Post on 05-Mar-2023
ww.sciencedirect.com
i n t e r n a t i o n a l j o u r n a l o f h yd r o g e n e n e r g y x x x ( 2 0 1 4 ) 1e1 1
Available online at w
ScienceDirect
journal homepage: www.elsevier .com/locate/he
Stabilizing effect in nano-titania functionalized CdSphotoanode for sustained hydrogen generation
Alka Pareek a,b, Rahul Purbia a, Pradip Paik b, Neha Y. Hebalkar a,Hyun Gyu Kim c, Pramod H. Borse a,*a International Advanced Research Centre for Powder Metallurgy and New Materials, Balapur PO,
Hyderabad 500 005, AP, Indiab School of Engineering Science and Technology, Hyderabad Central University, Gachibowli, Hyderabad 500046, AP,
IndiacDivision of High Technology Materials Research, Korea Basic Science Institute (KBSI), Busan 618-230,
Republic of Korea
a r t i c l e i n f o
Article history:
Received 24 October 2013
Received in revised form
17 December 2013
Accepted 30 December 2013
Available online xxx
Keywords:
Photoelectrochemical cell
Hydrogen generation
Spray deposited CdS
TiO2 nanoparticles
Stability of photoanode
Photocorrosion
* Corresponding author. Tel.: þ91 4024452426E-mail addresses: phborse@arci.res.in, pb
Please cite this article in press as: Pareek Ahydrogen generation, International Journ
0360-3199/$ e see front matter Copyright ªhttp://dx.doi.org/10.1016/j.ijhydene.2013.12.1
a b s t r a c t
Efficient and stable photoanode has been fabricated by the surface functionalization of the
nanostructured film. For this, the surface of spray deposited CdS thin film was modified
through bi-functional molecule mediated chemisorption of TiO2 nanoparticles (NP).
Consequently, a systematic control over efficiency and photoanode stability against
corrosion has been investigated. An in-depth quantitative analysis of the photocorrosion of
these photoanodes is further studied using chronoamperometry, X-ray photoelectron
spectroscopy and induced coupled plasma spectroscopy. TiO2 NP modified photoanodes
show an enhanced efficiency and a stability. For photoelectrochemical (PEC) systems, the
stability factor (P
) has been defined for the first time based on the time dependent chro-
noamperometry, which clearly demonstrates thatP
modified >>P
bare. The modified pho-
toanode shows an improved Incident Photon to Current Efficiency of 22% than the bare CdS
(w8%) electrode. It gives an enhanced solar-to-hydrogen conversion efficiency of
STH w 0.7% w.r.t bare CdS (0.2%) under AM 1.5G solar simulator, at 0.2 V/SCE. Improved
stability of more than nine hours and enhanced efficiency is attributed to the controlled
passivation of CdS surface through TiO2 NP (5 nm), and inhibition of the charge recombi-
nation. Superior and stable performance of modified photoelectrode has been validated by
higher and stable hydrogen evolution over modified electrode.
Copyright ª 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights
reserved.
1. Introduction
A sustainable and continuous hydrogen generation by pho-
toelectrochemical water-splitting reaction is highly desirable.
; fax: þ91 4024442699.orse@yahoo.com, pborse
, et al., Stabilizing effectal of Hydrogen Energy (
2014, Hydrogen Energy P85
It is known that photoelectrochemical and photocatalytic
hydrogen production through solar water-splitting is one of
the most promising renewable energy generation technolo-
gies [1e6]. The cadmium chalcogenide comprises as one of the
@gmail.com (P.H. Borse).
in nano-titania functionalized CdS photoanode for sustained2014), http://dx.doi.org/10.1016/j.ijhydene.2013.12.185
ublications, LLC. Published by Elsevier Ltd. All rights reserved.
Fig. 1 e Schematic presentation of NPT adsorption
mechanism on CdS using thioglycerol (TG) molecules.
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y x x x ( 2 0 1 4 ) 1e1 12
most important class of semiconductor in the photo-
electrochemical (PEC) research, as it is the most promising
candidate that exhibits a direct band-gap of 2.4 eV. Addition-
ally, it is considered an excellent visible light responsive ma-
terial [7,8] with well-suited band-edge positions for the
cleavage of water molecule into hydrogen and oxygen. Un-
fortunately, chalcogenide electrodes show poor photo corro-
sion resistance, and hence not capable of sustainable
hydrogen production though they yield high efficiency pho-
toanodes. In present work, we sought cadmium sulphide as
the photo anodic material for photoelectrochemical hydrogen
application, with a view to apply it for sustained PEC hydrogen
generation.
