Fuel Cells and Fuel Cell Systems

ME 1065L. Schaefer

Proton Exchange Membrane

Cathode: ½O2 + 2 e- + 2 H+ => H2O

Anode: H2 => 2 H+ + 2 e-

Overall: H2 + 1/2 O2 => H2O

Problems with PEMs/PEFCs

Hydrogen Tank Rupture

Direct Methanol

Cathode: 3/2 O2 + 6e- + 6H+ => 3 H2O

Anode: CH3OH + H2O => 6H+ + CO2 + 6e-

Overall: CH3OH + 3/2 O2 => 2 H2O

DMFCs, cont.

Alkaline

Cathode: 1/2 O2 + H2O + 2e- => 2 OH-

Anode: H2 + 2(OH)- => 2H2O + 2 e-

Overall: H2 + 1/2 O2 => H2O

AFCs, cont.

Phosphoric Acid

Cathode: ½ O2 + 2 H+ + 2 e- => H2O

Anode: H2 => 2H+ + 2e-

Overall: H2 + 1/2 O2 => H2O

Molten Carbonate

Cathode: 1/2 O2 + CO2 + 2 e- => (CO3)=

Anode: H2 + (CO3)= => H2O + CO2 + 2 e-

Overall: H2 + 1/2 O2 + CO2 => H2O + CO2

MCFCs, cont.

Solid Oxide

Cathode: 1/2 O2 + 2 e- => O=

Anode: H2 + O= => H2O + 2 e-

Overall: H2 + 1/2 O2 => H2O

SOFCs, cont.

Basic Summary of Four Types

Fuel Cell Summary

Fuel Cell Governing Equations Heat/Mass Transfer Electrochemical Electrical Network

Governing Equations Heat and Mass Transfer Model

Continuity, Momentum, Energy, Concentration

0)()()(

zw

yv

xu

zu

xw

zxv

yu

yzw

yv

xu

xxp

zwu

yvu

xuu

32

34)()()(

qz

Tk

zy

Tk

yx

Tk

xz

wCpT

y

vCpT

x

uCpT

)()()(

)()()(

)()()()()()(

,,, z

YD

zy

YD

yx

YD

xz

wY

y

vY

x

uY jmj

jmj

jmj

jjj

Governing Equations Heat and Mass Transfer Model, cont.

Continuity, Momentum, Energy, Concentration

0r

)vr(

r

1

x

)u(

)(1

)()(1

)()(1)(

x

vr

rrx

u

xr

ur

rrx

u

xx

p

r

vur

rx

uu

qr

Tr

rrx

T

xr

CpvTr

rx

CpuT

)(1

)()(1)(

)r

YDr(

rr

1)

x

YD(

xr

)vYr(

r

1

x

)uY( jm,j

jm,j

jj

Hydrogen Fuel Cell ValuesForm of Water Product

Temp (°C) Gibbs Free Energy of Formation (kJ/mol)

Max EMF (V)

Efficiency Limit (%)

Liquid 25 -237.2 1.23 0.83

Liquid 80 -228.2 1.18 0.80

Gas 100 -225.3 1.17 0.79

Gas 200 -220.4 1.14 0.77

Gas 400 -210.3 1.09 0.74

Gas 600 -199.6 1.04 0.70

Gas 800 -188.6 0.98 0.66

Gas 1000 -177.4 0.92 0.62

Performance Curves

Fuel Cell Buses

SOFC Fuel

Turbine Unit

Recuperator

DC

AC

Power Conditioning

AC

Air

Combustor

Air

Exhaust

Exhaust

SOFC SOFC Fuel

Recuperator

DC

AC

Power Conditioning

AC

Air

Combustor

Air

Exhaust

Hybrid Power

Cogeneration and Cascading Energy Systems

PV

SOFC

Turbine

Chiller

Boiler

Electricity

ChilledWater

Hot Water

Unexpected Places!

Figure for Example Problem