Optimized Graphene Hydrogels for Electrochemical Applications from High-Concentration GO/Gnp Dispersions

Abstract

As the world combats climate change, energy storage solutions will be required to bridge the gap between the supply and demand of renewable energy sources. Supercapacitors have a higher power density and cyclic stability than batteries, making them more useful for selected applications. These devices utilize high surface area electrode materials, such as graphene, with enough active sites for sufficient ion adsorption to occur. Graphene hydrogels self-assemble via the hydrothermal reduction of graphene oxide (GO) dispersions. These three-dimensional structures have high specific surface areas while avoiding the use of binders. Binders usually negatively impact the conductivity of the material and require the use of conductive additives which lower specific performance data. As such, graphene hydrogels are attractive as a supercapacitor electrode material.Recently, graphene nanoplatelet (GNP) dispersions stabilized by small amounts of GO were used to form more cost-effective and better-performing hydrogels. Though GO/GNP hydrogels are a suitable alternative to those formed from dispersions of GO, the formulation of this material has yet to be optimized. In this work, we investigate the formation of GO/GNP hydrogels by assessing the influence of several input parameters on the specific surface area and mechanical stability of the hydrogel structure. A set of experiments based on a design of experiments is used. Based on the results, an optimized hydrogel is formed and characterized. Compared to typical hydrogels formed from dispersions of GO, the optimized GO/GNP hydrogel leads to significant improvements in both the specific surface area and conductivity of the material. When used in a supercapacitor, low internal resistance and high stability are observed while volumetric capacitance is increased by up to over 400%.