It is known that, chalcogenides suffer with a peculiar
problem of undesirable corrosion of electrode upon photo-
illumination [9,10]. This is because, when photogenerated
holes (hþ) in the valence band migrate to the surface, it
leads to the photocorrosion of chalcogenide electrode. This
phenomenon can be understood by following reaction:
CdSþ 4hþ þO2 þ 2H2O/Cd2þ þ SO2�4 þ 4Hþ (1)
In order to utilize suitable optoelectronic as well as pho-
toelectrochemical properties of CdS, it is highly desirable to
overcome or minimize its problem of photo-stability. In past,
there were few strategies implemented to suppress the pho-
tocorrosion. These strategies can be stated in following way.
First strategy say, exploits the use of the electron rich species
viz. sacrificial redox scavengers such as halides [11e13], EDTA
[14], FeðCNÞ4�6 [11,15,16], S2� [11,17,18], SO2�3 [11,17,18] to con-
tent the problem. Such negative species combine with the
photogenerated holes, thereby inhibiting the photocorrosion.
Second onemakes use of the catalytic metal (as Pt, Ru and Au)
particle over the electrode surface; the population of holes is
minimized to reduce the anodic oxidation process [17,19] and
thus avoiding unnecessary oxidation of lattice S atoms. Third
option to address the problem is by isolating the semi-
conductor surface from electrolyte via. a polymer such as a
polystyrene, polyacrylic acid [20e23] or stable metal oxide
semiconductor such as ZnO, TiO2 [24e27]. Such polymer/
metal oxide layer acts as a protective layer over the semi-
conductor electrode, and consequently inhibits the photo-
corrosion process. Additionally, hybrid system of Cd
chalcogenides with carbon related compounds has been re-
ported [28e30], but there is no detailed and particular
emphasis on the stability studies. Among all the approaches,
surface passivation using metal oxide TiO2 coating has been
expected to bemost eligible as it is highly stable and economic
semiconductor system [31].
There have been reports on modification of TiO2 powder/
colloidal photocatalyst using CdS to enhance the visible
light induced water splitting [25e27,32e34] activity in TiO2.
However, a fewer reports exist on the modification of CdS
[35,36] films using TiO2, and specific focus on the modifica-
tion of nanostructured CdS film using TiO2 nanoparticles is
scarce in context to stability aspect of CdS electrode. It is
expected that the TiO2 led surface modification of an un-
stable chalcogenide (as CdS) photoanode surface can ideally
inhibit the photogenerated electronehole recombination
during the photoelectrochemical reactions, and thereby
Please cite this article in press as: Pareek A, et al., Stabilizing effechydrogen generation, International Journal of Hydrogen Energy (
yield an enhanced photoelectrochemical performance. In
addition, the passivation using such chemically stable ma-
terial yields a photocorrosion-proof electrode surface [35].
TiO2 can modify CdS film in two ways viz. physio-sorption
and chemisorption. Physio-sorption includes the formation
of TiO2 layer over CdS photoanode by making use of TiO2
precursor, which is followed by an annealing step [36].
Chemisorption, process involves the use of organic linkers,
an organic molecule [37e41], especially for creating a
chemical linking between the two material systems, say CdS
surface and TiO2 nanoparticles in the present case. As
already reported, chemisorption is an efficient way for the
adsorption of TiO2 nanoparticles on the CdS photoanode
surface [42]. Here an affinity of CdS and TiO2 towards thi-
ol(ReSH) and hydroxyl (eOH) groups respectively has been
useful to form a hybrid structure. In this chemical approach
an electron transfer and the consequent charge transport
properties mainly depends on the length of the bi-functional
(linker) molecule [43]. However, it is important to note that
lengthy bi-functional molecule causes hindrance in the
transfer of electrons from one semiconductor to other
semiconductor. There are various reports on the use of
linking agents for linking CdS nanoparticles to TiO2 base
electrodes [37e40]. In present work, we have attached the
CdS photoanode surface with “TiO2 nanoparticles” hence-
forth termed as NPT using thioglycerol (TG) as an organic
linker via. a simple adsorption technique. The procedure
can be easily described as shown in Fig. 1. We report here a
detail study of the synthesis, characterization and photo-
electrochemical properties of NPT modified CdS photo-
anodes. Reduction in the density of surface states of the CdS
surface by adsorption of NPT leads to a decrement in the
electronehole recombination process [44] thereby resulting
in an overall increase in PEC efficiency. More over TiO2 is a
stable metal oxide, which helps in the passivation of the
CdS photoanode surface and hence additionally provides
the photocorrosion stability. The work focuses on the sta-
bility improvement investigations over CdS photoanode
achieved via. NPT.
