Dual-carbon coupling modulated bimetallic sulfides as high-efficiency bifunctional oxygen electrocatalysts in rechargeable Zn-air battery

Abstract

Design and construction of high-efficiency carbon based non-precious metal electrocatalysts for the kinetic sluggish oxygen reduction and oxygen evolution reactions (ORR and OER) is of great vital but still remain a big challenge. In this work, a 3D hybrid of bimetallic (Co/Fe) sulfides nanoparticles anchored on nitrogen doped graphene and CNT (Co0.2Fe0.6Sx-Gra/CNT) is fabricated via ball-milling assisted in-situ pyrolysis process. Benefitting from the synergetic effects between carbon matrix and sulfides, the optimized Co0.2Fe0.6Sx-Gra/CNT hybrid exhibits a high half-wave voltage up to 0.822 V for ORR and a low overpotential of 540 mV at 10 mA cm-2 for OER, outperforming the Co0.2Fe0.6Sx-Gra and even the commercial Pt/C catalyst. Meanwhile, the home-made Zn-air battery with the hybrid as cathode catalyst delivers a maximum power density up to 366 mW cm-2, along with a long-term charge and discharge stability at the current of 10 mA cm-2. The excellent performances of the hybrid toward ORR and OER are mainly attributed to the plentiful electron transfer channels provided by the 3D intertwined carbon matrix and enriched active sites derived from dual-carbon coupling enhancement effect, which induce change of the electronic structure and increase of the electron cloud density of the bimetallic sulfides and nitrogen dopants configuration. This work proves the important of the carbon support to enhance the catalytic performance of non-precious metal based catalysts, and also provide possibility of the metal sulfides as bifunctional catalysts for ORR/OER in rechargeable Zn-air battery.