Direct Enrichment of Metallic Single-Walled Carbon Nanotubes by Using NO₂ as Oxidant to Selectively Etch Semiconducting Counterparts

We report an efficient method for enriching high-purity metallic single-walled carbon nanotubes (m-SWCNTs) by using NO₂ as oxidant to remove semiconducting components at 220 °C. After etching, m-SWCNTs with purity higher than 90% were obtained. The surviving m-SWCNTs retain an intact structure without any extra defects on their surface

MnO₂ Nanofilms on Nitrogen-Doped Hollow Graphene Spheres as a High-Performance Electrocatalyst for Oxygen Reduction Reaction

Platinum is commonly chosen as an electrocatalyst used for oxygen reduction reaction (ORR). In this study, we report an active catalyst composed of MnO₂ nanofilms grown directly on nitrogen-doped hollow graphene spheres, which exhibits high activity toward ORR with positive onset potential (0.94 V vs RHE), large current density (5.2 mA cm^–2), and perfect stability. Significantly, when it was used as catalyst for air electrode, a zinc–air battery exhibited a high power density (82 mW cm^–2) and specific capacities (744 mA h g^–1) comparable to that with Pt/C (20 wt %) as air cathode. The enhanced activity is ascribed to the synergistic interaction between MnO₂ and the doped hollow carbon nanomaterials. This easy and cheap method paves a way of synthesizing high-performance electrocatalysts for ORR

Ammonia Defective Etching and Nitrogen-Doping of Porous Carbon toward High Exposure of Heme-Derived Fe–N_<i>x</i> Site for Efficient Oxygen Reduction

The utilization of metal and nitrogen doped carbon as a Pt-free oxygen reduction electrocatalyst depends largely on the homogeneous composition of the metal–nitrogen sites with limited content. Herein a simple and feasible ammonia defective activation strategy is explored on ordered mesoporous carbon (APC) to confine hematin precursor and suppress the formation of inorganic Fe-based derivatives during pyrolysis. Thus, a hierarchically nanoporous Fe/N/APC catalyst with high numbers of exposed iron–nitrogen sites exhibits an impressive performance for oxygen reduction reaction in alkaline media, with large diffusion-limited current density and positive half-wave potential with respect to commercial Pt/C catalyst. The enhanced ORR properties can be majorly ascribed to synergistic contributions of high numbers of exposed catalytic sites completion from high contents of Fe–N and pyridinic N along with the fast mass-transport properties arising from the etched high permeable porous structure. When applied as cathodic catalyst in Zn-air battery, it demonstrates a power density of 200 mW cm^–2 and a specific capacity of 605 mA h g^–1_Zn higher than those of Pt/C catalyst