2. Experimental
2.1. Deposition of nanostructured CdS thin films
An automated spray pyrolysis setup has been used for the CdS
thin film deposition. Several optimizations were carried out to
achieve the nanostructured CdS thin film as reported earlier
t in nano-titania functionalized CdS photoanode for sustained2014), http://dx.doi.org/10.1016/j.ijhydene.2013.12.185
Table 1 e Name convention followed for NPTphotoanodes obtained after different treatmenttime.
Time of treatment NPT/CdS
3 min NPT-a
7 min NPT-b
15 min NPT-c
30 min NPT-d
i n t e r n a t i o n a l j o u r n a l o f h yd r o g e n e n e r g y x x x ( 2 0 1 4 ) 1e1 1 3
[45]. The automated computer interface system has ability to
control the inert gas pressure, precursor flow rate, substrate
temperature and the film thickness. Equal amount of solu-
tions of CdCl2 (0.1 M) & (NH2)2CS (0.1 M) were used in double
distilled water to prepare the precursor for film deposition.
Fluorine doped tin oxide; FTO (Pilkington TCO-15) with re-
sistivity 12Ucm has been used as substrate with PEC active
area of 2 cm2. The distance between nozzle and substrate was
maintained at 23 cm throughout the experiment.
2.2. Modification of CdS photoanode
After the film deposition, the surface of nanostructured CdS
photoanode was modified by NPT via. thioglycerol as organic
linker. Optimum concentration of thioglycerol (TG) was used
for complete adsorption of NPT on the CdS photoanode sur-
face. The concentration of TG is optimized by varying its
volume ratio in the range 0.1e1.0 (Fig. S.I. 1). It was found that
very low TG concentration (<0.1 v/v) was insufficient to attach
enough nanoparticles, whereas when higher concentration
(>>0.1 v/v) of TGwas used it deteriorated the photoanode, and
the CdS films peeled off (Fig. S.I. 2) from the FTO substrate. Our
optimization shows that stable film and the best PEC perfor-
mance can be achieved at TG concentration of 0.1 v/v%, which
is used in present study.
Further, NPT adsorption was carried-out on the TG
treated CdS photoanode as described in previous paragraph.
For this, NPT were synthesized using TiCl4 precursor in
aqueous medium via. known procedure in literature [46,47].
Precisely titanium tetrachloride is dissolved in the distilled
water at ice-cold temperature and further mixed with
ammonia solution. Thus obtained mixture was stirred for an
hour and refluxed for w18 h. As received precipitate was
collected by centrifugation and washed in distilled water to
remove any un-reacted impurities, and then air-dried. The
NPT (5 nm) were characterized (Fig S.I.3 and S.I.4) and used
for linking on the CdS surface by simple adsorption method.
Briefly, the as-prepared CdS thin films were treated with
optimum concentration of TG solution and later with NPT
dispersion (anatase 0.5 wt.%) so that NPT can be linked on
CdS photoanode surface in the manner shown in Fig. 1. Ef-
fect of amount of NPT adsorption on CdS surface was
studied based on the treatment times viz. 5 min (NPT a),
7 min (NPT b), 15 min (NPT c) and 30 min (NPT d) and named
as NPT a-d, henceforth throughout the manuscript, unless
specified.
The process was repeated with NPT dispersion made by
using rutile TiO2 (0.5 wt.%) dispersion. This was done to study
the “effect of TiO2 phase on the stabilization of CdS electrode”.
The PEC performance of these modified photoanodes was
considered for further optimization (Fig. S.I. 5). Expectedly,
anatase phase NPT shows efficient PEC performance. The NPT
adsorption on TG treated CdS thin films were carried out for
different time intervals, to understand the “effect of TG treat-
ment time” on the PEC performance. Further, its effect on the
optical properties is also studied to validate if TG adsorption
has taken place over the CdS film and that it does not degrade
the PEC performance. A typical case of 7 min treatment time
(Fig. S.I.6) has been shown in the transmission spectra that
revealed the optimum coverage of NPT.
