod t(e consu%$tion in t(etes of A%erica was !1 %illion barrels $er day. *+nited States Energy ,nfor%ation Ad%inistration http://www.eia.doe.gov/emeu/ipsr/t21.ls, auary 2$$%&.

ther, as more nations become industrialied, the consumption of these fied oil reserves increases. he last few decades of the 2$ thcentury alone saww nations become significantly industrialied. he depleting supply of fossil fuel alone is a reason to see* an alternative fuel for the world. +s a finrgy generation from fossil fuel has led to significantly increased atmospheric greenhouse gas (e.g., -, - 2) levels as well as those of byproducts (-

iculate matter, hydrocarbons etc.).

e Hydrogen Econo%y and Fuel Cells

uturistic view ofenergy su$$ly is based on (ydrogen rat(er t(an fossil fuels. he coined term 0(ydrogen econo%yis a hypothetical economy irgy for vehicular transportation and electricity is derived from reacting hydrogen ( 2) with oygen (-2). Depending upon the hydrogen source, a sh

rogen economy may diminish fossil fuel usage and greenhouse gas emissions. + *ey technology to enabling a hydrogen economy is the fuel cell.

l cells are electrochemical energy conversion devices that yield electrical energy from chemical reactions. hese devices vary depe nding on t(e c(ctions generating t(e electricity. Furt(er%ore fuel cells are scalable, as they can be used for a wide range of uses from small as portable electroni

wer plants. n addition, fuel cells operate 3uietly and efficiently.

gineers calculate the efficiency of any energy converting technology such as fuel cells as a means to discuss the merits of its design to do wor*. -ne meculate the efficiency of a fuel cell at converting chemical energy into electrical energy is to calculate the ratio of actual electrical energy obtained to the

would be obtained if all the heat energy released from the chemical reactions ta*ing place were completely converted into electrical energy.

l cells are under consideration to replace traditional technologies such as the internal combustion engines for transportation applications because they acient at converting chemical energy to electrical energy. n the internal combustion engine, the chemical energy in the fuel is converted into heat which isvide wor* to move the vehicle. he engine efficiency is highly dependent upon the load. owever, in the fuel cell the chemical energy of the fuel is coelectricity. he electrical energy is then converted into wor* to move the vehicle using an efficient electric motor. hough conversion efficiency varies w

e of fuel cell, the fuel5to5electricity efficiencies are typically 6$7 8 9$7. n stationary applications, the waste heat of the fuel cell can also be used, resuher overall efficiencies.

l cells may also have applications in modern electrical power plants due to their modular design, scalability, and rapid response to load changes. here m

advantages to more localied electricity generation.

el Cell 0y$es

first fuel cell; noted was discovered by 2ritis( scientist Sir 3illia% 4rove in 1'&. He reacted (ydrogen wit( o5ygen to for% water and $r

ect current 6/C7 electricity. 0(e (alf8cell reactions are si%$le and can $rovide clean drin9able water to %any $arts of t(e world. Since t(e $io

l cell several ot(er electroc(e%ical reactions (ave been e%$loyed to generate electricity t(ereby for%ing t(e basis for a large variety of fueeral fuel cell ty$es are $resented in 0able 1 along wit( t(eir res$ective o$erating te%$erature and range of $ower out$ut.

0able 1. Fuel Cell 0y$es and O$erating anges;

ype ange

-perating emperature +pplication

+l*aline 'uel ell(+')

-5 9$$ ? 8 1$ *? 9$ 8 2$$ o pace program

=roton 4change

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ctroc(e%istry of A

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formance of a =4

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l cell stac*s are used when the cell voltage needed is greater than $.K51.$ volts. his typically correlates with 1 ?att of power. +s with all electrical sages placed in series are additive. Thus, a fuel cell stack with n cells has an effective stack voltage Vstackequal to the sum of the cell voltages, or Vstacen operating at the same current, more electrical power is produced.

Figure '. + schematic of a polymer electrolyte membrane fuel cell stac*

x

Ley

Mas flow in

Mas flow out

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a%$le