1. duction
Magnéli phases Functionally graded
fibres
Flat band
potential
1.92 V vs SCE -2.33 V vs SCE
Carriers
density
4.16x1014 cm-3 5.72x1017 cm-3
Schematicdiagramoftheflowerstructure
formationmechanism
Ti-suboxides structures for water splitting
V. Adamaki1, P. Mougoyannis1, A. Sergejevs2, C. Clarke2, C. R. Bowen1, R. Stevens1
1
Mechanical Engineering Department,University of Bath, BA2 7AY, UK
2Electrical Engineering Department,University of Bath, BA2 7AY, UK
Introduction
The photo-electro-chemical (PEC) splitting of water requires semiconductors with minimum energy gap of 1.23 eV and with conduction and
valence bands overlapping the oxidation of H2O and the reduction of H+ respectively [1]. Titania (TiO2) has been extensively investigated as
photo-anode for PEC water splitting due to its suitable band-edge position, chemical resistance, environmental suitability and low cost [2-5].
The main limitations of stoichiometric TiO2 are its wide band gap (3.2 eV) and electron-hole recombination. It has been shown that the oxygen
vacancies in the structure of Ti-suboxides increase the carriers’ density and thus the photocurrent efficiency [6]. Other parameters to increase
the efficiency is to increase the surface area and use composites structures (i.e. thin films on ferroelectrics) to enhance electron-hole
separation. The approach of this work is investigating both parameters and measuring the photocurrent efficiency. TiO2 flowerlike structures
were grown on a Ti mesh that were then heat-threated in a reducing atmosphere introducing oxygen vacancies in the structure. The
structures on a Ti mesh offer very high surface area. The water-splitting efficiency of sub-stoichiometric functionally graded titania fibres was
also investigated.
Photoelectrochemical (PEC) measurements
• 3-electrode electrochemical system
• Saturated calomel electrode (SCE) reference electrode and a
platinum wire as a counter electrode in 1M KOH electrolyte
• 6 wavelengths UV to visible light
• Homogeneous illumination
• Overheating protection
Sub-stoichiometric functionally graded titania fibres
Through carbo-thermal re Electrochemical Impedance
Spectroscopy (EIS) TiO2
Photocurrent – 760W/m2 – 368nm
Functionally graded fibres
TiO2-x
Magnéli
Rutile TiO2
Ti8O15/Ti9O17/Ti10O19
Ti3O5/Ti4O7/
Magnéli
phases
dark
under
UV light
(368nm)
under
UV light
(368nm)
under
UV light
(368nm)
dark
phases
Ti5O9/Ti6O11 dark
Material IPCE (%)
TiO2 1.42
Magnéli phases 2.88
Graded (TiO2-x- Magnéli phases) 34.8
• Titanium dioxide flowerlike structure
prepared by anodisation of Ti-mesh
electrode
High surface area TiO2 flower structure
Initial surface oxide formed
• Potentiostatic conditions (30 volts) at room (a) (b)
temperature for 9.16h.
• Ethylene Glycol with 0.45 wt % Ammonium
Fluoride
• Heat treatment in a reducing atmosphere
and PEC measurements will be conducted
Pores on
the oxide layer
Tubes
Further etching of the
nanotubes walls
Due to surface stress the oxide structure separates Flower-like structure due to stress relaxation by viscous flow
Cracks run
along the
length of the
wire
(c) (d) (e)
[1]: A. Fujishima, K. Honda, Nature, 238 (1972)37 [3]: J. Ba,Nature Nanotechnology, 10 (2015)19 [5]: J. Yu, L. Qi, M. Jaroniec, J. of Physical Chemistry C, 114(2010) 13118
[2]: C. Cheng, Y. Sun, Applied Surface Science, 263 (2012) 273[4]: D. Regonini, A. K. Alves, F. A. Berutti, F. Clemens, Int. J. of Photoenergy, 2014(2014) 1 [6]: G. Wang, H. Wang, Y. ling, Y. Tang, X. Yang, R. C. Fitzmorris,Y. Li,Nano Letters, 11 (2011) 3026
The research leading to the materials development and characterisation was from the European Union’s Seventh Framework Programme (FP7/2007-2013)/ERC Grant Agreement no. 320963 on Novel Energy Materials,
Engineering, Science and Integrated Systems (NEMESIS).