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

The design and construction of high-efficiency carbon based non-precious metal electrocatalysts for oxygen reduction and oxygen evolution reactions (ORR and OER) with sluggish kinetics are of great importance but remain a big challenge. In this work, a 3D hybrid of bimetallic (Co/Fe) sulfide nanoparticles anchored on nitrogen-doped graphene and CNTs (Co0.2Fe0.6Sx-Gra/CNT) is fabricated via a ball-milling assisted in situ pyrolysis process. Benefitting from the synergetic effects between the carbon matrix and metallic sulfides, the optimized Co0.2Fe0.6Sx-Gra/CNT hybrid exhibits a high half-wave voltage up to 0.822 V for the ORR and a low overpotential of 540 mV at 10 mA cm-2 for the OER, outperforming Co0.2Fe0.6Sx-Gra and even a commercial Pt/C catalyst. Meanwhile, a home-made Zn-air battery with the hybrid as a cathode catalyst delivers a maximum power density up to 366 mW cm-2, along with a long-term charge and discharge stability at 10 mA cm-2. The excellent performances of the hybrid toward the 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 a dual-carbon coupling enhancement effect, which induce a change in the electronic structure and increase in the electron cloud density of the bimetallic sulfides and nitrogen dopant configuration. This work proves the importance of a carbon support to enhance the catalytic performance of non-precious metal-based catalysts and provides possibility of metal sulfides as bifunctional catalysts for the ORR/OER in a rechargeable Zn-air battery. A hybrid of bimetallic sulfides modulated by 1D/2D carbon displays highly efficient bifunctional electrocatalytic performance for the ORR/OER in a rechargeable Zn-air battery.