Effect of the different crystallinity of ionic liquid based solid polymer electrolyte on the performance of amperometric gas sensor

Disadvantages of classical liquid electrolytes are overcome by the usage of solid polymer electrolyte (SPE) which is usually based on organic ionic liquid immobilized in polymer matrix. Ionic liquids are currently widely used in various fields of electrochemistry and chemistry because of their unique properties, which are partially implemented in SPE. The advantage lays in the composition, which offers an opportunity to prepare SPE layers with different porosity and microstructure.

The experimental study was carried out on semi-planar three-electrodes amperometric sensor with the layer of SPE, that consists of 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide[BMPYR][N(Tf)2], poly(vinylidene fluoride), and 1-methyl-2-pyrrolidone. The SPE layer was deposited by drop casting on alumina substrate with platinum electrodes. The substrate with SPE layer was placed on a hot plate where the sample was kept at an appropriate temperature for a specific time in order to achieve different crystalline forms of the polymer in the solvent. Afterwards, the working electrode was deposited by airbrushing of spherical glassy carbon powder. All electrical measurements were provided under equilibrium conditions when the sensor was being kept at particular NO₂ concentration for the required amount of time to fulfill the memorylessness of current fluctuations.

The study shows how SPE of different crystallinity affects the performance of amperometric gas sensor from the point of view of current response (sensitivity), limit of detection and current fluctuations. The sensor with the SPE of the highest temperature and the longest interval of treatment after deposition showed the highest current fluctuations in the frequency range as well as the highest current response on change of detected gas concentration.