Hematite is a potential candidate for hydrogen production by photoelectrochemical (PEC)
decomposition of water due to its good bad gap and excellent chemical stability. However, its poor
conductivity limits its PEC performance. Titanium has been predicted to be a good choice of dopant for
improving the conductivity. Most of the Ti-doped hematite films are produced by solution based
method. However, such procedure may introduce impurities. RF sputtering is a clean vacuum deposition
technique, which is perfect for the synthesis of metal oxide. In this paper, we report our synthesis of Tidoped
hematite thin films by RF magnetron co-sputtering of iron oxide and titanium targets at various
conditions. Our work shows that the structure and morphology of iron oxide can be modified by
controlling the doping concentration of titanium. Moreover, we confirmed that the PEC performance of
Ti-doped iron oxide film is significantly better than the undoped one.
There is an increasing interest in semiconductor/ electrolyte systems in connection with their application as
phototelectrolytic energy conversion devices (e.g. hydrogen evolution). There are several requirements in
order to produce hydrogen by photoelectrolysis using oxides metals and semiconductors. One of the most
interesting semiconductor materials is the GaN which is a direct ban gap semiconductor.
In this paper shows the formation of GaN prepared via electrodeposition, using ammonium nitrate at
different concentration as type sources of nitrogen in order to growth a thin film. A standard three-electrode
cell was used to prepare it using potenciostatic conditions. The average thickness of the samples was
measured. The annealed films were characterized by electrochemical; photoelectrochemical, compositional,
and morphologic methods in order to know its potential for water splitting.
Efficient photo-electrochemical (PEC) splitting of water to hydrogen usually requires photoelectrodes to have certain
electronic properties. Unfortunately, at present available semiconductors do not meet all these criteria. So, a thorough
understanding of band-engineering for mixed alloys is necessary to successfully design these photoelectrodes. Among
the semiconductors, transition metal oxides are of particular interest due to their low cost and relatively high stability in
aqueous media. Here, we will present a theoretical study of delafossite-alloys for PEC photo-electrodes. Previous studies
have indicated that the group IIIA delafossite family (CuMO2, M = Al, Ga, In) do not exhibit direct band gaps. Their
fundamental band gaps are significantly smaller than their reported optical band gaps. On the other hand group IIIB
delafossite family (CuMO2, M = Sc, Y, La) in general show direct band gaps and, except for CuLaO2, band gaps are
above 3.00 eV. However, both of these two families exhibit p-type conductivity. We will show that by appropriate
alloying of these two delafossite-families we can tune their band gaps and other opto-electronic properties. These types
of alloying are desirable, as these introduce no localized impurity states in the band gap due to isovalent alloying. Also,
the electronic effective masses can be lowered by selective doping of main group elements. Finally, it will be discussed
that, lowering the symmetry constraints of these alloys would enhance their optical absorption properties. We'll also
discuss that alloying with other 3d metal elements may decrease the band gap, but would increase the effective masses of
the photo-electrons.
We combine first-principles density functional theory, material synthesis and characterization, and photoelectrochemical
(PEC) measurements to explore methods to effectively reduce the band gap of ZnO for the application of PEC water
splitting. We find that the band gap reduction of ZnO can be achieved by N and Cu incorporation into ZnO. We have
successfully synthesized ZnO:N thin films with various reduced band gaps by reactive RF magnetron sputtering. We
further demonstrate that heavy Cu-incorporation lead to both p-type doping and band gap significantly reduced ZnO thin
films. The p-type conductivity in our ZnO:Cu films is clearly revealed by Mott-Schottky plots. The band gap reduction
and photoresponse with visible light for N- and Cu-incorporated ZnO thin films are demonstrated.
Ceramic semiconductor photoelectrodes made of the Fe2O3-Nb2O5 solid solutions were synthesized. The spectral and
capacitance-voltage characteristics of the photoelectrodes were determined, and the dynamic polarization with chopped
light was investigated. The anodic photocurrent onset potential, the flat band potential and the shallow and deep donor
density of these materials were determined. The threshold photon energies corresponding to the inter-band optical
transitions near the edge of the fundamental absorption of the semiconductor photoelectrode were calculated. Analysis
of the frequency dispersion of the real and imaginary parts of the complex impedance of photoelectrochemical cell was
carried out. On the basis of this analysis, equivalent circuits describing the structure of the double electrical layer of the
semiconductor - electrolyte interface were proposed and their parameters were calculated. The main limiting steps of the
electrode processes, which determine the electrode polarization and current, are determined.
Conference Committee Involvement (11)
Solar Hydrogen and Nanotechnology XI
30 August 2016 | San Diego, California, United States
Solar Hydrogen and Nanotechnology X
9 August 2015 | San Diego, California, United States
Solar Hydrogen and Nanotechnology IX
19 August 2014 | San Diego, California, United States
Solar Hydrogen and Nanotechnology VIII
28 August 2013 | San Diego, California, United States
Solar Hydrogen and Nanotechnology VII
13 August 2012 | San Diego, California, United States
Solar Hydrogen and Nanotechnology VI
23 August 2011 | San Diego, California, United States
Solar Hydrogen and Nanotechnology V
3 August 2010 | San Diego, California, United States
Solar Hydrogen and Nanotechnology IV
3 August 2009 | San Diego, California, United States
Solar Hydrogen and Nanotechnology III
11 August 2008 | San Diego, California, United States
Solar Hydrogen and Nanotechnology II
27 August 2007 | San Diego, California, United States
Solar Hydrogen and Nanotechnology
14 August 2006 | San Diego, California, United States
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