Electrochemical Activity of Graphene Based Electrodes for Redox Flow Battery Applications

The increase in global energy demand forces us to find solutions for energy storage that can provide power at the terawatt scale. Redox flow batteries (RFBs) have many attractive features for grid scale energy storage including the decoupling in design of energy and power, modular scalability, and the potential for lower cost. Introducing nanostructured materials into RFB applications has shown better performance compared with the conventional RFBs (1-6). In particular, carbon-based hybrid materials have shown better performance in flow battery systems (7-9).

Possibilities to modify and fabricate graphene based electrodes will be studied in detail. The electrochemical activity will be studied using single and static cell RFB measurements to determine the advantage of using these modified electrodes. Fabrication of the electrode materials will be based on optimized design of nanostructured materials and electrode design through a simplified two-dimensional model that describes the kinetics on the electrode surface. All these materials will be studied using an aqueous system and possibly extended to non-aqueous system.

Redox chemistry and detailed electrochemical kinetic studies will be performed to understand the performance of these nanomaterials for RFB applications. The charge, discharge characteristic will be studied using static cell (batch reactor) experiments. The evaluation of these factors, as well as that of the long-term stability of these materials in the solution will be analyzed for the prototype flow cell applications.

The static cell operations are inherently transient. While these cells are easy to fabricate in the lab and are very efficient to test electrode properties, they suffer from the continuously changing environment during the cell operation, which makes it difficult to quantify the effects of individual factors. In addition, side reactions (evolution of hydrogen and oxygen (10) and corrosion at the surface of electrodes) make the analysis more challenging. A detailed model, based on previous work by Shah et al. (11), Khehr et al.(12) and Boovaragavan et al.(13), considering diffusion, kinetics and corrosion will be developed to understand the electrode surface kinetics.

Acknowledgements

The authors are thankful for the financial support by SunEdison, St. Peters, Missouri, USA and American Chemical Society (ACS-PRF). In addition, T.S. acknowledges Fondazione Oronzio e Niccolò De Nora Fellowship in Applied Electrochemistry (2013).

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