Passivation of surface states of α-Fe2O3(0001) surface by deposition of Ga2O3 overlayers: A density functional theory study.

There is a big debate in the community regarding the role of surface states of hematite in the photoelectrochemical water splitting. Experimental studies on non-catalytic overlayers passivating the hematite surface states claim a favorable reduction in the overpotential for the water splitting reaction. As a first step towards understanding the effect of these overlayers, we have studied the system Ga2O3 overlayers on hematite (0001) surfaces using first principles computations in the PBE+U framework. Our computations suggest that stoichiometric terminations of Ga2O3 overlayers are energetically more favored than the bare surface, at ambient oxygen chemical potentials. Energetics suggest that the overlayers prefer to grow via a layer-plus-island (Stranski-Krastanov) growth mode with a critical layer thickness of 1-2 layers. Thus, a complete wetting of the hematite surface by an overlayer of gallium oxide is thermodynamically favored. We establish that the effect of deposition of the Ga2O3 overlayers on the bare hematite surface is to passivate the surface states for the stoichiometric termination. For the oxygen terminated surface which is the most stable termination under photoelectrochemical conditions, the effect of deposition of the Ga2O3 overlayer is to passivate the hole-trapping surface state.

[1]  M. Grätzel,et al.  Controlling Photoactivity in Ultrathin Hematite Films for Solar Water‐Splitting , 2010 .

[2]  E. Longo,et al.  The influence of the film thickness of nanostructured alpha-Fe2O3 on water photooxidation. , 2009, Physical chemistry chemical physics : PCCP.

[3]  Michael Grätzel,et al.  Light-induced water splitting with hematite: improved nanostructure and iridium oxide catalysis. , 2010, Angewandte Chemie.

[4]  V. Anisimov,et al.  Band theory and Mott insulators: Hubbard U instead of Stoner I. , 1991, Physical review. B, Condensed matter.

[5]  Michael Grätzel,et al.  Passivating surface states on water splitting hematite photoanodes with alumina overlayers , 2011 .

[6]  G. Kresse,et al.  A first-principles study of bulk oxide formation on Pd(100). , 2009, The Journal of chemical physics.

[7]  Burke,et al.  Generalized Gradient Approximation Made Simple. , 1996, Physical review letters.

[8]  R. Gebauer,et al.  Photo-Oxidation of Water on Defective Hematite(0001) , 2015 .

[9]  R. Gebauer,et al.  Defective α-Fe2O3(0001): an ab initio study. , 2014, Chemphyschem : a European journal of chemical physics and physical chemistry.

[10]  Michel Dupuis,et al.  Charge Transport in Metal Oxides: A Theoretical Study of Hematite α-Fe2O3 , 2005 .

[11]  Nerine J. Cherepy,et al.  Ultrafast Studies of Photoexcited Electron Dynamics in γ- and α-Fe2O3 Semiconductor Nanoparticles , 1998 .

[12]  G. Henkelman,et al.  Hybrid density functional theory band structure engineering in hematite. , 2011, The Journal of chemical physics.

[13]  Stefano de Gironcoli,et al.  QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials , 2009, Journal of physics. Condensed matter : an Institute of Physics journal.

[14]  Computational study of α-M2O3 (M = Al, Ga): surface properties, water adsorption and oxidation , 2015 .

[15]  D. Vanderbilt,et al.  Soft self-consistent pseudopotentials in a generalized eigenvalue formalism. , 1990, Physical review. B, Condensed matter.

[16]  R. Gebauer,et al.  Water adsorption and dissociation on α-Fe2O3(0001): PBE+U calculations. , 2013, The Journal of chemical physics.

[17]  O. Neufeld,et al.  A First-Principles Study on the Role of an Al2O3 Overlayer on Fe2O3 for Water Splitting , 2015 .

[18]  Juan Bisquert,et al.  Photoelectrochemical and impedance spectroscopic investigation of water oxidation with "Co-Pi"-coated hematite electrodes. , 2012, Journal of the American Chemical Society.

[19]  R. Gebauer,et al.  Nitrogen electrochemically reduced to ammonia with hematite: density-functional insights. , 2015, Physical chemistry chemical physics : PCCP.

[20]  Michael Grätzel,et al.  Solar water splitting: progress using hematite (α-Fe(2) O(3) ) photoelectrodes. , 2011, ChemSusChem.

