Organic molecules are currently investigated as redox species for aqueous low-cost redox flow batteries (RFBs). The envisioned features of using organic redox species are low cost and increased flexibility with respect to tailoring redox potential and solubility from molecular engineering of side groups on the organic redox-active species. In this paper 33, mainly quinone-based, compounds are studied experimentially in terms of pH dependent redox potential, solubility and stability, combined with single cell battery RFB tests on selected redox pairs. Data shows that both the solubility and redox potential are determined by the position of the side groups and only to a small extent by the number of side groups. Additionally, the chemical stability and possible degradation mechanisms leading to capacity loss over time are discussed. The main challenge for the development of all-organic RFBs is to identify a redox pair for the positive side with sufficiently high stability and redox potential that enables battery cell potentials above 1 V.

A semi-organic, differential pH flow battery with increased cell voltage shows stable operation for at least 30 days.

Solar redox flow batteries have attracted attention as a possible integrated technology for simultaneous conversion and storage of solar energy.

We report relations between nitrogen-binding-energy descriptors obtained from experimental thermochemical data and limiting potentials from density functional theory data. We use the relations to build the largest volcano plot for nitrogen reduction reaction (NRR). We found that (1) Mn, Ga, and In are overlooked catalysts and (2) there are unidentified materials on the top of the volcano. Using experimental exchange current densities of hydrogen evolution reaction (HER) and Pourbaix diagrams we have identified conditions at which Mn, Ga, and In remain stable in water and selectively catalyze NRR over HER. We found that Fe, Au, Cu, Bi, and Pd, on contrary to what was reported earlier, need smaller applied potentials to start the onset of HER than NRR in water. We make a critical discussion about them and other candidates and we believe our results can be used to identify false positive measurements in the research field.