An Overview of Engineered Graphene-Based Cathodes: Boosting Oxygen Reduction and Evolution Reactions in Lithium- and Sodium-Oxygen Batteries.

The depletion of fossil fuels, the rapid evolution of the global economy, and high living standards require the development of new energy-storage systems that can meet the needs of the world's population. Metal-oxygen batteries (M=Li, Na) arise, therefore, as promising alternatives to widely used lithium-ion batteries, due to their high theoretical energy density, which approaches that of gasoline. Although significant progress has been made in recent years, there are still several challenges to overcome to reach the final commercialization of this technology. One of the most limiting and challenging factors is the development of bifunctional cathodes towards oxygen reduction and evolution reactions. In this sense, graphene, which is very promising and tunable, has been widely explored by the research community as a key material for this technology. Herein, a wide literature overview is presented and analyzed with the aim of guiding future research in this field.