Insight into the effects of microstructure and nitrogen doping configuration for hollow graphene spheres on oxygen reduction reaction and sodium-ion storage performance

Herein, the relationship between oxygen reduction reaction (ORR) catalytic activities of N-doped hollow graphene spheres (N-HGSs) and their morphologies, microstructures, and nitrogen doping configuration is deeply investigated. Based on all detection results it can be concluded that all of the level and configuration of doped-N atoms, the surface area, the mesopore structure of fabricated hollow graphene spheres related to the exposure of edges and vacancies correlating with the active sites, will ultimately affect the ORR catalytic performance of N-HGSs. Therefore, the optimized synthesis of N-HGSs can produce efficient electrocatalyst for ORR, which is better than the noble-metal Pt/C catalysts and most highly active graphene-based ORR catalysts reported to date. Additionally, the optimized synthesis of N-HGSs also exhibit excellent performance in sodium-ion storage. Because the large specific surface area, the well-connected hollow spherical and mesopore structures and the increased hydrophilicity induced by the doped-N atoms facilitate a ready transfer of charges and adsorption, diffusion and desorption of Na+ ions in and out of the active material, which could enhance sodium ion storage capacity. Additionally, expect the storage of Na+ ions by surface electro-adsorption/desorption, the insertion/extraction of Na+ through the thinner graphene shell makes a significant contribution to the improvement of sodium-ion storage capacity. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.