Environmental Engineering Reference
In-Depth Information
SYMBOLS
E
reversible (Nernst) voltage
[V]
mol
−1
]
F
Faraday constant
[C
mol
−1
]
Δ
g
molar Gibbs energy change
[J
mol
−1
]
Δ
h
molar enthalpy change
[J
I
current
[A]
n
number of electrons
[
-
]
n
:
j
s
−1
]
molar flow rate of species
j
[mol
power
P
[W]
p
pressure
[Pa]
mol
−1
K
−1
]
R
u
universal gas constant
[J
R
electrical resistance
[
Ω
]
T
temperature
[K]
U
j
utilization factor of species
j
[
-
]
U
:
total chemical power
[W]
x
mole fraction
[
-
]
V
cell voltage
[V]
η
a
anodic polarization losses
[V]
η
c
cathodic polarization losses
[V]
η
rev
reversible efficiency
[
-
]
s
−1
]
φ
m
mass flow rate
[kg
Subscripts
e
electrical
f
fuel
i
internal
r
reaction
16.1
INTRODUCTION
Fuel cells (FC) are energy conversion devices that directly convert the chemical
energy of a fuel into electrical energy. There are five major types of fuel cells, namely,
phosphoric acid fuel cells (PAFCs), polymer electrolyte membrane fuel cells
(PEMFCs), alkaline fuel cells (AFCs), molten carbonate fuel cells (MCFCs), and solid
oxide fuel cells (SOFCs). These FC types operate in different temperature regimes,
use different materials, and have different fuel tolerance and performance character-
istics (O
Hayre et al., 2009). MCFCs and SOFCs are high-temperature (>600
C) FC
that can operate using various fuels, such as H
2
, CO, and CH
4
. Because syngas
produced by biomass gasification contains mainly H
2
, CO, and CH
4
, biosyngas
can be used as a fuel for MCFCs and SOFCs provided that it is sufficiently clean.
'
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