Homolytic versus Heterolytic Hydrogen Evolution Reaction Steered by a Steric Effect
Xiaojun Guo, Ni Wang, Xialiang Li, Zongyao Zhang, Jianping Zhao, Wanjie Ren, Shuping Ding, Gelun Xu, Jianfeng Li, Ulf‐Peter Apfel, Wei Zhang, Rui Cao
Abstract
Abstract 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 H 2 . Understanding HER processes, especially controllable switching between homolytic and heterolytic H−H bond formation pathways through molecular engineering, is unprecedented in electrocatalysis.