5. Chemical resistance

The final point to note about the performance of these palladium nanowire-based sensors is their exceptional insensitivity to common poisonous gases such as oxygen, methane and, above all, carbon monoxide. Even at concentrations as low as 20 to 50 ppm, the presence of carbon monoxide multiplies the response time of conventional sensors by a factor of 2 to 10. In mixtures of 8% hydrogen in air, our sensors have been exposed to carbon monoxide levels as high as 3,000 ppm without any noticeable alteration in either the amplitude of the measured signal or response time.

Two hypotheses can be put forward to explain this insensitivity:

• a coverage rate or concentration effect: a low carbon monoxide concentration (down to a few tens of ppm) can rapidly block the small number of hydrogen dissociation sites on the surface of...