Effect of HCl and H2SO4 Dilutant on Emeraldine Gas Sensor for Ammonia—Numerical Model

Abstract

Polyaniline changes its resistivity in the presence of various gas molecules, and therefore, it is currently studied for its deployment as a gas sensor, sensitivity to very small gas concentrations (lower than 1 ppm), selectivity to ammonia, nitrogen dioxide, or hydrogen, and long-term stability for thousands of voltage cycles. The preparation of this polymer is low cost using a very low pH environment where the polyaniline variety emeraldine base can be preceded to emeraldine salt, using hydrochloric acid, sulfuric acid, and others. After oxidative polymerization in the presence of an ammonium peroxidisulfate catalytic converter, the rest of the acid can be washed out. The effect of different acids on the final product emeraldine salt gas sensor conductivity was studied. One 32-mer-long polymer of emeraldine salt was simulated using QuantumATK as an electrical device, and its <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$I-V$</tex-math></inline-formula> characteristic was computed for pure polyaniline and polyaniline polluted by hydrochloric acid and sulfuric acid ions. The pollution concentration was 3 ppm. The results show that the resistance of polluted PANI increased a little for both acids. The results were compared with the recently published experimental data showing good accordance with them. The dilutants raise the resistance of the sensors, making them slightly less sensitive.