Efficient low temperature formic acid sensing based on CdS-sensitized {111}-faceted NiCo2O4 octahedral p-n junction: Experimental and theoretical studies

Abstract

Resistive semiconductor gas sensors provide an effective means for detecting volatile organic compounds (VOCs) formic acid. However, relevant research is still in its initial stage, and the gas sensing performance urgently needs to be improved, especially the high operating temperatures and detection limits. Here, a NiCo₂O₄/CdS octahedral p-n junction which is composed of active {111} crystal facets exposed NiCo₂O₄ octahedron as substrate and highly-dispersed CdS nanoparticles as sensitizer is designed for formic acid sensing. Research has shown that the NiCo₂O₄/CdS octahedral p-n junction can achieve efficient detection of formic acid at relatively low operating temperature of 200°C, which displays an acceptable response value of 5.68 (R_g/R_a) towards 100 ppm formic acid, a low detection limit of 0.421 ppm, excellent long-term stability and selectivity. In-depth research on the formic acid sensing mechanism at the atomic and electronic levels is conducted through combining first principles calculations and experimental characterization. This study not only provides a highly promising gas sensing material for the efficient detection of formic acid at relatively low operating temperature, but also greatly enriches the relevant gas sensing mechanism, which has important guiding significance for the further development of VOCs gas sensors.