Gadolinium-Doped CeO2 Gas Sensor for H2S Sensing

Dihydrogen sulfide (H₂S) gas has a flammable nature and is one of the most toxic and dangerous gases. Even small concentrations can be fatal to humans. Herein, we investigated the H₂S gas-sensing features of commercial pristine cerium oxide (CeO₂ ) and gadolinium (Gd)-doped CeO₂ (GDC) nanoparticles. First, the sensing materials were well-characterized using various methods including X-ray photoelectron spectroscopy, transmission electron microscopy and X-ray diffraction to gain insight into their chemical composition, morphology, phases, and crystallinity, respectively. In the next step, gas sensors were fabricated using a top electrode (Au/Ti) configuration. Preliminary H₂S-gas-sensing studies revealed that GDC gas sensor had a superior gas response to H₂S gas than the pristine CeO₂ gas sensor at 350°C. The responses of the pristine CeO₂ gas sensor to 20 ppm H₂S gas was 1.542, while the response of the GDC gas sensor to the aforementioned H₂S concentration was 3.489. In addition, the GDC sensor exhibited good selectivity to H₂S gas among C₂H₅OH, C₇H₈ and NH₃ gases. Also, we investigated the response of the sensor in up to 60% relative humidity. The enhanced response of the GDC gas sensor to H₂S gas was mainly related to the formation of oxygen defects as a result of Gd-doping in CeO₂ . Also, good selectivity to H₂S was related to the sensing temperature, the higher reactivity of H₂S relative to other gases and the small bond energy of H-SH. This study demonstrates the promising ability of Gd-doping to enhance the H₂S gas-sensing characteristics of CeO₂ , which can be applied to other similar systems based on semiconducting metal oxides.