In this work, ZnO thin films were investigated to sense NO2, a gas exhausted by the most common combustion systems polluting the environment. To this end, ZnO thin films were grown by RF sputtering on properly designed and patterned substrates to allow the measurement of the electrical response of the material when exposed to different concentrations of the gas. X-ray diffraction was carried out to correlate the material’s electrical response to the morphological and microstructural features of the sensing materials. Electrical conductivity measurements showed that the transducer fabricated in this work exhibits the optimal performance when heated at 200 °C, and the detection of 0.1 ppm concentration of NO2 was possible. Ab initio modeling allowed the understanding of the sensing mechanism driven by the competitive adsorption of NO2 and atmospheric oxygen mediated by heat. The combined theoretical and experimental study here reported provides insights into the sensing mechanism which will aid the optimization of ZnO transducer design for the quantitative measurement of NO2 exhausted by combustion systems which will be used, ultimately, for the optimized adjustment of combustion resulting into a reduced pollutants and greenhouse gases emission.

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We have investigated the gas sensing properties of ZnO thin films (100 to 200 nm thickness) deposited by roomtemperature radio frequency magnetron sputtering. The sensitivity of the films to ethanol vapor was measured in the 10 to 50 ppm concentration range at operating temperatures between 200 and 400°C. A synergetic effect of decreasing grain size and increasing operating temperature was observed towards the improvement of the sensitivity, reaching a value of 54 and a limit of detection as low as 0.61 ppm. The decrease in the grain size resulted in prolonged response time but faster recovery. In any case, both response time and recovery time are < 400 s. The results demonstrate that room-temperature magnetron sputtering is a viable approach to enhance the performances of ZnO films in sensors for ethanol vapor.

A simple chemical approach was employed to reduce graphene oxide in order to fabricate electrode coatings in close correlation with industrial production standards for supercapacitors. The morphology, structure, thermal stability and the residual oxygen functional groups in chemically reduced graphene oxide were analyzed. Cyclic voltammetry and charge/discharge measurements were employed to study the electrochemical performance of the coatings as a function of active material loading. The results showed an increase in the specific capacitance for chemically reduced graphene oxide-based coatings in comparison to commercial activated carbon, while the desired value needs to be optimized with respect to the conductivity of such materials.