Hu, Shu and Shaner, Matthew R. and Beardslee, Joseph A. and Lichterman, Michael and Brunschwig, Bruce S. and Lewis, Nathan S. (2014) Amorphous TiO_2 coatings stabilize Si, GaAs, and GaP photoanodes for efficient water oxidation. Science, 344 (6187). pp. 1005-1009. ISSN 0036-8075. http://resolver.caltech.edu/CaltechAUTHORS:20140515-133039268
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Although semiconductors such as silicon (Si), gallium arsenide (GaAs), and gallium phosphide (GaP) have band gaps that make them efficient photoanodes for solar fuel production, these materials are unstable in aqueous media. We show that TiO_2 coatings (4 to 143 nanometers thick) grown by atomic layer deposition prevent corrosion, have electronic defects that promote hole conduction, and are sufficiently transparent to reach the light-limited performance of protected semiconductors. In conjunction with a thin layer or islands of Ni oxide electrocatalysts, Si photoanodes exhibited continuous oxidation of 1.0 molar aqueous KOH to O_2 for more than 100 hours at photocurrent densities of >30 milliamperes per square centimeter and ~100% Faradaic efficiency. TiO_2-coated GaAs and GaP photoelectrodes exhibited photovoltages of 0.81 and 0.59 V and light-limiting photocurrent densities of 14.3 and 3.4 milliamperes per square centimeter, respectively, for water oxidation.
|Alternate Title:||Amorphous TiO2 coatings stabilize Si, GaAs, and GaP photoanodes for efficient water oxidation|
|Additional Information:||© 2014 American Association for the Advancement of Science. All Rights Reserved. Received for publication 28 January 2014. Accepted for publication 1 May 2014. This work is supported through the Office of Science of the U.S. Department of Energy (DOE) under award no. DE-SC0004993 to the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub. M.S. acknowledges the Resnick Sustainability Institute for a graduate fellowship, and B.S.B. acknowledges the Beckman Institute at the California Institute of Technology for support. XPS was performed at the Molecular Materials Research Center in the Beckman Institute at the California Institute of Technology. TEM imaging and spectroscopy were performed at the Center for Electron Microscopy and Microanalysis, University of Southern California. We thank H.- J. Lewerenz, C. Koval, and F. Houle for fruitful discussions; Y. Guan for secondary-ion mass spectrometry measurements; S. R. Nutt for use of the microscopy and microanalysis facility; P. D. Dapkus for the use of the metal-organic chemical vapor deposition facility; S. Ardo for help in boron-diffusion doping; and K. Papadantonakis for assistance with editing this manuscript. The authors’ institution (California Institute of Technology) has filed a provisional U.S. patent application directly relating to the work described in the paper (patent application no. 61/889,430, filed on 10 October 2013).|
|Group:||Resnick Sustainability Institute|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||George Porter|
|Deposited On:||29 May 2014 18:06|
|Last Modified:||29 May 2014 18:10|
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