
345Fuel Cell Characterization
lm is formed and grown on the surfaces when the two surfaces are dis-
connected and exposed to the environment. When the two surfaces are in
contact and a direct current is passed through the samples, the DC electri-
cal resistance of the system is determined using Ohm’s law by measuring
the voltage drops. Since the bulk metal has high conductivity, the voltage
drop is mainly due to the passive lm or interface of the metal and pas-
sive lm.
The contact resistance is calculated as
R
E
EE
R
c
c
=
−
, (8.39)
where E
c
is the contact voltage, E
s
is the separation voltage, and R
2
is the
shunt resistance.
Characterization studies ...