Highly Tunable and Ordered Graphene-Oxide-Based Materials for Energy Applications

Carbon materials are an integral part of devices including fuel cells, super-capacitors, and batteries. Current technologies are marred with issues such as long-term durability under high potentials (e.g., fuel cells), low energy/power density (super capacitors), and metal intercalation issues (batteries). State-of-the-art devices have typically been synthesized from highly heterogeneous precursors and amorphous carbon materials. Materials based on graphene and graphene-oxide (GO) are more homogeneous and possess properties, such as good chemical stability, excellent conductivity, and more importantly, can be functionalized in a controlled manner. These unique properties have led to explosion in research in areas of graphitic materials as catalyst support/material for oxygen reduction reaction (ORR) and high energy density thin film super capacitors.

In this study, we report the synthesis of highly structured GO based materials prepared using Hummers method. We specifically target the control of functional groups and d-spacing of GO materials using drying and solvent treatments. XPS, FTIR and XRD studies were used to unravel the structure-function correlation of the resulting materials. The synthesized graphene oxide structures were further subjected to reduction and doping in different conditions to obtain an optimum energy storage/support material. Although most reduced materials possess similar structural properties, they have a variable electrochemical performance and stability. In this study we obtain a fundamental understanding of the effect of pre-treatment on the structure and function of reduced materials.

We specifically study these materials for oxygen reduction reaction and super capacitors. In a 0.5 M H₂SO₄ electrolyte, a shift in half wave potential and decrease in peroxide production is obtained depending upon the graphene oxide treatment. These catalyst materials perform well in an alkaline electrolyte as well. These catalyst systems are highly durable and a drop of less than 30 mV drop was obtained over 2000 cycles in acid electrolyte in presence of oxygen indicating the role of high graphitic content in providing stability. Furthermore, we identify that the pyridinic nitrogen content is important for high electrochemical activity. We also demonstrate high power density super capacitors obtained using similar pretreatments. 

Acknowledgment

Financial support from the Los Alamos National Laboratory Laboratory-Directed Research and Development (LDRD) Program is gratefully acknowledged.