Abstract
A facile method has been developed based on extremely rapid heating (temperature ramp greater than 150°C sec−1) for the synthesis of graphene nanosheets with heterogeneously doped nitrogen atoms (ex-NG) in a one-step process. The nanosheets are uniquely characterized by large expansions and openings between the layers that facilitate in the diffusion of the electrolyte to perform highly active oxygen reduction reaction (ORR). Electron microscopy has verified a voile-like morphology of thermally reduced ex-NG, and X-ray photoelectron spectroscopy has confirmed successful ammonia treatment of nitrogen incorporation into the graphitic network. The ORR activity of the graphene nanosheets is evaluated using both half-cell and single-cell performance tests. The half-cell test is conducted by rotating disk electrode measurements where the nanosheets have showed very comparable ORR activity to that of state-of-the-art commercial Pt/C catalyst. A practical zinc-air battery have been utilized to test the single-cell performance of ex-NG1100, which have exhibited superior battery discharge voltages and reduced charge transfer resistance during the ORR compared to that of Pt/C. This outstanding catalytic activity of metal-free carbon-based graphene nanosheets is attributed to the opened structured attained by facile synthesis technique utilizing a rapid heating process.
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