Quantitative investigation of CeO₂ surface proton conduction in H₂ atmosphere

This report is the first describing a study quantitatively analysing aspects of oxide surface protonics in a dry H₂ atmosphere. Elucidating surface protonics is important for electrochemical and catalytic applications. In this study, AC impedance spectroscopy was used to investigate surface conduction properties of porous CeO₂ at low temperatures (423-573 K) and in a dry H₂ atmosphere. Results demonstrated that the conductivity increased by several orders of magnitude when H₂ was supplied. Dissociative adsorption of H₂ contributes to conduction by forming proton-electron pairs. Also, H/D isotope exchange studies confirmed protons as the dominant conduction carriers. Furthermore, H₂ adsorption equilibrium modelling based on the Langmuir mechanism was applied to explain the H₂ partial pressure dependence of conductivity. For the first time, the obtained model explains the experimentally obtained results both qualitatively and quantitatively. These findings represent new insights into surface protonics in H₂ atmosphere.