Abstract
We report a robust method for the facile synthesis of N-doped carbon nanospheres with uniform and tunable sizes. Instead of involving a surfactant or other templates, this synthesis relies on the incorporation of ethylenediaminetetraacetic acid (EDTA) into the emulsion droplets of phenolic resin oligomers. The EDTA provides a high density of surface charges to effectively increase the electrostatic repulsion between the droplets and thereby prevent them from coalescing into irregular structures during polymerization-induced hardening. The EDTA-loaded polymer nanospheres are highly uniform in terms of both size and shape for easy crystallization into opaline structures. While maintaining good uniformity, the diameters of the resultant N-doped carbon nanospheres can be readily tuned from 100 to 375 nm, allowing for the fabrication of opaline lattices with brilliant structural colors. The EDTA also serves as an additional nitrogen source to promote the formation of graphitic-N, making the N-doped carbon nanospheres highly active, metal-free bifunctional electrocatalysts toward oxygen reduction and oxygen evolution reactions.