Approach to the Mechanism of Hydrogen Evolution Electrocatalyzed by a Model Co Clathrochelate: A Theoretical Study by Density Functional Theory

• Published in: Chemphyschem 2018-10, Vol.19 (19), p.2549-2558
• Main Authors: Antuch, Manuel, Millet, Pierre
• Format: Article
• Language: English
• Subjects: Activation; Cages; Catalysis; Catalytic activity; clathrochelate; Clean energy; Cobalt; Coordination compounds; density functional calculations; Density functional theory; electrocatalysis; Electron transfer; hydrogen evolution reaction; Hydrogen evolution reactions; Ligands; Oxidation; Platinum; Protonation; reaction mechanisms; Renewable energy sources; Transition metals; Valence
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.201800383

The hydrogen evolution reaction (HER) has attracted much attention within the scientific community because of increasing demands of modern society for clean and renewable energy sources. Molecular complexes of 3d‐transition metals, such as cobalt, hold potential to replace platinum for the HER in acidic media. Among these, cage complexes such as tris‐glyoximate metal clathrochelates, have demonstrated promising catalytic properties towards the HER. However, it is not clear whether the catalytic activity of this molecule stems from metal‐centered activation of H+, due to a low oxidation state of the metal stabilized by the surrounding organic cage, or if it is the organic cage playing a further cooperative role in bringing protons together. Herein, we report on a density functional theory study of two possible mechanisms for the HER catalyzed by a model Co clathrochelate. To assess the putative ligand involvement in the mechanism, several combinations of single and double protonation sites were investigated. The structural and energetic analysis of relevant intermediates suggests that the electrocatalytic mechanism is not based on the cooperation between the ligand and the metal. Instead, it is mainly due to the activation of H+ by the Co metallocenter. Our calculations further suggest that the last step in the mechanism is a proton coupled electron transfer step. Which mechanism? We present a density functional theory study of two possible mechanisms for the HER catalyzed by a model Co clathrochelate. Several protonation sites located in the organic cage and in the metal, along with several combinations of double protonation, were investigated.