Oxygen Reduction by Lithiated Graphene and Graphene-Based Materials

Oxygen reduction reaction (ORR) plays a key role in lithiumair batteries (LABs) thatattract greatattention thankstotheir hightheoreticalspecificenergyseveraltimes exceeding that of lithium-ion batteries. Because of their high surface area, high electric conductivity, and low specific weight, various carbons are often materials of choice for applications as the LAB cathode. Unfortunately, the possibility of practical application of such batteries is still under question as the sustainable operation of LABs with carbon cathodes is not demonstrated yet and the cyclability is quitepoor, whichisusually associatedwithoxygen reduced speciessidereactions. However,themechanisms ofcarbonreactivity towardthesespeciesare still unclear. Here, we report a direct in situ X-ray photoelectron spectroscopy study of oxygen reduction by lithiated graphene and graphene-based materials.Althoughlithiumperoxide(Li2O2)andlithiumoxide(Li2O)reactionswithcarbonarethermodynamicallyfavorable,neitherofthemwasfoundto react even at elevated temperatures. As lithium superoxide is not stable at room temperature, potassium superoxide (KO2) prepared in situ was used instead to test the reactivity of graphene with superoxide species. In contrast to Li2O2 and Li2O, KO2 was demonstrated to be strongly reactive.