Hydrogen sensing apparatus and method

Abstract

An apparatus and methods are provided for the accurate determination of hydrogen content in fluid media at elevated temperatures. The apparatus consists of a proton conducting solid electrolyte in contact with an internal metal / hydrogen reference standard, in which the electrolyte and the reference material are in a chemically stable contact. The electrical signal generated is a function of the hydrogen concentration on the measuring side.

Description

FIELD OF INVENTION [0001] The present invention relates to apparatus and a method for measuring the concentration of hydrogen in fluid media at elevated temperatures using a high temperature proton-conducting solid electrolyte in conjunction with an internal hydrogen standard. BACKGROUND OF THE INVENTION [0002] The monitoring and control of hydrogen concentration in gaseous and liquid media is an important technological issue. Fields of application include, for instance, the analysis of gas composition on the fuel side of hydrogen-based fuel cells and the determination of dissolved hydrogen content in molten metals like aluminium. It is therefore desirable to develop simple, easily applicable, reliable and inexpensive sensors having high sensitivity and selectivity. [0003] One concept of constructing hydrogen sensors for operation at elevated temperatures is to utilise a proton conducting solid electrolyte that compares the hydrogen partial pressure on the measuring side with a know...

AI Technical Summary

Benefits of technology

[0012] The present invention may thus advantageously provide a sensor with a novel hydrogen standard that establishes a defined and reproducible reference hydrogen partial pressure and ensures chemical stability of the electrolyte / reference interface.

[0016] Secondly, a chemically stable interface between the solid electrolyte and the reference material may advantageously be ensured. It is important to note that even minute changes in the oxygen concentration may have a dramatic impact on the electrochemical properties of oxide-based proton conducting solid electrolytes. In fact, the release of small amounts of oxygen has been shown to convert these materials from pure proton conductors into mixed conductors, oxygen ion conductors or semiconductors, which makes them inappropriate for the application envisaged. Accordingly, very reactive metals like alkali metals, alkaline earth metals and rare earth metals, which also form two-phase areas with hydrogen, are not preferred for use as the reference material, since they reduce the oxide-based solid electrolyte at elevated temperatures. Even less reactive metals like titanium, zirconium and hafnium may, in their pure state, be sufficiently reducing to affect the performance of the solid electrolyte. However, and in contrast to the previously mentioned metals, the reactivity of titanium, zirconium and hafnium may be lowered considerably through the presence of only small amounts of oxygen. In this way, the electrolyte / reference interface may be rendered chemically stable, whilst the two-component / two-phase approach is not compromised.

Problems solved by technology

The monitoring and control of hydrogen concentration in gaseous and liquid media is an important technological issue.

The incorporation of a hydrogen reference standard into the sensor unit constitutes a scientific and technological problem.

However, the use of a reference gas has been found awkward, and no breakthrough with this technology has been achieved.

However, incorporation of hydrates fixes the water rather than the hydrogen partial pressure and, even though some response behaviour to hydrogen has been observed in a few cases, these sensors require calibration and their signal stability is insufficient for practical applications.

However, this combination was only found to work at comparatively low temperatures, i.e., below 600° C., and for relatively short times, i.e., a few hours, otherwise a continuous drift of the sensor signal towards zero was observed.

The reason for the failure was identified to be the chemical instability of the electrolyte / reference interface.

This causes a chemical reaction between the highly reducing reference material and the oxide-based solid electrolyte, which gradually converts the ion (proton) conductor into a mixed conductor and renders sensor readings impossible to interpret.

Overall, no hydrogen sensor relying on a solid reference material has as yet proven to be viable in any practical application.

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