Figure 8. Representation of the humic acid molecule (blue box: oxidisable hydroxy groups; pink box: ketone groups) and the reaction scheme of the humic acid / humic acid battery

From

Organic (Redox-Flow-)Batteries Using Compounds out of Bark and Peat as well as Humic Acids

Dominique Rosenberg, Katharina Dick, Steffen Gudenschwager, Maike Busker, Walter Jansen

World Journal of Chemical Education. 2019, 7(2), 145-152 doi:10.12691/wjce-7-2-14