Research Progress on Carbon Nanotubes in Noble-Metal-Free Electrocatalytic Oxygen Reduction Reaction

Fuel cell and metal-air batteries are green batteries which directly convert chemical energy into electricity, possessing important merits compared to the traditional energy, examples of high energy density, safety and environmental benignity. However, the low reserves, high cost, easy poisoning and deactivation of precious metal platinum (Pt) used in cathodic oxygen reduction reactions (ORR) have severely limited the development of the fuel cell in large-scale. Therefore, the research on development of cheap, efficient and stable non-precious metal catalyst has become a hotspot. Carbon nanotubes (CNTs), owning to the outstanding feature such as the intrisic sp(2) hybrid structure, excellent conductivity, high specific surface area, good chemical stability, etc, have received wide attentions. Firstly, the recent progress in the noble-metal-free CNTs-based ORR catalysts were summarized, mainly including non-metal element doping, transition metal-nitrogen-CNTs, CNTs supported transition metals and their derivations (oxides, carbides, nitrides, sulfides, etc), CNTs supported single atoms, composited with other carbon materials (graphene, porous carbon, carbon nanofibers) and self-standing electrodes based on CNTs. Finally, the prospect and the future research direction of CNTs-based ORR catalysts are also discussed.