Mechanical
grinding is exploited to effectively rupture biomass
cotton microfibers into metal-free, nitrogen-doped carbon nanosheets
with a large number of mesoporous textures. Experimentally, raw microfibers
of absorbent cotton are presoaked with fuming sulfuric acid to generate
plenty of hierarchical pores/cavities, which sufficiently expose the
inner parts of cotton microfibers to nitrogen source for efficient
incorporation of nitrogen dopants onto carbon skeletons in subsequent
thermal annealing process. Mechanical grinding of these thermally
annealed carbon microfibers leads to exfoliated nitrogen-doped thin
carbon nanosheets with a high surface area of 912.1 m2/g
as well as abundant mesopores and a considerable nitrogen content
of 8.5 at. %. These characteristics contribute to an excellent electrocatalyst
with marked catalytic activities toward oxygen reduction reaction
in an alkaline electrolyte solution, including a more positive half-wave
potential, much higher diffusion-limiting current, remarkably enhanced
operation stability, and stronger immunity against fuel-crossover
effects, as compared to commercial Pt/C catalysts. The present results
provide a novel facile method to the scalable preparation of biomass-derived
highly porous two-dimensional carbons for efficient electrochemical
energy devices.
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