Solid‐State Hydrogen Sensors Using Palladium‐Nickel Alloys: Effect of Alloy Composition on Sensor Response

Thin film alloys of Pd and Ni make good sensors for hydrogen partial pressures ( p H 2 ) over a very wide range: from 10 − 3 to 700 Torr . For p H 2 from 1 to 700 Torr the atomic percent of Ni in the alloy has a strong effect on the change in film resistance which is used as the sensing property. The phase transition from the α‐ to the hydride β‐phase must be avoided to maintain a reversible sensor. The characteristics of alloys with Ni of 3, 5.3, 8, and 15% are reported. The phase transition was found in the 5.3% alloy at about 250 Torr, but alloys of Ni > 8 % showed no phase change behavior up to 630 Torr (pure H 2 ) at ambient temperatures. Other characteristics of the Pd/Ni alloy sensors are also reported, including the effect of temperature, oxygen, and relative humidity, and the speed of response to step changes in p H 2 .