Aqueous redox flow battery using iron 2,2‐bis(hydroxymethyl)‐2,2′,2′‐nitrilotriethanol complex and ferrocyanide as newly developed redox couple

Abstract

Summary An all‐iron aqueous redox flow battery using iron (Fe) 2,2‐bis(hydroxymethyl)‐2,2′,2′‐nitrilotriethanol (BIS‐TRIS) complex (Fe(BIS‐TRIS)) and Ferrocyanide (Fe[CN]6) as redox couple is newly suggested. The redox potential of Fe(BIS‐TRIS) is −1.11 V (vs Ag/AgCl) and this makes Fe(BIS‐TRIS) appropriate as active material for anolyte, while Fe(CN)6 is proper for catholyte due to its excellent redox reactivity, redox potential, and cheap cost. According to quantitative evaluations, Fe(BIS‐TRIS) does not produce any side reactions and is more stable than Fe triethanolamine (TEA) (Fe(TEA)) complex that is conventionally considered for the purpose. This fact is confirmed by computational analysis using density functional theory. In the calculation, energy barrier of Fe(BIS‐TRIS) suppressing the occurrence of undesirable side reactions is higher than that of other Fe‐ligand complexes, indicating that desirable redox reaction of Fe(BIS‐TRIS) occurs more stably. In redox flow battery (RFB) tests, RFBs using Fe(BIS‐TRIS) do not show any side reactions even after 250 cycles with excellent performances, such as capacity of 11.7 Ah L−1 and coulombic efficiency and capacity retention rate of 99.8 and 99.9%, respectively. This corroborates that RFBs using Fe(BIS‐TRIS) have excellency in both performance and stability, while the cheap cost of BIS‐TRIS and Fe(CN)6 enhances the economic benefit of RFBs.

Density Functional Theory‐Based Protocol to Calculate the Redox Potentials of First‐row Transition Metal Complexes for Aqueous Redox Targeting Flow Batteries

“…The redox potentials of trigonal bipyramidal iron(III) complexes with triethanolamine derivatives (triethanolamine (TEA), trisopropanolamine (TIPA), 3‐[bis (2‐hydroxyethyl) amino]‐2‐hydroxypropanesulfonic acid (DIPSO), and BIS‐TRIS, Figure 2), and of iron(III) complexes with straight chain acidic ligands (lactic acid and glycolic acid) found in the redox‐flow literature were also calculated [14,46–49] . As with the rest, the accuracy increases going from B3LYP, to M06‐2X and finally by using the COSMO‐RS solvation model, but the errors remain higher for the trigonal bipyramidal complexes than for the other groups.…”

“…[41] The hydroxyl groups of BIS-TRIS are reported to have high pK a , [57] and are similarly considered protonated by Shin et al in their study on an all iron RFB using iron BIS-TRIS and ferrocyanide. [46] The functional groups of DcBpy were considered deprotonated when complexed. The experimental reduction potential for the iron DcBpy complex is taken from the work of Li et al on aqueous redox flow batteries with neutral-toalkaline pH, [42] who also considered the carboxyl groups to be deprotonated.…”

Development of flow battery technologies using the principles of sustainable chemistry

“…Subsequently, all-liquid IFBs with iron complexes as redox species are widely studied. [63][64][65] The stable hexa-coordinate structure of the irongluconate complex enabled a battery with a high CE of 99% and EE of 83% at 80 mA cm À2 over 950 cycles and long duration energy storage (12,16 and 20 h per cycle) (Fig. 6c).…”

Vanadium Redox Flow Battery Using Activated Carbon Catalyst Produced from Low‐Density Polyethylene

“…Furthermore, RFBs are very safe devices when they are operated with aqueous electrolytes, while they can control the capacity sector and power sector independently [8–11] . Because of these advantages, RFBs can be considered as battery solution for large‐scale energy storage systems [12–16] …”

“…[8][9][10][11] Because of these advantages, RFBs can be considered as battery solution for large-scale energy storage systems. [12][13][14][15][16] Among various types of RFBs, vanadium redox flow batteries (VRFBs) have received deep attention because they use only four vanadium ions as active material (VO 2 + , VO 2 + , V 2 + and V 3 + ). In particular, cathode of VRFB uses redox reaction of VO 2 + /VO 2 + ions, while anode uses redox reaction of V 2 + /V 3 + ions.…”