Revolutionizing n‐type Co3O4 Nanowire for Hydrogen Gas Sensing

This study presents conductometric sensors based on Co 3 O 4 nanowires for hydrogen detection at ppb levels. The nanowires are synthesized through thermal oxidation of a 50 nm cobalt layer, exhibiting diameters between 6–50 nm and lengths of 1–5 μm, primarily growing along the (311) direction of spinal Co 3 O 4 . Raman investigation reveals five characteristic peaks at 195, 482, 521, 620, and 692 cm −1 , corresponding to symmetric phonon modes of crystalline Co 3 O 4 . Electron paramagnetic resonance measurements confirm the presence of a ferromagnetic phase, attributed to incomplete cobalt oxidation, which disappears after 8 h of thermal aging at 400 °C. Conductometry measurements are performed in the temperature range of 300–500 °C. At temperatures above 300 °C, sensors exhibit abnormal n‐type semiconducting behavior due to lattice oxygen's involvement in the hydrogen sensing mechanism. Operating at 450 °C in dry air, the sensor shows a higher 232% response to 100 ppm H 2 compared to ethanol, acetone, methane, carbon monoxide, and nitrogen dioxide. Remarkably, the sensor maintains a consistent conductance baseline even under high humidity (90%) for 25 d, with three‐cycle repeatability. This distinctive gas‐sensing capability is attributed to the catalytic activity and elevated operating temperature.