Room-Temperature Low-Bias LPG Sensing via Barrier Modulation in WO3/Polyaniline Heterojunction Diodes

We demonstrate a room-temperature liquefied petroleum gas (LPG) sensor based on a tungsten oxide /polyaniline heterojunction diode fabricated on a tungsten substrate. Tungsten oxide nanostructures were grown by hydrothermal synthesis, and polyaniline was deposited by cell-voltage-controlled electrodeposition, where the deposition time (10–25 s) tuned junction coverage. The optimized device (20 s) exhibited pronounced suppression of forward current upon LPG exposure at 300 K. To ensure interpretable quantification under variable ambient backgrounds, an air–N₂–LPG sequence was employed and a purge-referenced normalized response, S(%), was defined using the N₂-purged baseline at a fixed operating voltage (V* = 0.60 V). A baseline shift of 27.87% during air-to-N₂ switching confirms strong sensitivity to background constituents, motivating the purge-referenced protocol to decouple LPG-induced modulation from ambient-dependent baseline variations. At V* = 0.60 V, the response increased monotonically over 100–900 ppm LPG and reached a representative value of 71.61% at 500 ppm. Within 300–700 ppm, a quasi-linear operating window was identified with a segment sensitivity of 0.0481%·ppm−1 (${\bm{R}}_{\mathrm{adj}}^2$ = 0.966). The measured response/recovery times (t₉₀ ≈ 20 s; Tr₉₀ ≈ 7 s) represent system-level upper bounds under the present gas delivery configuration. Repeatability and device-to-device reproducibility of S(%) were 5.33% (n = 5) and 9.70% (n = 3) relative standard deviation (RSD), respectively. These results support low-bias diode readout as a practical route to room-temperature LPG sensing and provide a purge-referenced framework for interpreting diode-type gas signals under variable backgrounds.