We synthesized a hybrid graphene/Co3O4 catalyst by a simple chemical reduction method, and demonstrated that a Li–O2 cell with the hybrid catalyst delivers a highly reversible capacity. We examined the role of the catalyst in Li–O2 batteries and through careful analyses of the reactions in the battery, we found that the reaction path fundamentally changes with the use of catalyst, and propose a mechanism of how the rechargeability is improved in Li–O2 batteries.