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Title: High-Throughput Experimental Study of Wurtzite Mn 1–xZn xO Alloys for Water Splitting Applications

Abstract

We used high-throughput experimental screening methods to unveil the physical and chemical properties of Mn 1–xZn xO wurtzite alloys and identify their appropriate composition for effective water splitting application. The Mn 1–xZn xO thin films were synthesized using combinatorial pulsed laser deposition, permitting for characterization of a wide range of compositions with x varying from 0 to 1. The solubility limit of ZnO in MnO was determined using the disappearing phase method from X-ray diffraction and X-ray fluorescence data and found to increase with decreasing substrate temperature due to kinetic limitations of the thin-film growth at relatively low temperature. Optical measurements indicate the strong reduction of the optical band gap down to 2.1 eV at x = 0.5 associated with the rock salt-to-wurtzite structural transition in Mn 1–xZn xO alloys. Transmission electron microscopy results show evidence of a homogeneous wurtzite alloy system for a broad range of Mn 1–xZn xO compositions above x = 0.4. The wurtzite Mn 1–xZn xO samples with the 0.4 < x < 0.6 range were studied as anodes for photoelectrochemical water splitting, with a maximum current density of 340 μA cm –2 for 673 nm-thick films. These Mn 1–xZn xO films were stable in pHmore » = 10, showing no evidence of photocorrosion or degradation after 24 h under water oxidation conditions. Doping Mn 1–xZn xO materials with Ga dramatically increases the electrical conductivity of Mn 1–xZn xO up to ~1.9 S/cm for x = 0.48, but these doped samples are not active in water splitting. Mott–Schottky and UPS/XPS measurements show that the presence of dopant atoms reduces the space charge region and increases the number of mid-gap surface states. Overall, this study demonstrates that Mn 1–xZn xO alloys hold promise for photoelectrochemical water splitting, which could be enhanced with further tailoring of their electronic properties.« less

Authors:
ORCiD logo [1]; ORCiD logo [2];  [3]; ORCiD logo [1];  [1]; ORCiD logo [1];  [1];  [4];  [1];  [1]; ORCiD logo [1];  [1]
  1. National Renewable Energy Lab. (NREL), Golden, CO (United States). Materials Science Center
  2. Univ. of Arizona, Tucson, AZ (United States). Dept. of Materials Science and Engineering
  3. Indian Inst. of Technology Hyderabad, Kandi (India). Dept. of Materials Science and Metallurgical Engineering
  4. National Renewable Energy Lab. (NREL), Golden, CO (United States). Materials Science Center; Colorado School of Mines, Golden, CO (United States). Dept. of Metallurgical and Materials Engineering
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1508685
Alternate Identifier(s):
OSTI ID: 1510035; OSTI ID: 1512675
Report Number(s):
NREL/JA-5900-73457
Journal ID: ISSN 2470-1343
Grant/Contract Number:  
AC36-08GO28308
Resource Type:
Published Article
Journal Name:
ACS Omega
Additional Journal Information:
Journal Volume: 4; Journal Issue: 4; Journal ID: ISSN 2470-1343
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 36 MATERIALS SCIENCE; analytical chemistry; catalysts; combinatorial chemistry; crystal structure; electric properties; energy level; phase; phase transition; semiconductors; solid state electrochemistry; solubility; spectra; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS

Citation Formats

Ndione, Paul F., Ratcliff, Erin L., Dey, Suhash R., Warren, Emily L., Peng, Haowei, Holder, Aaron M., Lany, Stephan, Gorman, Brian P., Al-Jassim, Mowafak M., Deutsch, Todd G., Zakutayev, Andriy, and Ginley, David S. High-Throughput Experimental Study of Wurtzite Mn1–xZnxO Alloys for Water Splitting Applications. United States: N. p., 2019. Web. doi:10.1021/acsomega.8b03347.
Ndione, Paul F., Ratcliff, Erin L., Dey, Suhash R., Warren, Emily L., Peng, Haowei, Holder, Aaron M., Lany, Stephan, Gorman, Brian P., Al-Jassim, Mowafak M., Deutsch, Todd G., Zakutayev, Andriy, & Ginley, David S. High-Throughput Experimental Study of Wurtzite Mn1–xZnxO Alloys for Water Splitting Applications. United States. doi:10.1021/acsomega.8b03347.
Ndione, Paul F., Ratcliff, Erin L., Dey, Suhash R., Warren, Emily L., Peng, Haowei, Holder, Aaron M., Lany, Stephan, Gorman, Brian P., Al-Jassim, Mowafak M., Deutsch, Todd G., Zakutayev, Andriy, and Ginley, David S. Wed . "High-Throughput Experimental Study of Wurtzite Mn1–xZnxO Alloys for Water Splitting Applications". United States. doi:10.1021/acsomega.8b03347.
@article{osti_1508685,
title = {High-Throughput Experimental Study of Wurtzite Mn1–xZnxO Alloys for Water Splitting Applications},
author = {Ndione, Paul F. and Ratcliff, Erin L. and Dey, Suhash R. and Warren, Emily L. and Peng, Haowei and Holder, Aaron M. and Lany, Stephan and Gorman, Brian P. and Al-Jassim, Mowafak M. and Deutsch, Todd G. and Zakutayev, Andriy and Ginley, David S.},
abstractNote = {We used high-throughput experimental screening methods to unveil the physical and chemical properties of Mn1–xZnxO wurtzite alloys and identify their appropriate composition for effective water splitting application. The Mn1–xZnxO thin films were synthesized using combinatorial pulsed laser deposition, permitting for characterization of a wide range of compositions with x varying from 0 to 1. The solubility limit of ZnO in MnO was determined using the disappearing phase method from X-ray diffraction and X-ray fluorescence data and found to increase with decreasing substrate temperature due to kinetic limitations of the thin-film growth at relatively low temperature. Optical measurements indicate the strong reduction of the optical band gap down to 2.1 eV at x = 0.5 associated with the rock salt-to-wurtzite structural transition in Mn1–xZnxO alloys. Transmission electron microscopy results show evidence of a homogeneous wurtzite alloy system for a broad range of Mn1–xZnxO compositions above x = 0.4. The wurtzite Mn1–xZnxO samples with the 0.4 < x < 0.6 range were studied as anodes for photoelectrochemical water splitting, with a maximum current density of 340 μA cm–2 for 673 nm-thick films. These Mn1–xZnxO films were stable in pH = 10, showing no evidence of photocorrosion or degradation after 24 h under water oxidation conditions. Doping Mn1–xZnxO materials with Ga dramatically increases the electrical conductivity of Mn1–xZnxO up to ~1.9 S/cm for x = 0.48, but these doped samples are not active in water splitting. Mott–Schottky and UPS/XPS measurements show that the presence of dopant atoms reduces the space charge region and increases the number of mid-gap surface states. Overall, this study demonstrates that Mn1–xZnxO alloys hold promise for photoelectrochemical water splitting, which could be enhanced with further tailoring of their electronic properties.},
doi = {10.1021/acsomega.8b03347},
journal = {ACS Omega},
number = 4,
volume = 4,
place = {United States},
year = {2019},
month = {4}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
DOI: 10.1021/acsomega.8b03347

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