Nano-confinement of metal-based nanostructures in one-dimensional carbon nanotubes (M@CNTs) is an interesting and effective way to achieve new functional materials with unique physical and chemical properties for various energy applications with enhanced performance. In this unique structure, the inner cavity of CNTs can act as a nanoreactor with a diameter of a few nanometers and length in microns. The nano-confinement of metals into CNTs not only improves the local environment of CNTs but also prevents metal leaching and aggregation. This critical review summarizes recent advances in developing advanced nano-confinement methods for different functional nanoparticles, such as metals, metal oxides, metal sulfides, metal phosphides, metal carbides, etc. Particular attention is paid to their catalytic activities and stabilities, strategies for the enhancement of storage capacities of Zn–air batteries, Li–O2 batteries and lithium ion batteries. The demonstrated examples provide an understanding of M@CNTs for use as electrocatalysts and electrodes for batteries. Finally, challenges and future prospects of M@CNTs are highlighted for electrochemical energy conversion and storage devices.
