Synthesis and characterization of α-Fe₂O₃ nanoparticles for high-performance CO gas sensor

To develop electrochemical sensor for detecting ppm level CO, pure and Ni²⁺ doped α-Fe₂O₃ nanopowder was synthesized by solution combustion technique. The basic properties of the synthesized materials were studied. XRD and Raman studies showed that at ≥ 10 mol% doping, NiO phase appear due to segregation. Band gap decreased with doping concentration. In the amperometric mode a constant bias voltage of + 1 V was applied at α-Fe₂O₃ based electrode with respect to a fixed lanthanum strontium cobaltite (LSC55) electrode with 15 mol% Gd doped CeO₂ (GDC) as solid electrolyte in the sensor structure 3–40 ppm CO tested in base gas (5% O₂ + N₂) from 350 ºC to 650 ºC with the aim of exhaust gas like application. With pure α-Fe₂O₃ electrode highest sensitivity of 324 μA/decade was obtained at 500 ºC. The response and recovery times were found to vary from 40 to 125 s and 42 s to 260 s respectively in the concentration range 3 ppm to 40 ppm. Sensor with 10 mol% Ni²⁺ doped α-Fe₂O₃ showed inferior performance. In short term repeatability test sensor showed consistently ~ 60 μA change upon 3 ppm CO sensing for several consecutive cycles at 500 ºC. High selectivity to CO with respect to sensing of other coexisting gases makes such sensor promising for application.