A higher voltage Fe(ii) bipyridine complex for non-aqueous redox flow batteries. Issue 3 (21st December 2020) - Cammack, Claudina X.
Abstract : A new family of tunable iron bipyridine coordination complexes has been synthesized and tested in a non-aqueous flow battery. Abstract : Non-aqueous redox flow batteries (RFBs) offer the possibility of higher voltage and a wider working temperature range than their aqueous counterpart. Here, we optimize the established 2.26 V Fe(bpy)3 (BF4 )2 /Ni(bpy)3 (BF4 )2 asymmetric RFB to lessen capacity fade and improve energy efficiency over 20 cycles. We also prepared a family of substituted Fe(bpyR)3 (BF4 )2 complexes (R = –CF3, –CO2 Me, –Br, –H, – t Bu, –Me, –OMe, –NH2 ) to potentially achieve a higher voltage RFB by systematically tuning the redox potential of Fe(bpyR)3 (BF4 )2, from 0.94 V vs. Ag/AgCl for R = OMe to 1.65 V vs. Ag/AgCl for R = CF3 (Δ V = 0.7 V). A series of electronically diverse symmetric and asymmetric RFBs were compared and contrasted to study electroactive species stability and efficiency, in which the unsubstituted Fe(bpy)3 (BF4 )2 exhibited the highest stability as a catholyte in both symmetric and asymmetric cells with voltage and coulombic efficiencies of 94.0% and 96.5%, and 90.7% and 80.7%, respectively.