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which detects the hydrogen concentration by measuring the electric potential.
The amperometric solid electrolyte hydrogen gas sensor need to pump the stan-
dard concentration oxygen to the reference electrode as the reference gas [2]. The
amperometric sensor has the disadvantages of large volume and complex struc-
ture. In addition, the redox reaction between the two electrodes can increase
the temperature of the generated substance, which in turn make the electrolyte
dehydration. Therefore, the performance of this kind of sensor is not stable and
the service life become shorter. The further problem is that the long recovery
time of the reaction between the two electrodes will make the sensor impossible
to use. The potentiometric sensor can also be divided into two kinds. one kind of
potentiometric sensor adopted the same substance as its electrodes material such
as platinum (Pt) and used Nafion [3] as the electrolyte. This kind of potentio-
metric sensor have a complex structure and require the reference gas. The other
kind of potentiometric sensor employed different substance to be its electrode
materials [4-7] such as using Pt for the measuring electrode and tungsten (W)
for the reference electrode. This kind of sensor indicates the future development
direction because it has some advantages such as working without the reference
gas, simple structure, small volume, convenient use, easy miniaturization. How-
ever, this kind of sensor is only effective for low concentration hydrogen, which
is below 1%. For high concentration hydrogen, It is dicult to identify because
of its terrible dynamic performance.
In our study presented here we describe the properties of two-electrode solid
electrolyte hydrogen gas sensor and then introduce the fabrication of the new
three-electrode solid electrolyte hydrogen gas sensor. In the design of the three-
electrode sensor, Pt is used as the measuring electrode, W is used as the reference
electrode and nickel (Ni) is used as the adjusting electrode. The experiment
were conducted to compare performance of the two-electrode solid electrolyte
hydrogen gas sensor and the three-electrode solid hydrogen gas sensor.
2 Design of the Two-Electrode Solid Electrolyte
Hydrogen Gas Sensor
A common approach in the solid electrolyte hydrogen gas sensor is based on the
two-electrode structure. In this study, platinum is chosen to be the measuring
electrode and tungsten is chosen to be the reference electrode. Phosphotungstic
acid is utilized to make the electrolyte. When the hydrogen is pumped, the redox
reactions will take place on the platinum electrode for hydrogen and phospho-
tungstic acid. The reactions can be described by equation (1) and (2).
2
H
+
+2
e
−
H
2
→
(1)
PW
12
(
VI
)
O
3
−
40
+
e
−
→
PW
11
(
VI
)
W
(
V
)
O
3
−
40
(2)
[
PW
12
(
VI
)
O
3
−
40
]and[
PW
11
(
VI
)
W
(
V
)
O
3
−
40
] indicate the concentration of phos-
photungstic acid in the oxidation state and in the reduced state respectively.
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