Preparation and electrocatalytic performance of N-doped hierarchical porous carbon loaded with Fe/Fe5C2 nanoparticles

Abstract

The development of efficient non-precious-metal catalysts for oxygen reduction reaction (ORR) is greatly important for accelerating the commercial application of fuel cells. Herein, polystyrene (PS) nanospheres are used as templates for the growth of zeolitic imidazolate framework (ZIF) complex precursors with variable molar ratios of Fe3+ to Zn2+ in situ. Through carbonization at a high temperature, the hierarchical porous carbon (HPC) materials with different proportions (xFeyZn-HPC, x + y = 100) have been prepared. The typical product 5Fe95Zn-HPC is composed of nitrogen (N)-doped hierarchical porous carbon loaded with Fe/Fe5C2 nanoparticles obtained at optimal molar ratio. As an electrocatalyst, the 5Fe95Zn-HPC shows a positive onset potential of 0.92 V (vs. RHE), half-wave potential of 0.77 V (vs. RHE) and limiting current density of 5.60 mA cm−2 at 0.055 V (vs. RHE). The hydrogen peroxide yield is less than 4.2%, and the electron transfer numbers are between 3.91 and 3.99 at 0.055 V~1.055 V in the catalytic ORR, which indicate that the reaction is dominated by four-electron reduction. The 5Fe95Zn-HPC has higher stability and methyl alcohol resistance in alkaline and acidic solutions. The above results indicate the excellent catalytic ORR performance of the 5Fe95Zn-HPC, almost as the commercial Pt/C. Additionally, 5Fe95Zn-HPC has the capacity to catalyze oxygen evolution reaction (OER) and adsorb methylene blue pollutants. Therefore, this work provides a practical method to design the hierarchical porous carbon-based material with outstanding multi-functions.