Previous works that describe the use of Ni catalysts show their lack of working stability and so the
developed sensors were applied as single-use devices. Regarding other reported approaches using NiCu and CoO and CuO/AgO, these appear to be more stable and could be used for extended
periods from 1 week (NiCu when the sensor was stored in DI water at RT) up to several months (CuO/AgO when the sensor was stored in air at RT).