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.