[21]  Michael Grätzel,et al.  Cathodic shift in onset potential of solar oxygen evolution on hematite by 13-group oxide overlayers , 2011 .

[22]  Michael Grätzel,et al.  New Benchmark for Water Photooxidation by Nanostructured α-Fe2O3 Films , 2006 .

[23]  Juan Bisquert,et al.  Water oxidation at hematite photoelectrodes: the role of surface states. , 2012, Journal of the American Chemical Society.

[24]  Stefano de Gironcoli,et al.  Linear response approach to the calculation of the effective interaction parameters in the LDA + U method , 2004, cond-mat/0405160.

[25]  R. Gebauer,et al.  Photo-driven oxidation of water on α-Fe2O3 surfaces: an ab initio study. , 2014, The Journal of chemical physics.

[26]  Thomas W. Hamann,et al.  Photocatalytic water oxidation with hematite electrodes , 2013 .

[27]  A. Kiejna,et al.  Surface properties of clean and Au or Pd covered hematite (α-Fe2O3) (0001) , 2012, Journal of physics. Condensed matter : an Institute of Physics journal.

[28]  O. Neufeld,et al.  Toward Settling the Debate on the Role of Fe2O3 Surface States for Water Splitting , 2015 .

[29]  J. Coey,et al.  A study of hyperfine interactions in the system (Fe1-xRhx)2O3 using the Mossbauer effect (Bonding parameters) , 1971 .

[30]  Alexander J. Cowan,et al.  Charge carrier trapping, recombination and transfer in hematite (α-Fe2O3) water splitting photoanodes , 2013 .

[31]  Frank E. Osterloh,et al.  Photocatalytic water oxidation with suspended alpha-Fe2O3 particles-effects of nanoscaling , 2011 .

[32]  Tersoff.  Stress-induced layer-by-layer growth of Ge on Si(100). , 1991, Physical review. B, Condensed matter.

[33]  Fujio Izumi,et al.  VESTA 3 for three-dimensional visualization of crystal, volumetric and morphology data , 2011 .

[34]  D. Gamelin,et al.  Photoelectrochemical water oxidation by cobalt catalyst ("Co-Pi")/alpha-Fe(2)O(3) composite photoanodes: oxygen evolution and resolution of a kinetic bottleneck. , 2010, Journal of the American Chemical Society.

[35]  E. Barea,et al.  Water Oxidation at Hematite Photoelectrodes with an Iridium-Based Catalyst , 2013 .

[36]  Richard M. Martin.  Electronic Structure: Frontmatter , 2004 .

[37]  Juan Bisquert,et al.  Electrochemical and photoelectrochemical investigation of water oxidation with hematite electrodes , 2012 .

[38]  E. Carter,et al.  Electron transport in pure and doped hematite. , 2011, Nano letters.

[39]  E. Carter,et al.  Testing variations of the GW approximation on strongly correlated transition metal oxides: hematite (α-Fe2O3) as a benchmark. , 2011, Physical chemistry chemical physics : PCCP.

[40]  Alexander J. Cowan,et al.  Dynamics of photogenerated holes in surface modified α-Fe2O3 photoanodes for solar water splitting , 2012, Proceedings of the National Academy of Sciences.

[41]  Michael Grätzel,et al.  The Transient Photocurrent and Photovoltage Behavior of a Hematite Photoanode under Working Conditions and the Influence of Surface Treatments , 2012 .

[42]  A. J. Bosman,et al.  Small-polaron versus band conduction in some transition-metal oxides , 1970 .

[43]  Beniamino Iandolo,et al.  The role of surface States in the oxygen evolution reaction on hematite. , 2014, Angewandte Chemie.

[44]  M. Grätzel,et al.  Decoupling feature size and functionality in solution-processed, porous hematite electrodes for solar water splitting. , 2010, Nano letters.

[45]  Michael Grätzel,et al.  Influence of Feature Size, Film Thickness, and Silicon Doping on the Performance of Nanostructured Hematite Photoanodes for Solar Water Splitting , 2009 .

[46]  J. P. Remeika,et al.  Bond Lengths in the α‐Ga2O3 Structure and the High‐Pressure Phase of Ga2−xFexO3 , 1967 .