Study and development of hydrogen gas sensors based on a conductive polymer functionalized with palladium

This thesis is focused on the research area of hydrogen gas detection and was developed in collaboration with the company Enereco S.p.A. Hydrogen is considered a promising green energy vector and so a key element for the future global clean energy transition. Despite this, it is an explosive gas with a wide flammability range of [ 4 – 77] % in air that makes mandatory the presence of efficient hydrogen detectors in any location in which the gas is used. This work aims to study and develop a new hydrogen gas sensor based on the conductive polymer poly (3,4 – ethylenedioxythiophene): polystyrene sulfonate, PEDOT:PSS, functionalized with palladium, an efficient hydrogen sensitive material. Two functionalization processes of the polymer active layer, dip coating and electrodeposition, have been studied and the sensors’ performances upon hydrogen exposure have been evaluated in a two and three – terminal configuration (as Organic Electrochemical Transistors, OECTs) in liquid and gaseous environments. Moreover, the sensors’ performances dependence on the thickness of the PEDOT:PSS film have been analyzed by testing thicknesses of 2 μm, 230 nm and 150 nm. Sensors have been measured following exposure to hydrogen concentrations of 0.36%, 1%, 2%, 3%, 4% and 5% in nitrogen environment. An interpretation of the hydrogen sensing mechanism and a study of the physical and electrical properties of the functionalization process have been realized. The thinner dip coated PEDOT:PSS two – terminal device in gaseous environment shows the best performances as hydrogen sensor in terms of current variation percentage, ≈70% at 0.36% H2, and, since the sensors’ signal is very stable in pure nitrogen or air environments, it allows to reliably detect in about 30 s a small hydrogen leak. In addition, sensors’ response is not affected by other gases possibly present in ambient air and by ambient air humidity, making them suitable for applications in a real – life environment.