Nickel-Containing Keggin-Type Polyoxometalates as Hydrogen Evolution Catalysts: Photochemical Structure-Activity Relationships

• Published in: ChemPlusChem (Weinheim, Germany) Vol. 80; no. 9; pp. 1389 - 1398
• Main Authors: von Allmen, Kim, Moré, René, Müller, Rafael, Soriano-López, Joaquín, Linden, Anthony, Patzke, Greta R.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01.09.2015; WILEY‐VCH Verlag; Blackwell Publishing Ltd
• Subjects: Catalysis; Chemistry; electrochemistry; Electrodes; Influence; Investigations; Light; Nickel; photochemistry; polyoxometalates; structure-activity relationships; nickel; electrochemistry; structure-activity relationships; photochemistry; polyoxometalates
• ISSN: 2192-6506; 2192-6506
• DOI: 10.1002/cplu.201500074

In search of structure–activity relationships for polyoxometalate (POM)‐based water reduction catalysts, nickel‐monosubstituted Keggin‐type POMs ([Ni(H2O)XW11O39]n−; XP, Si, Ge) were compared with respect to their activity in photochemical hydrogen evolution. The title compound series was characterized by single‐crystal X‐ray diffraction methods and a wide range of spectroscopic and electrochemical techniques. Nickel substitution was identified as a crucial feature for catalytic activity through comparison with nickel‐free reference POMs. Furthermore, turnover number (TON) and turnover frequency strongly depended on the heteroatom X, and the highest TON among the series was recorded for [Ni(H2O)GeW11O39]6−. Photochemical hydrogen evolution activity was compared with redox and onset potentials obtained from electrochemical analyses. Furthermore, activity trends were correlated with electronic structure properties derived from density functional theory calculations. Nickel for your POMs: A series of Keggin‐type polyoxometalates (POMs; [Ni(OH2)XW11O39]n− (X=P, Si, Ge) were tested for catalytic activity in visible‐light‐driven hydrogen evolution without co‐catalysts. The photocatalytic activity of the nickel POMs can be tuned through heteroatom X. The highest turnover number among the series was found for the germanium‐containing POM (see figure).