A novel strategy for realizing high nitrogen doping in Fe3C-embedded nitrogen and phosphorus-co-doped porous carbon nanowires: efficient oxygen reduction reaction catalysis in acidic electrolytes

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Vol. 7; no. 30; pp. 17923 - 17936
• Main Authors: Li, Mian, Liu, Yang, Han, Lina, Xiao, Jie, Zeng, Xiaoyuan, Zhang, Chengxu, Xu, Mingli, Peng, Dong, Zhang, Yingjie
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 2019
• Subjects: active sites; Carbon; Catalysis; Catalysts; catalytic activity; Cementite; Chemical reduction; Doping; durability; Electrochemistry; Electrolytes; Iron carbides; methanol; Nanotechnology; Nanowires; Nitrogen; Oxygen; Oxygen reduction reactions; Phosphoric acid; Phosphorus; platinum; Polyvinylpyrrolidone; potassium hydroxide; Pyrolysis; Sulfuric acid; Surface chemistry
• ISSN: 2050-7488; 2050-7496; 2050-7496
• DOI: 10.1039/c9ta04388h

The achievement of higher nitrogen doping density is a prospective approach to further boost the oxygen reduction reaction (ORR) catalytic efficiency of non-precious-metal catalysts under acidic conditions. In this study, we report a novel methodology for powerfully promoting the N doping amounts in three-dimensional (3D) Fe3C-embedded N and P-co-doped porous carbon hybrid nanowires (i.e. Fe3C@NP-PCFs). Via pyrolysis of the 3D polyvinylpyrrolidone (PVP)-cyanamide-Fe(C2H3O2)2–H3PO4 precursor networks woven by the electrospinning technology, the desired products were successfully synthesized. In the pyrolysis process, upon the activation of phosphoric acid, the surfaces of the 3D Fe3C@NP-PCF networks in situ formed abundant micro/mesopores and high-density carbon edges/defects, which contributed towards the instantaneous doping of more N atoms (9.26 at%) into the carbon frameworks of Fe3C@NP-PCFs. The resultant Fe3C@NP-PCF catalyst displayed highest ORR activity, comparable to that of 20 wt% Pt/C in 0.1 M KOH. In particular, the Fe3C@NP-PCF catalyst revealed excellent ORR activity with the onset potential and half-wave potential being just 10.1 mV and 27.7 mV more negative than those of 20 wt% Pt/C, respectively. Its limited diffusion current density was even much larger than that of 20 wt% Pt/C in 0.5 M H2SO4. The electrochemical measurement results show that the Fe3C@NP-PCFs catalyst also possesses better durability and methanol tolerance than 20 wt% Pt/C in both acidic and alkaline electrolytes. The special 3D hierarchically porous structures of the Fe3C@NP-PCF nanowires and the fairly high active site dispersion along their surfaces are responsible for the excellent ORR activity of this catalyst.