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solid electrolyte
(Phosphotungstic acid)
H
2
H
2
E
1
E
2
Measuring
electrode Pt
Adjusting
electrode Ni
H
2
H
2
Reference
electrode W
H
2
H
+
H
+
H
2
H
+
Pt eletecrode
three-phase surface
Ni eletecrode
three-phase surface
W eletecrode three-
phase surface
Fig. 2.
The structure of the three-electrode solid electrolyte hydrogen gas sensor
electrode and W the reference electrode. The three electrodes are settled in par-
allel spatially. The potential difference between the measuring electrode and the
reference electrode is
E
1
, the potential difference between the adjusting electrode
and the reference electrode is
E
2
.
The redox reaction of the hydrogen and the phosphotungstic acid are taken
place simultaneously on each electrode. the kinetics disciplines of the conjugate
reaction determine the mixed potential of the electrodes. The potential is the
mixed potential when the oxidization rate of hydrogen is equivalent to the re-
duction rate of phosphotungstic acid. The oxidation reaction of hydrogen and
the reduction reaction of phosphotungstic acid are taken place in the strong po-
larization zone, Tafel relationship can be applied to the kinetics disciplines. The
oxidation current of hydrogen and the reduction current of phosphotungstic acid
canbeexpressedasfollows:
i
a
=
i
0
H
+
/H
2
exp
[
2
β
H
F
(
E
μ
−
E
H
+
/H
2
)]
(3)
RT
i
c
=
i
0
HPW
exp
[
2
α
HPW
F
RT
(
E
HPW
−
E
μ
)]
(4)
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