Water Processable Energy Storage Hybrid Materials Using Graphene Oxide as Dispersing Agent

Bulk quantities of chemically modified graphene can be obtained by first chemically exfoliating graphite powders, followed by reducing of the graphite oxide or graphene oxide (GO) product. Due to its electrical conductivity and high surface area, chemically modified graphene (a.k.a., reduced GO, r-GO) has attracted significant interest as electrode materials for electrochemical applications such as sensors, fuel cells and ultracapacitors. While the two-dimensional (2D) shape of graphene is desirable for many of its applications, it can limit their potential to be fully realized in electrochemical devices. For example, 2D sheets can easily stack to form lamellar microstructures parallel to the current collectors, especially when compressed during electrode preparation. This could affect the device performance adversely in two ways: The effective surface area of the electrodes can be reduced due to aggregation of graphene sheets. The horizontal alignment of the graphene stacks can hinder electron and ion transport since both of them prefer the direction perpendicular to the current collector. Vertically aligned graphene sheets directly grown on current collector have been reported, and indeed showed outstanding ultracapacitor performance. However, the amount of graphene grown on the current collector is very small, which leads to low overall device capacity. Since chemically modified graphene can be made in bulk quantities, if one can avoid creating extensive lamellar structures in the bulk materials, we can maintain device performance as more material is used. Graphene sheets with different morphologies can act in different roles in ultracapacitor to maximized device performance. For example, heavily deformed sheets should be good as the active phase. Flat sheets should be good as the current collector and binder. Combining them together rationally could lead to all-graphene ultracapacitors with improved performance without using conventional binders or current colle