Co<sub>8</sub>FeS<sub>8</sub>/N,S-Doped Carbons Derived from Fe-Co/S-Bridged Polyphthalocyanine: Efficient Dual-Function Air-Electrode Catalysts for Rechargeable Zn-Air Batteries
Lu Chen, Lili Cui, Zizhun Wang, Xingquan He, Wei Zhang, Tewodros Asefa
Abstract
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 °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 (E1/2) 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 (η10) 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-900-sp 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.