Energy storage systems for commodity scale storage (e.g., grid integration of renewables and/or load management) requires batteries with lifetimes in the order of twenty years even when undergoing multiple deep discharge cycles each day.  Of the current practical electrochemical energy storage systems, flow cell and hybrid batteries have been suggested as excellent options.  For these systems, while the lifetime effects on electrolyte and balance of plant are well understood, little has been published in the open literature on the changes to electrodes surfaces in these strongly oxidizing environments.  For this reason we have undertaken the characterization of the evolution of electrochemical parameters for graphitic surfaces using the bromide side of a zinc bromine flow cell as an example environment. By measuring the changes in the exchange current density and charge transfer coefficients of Tafel scans of the material as it ages we characterized the system's evolution. By using a home built multi-galvanostat we collected aging data on pure graphite rods, to separate the effects of potential matrix degradation, with the rapid degradation of the exchange current density to about 20% of the original over the course of 100 Ah.cm-2 bromide oxidation at the electrode .  Similar scans carried out on graphite electrodes treated by partial oxidation with aqueous HF/K2MnF6 followed by immersion in a second aqueous solution containing a C6F5SO3- salts led to less than 4% decrease in exchange current density after 190 Ah.cm-2 bromide oxidation occurred.  These results will be shared in detail in the presentation.

Graphite electrode aging in the strongly oxidizing environments in flow cell batteries

246th National Meeting (2013)

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