Revolutionizing n‐type Co3O4 Nanowire for Hydrogen Gas Sensing

Abstract

This study presents conductometric sensors based on Co3O4 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 Co3O4. Raman investigation reveals five characteristic peaks at 195, 482, 521, 620, and 692 cm−1, corresponding to symmetric phonon modes of crystalline Co3O4. 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 H2 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.

Keywords

• Co3O4 nanowires
• gas sensors
• hydrogen sensors
• metal oxides
• thermal oxidation