Three-Dimensional Hierarchical Porous Nitrogen and Sulfur-Codoped Graphene Nanosheets for Oxygen Reduction in Both Alkaline and Acidic Media

摘要

Heteroatom-doped carbon materials show superior oxygen reduction reaction (ORR) performance and served as alternatives to Pt-based catalysts for the commercialization of fuel cells. However, these doped carbon materials only show good ORR activity in alkaline medium, they are generally less effective in acidic electrolytes. The appropriate combination of high dopant distribution and engineered morphology of doped carbon materials is essential to realize high ORR performance. Herein, we propose a novel and effective approach to synthesize three-dimensional hierarchical porous nitrogen and sulfur-codoped graphene nanosheets (NSG) as ORR catalysts in both alkaline and acid media. Firstly, the self-assembled pyrrole layer was polymerized on graphene oxide template to form a molecule-thick polypyrrole (PPy) layer using (NH4)(2)S2O8 oxidant, resulting in a sandwich-like S-containing PPy/GO nanosheets (S-PPy-GO-PPy-S), then the S-PPy-GO-PPy-S was pyrolyzed to generate 3D hierarchical porous NSG with uniformly distributed high level multiple dopant (9.05 at% of N and 1.65 at% of S). As a result, the NSG exhibits comparable or even better ORR performance in both alkaline and acid media than the noble metal Pt/C catalyst. The achieved high performance is ascribed to the uniformly distributed high content doped elements and three-dimensional hierarchical porous structure, providing more active sites for ORR.