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ference of about 0.5V between the two
cells (refer to Figure­4). The H 2 produc­
tion rate varied with the choice of buffers
and electrolytes. A feasible reaction
mechanism has been developed.
Figure­4: Two­chamber photo/bio­
catalytic hydrogen production system
using a salt bridge (KIER).
At Delft University of Technology
(DUT), R&D on using C­doped TiO 2 (an­
atase) as photoanode material contin­
ued. The C­doped TiO 2 was produced
by a post­deposition thermal treatment
in an argon/hexane gas mixture. But
as with similar efforts elsewhere, no
enhanced photocatalytic activities have
been found in the VIS part of the solar
spectrum due to a too low concentra­
tion of carbon. Nevertheless, at low
C­concentrations the anatase­to­rutile
phase transformation temperature was
shifted beyond 800°C. This has the
the temperature window for processing
anatase TiO 2 ­based photocatalysts. Ad­
ditionally, investigations into using InVO 4
as alternative photocatalyst material
have started. Phase­pure InVO 4 thin
with a low­cost spray deposition pro­
cess (refer to Figure­5). Sub­bandgap
optical absorption starts at ~1.9 eV,
but is much less pronounced than the
optical absorption of InVO4 in powder
form that is observed by others. A small
photocurrent was measured at energies
above 2.75 eV. The true bandgap of
the material is estimated to be 3.3 ± 0.3
eV. The incident photon­to­current ef­
wavelengths. This is attributed to a high
donor density in the material, which is
estimated to be >2x10 20 cm ­3 . Efforts to
decrease the donor density by counter­
doping with acceptor­type dopants have
not yet been successful, but studies
continue.
Figure­5: Optical absorption spec­
(Delft).
ence of doping / defects sites on the
local microscopic charge carrier mobili­
ties is being studied using a Terahertz
(THz) Time Domain Spectrosopy set­up.
Small amounts of carbon dopant in ana­
tase TiO 2 enhance the recombination
rate and decrease the number of free
charge carriers by a factor of ~ 3. For
Fe­doped anatase, the recombination
is even faster (~ 50 ps). Also at LU, the
metal oxide photoanode surface is being
modelled with Quantum Transition State
Theory (QTST). Density functional theo­
ry (DFT) is being employed to calculate
the stability of the various dopants at the
surface.
At the University of Geneva (UG)
as well as the Swiss Federal Institute of
Technology (EPFL), α­Fe 2 O 3 (hematite)
photoanodes are being developed. At
from spray­pyrolysis of Fe(III)­contain­
+ ing solutions and doped with Ti (5%)
4
+ and Al (1%) resulted in photocurrents
3
of 4.3 mA/cm 2 in 0.1 M NaOH (under
aq
4
25
“At low C­
concentrations the
anatase­to­rutile
phase transformation
temperature was
shifted beyond
800°C. This has
the advantage
extending the
temperature window
for processing
anatase TiO 2 ­based
photocatalysts.”