Sensing in harsh conditions: How to protect SnO2 sensing layer

The detection of low CO amounts in fuel cell conditions - high hydrogen background in almost the absence of oxygen - is a challenging problem for SnO
2
based gas sensors. SnO
2
- the most used material for metal-oxide based gas sensors - is not stable in hydrogen-rich atmospheres at high temperatures being reduced to metallic tin. To prevent SnO
2
reduction, a SnO
2
based sensing layer, previously deposited by screen-printing onto an alumina substrate, was coated with the additional microporous ceramic Si-B-C-N layer. The ceramic coating prevents the reduction of SnO
2
and allow for the diffusion of the target gas molecules towards the SnO
2
layer for their detection, acting as a filter. The Si-B-C-N coated SnO
2
sensors show stable sensor signals towards hydrogen and carbon monoxide in the absence of oxygen whereas the unprotected SnO
2
sample becomes reduced over time.