New Insights on Photocatalytic H2 Liberation from Water Using Transition-Metal Oxides: Lessons from Cluster Models of Molybdenum and Tungsten Oxides
2013
Ramabhadran, Raghunath Ozhapakkam | Mann, Jennifer E. | Waller, Sarah E. | Rothgeb, David W. | Jarrold, Caroline C. | Raghavachari, Krishnan
Molecular hydrogen (H₂) is an excellent alternative fuel. It can be produced from the abundantly present water on earth. Transition-metal oxides are widely used in the environmentally benign photocatalytic generation of H₂ from water, thus actively driving scientific research on the mechanisms for this process. In this study, we investigate the chemical reactions of W₃O₅– and Mo₃O₅– clusters with water that shed light on a variety of key factors central to H₂ generation. Our computational results explain why experimentally Mo₃O₅– forms a unique kinetic trap in its reaction while W₃O₅– undergoes a facile oxidation to form the lowest-energy isomer of W₃O₆– and liberates H₂. Mechanistic insights on the reaction pathways that occur, as well as the reaction pathways that do not occur, are found to be of immense assistance to comprehend the hitherto poorly understood pivotal roles of (a) differing metal–oxygen and metal–hydrogen bond strengths, (b) the initial electrostatic complex formed, (c) the loss of entropy when these TMO clusters react with water, and (d) the geometric factors involved in the liberation of H₂.
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