PNNL

Abstract

In this study, a promising metal-organic complex, Fe-NTMPA2, consisting of Fe(III) chloride and nitrilotri methylphosphonic acid (NTMPA), is designed for use in all soluble Fe redox flow batteries. A full-cell testing, where a concentrated Fe-NTMPA2 anolyte (0.67 M) was paired with a Fe-CN catholyte, demonstrates exceptional cycling stability over 1000 charge/discharge cycles, and noteworthy performances, including 96% capacity utilization, a minimal capacity fade rate of 0.0013% per cycle (1.3% over 1,000 cycles), high Coulombic efficiency (CE) energy efficiency (EE) near 100% and 87%, respectively, all achieved under a current density of 20 mA·cm?². Furthermore, density functional theory (DFT) unveils two potential coordination structures for Fe-NTMPA2 complexes, shedding light on new understandings between the ligand coordination environment and electron transfer kinetics. Additionally, when paired with a high redox potential Fe-Dcbpy/CN catholyte, Fe-NTMPA2 demonstrated a notably elevated cell voltage of 1 V, potentially enabling a practical energy density of up to 9 Wh/L.