H₂S Sensing with SnO₂-Based Gas Sensors: Sulfur Poisoning Mechanism Revealed by Operando DRIFTS and DFT Calculations

Real-time detection of toxic and flammable H₂S remains challenging for cost-effective semiconducting metal oxide (SMOX) sensors due to the insufficient focus on and inherently poor understanding of the sulfur-poisoning effect. This research, focusing on SnO₂ as a model for SMOX sensors, identifies the formation of sticky sulfite and sulfate surface species as the root cause of poisoning through the detailed analyses of results obtained from operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments and density functional theory (DFT) calculations. The formation of the poisoning species is highly energetically favorable. Meanwhile, the decomposition of sulfite and sulfate appears unfavorable at the typical operating temperature of 300 °C and is only feasible around the literature-reported 500 °C. The sulfur poisoning effect is also likely to occur with SO₂ and other sulfur-containing volatile organic compounds (VOCs). Overcoming this issue is expected to require surface additives and/or alternative SMOX materials capable of providing different reaction pathways. The significance of metal-sulfur-oxygen chemistry extends beyond SMOX gas sensors to desulfurization catalysts, denitration catalysts, and solid oxide fuel cells.