Ionic liquid-assisted synthesis of N/S-double doped graphene microwires for oxygen evolution and Zn-air batteries

Abstract

Catalysts with both dense active sites and large effective surface area are crucial to the realization of high activity and fast kinetics in catalytic applications, but are very challenging to produce. In this work, we report a facile protocol to synthesize such a material of nitrogen (N), sulfur (S)-double doped graphene microwires. The critical step in this protocol is the preparation of catalyst precursor, which was obtained by the infiltration of graphene framework with the ion liquid, N-methyl pyrrolidone hydrosulfate. The subsequent carbonization of catalyst precursor can result in the material with not only heavy heteroatom-doping content (N: 10.8%; S: 2.4%), but also densely packed microstructure (packing density: 1.4 g cm−3) and rich porosity (surface area: 351 m2 g−1). Because of these remarkable structural properties, the material can work as an efficient catalyst electrode for oxygen evolution reaction (OER), showing a low overpotential of 0.31 V at the current density of 10 mA cm−2, high Faradaic efficiency of ~95%, and stable operation for 25 h. Moreover, the electrode can also serve as a cathode for catalyzing the charging and discharging processes of a Zn–air battery. This new class of electrode, having a free-standing one-dimensional (1D) architecture, can work without extra supports, which is easily incorporated into various renewable energy devices.