Two-dimensional carbon-based heterostructures as bifunctional electrocatalysts for water splitting and metal–air batteries

The continuous depletion of fossil fuels and the effects of climate change have encouraged prompt action to attain carbon neutrality. Technologies that transform and store renewable energy are crucial for creating a sustainable society, which is independent of fossil fuels. In this regard, electrochemical water splitting based on the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is an attractive technique for producing carbon-free hydrogen fuels. Additionally, rechargeable metal–air batteries (MABs) are another intriguing way for renewable energy storage through reversible oxygen reactions (OER and the oxygen reduction reaction, ORR). Herein, we comprehensively review bifunctional electrocatalysts for water splitting (HER and OER) and MABs (OER and ORR), particularly 2D carbon material-derived heterostructures. The synthesis and properties of 2D carbon materials and their energy conversion and storage mechanisms are discussed to highlight the bifunctionality of the heterostructures. Recent studies on bifunctional electrocatalysts based on 2D carbon-derived heterostructures are also reviewed. Finally, perspectives for future studies and multifunctional catalysts are presented.