Ferromagnetic Cobalt Oxide With Structural Distortion and Oxidation State Changes for Hydrogen Sulfide Gas Detection

Fabricating ordered micropillar arrays via magnetic assembly of ferromagnetic materials can enhance H₂S gas sensors. However, this approach is limited to iron oxide-based ferromagnetic materials, which are unsuitable for H₂S gas detection. Cobalt oxide is advantageous for H₂S detection despite being intrinsically antiferromagnetic. The key challenge is thus inducing a net ferromagnetic moment in Co₃O₄ for the fabrication of micropillar arrays, designed to enhance H₂S gas sensitivity. Herein, a lithiation-based galvanostatic reduction (LiGr) process synthesizes a material (LiGr-Co) featuring a Co₃O₄/CoO heterointerface, few-nanometer-scaled particles, and oxygen vacancies. The sub-nanometer-sized particles and oxygen vacancies significantly enhance H₂S gas-sensing performance by promoting the formation of short-range order between Co²⁺ and Co³⁺ ions. Furthermore, the Co₃O₄/CoO heterointerface provides the pathway to induce the desired magnetism, as a resulting crystallographic mistilt at the interface generates the required magnetic moment. The aligned LiGr-Co (A-LiGr-Co) sensor, under a magnetic field during the spray coating process, showed improved efficiency in gas adsorption and electron transfer, leading to a reduction of the base resistance and an enhancement of gas-sensing capabilities. A-LiGr-Co demonstrated a high response (Rg/Ra) of 39.7 at 5 ppm and high selectivity for H₂S detection at 150°C.