Energy Barrier Modulation vs Kinetic Acceleration: Tailoring WO ₃ Nanofibers for Trace-Level Mustard Gas Simulant Detection

Detection of chemical warfare agents (CWAs) such as sulfur mustard gas is essential for protecting warfighters and first responders. In this work, tungsten oxide (WO 3 ) nanofibers were defect-engineered via silver (Ag) decoration and strontium (Sr) doping to enhance the sensing performance toward 2-chloroethyl ethyl sulfide (2-CEES), a sulfur mustard simulant. The 2 at%Ag-WO 3 (AW2) and 1 at % Sr-WO 2.72 (SW4) nanofibers achieved experimental detection of 2-CEES at 100 ppb, and SW4 was estimated to have a theoretical detection limit of 55 ppb. The sensing mechanism was elucidated through energy barrier analysis, rate constant/activation energy correlation, and density functional theory (DFT) calculation. The enhanced 2-CEES sensing performance enabled by Ag decoration was mainly attributed to a larger change in the effective barrier height between air and N 2 atmospheres (Δ E b ), whereas the performance enhancement from Sr doping arose from an oxygen-vacancy-enriched structure, faster reaction kinetics, and stronger 2-CEES adsorption. By demonstrating trace-level detection of 2-CEES and unraveling the distinct contributions of electronic modulation and reaction kinetics, this study highlights AW2 and SW4 nanofibers as promising 2-CEES sensing materials and provides mechanistic guidance for the rational design of advanced metal oxide gas sensors.