Operando Spectroelectrochemical Characterization of a Highly Stable Bioinspired Redox Flow Battery Active Material

Durable and efficient energy storage is a critical aspect of modern electrical grids, especially those comprising energy from intermittent and renewable sources. Non-aqueous redox flow batteries (NRFB) are a promising technology to meet this growing need, with the potential to greatly exceed the energy density of their aqueous counterparts while maintaining key advantages over Li-ion batteries. These advantages include decoupled power and energy ratings, thermal stability and the capability of long-duration storage. Notwithstanding these promising attributes, the development of NRFB has been severely hampered by chemical instability of active materials charged and/or discharged states. Herein we demonstrate the excellent electrochemical stability of a recently reported NRFB active material, vanadium(iv/v)bis-hydroxyiminodiacetate (VBH) using operando spectroscopic measurements. This technique shows tight coupling between changes in the concentrations of the vanadium(iv) and vanadium(v) ions and the applied current. This direct measurement of electrochemical stability is widely available, and its routine use to characterize potential redox active species during cycling, verifying a clean transition between redox states, would be of great value to the NRFB community. Further, we report a method of large-scale preparation of VBH that makes use of inexpensive chemical feedstocks, overcoming another important obstacle to its implantation in an NRFB system.