Opposite sensing response of H2 and CO on In₂O₃−Co₃O₄ nanocomposite-based gas sensors over a wide temperature range

Utilizing p-n composite materials for the fabrication of metal-oxide semiconductor (MOS) gas sensors represents a promising strategy to achieve exceptional selectivity in detecting reducing gases such as hydrogen (H₂) and carbon monoxide (CO). However, previous studies have typically achieved this selectivity under fixed operating temperatures and single molar ratios. This study presents the successful synthesis of n-In₂O₃/p-Co₃O₄ nanoparticles, featuring a p-n heterojunction structure, using a simple composite preparation method. The gas-sensing properties, crystal structure, morphology, and chemical states were comprehensively characterized using an electrochemical workstation, XRD, TEM, HRTEM, and XPS. Experimental results show that the gas sensor responses of the n-In₂O₃/p-xCo₃O₄ composites (with x = 10.5, 15, 18, 21), annealed at 500°C within an operational temperature range of 350°C to 400°C, exhibit distinct behaviors for CO and H₂ gases. This addresses the challenge of achieving selective detection across varying conditions. Notably, the n-In₂O₃/p-18Co₃O₄ composites display opposing response characteristics for both gases across a broad temperature range of 200°C to 400°C. At 350°C, the n-In₂O₃/p-18Co₃O₄ sensor demonstrates optimal selectivity, significantly minimizing cross-sensitivity and improving detection accuracy and reliability. The sensor also shows excellent stability, with consistent responses under repetitive exposure conditions. By improving both sensor selectivity and stability, this research advances gas detection technologies, with potential applications in sustainable energy and public health monitoring.