Computing Free Energy Landscapes: Application to Ni-based Electrocatalysts with Pendant Amines for H₂ Production and Oxidation

A general strategy is reported for the computational exploration of catalytic pathways of molecular catalysts. Our results are based on a set of linear free energy relationships derived from extensive electronic structure calculations that permit predicting the thermodynamics of intermediates, with accuracy comparable to experimental data. The approach is exemplified with the catalytic oxidation and production of H2 by [Ni(diphosphine)2]2+ electrocatalysts with pendant amines incorporated in the second coordination sphere of the metal center. The analysis focuses upon prediction of thermodynamic properties including reduction potentials, hydride donor abilities, and pKa values of both the protonated Ni center and the pendant amine. It is shown that all of these chemical properties can be estimated from the knowledge of only the two redox potentials for the Ni(II)/Ni(I) and Ni(I)/Ni(0) couples of the nonprotonated complex, and the pKa of the parent primary aminium ion. These three quantities are easily acc...