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

• Published in: Chemistry : a European journal Vol. 29; no. 26; pp. e202203590 - n/a
• Main Authors: Ončák, Milan, Siu, Chi‐Kit, Linde, Christian, Kit Tang, Wai, Beyer, Martin K.
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 08.05.2023; John Wiley and Sons Inc
• 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; hydrated metal ions; mass spectrometry; hydrogen evolution; photochemistry; spectroscopy
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202203590

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.