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Synthesis

Light produces a banana-bond split

Water-splitting catalyst surprises with photodesorption

by Jyllian Kemsley
July 18, 2016 | APPEARED IN VOLUME 94, ISSUE 29

A banana-bond split may sound delicious, but actually, it’s a bit of surface chemistry. Specifically, the point at which an H2 molecule desorbs from a catalyst after light-induced water splitting. Although the desorption is typically thought to be a thermally driven event, a study conducted at Pacific Northwest National Laboratory indicates that the desorption, too, may be triggered by light (J. Am. Chem. Soc. 2016, DOI: 10.1021/jacs.6b05083). A common approach to dissociate water to produce hydrogen for fuel is to combine a semiconductor that can emit photoelectrons with a cocatalyst such as RuO2 to facilitate redox chemistry. Previously, researchers determined that after hydrogen is produced, it remains adsorbed to RuO2 by donating electron density from its σ bond to the Ru 4d orbital. This produces a three-center, two-electron system with bent—or banana-shaped—bonds. The PNNL team has now identified an additional electrostatic interaction—one that arises from RuIVpolarizing H2 and RuO2 counterpolarizing in response. The team also found that shining visible light on the complex induces an optical transition in RuO2 that redistributes charge and weakens the electrostatic interaction, releasing H2. The finding suggests that “there are optical transitions in cocatalysts that people haven’t recognized, and they should be recognized, understood, and exploited,” PNNL scientist Michael A. Henderson says.

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