Morphology engineering of hierarchical spinal nickel-cobaltite nanostructures for enhanced ethanol detection

In this article, the potential of solution-processed spinel nickel-cobaltite (NiCo2O4) nanostructures as chemiresistive sensors for detecting ethanol (C2H5OH) is demonstrated. Various techniques were used to characterize the structure, composition, and morphology of the as-synthesized NiCo2O4 samples prior to gas sensing studies. By adjusting the reaction time, cubic crystalline NiCo2O4 structures with different surface morphologies were obtained, including upright-standing nanoplatelets enclosed by nanoneedle-type structures. These nanoneedle-type structures are composed of numerous interconnected nanoparticles with diameters of ∼4–8 nm. These unique structural and morphological characteristics enable the NiCo2O4 nanostructures to exhibit excellent sensing properties towards C2H5OH gas at 140 °C, with significant changes in their resistance values observed upon exposure to 10–1000 ppm C2H5OH. Notably, the NiCo2O4 sample processed for 9 hours, with a specific surface area of 48.19 m2/g, was recognized as the most promising sensor among the various NiCo2O4 samples, showing a maximum response of 54.4% towards 200 ppm C2H5OH, with good repeatability and complete recovery characteristics. Additionally, we also investigated and discussed various sensing characteristics of the NiCo2O4 sensors, including their gas concentration dependent response, selectivity, temperature dependent response, reproducibility and stability. Moreover, the sensing interactions between NiCo2O4 and C2H5OH gas molecules were elucidated through the use of an energy band diagram, providing valuable insights into the sensing mechanism of these sensors. Overall, this research provides a practical and simple strategy for synthesizing spinel oxide nanostructures and demonstrates their potential in C2H5OH sensing applications.