Recent advances in Ni-based bio-inspired electrocatalysts obtained in the Center for Molecular Electrocatalysis (EFRC) at PNNL demonstrated the possibility of generating H2 or cleaving H2 heterolytically, with an efficiency that can be greater than that of the [Ni-Fe]-hydrogenase enzyme. In these catalysts the transformation between H2 and protons proceeds via the interplay between hydrogen transfer steps between the catalysts and an external base/acid mediated by pendant amine bases incorporated in a six-member ring, which act as proton relays . We present the results of a comprehensive theoretical investigation of the role of pendant amine ligands in the oxidation of H2 and formation of H2 by [Ni(P2RN2R')2]2+ electrocatalysts. By using density functional theory-based calculations and hybrid QM/MM meta-dynamics molecular dynamics simulations, we have carried out a detailed analysis of the various protonation/deprotonation steps required for both H2 oxidation and H2 production. Our study shows that the step for breaking of the H2 bond or the formation of this bond requires a relatively small activation barrier and that the required intermolecular protonation/deprotonation step are a bottleneck and may lead to inactive intermediates, whose presence is detrimental to catalysis. The ramifications of our results on the design of more effective catalysts are discussed.

Proton rearrangement through intermolecular exchange in Ni(P2CyN2Me)22+: A DFT study

243rd National Meeting (2012)

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