PNNL

The rational design of improved catalysts requires a detailed molecular-level understanding of the energetic and mechanistic factors controlling the activity of existing catalysts. We aim to determine and predict accurately, through computations, the thermodynamic properties and proton and electron movement for catalysts developed in the Energy Frontier Research Center for Molecular Electrocatalysis, in particular the Ni(P₂N₂)₂²⁺ catalysts for H₂ oxidation and evolution. These catalysts are mononuclear nickel complexes that include cyclic diphosphine ligands with amine bases incorporated in the ligands. The presence and positioning of the amine bases near the metal center is the critical structural feature for the activity and the efficiency of these catalysts, as these bases facilitate the heterolytic cleavage or formation of the H-H bond while acting as proton relays in the management of the proton and electron movement during the catalytic cycle. 

In this paper, we benchmarked a number of commonly used density functional theory (DFT) and electron-correlated molecular orbital theories in their ability to describe the free energy profile for H₂ oxidation/evolution, i.e., the formation of an H₂ adduct complex, of proton-hydride and di-proton intermediates, and the transition states between them. We found that DFT functionals B3P86, M06, and PBE show good accord with CCSD(T) calculations, while other widely used functional do not perform nearly as well.