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CCI Solar Events - July, 2017 Pick date

1 PM

CCI Cybermeeting - Bryan Hunter - Gray Group - Caltech

01:00 PM to 02:00 PM, July 13, 2017

Location: eZuce

Trapping an Iron(VI) Water Splitting Intermediate in Nonaqueous Media

The sustainable and economical conversion of solar energy into storable, transportable fuels by solar-driven water splitting is a grand challenge of 21st century chemistry.

The mechanisms by which heterogeneous materials perform the anodic half-reaction, water oxidation, are not well understood. In this seminar, we describe in-situ spectroscopic measurements in nonaqueous media designed to trap an exceptionally strong oxidant generated electrochemically from an iron-containing nickel layered double hydroxide ([NiFe]-LDH) material.

Anodic polarization of this material in acetonitrile produces prominent infrared absorption features (840 and 856 cm-1) that are quenched by the addition of water. These vibrational spectroscopic signatures along with a potential-dependent extremely narrow luminescence peak at 1633 nm indicate that the reactive intermediate is a cis-dioxo-iron(VI) species.

An absorption in the Mössbauer spectrum of the material, which disappears upon exposure to alkaline acetonitrile, is consistent with population of a high-valent iron-oxo species.

Importantly, chemical trapping experiments reveal that addition of H2O to the polarized electrochemical cell produces hydrogen peroxide; and addition of HO– generates oxygen. Re-polarization of the electrode restores the iron(VI) spectroscopic signatures, confirming that the high-valent oxo complex is active in the electrocatalytic water oxidation cycle.

Our work demonstrates that in-situ spectroscopy in nonaqueous media offers a powerful new approach to the study of aqueous redox mechanisms.