Synthesis of porous NiCo₂S₄ aerogel for supercapacitor electrode and oxygen evolution reaction electrocatalyst

We report the synthesis of porous NiCo₂S₄ and NiCo₂S₄-reduced graphene oxide composite aerogel with high surface area (up to 262.4 m²/g) and large pore volume (up to 1.44 cm³/g). The aerogel is prepared by “DL-Mercaptosuccinic acid accelerated” sol-gel method, which is different from the well-established “nanoparticle condensation” and “metathesis” methods in terms of precursors and reaction mechanism. The fundamental of such method relies on the dual functionality of DL-Mercaptosuccinic acid, which not only initiated the sol-gel transition, but also offered sulfur source for metal sulfide. The complex interactions between the functional groups (COOH, -SH etc.) in DL-Mercaptosuccinic acid and the metal ions yield robust gel networks. After supercritical drying in ethanol, well crystallized monolithic NiCo₂S₄ and NiCo₂S₄-reduced graphene oxide aerogel can be obtained. High specific capacitance of 1268 F/g at 1 A/g and high energy density of 13.4 Wh/kg at the power density of 0.75 kW/kg can be achieved when the aerogel is used as supercapacitor electrode. The low on-set overpotential of 250 mV and small Tafel slope of 70 mV/dec also confirmed the aerogel is good catalyst for electrochemical oxygen evolution reaction. © 2017 Elsevier B.V.