Proton Transfer in Molten Lithium Carbonate: Mechanism and Kinetics by Density Functional Theory Calculations

Using static and dynamic density functional theory (DFT) methods with a cluster model of [(Li₂CO₃)₈H]⁺, the mechanism and kinetics of proton transfer in lithium molten carbonate (MC) were investigated. The migration of proton prefers an inter-carbonate pathway with an energy barrier of 8.0 kcal/mol at the B3LYP/6-31 G(d,p) level, which is in good agreement with the value of 7.6 kcal/mol and 7.5 kcal/mol from experiment and FPMD simulation, respectively. At transition state (TS), a linkage of O-H-O involving O 2p and H 1 s orbitals is formed between two carbonate ions. The calculated trajectory of H indicates that proton has a good mobility in MC, oxygen can rotate around carbon to facilitate the proton migration, while the movement of carbon is very limited. Small variations on geometry and atomic charge were detected on the carbonate ions, implying that the proton migration is a synergetic process and the whole carbonate structure is actively involved. Overall, the calculated results indicate that MC exhibits a low energy barrier for proton conduction in IT-SOFCs.