Enhanced High-Temperature (600 °C) NO2 Response of ZnFe2O4 Nanoparticle-Based Exhaust Gas Sensors

Fabrication of gas sensors to monitor toxic exhaust gases at high working temperatures is a challenging task due to the low sensitivity and narrow long-term stability of the devices under harsh conditions. Herein, the fabrication of a chemiresistor-type gas sensor is reported for the detection of NO2 gas at 600 degrees C. The sensing element consists of ZnFe2O4 nanoparticles prepared via a high-energy ball milling and annealed at different temperatures (600-1000 degrees C). The effects of annealing temperature on the crystal structure, morphology, and gas sensing properties of ZnFe2O4 nanoparticles are studied. A mixed spinel structure of ZnFe2O4 nanoparticles with a lattice parameter of 8.445 angstrom is revealed by X-ray diffraction analysis. The crystallite size and X-ray density of ZnFe2O4 nanoparticles increase with the annealing temperature, whereas the lattice parameter and volume are considerably reduced indicating lattice distortion and defects such as oxygen vacancies. ZnFe2O4 nanoparticles annealed at 1000 degrees C exhibit the highest sensitivity (0.13% ppm(-1)), sharp response (tau(res) = 195 s), recovery (tau(rec) = 17 s), and linear response to 100-400 ppm NO2 gas. The annealing temperature and oxygen vacancies play a major role in determining the sensitivity of devices. The plausible sensing mechanism is discussed. ZnFe2O4 nanoparticles show great potential for high-temperature exhaust gas sensing applications.