3. Hydrogen response for two types of sensor

These sensors have proved insensitive to a number of commonly used pure gases: argon, helium, nitrogen, water vapour and oxygen. On the other hand, a rapid and reversible increase in the amount of current flowing through the circuit is observed in the presence of hydrogen (or deuterium). This evolution is in complete contrast to what is usually observed with all existing resistive hydrogen sensors. With conventional palladium-based resistive sensors, the presence of hydrogen in the gaseous state induces an increase in electrical resistance by a factor of 1.8 compared with pure palladium. This increase is explained by the progressive conversion of palladium to palladium hydride, PdH _x (x increasing from 0 to 0.7 under a hydrogen pressure of 1 atm at 25 ˚C).

On returning to a hydrogen-free atmosphere, the resistance of...