Three-dimensional hierarchical meso/macroporous Fe/Co-nitrogen-doped carbon encapsulated FeCo alloy nanoparticles prepared without any template or surfactant: High-performance bifunctional oxygen electrodes

Exploring highly efficient bi-functional electro-catalysts toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are critical for developing energy conversion and storage systems. Herein, for the first time, without any template or surfactant, a family of Fe/Co-N-doped three-dimensional (3D) hierarchical meso/macroporous carbon encapsulated FeCo nanoparticles (denoted as FexCo(1-x)-N/PC) have been successfully synthesized through pyrolyzing the low-cost biomass-based precursors in the NH3 atmosphere. After optimizing the molar ratio of Fe/Co, benefiting from the collaborative advantages of the Fe/Co-N-C species, cobalt-based electro-active phases, and unique 3D electrode configuration, the resultant Fe0.5Co0.5-N/PC amazingly shows considerable ORR activity comparable with commercial Pt/C catalyst via a 4e(-) pathway in alkaline electrolyte. When used for OER catalysis in an alkaline medium, Fe0.5Co0.5-N/PC achieves an extremely negative potential of 1.625 V vs. RHE at a current density of 10 mA cm(-2) and a low Tafel slope of 68.3 mV dec(-1). Furthermore, the overpotential (Delta E) between ORR and OER is just 0.813 V, which is nearly the minimum value for the non-precious metal catalysts. We believe that our present synthetic strategy can be further extended to develop other 3D hierarchical meso/macroporous carbonaceous catalysts for various applications, such as sensors, batteries, and supercapacitors. (C) 2016 Elsevier B.V. All rights reserved.