In-situ Surface-Enhanced Raman Spectroscopy Reveals a Mars-van Krevelen-Type Gas Sensing Mechanism in Au@SnO2 Nanoparticle- Based Chemiresistors

Molecular-level understandings of gas sensing mechanisms of oxide-based chemiresistors are significant for designing high-performance gas sensors; however, the mechanisms are still controversial due to the lack of direct experimental evidence. This work demonstrates efficient in situ surface-enhanced Raman spectroscopy (SERS) tracing of the highly representative SnO2-ethanol gas sensing using Au@SnO2 nanoparticles (NPs), where the Au core and SnO2 shell provide SERS activity and a gas sensing response, respectively. The in situ SERS evidence suggests that the sensing follows a Mars-van Krevelen mechanism rather than the prevailing adsorbed oxygen (AO) model. This mechanism is also observed in sensing other gases based on the Au@SnO2 NPs, showing its universality. This work offers efficient in situ tracing for gas sensing and experimental elucidation of the specific gas sensing mechanism, potentially ending the long-term controversy over the gas sensing mechanisms. Therefore, it is highly significant to this field.