High-Throughput Experimental Study of Wurtzite Mn 1- x Zn x O Alloys for Water Splitting Applications

Paul F. Ndione, Erin L. Ratcliff, Suhash R. Dey, Emily L. Warren, Haowei Peng, Aaron M. Holder, Stephan Lany, Brian P. Gorman, Mowafak M. Al-Jassim, Todd G. Deutsch, Andriy Zakutayev, David S. Ginley

Research output: Contribution to journalArticle

1 Scopus citations

Abstract

We used high-throughput experimental screening methods to unveil the physical and chemical properties of Mn 1-x Zn x O wurtzite alloys and identify their appropriate composition for effective water splitting application. The Mn 1-x Zn x O 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-x Zn x O alloys. Transmission electron microscopy results show evidence of a homogeneous wurtzite alloy system for a broad range of Mn 1-x Zn x O compositions above x = 0.4. The wurtzite Mn 1-x Zn x O 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-x Zn x O films were stable in pH = 10, showing no evidence of photocorrosion or degradation after 24 h under water oxidation conditions. Doping Mn 1-x Zn x O materials with Ga dramatically increases the electrical conductivity of Mn 1-x Zn x O 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-x Zn x O alloys hold promise for photoelectrochemical water splitting, which could be enhanced with further tailoring of their electronic properties.

Original languageEnglish (US)
Pages (from-to)7436-7447
Number of pages12
JournalACS Omega
Volume4
Issue number4
DOIs
StatePublished - Apr 24 2019

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)

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