Na2MoO4 as both etcher for three-dimensional holey graphene hydrogel and pseudo-capacitive feedstock for asymmetric supercapacitors

Abstract

Porous graphene hydrogel (pGH) have attracted considerable attention due to their unique properties and practical applications in the field of supercapacitors. Their exceptional porous structure (high degree of porosity, high pore volume and high specific surface area) combined with the inherent properties of graphene can fully broaden the ion channel and then improve the performance of the supercapacitor. Here a general and scalable synthesis method to prepare three-dimensional integrate electrode of porous graphene hydrogel (pGH) has been developed using Na2MoO4 as pore-making agent by a hydrothermal synthesis reaction. The as-prepared porous graphene hydrogel can be used as an electrode with a gravimetric capacitance of 473 F g−1, nearly three times that of the hydrogel electrode without puncturing pores, contributes to its highly specific area and ion channels. In addition, the nanocomposite of MoO3/GH can also works as positive electrode while the MoO3 nanoparticles produced during the hydrothermal process is an ideal material for pseudo-capacitance. At the same time, the sodium molybdate is added into the acidic electrolyte to interact with hydrogen ions to produce the pseudo-capacitance either. Then, an asymmetric supercapacitor (pGH||MoO3/GH) was fabricated by using pGH as negative electrode while MoO3/GH as positive electrode, and the maximum energy density is 40.34 W h kg−1 at a current density of 1 A g−1 while the power density is 565.13 W kg−1.