Abstract
Nitrogen-doped carbon materials, including nitrogen-doped carbon nanotubes (NCNTs) and nitrogen-doped graphene (NG), have attracted increasing attention for oxygen reduction reaction (ORR) in metal-air batteries and fuel cell applications, due to their optimal properties including excellent electronic conductivity, 4e− transfer and superb mechanical properties. Here, the recent progress of NCNTs- and NG-based catalysts for ORR is reviewed. Firstly, the general preparation routes of these two N-doped carbon-allotropes are introduced briefly, and then a special emphasis is placed on the developments of both NCNTs and NG as promising metal-free catalysts and/or catalyst support materials for ORR. All these efficient ORR electrocatalysts feature a low cost, high durability and excellent performance, and are thus the key factors in accelerating the widespread commercialization of metal-air battery and fuel cell technologies.
Highlights
Developing highly efficient electrocatalysts to facilitate sluggish cathodic oxygen reduction reaction (ORR) is a key issue in metal-air batteries and fuel cells [1,2,3,4,5]
To further take the merits of both carbon and ceramic-based supports for ORR, the Sun group employed the composite nanostructures of nitrogen-doped carbon nanotubes (NCNTs) coated with TiSi2Ox as Pt catalyst supports, and the results indicated that this composite showed better ORR performance than Pt/NCNT catalysts, thereby illustrating its promise as a catalyst for fuel cells [88]
ORR plays an essential role in energy-related areas, such as metal-air batteries and fuel cells, and traditionally, the Pt-based catalysts are regarded as the best choice for 4e− ORR
Summary
Developing highly efficient electrocatalysts to facilitate sluggish cathodic oxygen reduction reaction (ORR) is a key issue in metal-air batteries and fuel cells [1,2,3,4,5]. Carbon nanotubes (CNTs) and two-dimensional (2D) graphene (Figure 1) have attracted a great deal of attention for ORR due to their excellent electronic conductivity, huge specific surface area (SSA), as well as excellent thermal and mechanical properties [8]. Graphitic (or quaternary) N refers to the N atoms that replace the carbon atoms in the graphene plane Such doped N atoms can change the local density state around the Fermi level of N-doped graphitic carbons, which may play a vital role in tailoring the electronic properties and improving their ORR performance [14,16].
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