The study of the voltage drift in high-temperature proton conductor-based hydrogen sensors adopting the solid reference electrode

The long-term stability of the electrochemical hydrogen sensor comprised of the high-temperature proton conductor of CaZr0.9In0.1O3−δ and the solid reference material of Ti/TiH2/TiO mixture has been investigated. In the long-term stability test, the EMF drift of about 0.2–0.3 mV/h was observed. It may be caused by the extremely low oxygen partial pressure of 10−31 atm at 973 K evolved at the reference electrode due to the oxygen equilibrium reaction between TiO2 and Ti2O3. It gives rise to n-type conduction at the reference electrode compartment, which then leads to a depletion of protons in the electrolyte as confirmed by the Raman spectra. The origin of the EMF drift is considered to result from the gradual increase in the hydrogen pressure at the reference compartment owing to the released protons from the electrolyte.