Electronegativity principle for hydrogen evolution activity using first-principles calculations

Abstract

The catalytic activity of a heterogeneous catalyst is routinely described by the Sabatier principle using molecule/proton adsorption energy ΔG_H as the thermodynamic descriptor. This descriptor, however, fails in quantitatively tracking the reaction rate due to the lack of charge transfer information during a reaction. Herein, we use density functional theory (DFT) calculations combining both canonical and grand-canonical ensembles to report a positive correlation between reaction kinetics and interfacial charge transfer for the hydrogen evolution reaction (HER). The Sabatier relationship for the HER catalysts exhibits a large dispersion in the canonical calculation but an improved linearity under the grand-canonical ensemble, indicating that surface charges are indeed important. This charge effect can be well captured by the Mulliken electronegativity χ of a catalyst because the reaction barrier shows a linear dependence on χ for a wide range of catalysts. Specifically, a catalyst with lower electronegativity exhibits a lower barrier and thus a faster reaction rate. This electronegativity principle is reaction route and pH independent and is founded on the thermoneutral requirement on ΔG_H.