Nitrogen-doped carbon nanoflower with superior ORR performance in both alkaline and acidic electrolyte and enhanced durability

Abstract

In this work, three new types of nitrogen-doped carbon nanoflower (NCNF) are synthesized by a template method. The resultant carbon was extensively investigated with the transmission electron microscopy (TEM), X-ray diffraction (XRD), Nitrogen adsorption-desorption isotherms, X-ray photoelectron spectroscopy (XPS), and electrochemical methods. Firstly, the carbon precursor, viz. pyrrole, aniline and phenanthroline, is found to yield a considerable effect on the morphology, which can be attributed to their dynamic motion in the template during the synthesis. All of the NCNF materials possess well-developed 3D pore structure and high specific surface area, which are beneficial for the mass transfer of the reactant and accessibility of the active sites toward oxygen reduction reaction (ORR). Secondly, the optimal catalyst NCNF-PHEN-900, which acquires the largest specific surface area (1039 m2 g−1), exhibits a superior ORR performance in both alkaline and acidic media. NCNF-PHEN-900 exceeds the commercial Pt/C with 30-mV halfwave potential (E1/2) surpassing in alkaline media and is comparable to Pt/C in acidic media (E1/2 = 0.76 V). Lastly, NCNF-PHEN-900 outperforms Pt/C on both durability and methanol tolerance in both alkaline and acidic media. And the rotating ring-disk electrode (RRDE) test indicates NCNF-PHEN-900 is highly selective to a four-electron transfer pathway in both alkaline (electron transfer number = 3.98) and acidic (electron transfer number = 3.97) media. This work sheds light on the importance of large specific surface area, well-developed pore structure and dopant configuration on electrocatalysis, offering a conjoint viewpoint of developing metal-free catalysts for the ORR.