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

Abstract

Transition metal complexes are a promising class of redox mediators for targeting redox flow batteries due to the tunability of their electrochemical potentials. However, reliable time-efficient tools for the prediction of their reduction potentials are needed. In this work, we establish a suitable density functional theory protocol for their prediction using an initial experimental data set of aqueous iron complexes with bidentate ligands. The approach is then cross-validated using different complexes found in the redox-flow literature. We find that the solvation model affects the prediction accuracy more than the functional or basis set. The smallest errors are obtained using the COSMO-RS solvation model (mean average error (MAE) = 0.24 V). With implicit solvation models, a general deviation from experimental results is observed. For a set of similar ligands, they can be corrected using simple linear regression (MAE = 0.051 V for the initial set of iron complexes).

Experimental and Theoretical Investigation of the Mechanism of the Reduction of O2 from Air to O22– by VIVO2+–N,N,N-Amidate Compounds and Their Potential Use in Fuel Cells

“…Theoretical calculations confirm the above oxidation reactions. E 0 has been calculated by theory to be 1.756 V vs NHE in light with the respective experimentally derived E 0 being 1.63 V. The CVs of 1 ·H 2 O in solution (CH 3 CN) at various scan rates (Figure S17) show, at high scan rates, the appearance of two new cathodic peaks at ∼1.04 and −0.05 V, associated with the peak at 1.63 V, and were assigned to the one-electron reductions of [V V O­(η 2 -O 2 )­(κ 3 -pbq)­(H 2 O)] 2+ to [V V (O)­(η 2 -O 2 )­(κ 3 -pbq)­(H 2 O)] · + and of [V V (O)­(η 2 -O 2 )­(κ 3 -pbq)­(H 2 O)] ·+ to [V V (O)­(η 2 -O 2 )­(κ 3 -pbq)­(H 2 O)], respectively.…”

“…Theoretical calculations confirm the above oxidation reactions. E 0 has been calculated by theory to be 1.756 V vs NHE 91 in light with the respective experimentally derived E 0 being 1.63 V. The CVs of 1 ·H 2 O in solution (CH 3 CN) at various scan rates ( Figure S17 ) show, at high scan rates, the appearance of two new cathodic peaks at ∼1.04 and −0.05 V, associated with the peak at 1.63 V, and were assigned to the one-electron reductions of [V V O(η 2 -O 2 )(κ 3 -pbq)(H 2 O)] 2+ to [V V (=O)(η 2 -O 2 )(κ 3 -pbq)(H 2 O)] · + and of [V V (=O)(η 2 -O 2 )(κ 3 -pbq)(H 2 O)] ·+ to [V V (=O)(η 2 -O 2 )(κ 3 -pbq)(H 2 O)], respectively.…”

Beyond conventional batteries: a review on semi-solid and redox targeting flow batteries-LiFePO4 as a case study

“…DFT has demonstrated its efficacy in high-throughput screening of organic molecules for RFBs, achieving accuracies around 70 mV for calculated redox potentials. 152,200–203 Furthermore, the evolving landscape incorporates Machine Learning (ML) tools, which are gaining traction for similar applications. It's noteworthy that the diverse range of organic compounds results in various electronic structures, affinities, chemical bonding types, and molecular energy levels.…”

“…141,142 Several lithium insertion materials have been tested as catholyte and anolyte for targeting RFB such as LFP, NaV 2 (PO 4 ) 3 , TiO 2 , etc. 143–152…”