Heteroatom-doped graphene as electrocatalysts for air cathodes

Fuel cells and metal-air batteries are promising energy storage and conversion devices owing to their ultrahigh theoretical energy density. However, at present, it is still challenging to achieve the super-high energy density in practical applications due to the sluggish electrochemical reaction kinetics on air cathodes, which makes it urgent to exploit high-efficiency electrocatalysts. In the past decade, heteroatom-doped graphene (H-G) materials have drawn extensive attention due to their good catalytic activity, large specific surface area and high electrical conductivity. In this review, we focus on the summary of the latest advances regarding H-G electrocatalysts for air cathode-containing devices, including the synthetic methods of H-G materials and their applications to fuel cells, zinc-air batteries and lithium-air batteries. The working principles and catalytic reaction mechanisms are discussed in detail. Finally, the challenges and perspectives are presented to offer a guideline for the exploration of excellent H-G-based electrocatalysts.