Electrochemical Evaluation of Chromium Mixtures With N,O‐Containing Ligands for Iron–Chromium Flow Batteries

In this work, a series of chromium mixtures with N,O‐containing ligands were evaluated as candidate negolytes for iron–chromium flow batteries. Six systems were investigated, including three prepared with a single ligand and three prepared with pairs of chemically distinct ligands. The structurally characterized mixture‐1 was used as the reference, whereas the exact chromium coordination structures of mixtures 2–6 were not established. UV–vis spectroscopy was used to estimate the dissolved chromium concentrations of the studied mixtures in 1 M KCl. The results show that combining chemically distinct ligands increases dissolved chromium concentration, reaching up to approximately 150 mM compared with 13.5 mM for mixture 1. Cyclic voltammetry revealed that five electrochemically evaluated mixtures displayed quasireversible redox behavior, whereas one mixture did not show any clear redox activity. However, flow‐cell cycling of these electroactive mixtures at a nominal concentration of 10 mM revealed limited capacity utilization and substantial capacity fading. These results show that increasing the dissolved chromium concentration alone does not ensure improved electrochemical accessibility or stable flow‐cell cycling. Further optimization and solution‐speciation studies are required to improve cycling stability and identify the chromium species responsible for the observed electrochemical behavior.