Kinetic Model for H2S Adsorption on NiO Surface in Resistive MEMS Gas Sensors: Coupling Mass Transfer, Multisite Adsorption, and Surface Interactions

Abstract

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 H$_2$S 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 H$_2$S 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 signal, providing a physically grounded alternative to phenomenological relaxation models and a tool for generating synthetic training data for electronic-nose applications.