A review of nanocarbons in energy electrocatalysis: Multifunctional substrates and highly active sites

Nanocarbons are of progressively increasing importance in energy electrocatalysis, including oxygen reduction, oxygen evolution, hydrogen evolution, CO₂ reduction, etc. Precious-metal-free or metal-free nanocarbon-based electrocatalysts have been revealed to potentially have effective activity and remarkable durability, which is promising to replace precious metals in some important energy technologies, such as fuel cells, metal–air batteries, and water splitting. In this review, rather than overviewing recent progress completely, we aim to give an in-depth digestion of present achievements, focusing on the different roles of nanocarbons and material design principles. The multifunctionalities of nanocarbon substrates (accelerating the electron and mass transport, regulating the incorporation of active components, manipulating electron structures, generating confinement effects, assembly into 3D free-standing electrodes) and the intrinsic activity of nanocarbon catalysts (multi-heteroatom doping, hierarchical structure, topological defects) are discussed systematically, with perspectives on the further research in this rising research field. This review is inspiring for more insights and methodical research in mechanism understanding, material design, and device optimization, leading to a targeted and high-efficiency development of energy electrocatalysis.