Highly Crumpled Hybrids of Nitrogen/Sulfur Dual-Doped Graphene and Co₉S₈ Nanoplates as Efficient Bifunctional Oxygen Electrocatalysts

Abstract

A bifunctional electrocatalyst for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is highly attractive for the manufacture of clean energy conversion devices. In this work, highly crumpled hybrid of nitrogen and sulfur dual-doped graphene and quasi-hexagonal Co₉S₈ nanoplates (Co₉S₈/NSG_g-C3N4) is fabricated via a facile ionic assembly approach. The unique structure of Co₉S₈/NSG_g-C3N4 renders it high specific surface area (288.3 m² g^-1) and large pore volume (1.32 cm³ g^-1). As the electrocatalyst for ORR, Co₉S₈/NSG_g-C3N4 demonstrates excellent performance with the onset potential of -0.02 V vs Ag/AgCl and the limited current density of 6.05 mA cm^-2 at -0.9 V vs Ag/AgCl. Co₉S₈/NSG_g-C3N4 also presents outstanding catalytic activity toward OER by delivering a limited current density of 48 mA cm^-2 at 1 V vs Ag/AgCl. The bifunctional catalytic behaviors of Co₉S₈/NSG_g-C3N4 enable the assembly of a rechargeable Zn-air battery with it as the cathode catalyst, which exhibits stable discharge/charge voltage plateaus upon long time cycling over 50 h.