3D carbon nanotubes-graphene hybrids for energy conversion and storage applications

Abstract

Due to the global concerns on limited non-renewable energy resources, developing accessible renewable energy systems and expanding electrochemical energy-related devices are serious necessities. Recently, carbon-based metal-free materials have played a crucial role in electrochemical devices. Carbon-based metal-free electrocatalysts have been recognized as proper alternatives for the replacement of frequently used Pt in these devices. Carbon nanotubes-graphene (CNTs-G) hybrids are three-dimensional (3D) carbonaceous structures that have attracted researchers’ interest in the last decade. Because of the unique properties of sp2-hybridized carbon nanostructures viz. superb mechanical, electrical, and catalytic performances, plus recent extensive applications in various aspects, CNTs and graphene families are considered prospective heterostructure materials for next-generation technologies. Moreover, carbon-based materials have demonstrated excellent performance in key reactions like oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) that occur on the surface of catalysts or electrodes in electrochemical energy conversion/storage devices. The ability to accept functional groups and dopants, create defects, present a large surface area, high porosity, and superior electrolyte penetration, facilitate ion transport, accelerate charge transfer, and capability to form robust attachments between CNTs and graphene have made the CNTs-G hybrid materials suitable candidates in energy-related areas. This review discusses the recent achievements of 3D CNTs-G hybrid heterostructures from synthesis and theoretical concepts to developments and applications in oxygen- and hydrogen- involving electrocatalysts and energy-related devices such as batteries and supercapacitors. Significantly, research gaps and critical issues are identified in order to pave the way for the future study of CNTs-G hybrid materials.