Synergistically enhanced thermal conductivity sensor based on AlN@h-BN/MWCNT nanocomposite for SF6 leakage monitoring in GIS

Reliable, drift-resistant monitoring of SF 6 enrichment in air near gas-insulated switchgear (GIS) leak points remains challenging for compact and low-cost sensing nodes. Here we report a thermal-conductivity-differential sensor enabled by a materials-circuit co-design: a hierarchical AlN@h-BN/MWCNT nanocomposite coating is integrated onto a Pt-coil element and read out by a Wheatstone bridge with a sealed reference arm and differential amplification. The ternary architecture exhibits a well-developed mesoporous framework with a high BET surface area (111.03 m 2 ·g −1 ), promoting efficient gas transport within the sensing layer and strengthening the thermal-conductivity-induced perturbation of the bridge balance. Under synthetic dry air (21% O 2 /79% N 2 ) at 25 ± 1℃, the output is monotonic over 0.1–5.0% SF 6 , with a recommended linear regime of 0.1–1.0% for quantitative readout; the baseline noise (σ air = 0.16 mV) yields an estimated LOD (3σ) of 0.0654% (∼654 ppm), while 0.1% is the lowest experimentally validated concentration. The optimized excitation voltage (3.0 V) maximizes response by balancing gas-phase modulation against increased non-gaseous heat losses at higher temperatures. The sensor shows reversible cycling (52/23 s response/recovery), humidity-tolerant operation (± 8% deviation over 20–80% RH), and < 5% degradation over 90 days; as expected for a TCD-type mechanism, cross-responses are governed by thermal conductivity rather than chemical selectivity.