Aqueous redox flow batteries with organic active materials offer an
environmentally benign, tunable, and safe route to large-scale energy
storage. Development has been limited to a small palette of organics that
are aqueous soluble and tend to display the necessary redox reversibility
within the water stability window. We show how molecular engineering of
fluorenone enables the alcohol electro-oxidation needed for reversible
ketone hydrogenation and dehydrogenation at room temperature without the use
of a catalyst. Flow batteries based on these fluorenone derivative anolytes
operate efficiently and exhibit stable long-term cycling at ambient and
mildly increased temperatures in a nondemanding environment. These results
expand the palette to include reversible ketone to alcohol conversion but
also suggest the potential for identifying other atypical organic redox
couple candidates.