A Novel Three-Electrode Solid Electrolyte Hydrogen Gas Sensor - Intelligent Computing for Sustainable Energy and Environment - page 39

Hydrogen

Pt
H

W
H

Measuring
electrode

Reference
electrode

Fig. 1. The structure of the two-electrode solid electrolyte hydrogen gas sensor

The potential of the platinum electrode is determined by the dynamic rela-
tionship of the redox reaction when the concentration of the hydrogen is stable.
The redox reaction is substantially mutual conjugation reaction and the poten-
tial is also called the mixed potential. The reaction rate of the hydrogen is much
faster than that of the phosphotungstic acid due to the high catalytic activ-
ity of the platinum. Therefore the mixed potential established on the platinum
electrode is close to the balance potential of hydrogen, which has an identified
relationship with the hydrogen concentration. The redox reaction of hydrogen
and phosphotungstic acid take place simultaneously on the tungsten electrode,
which is used as the reference electrode. The mixed potential of the tungsten
electrode is primarily determined by the balance potential of phosphotungstic
acid because tungsten has a low catalytic activity. This also make the potential
of tungsten to be a relatively stable reference potential.
The potential between the platinum electrode and the tungsten electrode,
which is the mixed potential difference between the two electrodes, has an iden-
tified relationship with the hydrogen concentration. Although the relationship is
still a half logarithmic linear relationship, it can not follow the Nernst equation
entirely and the coecient in front of the logarithmic is also uncertain. The po-
tential varies slowly when the hydrogen concentration is higher than 1%, thus
the resolution is pretty low at this condition.

3 Design of Three-Electrode Solid Electrolyte Hydrogen
Gas Sensor

To extend the measuring range of the sensor, we introduce a third electrode,
which is defined as the adjusting electrode. The selection of the third electrode
is based on the hydrogen absorption ability of the material. By analyzing and
making preliminary experiment, nickel is used to be the material of the adjust-
ing electrode. The structure of the three-electrode solid electrolyte hydrogen gas
sensor is shown in Figure 2. Pt is the measuring electrode, Ni is the adjusting