Hydrogen sulfide sensing properties of NiFe2O4 nanopowder doped with noble metals

The paper reports the preparation and gas sensing characteristic of NiFe2O4 nanopowder with and without different noble metal dopants such as Au, Pt, Pd. Ultrafine NiFe2O4 powders were prepared by solid-state reaction of inorganic reagents, Ni(Ac)2, Fe(NO3)3, and NaOH. XRD and Raman spectrometer were used to confirm the material structure and TEM to depict the crystallite microstructure. Au, Pd and Pt with different concentration were incorporated into NiFe2O4 by impregnation technique. The electrical resistance response to H2S gas of the sensors based on the materials was investigated at different operating temperature and different gas concentrations. The results show that NiFe2O4 is a p-type semiconductor and the sensor response of the doped NiFe2O4 sensors was superior to that of the undoped ones. The sensor response increased linearly with the H2S gas concentration up to 100 ppm. The sensor with the 1.5 wt.% Au doped NiFe2O4 showed excellent electrical resistance response towards 5 ppm H2S gas and the sensor response was up to 35.8 at 300 °C. The 1.5 wt.% Pt doped one was less sensitive to H2S but work at lower temperature, 240 °C. The gas-sensing behavior of these materials with respect to various reducing gases like liquefied petroleum gas (LPG), methane (CH4), carbon monoxide (CO), butane (C4H10) and hydrogen gas (H2) suggested that the H2S gas sensor developed possesses an excellent selectivity. The interaction mechanism and correlations between the electrical resistance response and noble metal dopants were discussed.