Carbon-based metal-free electrocatalysts for the oxygen reduction reaction (ORR) in alkaline medium have been extensively investigated with the aim of replacing the commercially available, but precious platinum-based catalysts. For the proper design of carbon-based metal-free electrocatalysts for the ORR, it would be interesting to identify the active sites of the electrocatalyst. The ORR was now studied with an air-saturated electrolyte solution droplet (diameter ca. 15 μm), which was deposited at a specified position either on the edge or on the basal plane of highly oriented pyrolytic graphite. Electrochemical measurements suggest that the edge carbon atoms are more active than the basal-plane ones for the ORR. This provides a direct way to identify the active sites of carbon materials for the ORR. Ball-milled graphite and carbon nanotubes with more exposed edges were also prepared and showed significantly enhanced ORR activity. DFT calculations elucidated the mechanism by which the charged edge carbon atoms result in the higher ORR activity.

Nanoparticle-stacked porous Ni3FeN nanosheets were synthesized through a simple nitridation reaction of the corresponding LDHs. The nanosheet is composed of stacked nanoparticles with more active sites exposed for electrocatalytic reactions. Thus, it exhibited excellent oxygen evolution reaction performance having an extremely low overpotential of 223 mV at 10 mA/cm(2) and hydrogen evolution reaction property with a very low overpotential of 45 mV at 10 mA/cm(2). This electrocatalyst as bifunctional electrodes is used to overall water splitting in alkaline media, showing a high performance with 10 mA/cm(2) at a cell voltage of 1.495 V.

Fe 2 O 3 supported on nitrogen-doped graphene (Fe 2 O 3 /N-rGO) hydrogel was prepared by a facial one-pot hydrothermal method. The efficient Fe 2 O 3 loading and nitrogen doping of graphene was realized with this method. The morphology and structure of the samples were characterized by scanning electron microscopy, high-resolution transmission electron microscopy, thermal gravimetric analysis, Raman spectra, X-ray diffraction, and nitrogen isothermal adsorption−desorption. The chemical environment of the surface composition of the samples was recorded by X-ray photoelectron spectroscopy. The electrochemical performance was tested with a three-electrode system in the aqueous electrolyte of 1 M KOH. The electrochemical measurement demonstrated that Fe 2 O 3 /N-rGO shows a specific capacitance as high as 618 F g −1 at a discharge current density of 0.5 A g −1 . Even at the current density of 10 A g −1 , the specific capacitance is still as high as 350 F g −1 . After 5000 cycles, the capacity retention is still maintained at 56.7%.

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Developing high-performance and low-cost electrocatalysts for oxygen reduction reaction (ORR) is still a great challenge for Al-air batteries. Herein, CeO, a unique ORR promoter, was incorporated into ketjenblack (KB) supported CoO catalyst. We developed a facile two-step hydrothermal approach to fabricate CoO-CeO/KB as a high-performance ORR catalyst for Al-air batteries. The ORR activity of CoO/KB was significantly increased by mixing with CeO nanoparticles. In addition, the CoO-CeO/KB showed a better electrocatalytic performance and stability than 20 wt % Pt/C in alkaline electrolytes, making it a good candidate for highly active ORR catalysts. CoO-CeO/KB favored a four-electron pathway in ORR due to the synergistic interactions between CeO and CoO. In full cell tests, the CoO-CeO/KB exhibited a higher discharge voltage plateau than CeO/KB and CoO/KB when used in cathode in Al-air batteries.