Phosphoric acid-assisted synthesis of layered MoS2/graphene hybrids with electrolyte-dependent supercapacitive behaviors

Abstract

A reformative graphene-supported MoS₂ hybrid has been synthesized by a phosphoric acid (H₃PO₄)-assisted hydrothermal process. The effect of H₃PO₄ on the growth, morphology, structure, and composition of the MoS₂/graphene hybrid has been explored by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The results indicate that H₃PO₄ can control the process of both the reduction of graphene oxide and the crystallization of MoS₂. The electrochemical performance suggests that involvement of H₃PO₄ in the reaction bestows the hybrid with electrolyte-dependent capacitive behaviors in which contribution from electric double-layer capacitance (EDLC) and pseudocapacitance can be distinguished in acidic and alkaline electrolytes, respectively. While the quasi-EDLC behavior of the hybrid dominates in an alkaline electrolyte (258 F g⁻¹ at 2 A g⁻¹), the pseudocapacitance of the hybrid in an acidic electrolyte can be significantly enhanced due to oxygen-containing groups and Mo active in the total capacitance value (351 F g⁻¹ at 2 A g⁻¹). Moreover, a superior cycling performance and quick frequency response of the hybrid reinforces its potential for supercapacitor applications.