First-principles study of V3+ adsorption on MXene toward vanadium redox flow battery

The sluggish kinetic of V2+/V3+ redox reaction limits the performance of vanadium redox flow battery (VRFB). As one of the critical steps of negative reaction, the adsorption process of V3+ on catalyst plays a significant role. Owing to the high conductivity and catalytic activity of MXene materials, the adsorption behavior of V3+ on MXenes (Ti3C2O2, Nb3C2O2, Sc3C2O2) and MXenes with oxygen vacancy (Vo-Ti3C2O2, Vo-Nb3C2O2, Vo-Sc3C2O2) were revealed through first-principles based on density functional theory (DFT). Band structure, adsorption energy, Mulliken charge population, density of state, partial density of states and charge density difference were calculated. The results show that the adsorption mechanism of V3+ on MXenes is chemisorption and oxygen vacancy efficiently promotes the adsorption energy for V3+. The strong interaction between V3+ and MXenes is ascribed to orbital hybridization and overlapping. The adsorption energy of V3+ on Sc3C2O2 with oxygen vacancy (Vo-Sc3C2O2) reaches −98.255 kcal/mol. Meanwhile, the most obvious electron transfer phenomenon exists on the surface of Vo-Sc3C2O2. Vo-Sc3C2O2 shows the strongest metallicity and the largest adsorption energy for V3+, which presents potential candidate as catalyst for V2+/V3+ redox reaction.