Synergistic charge transfer in 3D-V₂O₅/1D-Co₃O₄ composite for ultra-sensitive NO₂ gas detection

The development of high-performance gas sensors for industrial safety and environmental protection demands innovative material design. Thus, advancing gas sensor technology necessitates innovative approaches to material synthesis, particularly in developing high-performance composites. This study presents a surfactant- and reducing agent-free method to synthesize 3D V₂O₅ with a high surface area (72 m² g⁻¹) and 1D Co₃O₄ with superior charge transfer capabilities. The distinct surface energy (-40 mV for V₂O₅ vs. -5 mV for Co₃O₄) and Fermi level differences (-5.62 eV for Co₃O₄ vs. -4.36 eV for V₂O₅) enable the formation of a robust 3D-V₂O₅/1D-Co₃O₄ composite. This composite, investigated as a gas sensor for the first time, demonstrated significant synergistic effects. Among various ratios, the 0.5:0.5 V₂O₅:Co₃O₄ composite demonstrated exceptional NO₂ sensing performance, with high responses (0.1 % to 250 ppb, 3.7 % to 50 ppm), sensitivity (0.53 Ω ppm⁻¹ over 5–200 ppm), and rapid response/recovery times (25 s/22 s) at 270 °C. The sensor's selectivity towards NO₂ is attributed to the NO₂'s high electron affinity and it unpaired electron, which bond with surface oxygen atoms, enhancing chemisorption and electron transfer. Notably, each composite outperforms bare and layered (Co₃O₄/ V₂O₅) structures due to efficient charge transfer, increased surface area, and synergistic effects. Gas sensing mechanism and synergistic effects were confirmed via Mott-Schottky, XPS, Raman, zeta potential and Tauc-law analyses. The sensor achieved a low detection limit (250 ppb) and stable performance (>30 days), highlighting its practical potential for environmental and industrial safety applications.