Surface-scale affinity and adsorption selectivity of alkaline earth metal oxides to H2O and CO2: Insight into SOFC anode modification

Abstract

Periodic density functional theory (DFT) calculations have been performed to investigate the adsorption selectivity of H2O over CO2 on alkaline earth metal oxide (AEMO) surfaces. A simple gridding-based interpolation method is innovatively employed to determine the surface-scale affinity. The results show that AEMO surfaces exhibit higher affinity to H2O than CO2 in perspective of whole surface scale. Both the affinity strengths to H2O and CO2 follow the trend BaO > SrO > CaO > MgO. The adsorption selectivity of H2O over CO2 on AEMO surfaces is sensitively dependent on temperature and partial pressure ratio. Based on thermodynamic equilibrium prediction, the estimated adsorption selectivity of H2O over CO2 on AEMO surface is extremely high under SOFC operating condition. This indicates that the anti-coking behavior of AEMO-modified Ni-based solid oxide fuel cell (SOFC) anodes is for the most part governed by H2O capture, which serves an explanation for the experimental finding and anti-coking mechanism proposed in literatures.