Size-Dependent Effects in Fullerene-Based Catalysts for Nonaqueous Li–Air Battery Applications

Nonaqueous Li–air batteries have attracted great attention in the last few decades. Efficient catalysts need to be developed for circumventing the slow kinetics of the discharging oxygen reduction reaction (ORR) and charging oxygen evolution reaction (OER) on the cathode of Li–air batteries. In this study, fullerenes are proposed as active ORR/OER catalysts for Li–air batteries. The reaction mechanisms and final discharge products are investigated for C20, C40, C60, and C180 fullerenes. Evolutionary patterns of intermediate configurations and energetics of the lithiation processes are scrutinized. A direct size vs activity relationship is established along the O2 nucleation pathway, which is attributed to the finite-size effects and selective stabilization of (LiO2)n clusters over different fullerenes. The lowest discharging overpotential of 0.66 V is identified for C180 fullerene, which marks a significant improvement in the theoretical ORR overpotential compared to the corresponding reports of standard Li–air battery catalysts such as graphene and comparable activity to that of the Pt(111) surface. The varying surface distribution of pentagons and hexagons on different fullerenes is found to have a significant effect in determining their catalytic activity. In addition to reporting fullerenes as potential catalysts for Li–air batteries for the first time, the study also provides insights into the tunable ORR/OER activity, which can be achieved by regulating the size of fullerenes.