Co8FeS8/N,S-Doped Carbons Derived from Fe-Co/S-Bridged Polyphthalocyanine: Efficient Dual-Function Air-Electrode Catalysts for Rechargeable Zn-Air Batteries

Efficient, durable, nonprecious metal-based catalysts for electrochemical reactions involving oxygen are needed to advance the widespread use of fuel cells and Zn-air batteries. In this work, hybrid materials composed of bimetallic (Co and Fe) sulfide (Co8FeS8) nanoparticles supported on N,S-doped carbon microparticles that can serve as dual-function oxygen electrocatalysts are synthesized. The synthesis of the materials is performed by preparing and then pyrolyzing silica-protected Fe- and Co-modified, S-containing polyphthalocyanine at different temperatures. The materials are named (Fe,Co)SPPc-T-sp, where T denotes the pyrolysis temperature and sp represents the silica protection applied for their synthesis. Among them, the material synthesized at 900 degrees C, denoted (Fe,Co)SPPc-900-sp, shows superb electrocatalytic activities in an alkaline solution both toward the oxygen reduction reaction (ORR), with a half-wave potential (E-1/2) of 0.830 V vs RHE, and toward the oxygen evolution reaction (OER), with a current density of 10 mA cm(-2) at an overpotential (eta(10)) of 353 mV. The catalytic activities of this material for both reactions are comparable with those of the respective benchmark, precious-metal-based catalysts, namely, Pt/C (20 wt %) and RuO2, respectively. An alkaline Zn-air battery assembled using (Fe,Co)SPPc-900sp as an air electrode delivers a high peak power density (158.6 mW cm(-2)) and outstanding charge-discharge cycling stability (for over 50 h). These catalytic performances are better than those of the corresponding battery containing Pt/C and RuO2 electrocatalysts. This work also offers a facile synthetic strategy for the fabrication of robust, inexpensive dual-function electrocatalysts for Zn-air batteries.