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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. OPEN ACCESSCatalysts 2015, 5 1575

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Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are the cornerstones of rechargeable zinc–air batteries (ZABs). The exploration and rational design of high‐performance, durable, and nonprecious metal bifunctional oxygen electrocatalysts is highly desired for the large‐scale application of rechargeable ZABs. Herein, an effective and straightforward coupling approach is developed to fabricate high‐performance bifunctional ORR/OER electrocatalysts based on novel nanostructured amorphous bimetal Fe/Co hydroxide/oxide nanoparticles (10–20 nm) inlaid on multiwalled N‐dopted carbon nanotubes (FeCo‐DHO/NCNTs). Fe/Co nanoparticles achieve a maximum contact area on the NCNTs, effectively facilitating the rapid electron transport and preventing the aggregation of nanoparticles. Consequently, the as‐prepared FeCo‐DHO/NCNTs show a half‐wave potential of 0.86 V for ORR and a low operating potential of 1.55 V at 10 mA cm−2 for OER in 1.0 m KOH, superior to most bifunctional oxygen electrocatalysts reported so far. Moreover, the assembled all‐solid‐state zinc–air batteries with FeCo‐DHO/NCNTs catalyst as the air electrode demonstrate remarkable stability over long‐term cycling and excellent charging–discharging performance, with a low voltage gap (1.085 V at 60 mA cm−2) and high energy efficiency (60% at 10 mA cm−2) under ambient conditions.

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