Rupturing Cotton Microfibers into Mesoporous Nitrogen-Doped\nCarbon Nanosheets as Metal-Free Catalysts for Efficient Oxygen Electroreduction

Abstract

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