Fabricating carbon nanocages as ORR catalysts in alkaline electrolyte from F127 self-assemble core-shell micelle

Abstract

In order to reduce the cost of oxygen reduction reaction (ORR) catalyst in fuel cell, polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO) three-block copolymer (F127) and Zn(OH)2 were used as carbon resource and morphology retaining agent to prepare porous nanocages for ORR catalyst in alkaline solution. Its composition and microstructure were characterized by X-ray diffraction Raman spectroscopy (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) method. Electrochemical properties were evaluated in O2 saturated alkaline solution. Results showed the sample obtained at 700 °C (C-700) was composed of porous carbon nanocages with diameter of 50 nm and shell thickness of 4 nm. C-700 had the maximum surface area (1011 m2 g−1) and the best ORR catalytic performance. The main reason is that polypropylene oxide (PPO) group at the lipophilic end begins to decompose at 500 °C, and the polyethylene oxide (PEO) group at the lipophilic end at 700 °C decomposes completely. In O2 saturated 0.1 M KOH solution, C-700's oneset potential, limit current density and half-wave potential, which were 0.89 V, 5.59 mA/cm2@0.45 V and 0.71 V, respectively, were close to that of commercial 20% Pt/C catalyst. It was noted that the oneset potential and half-wave potential of C-700 had barely change, and limit current density attenuated about 87.8% after 2000 CV cycle. The obtained catalyst behaved good catalytic activity and stability for ORR in alkaline solution and a potential application prospect in fuel cells.