Synthesize of Ni_0.75Zn_0.25Fe₂O₄ Spinel Oxide as a Working Electrode for Formaldehyde Electrochemical Gas Sensors

Gas sensor with yttrium stabilized zirconia film in electrochemistry have been rapidly applied in the monitoring of toxic and harmful gases, and nickel spinel ferrite (NFO) is one of the most studied working electrodes. However, the sensing performance to formaldehyde (HCHO) is quiet poor. In this work, the sol-gel method was used to prepare Zn-doped NFO (Ni0.75Zn0.25Fe2O4) oxide, and the Zn-doped NFO was applied as the working electrode of the electrochemical gas sensor of HCHO. The phase structure, micromorphology, and surface area of the prepared Ni0.75Zn0.25Fe2O4 oxide were evaluated for the working electrode. The results showed that when the operating temperature reached 480 C-degrees, the sensor with Ni(0.75)Zn(0.25)Fe(2)O(4 )as the working electrode achieved high response value of -17 mV to 5 ppm HCHO, and the response/recovery time was 28/20 s. The polarization curve was further performed to validate the mechanism of the observed sensing behavior. Meanwhile, the response signal of the fabricated sensor increased logarithmically with the log (HCHO) in the investigated range of 1-5 ppm, and the corresponding sensitivity reached -29.08 mV/decade.