Development of LaCoO3 based thick film sensors for selective CO2 detection in greenhouse gas monitoring

Abstract

This study explores the potential of lanthanum-based LaCoO₃ perovskite oxide as a thick-film gas sensor for carbon dioxide (CO₂) detection. LaCoO₃ was synthesized via a hydrothermal method at varying temperatures (90, 120, 150, and 180 °C) to optimize the material properties for gas sensing applications. The synthesized powders were formulated into pastes and screen-printed onto glass substrates using a suitable binder to fabricate thick films. Structural characterization using X-ray diffraction (XRD) confirmed the formation of nanostructured LaCoO₃ with a hexagonal phase, exhibiting an average crystallite size between 20.14 nm and 23.85 nm. Surface morphology was examined using scanning electron microscopy (SEM), while transmission electron microscopy (TEM) provided nanoparticle size information. The elemental composition was verified through energy-dispersive X-ray spectroscopy (EDAX). Optical properties, including bandgap energy (1.49–1.73 eV), were analyzed using UV–visible spectroscopy. Fourier-transform infrared (FT-IR) spectroscopy identified the vibrational modes associated with M − O bonding. The gas sensing performance of the LaCoO₃ thick films prepared from materials synthesized at varying hydrothermal reaction temperatures (90, 120, 150, and 180 °C) was evaluated against various greenhouse gases (CO, CO₂, HFCs, and water vapor) under different operating temperatures (400, 350, 300, 250, 200, 150, 100, 50 and 33 °C) and concentrations (100, 300, 500, 800, 1000 and 1200 ppm). The sensor exhibited the highest response to CO₂ at 250 °C and 1000 ppm, along with rapid response and recovery times. Parameters such as gas response, selectivity, and response behavior were systematically assessed. The enhanced sensing performance is attributed to the intrinsic properties of LaCoO₃, highlighting its promise for CO₂ detection in environmental monitoring applications.