Kinetic model for H₂S adsorption on an NiO surface in resistive MEMS gas sensors: coupling mass transfer, multisite...

Heterogeneous processes at gas-solid interfaces in resistive gas sensors involve external diffusion, multisite adsorption, surface migration and desorption, often complicated by site heterogeneity and lateral interactions. In this work, we develop a non-equilibrium kinetic framework that explicitly couples external mass transfer to multisite Langmuir-Hinshelwood adsorption-desorption with lateral adsorbate interactions and surface diffusion. The model is constructed to factorise material-specific (NiO site types and morphology), analyte-specific (molecular versus dissociative H₂S adsorption and concentration-dependent desorption) and transport-specific (MEMS-based gas delivery and mass-transfer limitations) contributions, which enables transfer of kinetic parameters across different sensing layers, morphologies and analytes. Validation on a MEMS-based NiO sensor for H₂S demonstrates that only a model including dissociative adsorption, chemisorption with long-lived sulfur-containing species and concentration-dependent desorption can reproduce the experimentally observed multistage transients and apparent relaxation times. By linking surface coverage dynamics directly to conductivity via a morphology-dependent power-law relation, the framework bridges microscopic surface chemistry and macroscopic sensor signals, providing a physically grounded alternative to phenomenological relaxation models and a tool for generating synthetic training data for electronic-nose applications.