Redox non-innocent bis(2,6-diimine-pyridine) ligand–iron complexes as anolytes for flow battery applications

Abstract

Diiminepyridines are a well-known class of "non-innocent" ligands that confer additional redox activity to coordination complexes beyond metal-centred oxidation/reduction. Here, we demonstrate that metal coordination complexes (MCCs) of diiminepyridine (DIP) ligands with iron are suitable anolytes for redox-flow battery applications, with enhanced capacitance and stability compared with bipyridine analogs, and access to storage of up to 1.6 electron equivalents. Substitution of the ligand is shown to be a key factor in the cycling stability and performance of MCCs based on DIP ligands, opening the door to further optimization.

Diiminepyridine‐Supported Phosphorus(I) and Phosphorus(III) Complexes: Synthesis, Characterization, and Electrochemistry

“…As befits the ability to isolate both P (I) and P (III) congeners, (irreversible) oxidation of [( dipp DIP t Bu )P][BPh 4 ] is observed electrochemically at ≈ +0.4 V vs. FcH 0/+ (FcH = ferrocene; Figure ). Interestingly, the complex also shows a reversible reduction at –1.38 V. This cathodic event is consistent with ligand‐based reduction, common for diiminepyridine complexes of metals , . However, one could also postulate the reduction as forming a formally neutral P (0) complex.…”

Organic Functionalization of Polyoxovanadate–Alkoxide Clusters: Improving the Solubility of Multimetallic Charge Carriers for Nonaqueous Redox Flow Batteries

“…Such systems enable symmetric flow battery design, wherein the anolyte and catholyte are comprised of the same material, owing to the widely spaced redox couples of the metal center. In addition to this large V cell , ligand design and optimization has yielded highly soluble charge carriers capable of facilitating multielectron transfer at each electrode . Despite advances, a majority of these metal coordination complexes experience ligand dissociation during electrochemical oxidation or reduction, rendering the redox couples unstable in deep charging schematics.…”

Polyoxovanadate-alkoxide clusters as multi-electron charge carriers for symmetric non-aqueous redox flow batteries

“…While previously reported metal coordination compounds have demonstrated fundamental advances in solubility as a result of systematic derivatization of the ligand, the assembly of these organic scaffolds requires multiple-step syntheses. 13 , 24 , 39 In contrast, the POV-alkoxide clusters reported here are accessible through a one-step synthesis from earth-abundant, commercially available starting materials. The crystalline electroactive molecule can be isolated on gram-scales directly from the reaction mixture.…”