One-pot solvothermal synthesis of hierarchical Co-doped NiO microspheres with enhanced hydrogen sulfide sensing performances

In this study we report, for the first time, the synthesis of Co-doped NiO microspheres assembled by two-dimension nanosheets using a facile solvothermal method. The H₂S gas-sensing performance of the as-prepared samples was systematically investigated. The result demonstrates that the Co–NiO sensor with Co/Ni molar ratio of 1% (1% Co–NiO) exhibits high response (12.9) and rapid response speed (110 s) to 20×10⁻⁶ H₂S at 200 °C in comparison with the pure NiO sensor. Moreover, excellent selectivity, repeatability, and stability were achieved. The sensing mechanism illustrates that the superior gas-sensing properties can be attributed to two factors. (1) The hierarchical microspherical construction with an ultrahigh specific surface area of 163.1 m² g⁻¹ provides adequate active sites for H₂S gas adsorption, porous structures, and an interlayer gap that accelerates the diffusion of H₂S gas, resulting in improved sensitivity and response speed of the sensor. (2) Co-doping results in a decrease in the particle sizes (ca. 4 nm) and increase in the number of adsorbed ionized oxygen species, which improves sensitivity and selectivity. Therefore, this study provides a facile approach for the synthesis of hierarchical Co–NiO microspheres with enhanced H₂S gas-sensing performance.