Homolytic versus Heterolytic Hydrogen Evolution Reaction Steered by a Steric Effect

Guo, X. and Wang, N. and Li, X. and Zhang, Z. and Zhao, J. and Ren, W. and Ding, S. and Xu, G. and Li, J. and Apfel, U.-P. and Zhang, W. and Cao, R.

Volume: 59 Pages: 8941-8946
DOI: 10.1002/anie.202002311
Published: 2020

Several H−H bond forming pathways have been proposed for the hydrogen evolution reaction (HER). Revealing these HER mechanisms is of fundamental importance for the rational design of catalysts and is also extremely challenging. Now, an unparalleled example of switching between homolytic and heterolytic HER mechanisms is reported. Three nickel(II) porphyrins were designed and synthesized with distinct steric effects by introducing bulky amido moieties to ortho- or para-positions of the meso-phenyl groups. These porphyrins exhibited different catalytic HER behaviors. For these Ni porphyrins, although their 1e-reduced forms are active to reduce trifluoroacetic acid, the resulting Ni hydrides (depending on the steric effects of porphyrin rings) have different pathways to make H2. Understanding HER processes, especially controllable switching between homolytic and heterolytic H−H bond formation pathways through molecular engineering, is unprecedented in electrocatalysis. © 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

« back