An integrated model for predicting the response, selectivity, and response/recovery time of composite gas sensors.

While composite gas sensors of high response, good selectivity, and fast response/recovery may be fabricated by synergistic coupling of the constituents and spillover effect, systematic design of the composite materials is still a challenge due to the lack of a quantitative model. In this work, an integrated theoretical model for n-type mixed and hierarchical composite gas sensors is developed by combining equivalent-circuit analysis, time-dependent adsorption/desorption kinetics, and spillover effects. This integrated model enables quantitative prediction of the composition-dependent gas response, selectivity, and response/recovery time from constituent-level transport, sensing, and effective kinetic parameters. The calculated performance is evaluated against reported experimental data from representative mixed and hierarchical composite materials and captures the broad composition-dependent trends observed at the reported compositions. The model shows that mixed and hierarchical composites follow different response-enhancement rules because of their distinct conduction structures. In mixed composites, response enhancement can occur under both σ1 > σ2 and σ1 < σ2 conditions, whereas in hierarchical composites, strong enhancement is more favorable when the coating material effectively participates in macroscopic conductance modulation. These results provide a quantitative basis for designing composite gas sensors with balanced response, selectivity, and sensing kinetics.