Thermally Activated vs. Photochemical Hydrogen Evolution Reactions–A Tale of Three Metals

Molecular processes behind hydrogen evolution reactions can be quite complex. In macroscopic electrochemical cells, it is extremely difficult to elucidate and understand their mechanism. Gas phase models, consisting of a metal ion and a small number of water molecules, provide unique opportunities t...

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Bibliographic Details
Published in:Chemistry : a European journal 2023-05, Vol.29 (26), p.e202203590-n/a
Main Authors: Ončák, Milan, Siu, Chi‐Kit, Linde, Christian, Kit Tang, Wai, Beyer, Martin K.
Format: Article
Language:English
Subjects:
Aluminum
Body temperature
Chemistry
Clusters
Concept
Concepts
Electrochemical cells
Electrochemistry
Evolution
Heavy metals
hydrated metal ions
Hydrogen
hydrogen evolution
Hydrogen evolution reactions
Irradiation
Magnesium
mass spectrometry
Metal ions
Nickel
Photochemical reactions
Photochemicals
photochemistry
Potential energy
Reaction mechanisms
Room temperature
spectroscopy
Ultraviolet radiation
Vanadium
Vapor phases
Water chemistry
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Summary:Molecular processes behind hydrogen evolution reactions can be quite complex. In macroscopic electrochemical cells, it is extremely difficult to elucidate and understand their mechanism. Gas phase models, consisting of a metal ion and a small number of water molecules, provide unique opportunities to understand the reaction pathways in great detail. Hydrogen evolution in clusters consisting of a singly charged metal ion and one to on the order of 50 water molecules has been studied extensively for magnesium, aluminum and vanadium. Such clusters with around 10–20 water molecules are known to eliminate atomic or molecular hydrogen upon mild activation by room temperature black‐body radiation. Irradiation with ultraviolet light, by contrast, enables hydrogen evolution already with a single water molecule. Here, we analyze and compare the reaction mechanisms for hydrogen evolution on the ground state as well as excited state potential energy surfaces. Five distinct mechanisms for evolution of atomic or molecular hydrogen are identified and characterized. All roads lead to hydrogen. an in‐depth analysis and comparison of hydrogen evolution reactions in gas phase model systems reveal five distinct mechanistic routes to form either atomic or molecular hydrogen.
ISSN:0947-6539
1521-3765
DOI:10.1002/chem.202203590