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), α-MoC(001), and Mo₂C(001) systems upon Li₂O₂ adsorption, but promotes the formation of the 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 to be 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, catalytic substrates for alkali-metal batteries.