Expanding the potential of redox carriers for flow battery applications

Abstract

Using theoretical modeling to guide our approach, substituents were selected to improve the negative and positive potentials associated with a representative metal-based redox carrier, a phenyl spaced nickel bispicolinamide complex, [Ni(bpb)], 1. To broaden the cell potential, electron donating groups were selected and installed on the pyridyl moieties, [Ni(bpb-(NMe₂)₂)], 2, while electron withdrawing groups were incorporated on the phenyl linker, [Ni(bpb-R)] (R = –F, –CF₃, and –NO₂), 3–5. Our model predicts an increase of ∼300 mV and ∼500 mV for the first and second negative waves of Ni(bpb-NMe₂), 2, and up to ∼330 mV and ∼210 mV increase to the first and second positive waves in 3–5. The modeled complexes were synthesized in good yields using a modification of the literature procedure. Due to limited solubility, the differential pulse voltammetry was measured on complexes 2–5 using a drop cast technique. Comparison of the observed and predicted potentials is discussed in acetonitrile (MeCN) and dimethylformamide (DMF) solvents.