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.