Facile Synthesis of Nitrogen and Sulfur Dual-doped Hierarchical Micro/mesoporous Carbon Foams as Efficient Metal-free Electrocatalysts for Oxygen Reduction Reaction

It's almost hardly to realize the large-scale practical application of fuel cells if the costly noble metal-based electrocatalysts for oxygen reduction reaction (ORR) cannot be replaced by other efficient, stable, and low-cost non-precious metal or even metal-free ORR electrocatalysts. Herein, we report the novel design and synthesis of N and S dual-doped hierarchical micro/mesoporous carbon (NS-MC) foams via high temperature treatment of polyaniline coated sulfur sphere composite without any side products. The highlight of our method lies in its environmental concept of green synthesis and simplicity for no use of toxic gas (NH3 or H2S) or templates (SiO2 or MgO). The main focus of this research is to develop a high-performance metal-free ORR electrocatalyst as well as to gain insight into the synergistic effects originating from multiple-element doping on ORR performance. It is found that much graphitic-N and thiophene-S binding configurations formed for NS-MC foams at 1000 degrees C, which shows excellent electrocatalytic activity (high onset potential (0.051 V vs. Ag/AgCl (sat.KCl)), large diffusion-limiting current density (5.61 mA cm(-2) at 1600 rpm) and kinetic current density (22.22 mA cm(-2) at 0.25 V)), high selectivity towards methanol and long durability compared to commercial Pt/C with a nearly four-electron transfer passway when they are employed as metal-free catalyst for ORR. Besides, the desired NS-MC1000 shows a strong amperometric response towards ethanol indicating its potential application as an anode metal-free electrocatalyst in the alkaline direct ethanol fuel cell. (C) 2015 Elsevier Ltd. All rights reserved.