Strong, Conductive, Foldable Graphene Sheets by Sequential Ionic and pi Bridging

The goal of this work is to develop an inexpensive low-temperature process that provides polymer-free, high-strength, high-toughness, electrically conducting sheets of reduced graphene oxide (rGO). To develop this process, we have evaluated the mechanical and electrical properties resulting from the application of an ionic bonding agent (Cr3+), a pi-pi bonding agent comprising pyrene end groups, and their combinations for enhancing the performance of rGO sheets. When only one bonding agent was used, the pi-pi bonding agent is much more effective than the ionic bonding agent for improving both the mechanical and electrical properties of rGO sheets. However, the successive application of ionic bonding and pi-pi bonding agents maximizes tensile strength, toughness, long-term electrical stability in various corrosive solutions, and resistance to mechanical abuse and ultrasonic dissolution. Using a combination of ionic bonding and pi-pi bonding agents, high tensile strength (821 MPa), high toughness (20 MJ m(-3)), and electrical conductivity (416 S cm(-1)) were obtained, as well as remarkable retention of mechanical and electrical properties during ultrasonication and mechanical cycling by both sheet stretch and sheet folding, suggesting high potential for applications in aerospace and flexible electronics.