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The universal linear scan voltammogram measurement on the rotating disk electrode (RDE) has been identified as a simple method to investigate the oxygen reduction activity of electrocatalysts. The steady‐state limiting current density Ilim indicates the maximum diffusion current density in the oxygen reduction reaction (ORR) during RDE measurement, which should be a fixed value in theory for a 4e ORR in a particular concentration solution and at a certain rotate speed. However, in experiments, Ilim is always variable and smaller than theoretical value even though with the same the catalyst, electrode, and rotator. So the impact of various experimental operating parameters on Ilim is highly necessary to be investigated. In this paper, factors, such as catalyst loading, O2 inlet condition, O2 flow rate, gas tightness, solution concentration, and purity, have been investigated for their effects on the Ilim of ORR on three typical catalysts (20 % commercial Pt/C, Iron/Nitrogen/Carbon‐catalyst and N‐doped carbon nanotubes). The results indicate that the catalyst loading and O2 inlet condition are the key factors influencing the Ilim of ORR. While, the O2 flow rate, gas tightness, solution concentration, and purity have little influence on the Ilim of ORR. The correct Ilim could be obtained under the optimized catalyst loading and the O2 inlet with an extended sand core tube.

Developing low cost, high-performance, and durable bifunctional catalysts for oxygen reduction and oxygen evolution reactions is critical for a commercial application of fuel cells and metal−air batteries. Nitrogen-doped carbon nanotubes encapsulated nickel nanoparticles are prepared through a simple pyrolysis procedure with melamine and nickel chloride hexahydrate as precursors. The catalyst is featured by nickel nanoparticles encapsulated inside nitrogen-doped carbon nanotubes, with abundant surface nitrogen doping. The optimized catalyst exhibits proximate oxygen reduction activity to platinum/carbon catalyst, comparable oxygen evolution activity to ruthenium dioxide catalyst, and better stability to noble metal catalysts in alkaline medium. The oxygen electrode activity parameter (the gap between the potential of oxygen evolution at 10 mA cm −2 and the half-wave potential of oxygen reduction) of the as-prepared catalyst is 0.754 V, which is among the state-ofthe-art bifunctional electrocatalysts reported to date. To explore the active sites, a series of catalysts with different bulk nickel and surface nitrogen contents are synthesized and served as the oxygen reduction and oxygen evolution reactions catalysts. The results reveal that the oxygen reduction activity of this catalyst arises from the doped nitrogen, while the oxygen evolution activity originates from the encapsulated nickel nanoparticles.

A novel gamma-MnO(2) hollow structure has been synthesized at room temperature using a simple chemical reaction between MnSO(4) and KMnO(4) in aqueous solution without using any templates, surfactants, catalysts, calcination and hydrothermal processes. The synthesized gamma-MnO(2) hollow structure was characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and BET analysis. It was found that the hollow structure consisting of short gamma-MnO(2) nanorods with diameters of 5-10 nm and lengths of 50-100 nm could form when the MnSO(4)/KMnO(4) mole ratio was equal to or larger than 2.3. The excess amount of Mn(2+) in solution was observed to promote the crystallization of gamma-MnO(2) nanorods and the formation of the gamma-MnO(2) hollow structure. In addition, the evolution of microstructure and morphology of the products obtained with a MnSO(4)/KMnO(4) mole ratio of 2.3 at different reaction times revealed that the hollow structure was formed via an Ostward ripening process. Furthermore, the obtained gamma-MnO(2) hollow structure was found to exhibit a better catalytic performance than conventional gamma-MnO(2) in the aerobic oxidation of benzyl alcohol to benzaldehyde, demonstrating its possible application in alcohol oxidation.