Stable ink dispersions suitable for roll-to-roll printing with sensitivity towards hydrogen sulphide gas

This work describes the development of a stable dispersion which is suitable for roll-to-roll printing of a film exhibiting hydrogen sulfide (H2S) gas sensing functionality. The dispersions are made from copper chloride in combination with either citric acid or citric acid and polyaniline (PANI). Aqueous PANI dispersions together with copper chloride (CC) have been shown to have H2S sensing properties, but the dispersion gets unstable with the addition of CC within a pH range from 5 to 8. In this study, a mixture of CC and citric acid (CA) was optimized for printability as well as for sensitivity towards H2S gas. Furthermore the stability of an aqueous PANI dispersion was studied after the addition of CC or a CC–CA mixture as a function of pH. The stable dispersions were printed on top of flexographically printed interdigitated silver electrodes and their sensitivity towards 10 ppm H2S was verified by following the change in resistance. The printed films were characterized by atomic force microscope (AFM), time-of-flight secondary ion mass spectroscopy (ToF-SIMS) and conductometry. The sensors showed almost a three orders of magnitude change in resistance upon exposure to 10 ppm H2S at ambient conditions.