New sensing modes

The origin of the short-circuit current is the imbalance of electrode reactions (36.5) and (36.6). The protons produced by (36.5) cannot be consumed completely by (36.6) under the present conditions. Excess protons migrate through the proton conductor (AA) towards the counter electrode to be consumed there, accompanied by an equivalent electronic 

Sensing mode Sensor signal characteristics Remarks Ref. 

-independent signal output has been achieved in thefour-probe type sensor shown in Fig. 36.4, where two additional Ag probes are inserted in the proton conductor bulk (AA) beneath the Pt electrodes. One of the Pt electrodes is covered by a layer of AA sheet, which acts as a sort of gas diffusion layer. The short-circuit current flowing between the two Pt electrodes is proportional to H2 concentration but dependent on R.H., just as in the previous amperometric sensor. On the other hand, the difference in potential between the two Ag probes (inner potential difference, AE g) with the outer Pt electrodes short-circuited is shown to be not only proportional to H2 concentration but also independent of R.H. as shown in Fig. 36.3b and Table 36.2. This mode of sensing has no precedence, and is noted as a new method to overcome the greatest difficulty in using proton conductor-based devices, i.e. their R.H. dependence. 

---