Fast Response Room Temperature Amperometric Gas Sensors with Modified Fe–N–C Electrodes for ppb-Level H₂S Detection

Monitoring halitosis indirectly by detecting H 2 S biomarkers with gas sensors is an emerging technique that holds great promise. However, developing H 2 S sensors with exceptional selectivity and sensitivity, as well as a detection limit in the ppb range, remains a significant technological challenge. To address these issues, we have fabricated amperometric H 2 S gas sensors utilizing modified Fe–N–C catalysts as electrodes. The modified Fe–N–C catalyst obtained by heat treatment of ammonium chloride salt exhibits a higher specific surface area, improved ORR catalytic performance, and excellent stability in acidic environments, which enhance the sensitivity and durability of amperometric H 2 S sensors. The amperometric sensors demonstrate a sensitivity of up to 502.0 nA ppm –1 for H 2 S and exhibit rapid response time with only 22.5 s for response and 9.0 s for recovery time toward 3 ppm of H 2 S. Moreover, they display good sensitivity (approximately 1506.0 nA at 3 ppm of H 2 S) and achieve a low limit of detection (LOD) of around 0.01 ppm. Additionally, the sensors exhibit excellent selectivity while being capable of detecting changes in trace amounts of H 2 S concentration within an exhaled breath environment. Our study presents experimental evidence demonstrating the successful detection of H 2 S in exhaled breath using amperometric sensors with modified Fe–N–C electrodes.