A bottom-up, template-free route to mesoporous N-doped carbons for efficient oxygen electroreduction

Herein, we report a facile, bottom-up route to the preparation of N-doped carbons with a high surface area as well as plenty of hierarchical pores by thermal annealing the black bread-like sulfuric acid-dehydrated sucrose. This simple sulfuric acid treatment created a remarkable surface area of 645.7 m²/g in the dehydrated sucrose, and the subsequent thermal annealing with activated reagent ZnCl₂ and nitrogen source NH₄Cl helped further generated more porous textures in the carbon matrix, which contributes to a high surface area of 2450 m²/g, a large number of hierarchical pores ranging from 2 to 150 nm in a highly porous N-doped carbon to sufficiently expose active sites and boost mass transfer. The best sample N/PC-800, which was thermally annealed at 800 °C, is able to selectively catalyze the 4e⁻ ORR process and shows higher working stability, stronger tolerance to methanol crossover effect, a very comparable onset potential and diffusion-limited current density in alkaline electrolyte, compared to the benchmark Pt/C catalyst. The results in this study signify the validity of present facile, robust template-free method in the synthesis of highly porous N-doped carbons for electrochemical energy conversion and storage.