ALD

Authors: 

He, Yumin; Thorne, James E.; Wu, Cheng Hao; Ma, Peiyan; Du, Chun; Dong, Qi; Guo, Jinghua; Wang, Dunwei

Journal: 

Chem

Year: 

2016

Abstract: 

Tantalum nitride (Ta3N5) is a promising photoelectrode for solar water splitting. Although near-theoretical-limit photocurrent has already been reported on Ta3N5, its low photovoltage and poor stability remain critical challenges. In this study, we used Ta3N5 nanotubes as a platform to understand the origins of these issues. Through a combination of photoelectrochemical and high-resolution electron microscope measurements, we found that the self-limiting surface oxidation of Ta3N5 resulted in a thin amorphous layer (ca. 3 nm), which proved to be effective in pinning the surface Fermi levels and thus fully suppressed the photoactivity of Ta3N5. X-ray core-level spectroscopy characterization not only confirmed the surface composition change resulting from the oxidation but also revealed a Fermi-level shift toward the positive direction by up to 0.5 V. The photoactivity degradation mechanism reported here is likely to find applications in other solar-to-chemical energy-conversion systems.

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Authors: 

Verlage, Erik; Hu, Shu; Liu, Rui; Jones, Ryan J. R.; Sun, Ke; Xiang, Chengxiang; Lewis, Nathan S.; Atwater, Harry A.

Journal: 

Energy Environ. Sci.

Year: 

2015

Abstract: 

A new strategy for preparing spatially-controlled, multi-component films consisting of molecular light absorbing chromophores and water oxidation catalysts on high surface area, mesoporous metal oxide surfaces is described. Atomic layer deposition (ALD) is used to embed a surface-bound chromophore in a thin layer of inert Al2O3, followed by catalyst binding to the new oxide surface. In a final step, catalyst surface-binding is stabilized by a subsequent ALD overlayer of Al2O3. The ALD assembly procedure bypasses synthetic difficulties arising from the preparation of phosphonic acid derivatized, covalentlylinked assemblies. An ALD mummy-based assembly has been used to demonstrate photoelectrochemical dehydrogenation of hydroquinone. Electrocatalytic water oxidation at pH 8.8 is observed over a 2 hour electrolysis period and light-assisted water oxidation over a 6 hour photolysis period with O2 detected with a generator–collector electrode configuration.

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