Trends in the Adsorption of Oxygen and Li2O2 on Transition-metal Carbide Surfaces: A Theoretical Study

In this work we performed fundamental investigations of the adsorption of O₂ and Li₂O₂ molecules on seven transition-metal carbide (TMC) surfaces, which present 3d, 4d, and 5d TM, where TM = Ti, V, Zr, Nb, Mo, Hf and Ta. We employed density functional theory (DFT) with the semilocal meta-GGA SCAN functional. The oxide layer behaves as a passivation layer on the TiC(111), ZrC(111) and MoC(001) systems upon Li₂O₂ adsorption, but promotes the formation of a Li₁O₃TM₁ layer on the VC(111), NbC(111), MoC(111), and HfC(111) surfaces due to the change in stoichiometry which is caused by the first adsorbed Li₂O₂ molecule. We showed that with increasing the number of the Li₂O₂ molecules on the TMC surfaces, the contribution of the TMC surface states turns out less important to the adsorption energy of the molecules. After the first layer of Li₂O₂ it approaches the native crystal values, which occurs faster with the occupation of the TM $d$-bands. This work can make a contribution in fundamental understanding and development of new, TMC-based, catalysts for alkali-metal batteries.