A Computational Protocol Combining DFT and Cheminformatics for Prediction of pH-Dependent Redox Potentials

Abstract

Discovering new materials for energy storage requires reliable and efficient protocols for predicting key properties of unknown compounds. In the context of the search for new organic electrolytes for redox flow batteries, we present and validate a robust procedure to calculate the redox potentials of organic molecules at any pH value, using widely available quantum chemistry and cheminformatics methods. Using a consistent experimental data set for validation, we explore and compare a few different methods for calculating reaction free energies, the treatment of solvation, and the effect of pH on redox potentials. We find that the B3LYP hybrid functional with the COSMO solvation method, in conjunction with thermal contributions evaluated from BLYP gas-phase harmonic frequencies, yields a good prediction of pH = 0 redox potentials at a moderate computational cost. To predict how the potentials are affected by pH, we propose an improved version of the Alberty-Legendre transform that allows the construction of a more realistic Pourbaix diagram by taking into account how the protonation state changes with pH.

Computation of Oxidation Potentials of Solvated Nucleobases by Static and Dynamic Multilayer Approaches

“…Typically, reduction potentials are given with respect to a reference potential. A common choice as reference is the standard hydrogen electrode (SHE), whose reduction potential is E red,SHE 0 = 4.281 V, used in previous works. − Although this value is a common choice when COSMO is employed to describe solvent effects, it is not clear which value is consistent with this solvent model . It is important to highlight here that the value of 4.281 V of the SHE was obtained using the Fermi–Dirac statistics to account for the free energy of the electron, whose value is −0.867 kcal/mol. − Therefore, it is necessary to cancel this electron contribution by explicitly including the free energy of the electron in the computation of the reaction free energy for the half reaction under investigation, for example, through eq .…”

Bridging the Experiment-Calculation Divide: Machine Learning Corrections to Redox Potential Calculations in Implicit and Explicit Solvent Models

“…5 In addition to the solvent, pH is also a critical environment parameter impacting redox potential because the one-electron reduction of some species (e.g., amines and phenols) also involves changes in the protonation state. A recent work by de Silva and co-workers 79 proposed a protocol combining chemical informatics and quantum chemistry to calculate the pH-dependent redox potential. The workflow first determines the most favorable protonation state at pH = 0 based on the SMILE string and then searches for the most stable conformer at the MM level.…”

Degradation of quinone-based flow battery electrolytes: Effect of functional groups on the reaction mechanism

“…The redox potential of quinones calculated with B3LYP funtional and implicit solvation model was shown to provide the best fit to experimental values. 25 For the acid-catalyzed pathway, we used the def2-TZVP basis set. 26 For the base-catalyzed pathway, we first optimized the geometries with B3LYP/def2-TZVP method and afterwards, single-point energy calculation was performed in solvent medium with B3LYP/def2-TZVPD 27 method to account for the negative charges.…”

“…The method to compute the redox potential is described in a previous publication. 25 To calculate the reduction potential, we assumed that the SO 3 H groups of the quinones remain fully protonated in both acid and base medium to avoid unwanted error originating from the energy calculation from negatively charged molecules.…”