Preparation of N-doped nano-hollow capsule carbon nanocage as ORR catalyst in alkaline solution by PVP modified F127

Abstract

In order to reduce the cost of oxygen reduction reaction (ORR) catalyst, a metal-free N-doped carbon nanocage as ORR catalysts is prepared by using Polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO) three-block copolymer (F127), polyvinyl pyrrolidone (PVP) and Zn (OH)2 as a carbon source, nitrogen source and the morphology retaining agent, respectively, via a self-template method. The structure and microstructure of the N-doped carbon nanocage are characterized via physical characterization methods such as X-ray diffraction, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller method, and X-ray photoelectron spectroscopy. Electrochemical properties are evaluated in an O2-saturated alkaline solution. The obtained sample pyrolyzed at 800 °C with 10% content of PVP (C–N-800) presents nano-hollow carbon capsule with a diameter of 100 nm and shell thickness of 8 nm, and has the maximum surface area of 978 m2·g−1. In O2-saturated 0.1 M KOH solution, C–N-800's onset potential, limit current density, and half-wave potential, which are 0.87 V, 5.73 mA/cm2@0.45 V, and 0.77 V, respectively, are close to those of commercial 20% Pt/C catalysts. Meanwhile, its electrochemical performance only loss 11.75% after 5000 cycles, showing excellent ORR catalytic performance and stability. During self-assembly of F127, the added PVP participated into the process. Pyrolysis at 800 °C would result in the complete decomposition of F127 and PVP's lipophilic. So, the metal-free N-doped carbon nanocage was obtained and behaved excellent ORR catalytic activity and stability.