Kinetic model for H2S adsorption on an 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 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.