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

ABSTRACT Fabricating ordered micropillar arrays via magnetic assembly of ferromagnetic materials can enhance H 2 S gas sensors. However, this approach is limited to iron oxide‐based ferromagnetic materials, which are unsuitable for H 2 S gas detection. Cobalt oxide is advantageous for H 2 S detection despite being intrinsically antiferromagnetic. The key challenge is thus inducing a net ferromagnetic moment in Co 3 O 4 for the fabrication of micropillar arrays, designed to enhance H 2 S gas sensitivity. Herein, a lithiation‐based galvanostatic reduction (LiGr) process synthesizes a material (LiGr‐Co) featuring a Co 3 O 4 /CoO heterointerface, few‐nanometer‐scaled particles, and oxygen vacancies. The sub‐nanometer‐sized particles and oxygen vacancies significantly enhance H 2 S gas‐sensing performance by promoting the formation of short‐range order between Co 2+ and Co 3+ ions. Furthermore, the Co 3 O 4 /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 ( R g / R a ) of 39.7 at 5 ppm and high selectivity for H 2 S detection at 150°C.