Please cite this article in press as: Pareek A, et al., Stabilizing effecthydrogen generation, International Journal of Hydrogen Energy (
2.3. Characterization
Surface morphology of bare nanostructured CdS and NPT
treated CdS thin films were observed using field emission
scanning electron microscopy (Hitachi model S4300SE/N)
operated at 20 kV. Energy-dispersive X-ray spectroscopic (EDS)
analysis was done for the elemental characterization of the
films. X-ray diffraction pattern were obtained by using Bruker
AX D8 XRD diffractometer equipped with CuKa X-ray gun. The
scan is taken in the range of 2q ¼ 10e70� with an increment of
0.010 per second at the grazing angle of incidence. X-ray
photoelectron spectroscopy (O-micron model) has been used
for elemental and compositional analysis. The transmission
spectra were recorded using UVeVis spectrometer (Perkin
Elmer, lambda 650). The presence of Cd2þ ions were detected
from Induced coupled plasma spectroscopic (ICP-OES VARIAN
720-ES) studies.
The surfacemodified CdS thin film electrodes of area 2 cm2
are used for PEC measurements and the results were con-
verted to obtain the current-density accordingly. The photo-
electrochemical analysis was carried out using
electrochemical works station (PARSTAT 2273 Model). A two
electrode configuration with the modified photoanode as
working electrode and graphite as counter electrode is used
for measurement, whenever cell performance was desirable.
Na2S (0.1 M) & Na2SO3 (0.01 M) is used as an electrolyte with a
view to maintain an inherent stability of CdS. A Hgearc lamp
(Oriel) of power 500 W equipped with 470 (�10) nm band-pass
filter delivering an output power of 50 mW/cm2 is used for PEC
measurements. The infrared rays were cut-off using water
filter before falling on the filter. During the hydrogen evolution
measurements, hydrogen was detected by gas chromatog-
raphy (GC 2010 plus), while the PEC reactionwas carried-out at
0.2 V (vs. SCE) bias. In order to study the solar hydrogen pro-
duction, the solar simulator (Oriel Model 91160) equipped
with A.M.0, A.M.1.0 and an AM 1.5 Global (Newport) filter was
utilized. The irradiance of 80 mW/cm2 was used in present
case.
3. Results and discussions
Photoanode were named according to the adsorption time of
TiO2 nanoparticles on the CdS photoanodes, and are displayed
in Table 1. In the following study, NPT-b, the optimal photo-
anode has been used as photoanode throughout, to study the
structural, optical, morphological and the charge transfer
properties of modified photoanodes w.r.t bare CdS
photoanodes.
in nano-titania functionalized CdS photoanode for sustained2014), http://dx.doi.org/10.1016/j.ijhydene.2013.12.185
Table 2 e Absorption edge position, and bandgapvariation for NPT photoanodes.
Sample name Absorption edge (nm) Bandgap (eV)
CdS 496 2.50
CdS-TG 491 2.52
CdS-NPT 496 2.50
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y x x x ( 2 0 1 4 ) 1e1 14
3.1. Structural and optical characterization ofunmodified and modified CdS photoanodes
Fig. 2(a) shows X-ray diffraction spectra of the bare CdS and
the modified photo electrodes. All the films exhibits hexago-
nal phase that belongs to P63MC (JCPDS file No. 00-006-0314)
space group. The peaks due to FTO substrate can be easily
observed indicating the existence of thin film over FTO sub-
strate at the background of the film. Peaks related to TiO2 were
not found in the spectra. The crystallite size was found to be
22 nm, as estimated from debye Scherrer equation. The study
indicated the formation of nanostructure film over FTO under
the given conditions. Further, the nanostructured CdS films
were used for the fabrication of modified electrode.
Fig. 2(b) shows the UVeVIS absorption spectra of bare CdS,
and modified CdS thin films. Bare CdS and TG modified films
showed very similar behaviour, whereas CdS/NPT showed a
blue shift in their absorptionwith respect to the bare film. The
result of optical analysis is presented in Table 2. The study
confirms that the optical property of the CdS film remain
unaffected after adsorption of TG. On the contrary, a small
blue-shift in the band-gap of other two modified samples is
attributed to the existence of nano-sized TiO2 in case of NPT
treated CdS photoanodes [45].
Fig. 2 e (a) XRD patterns and (b) absorbance spectra for the
comparison of bare CdS photoanodes with NPT modified
CdS photoanodes.
Please cite this article in press as: Pareek A, et al., Stabilizing effechydrogen generation, International Journal of Hydrogen Energy (
3.2. Morphological characterization of modifiedphotoanodes
Fig. 3 shows the schematic electrode representation and sur-
face morphologies of the bare and modified CdS films, along
with their EDS spectra. Bare CdS film displays a nano-
structured surface (Fig. 3(a)) consisting of randomly aligned
rods throughout, which undergoes filler-type morphology
changes, upon the NPT treatment, as seen in the SEM of
Fig. 3(b). When TG (i.e. S–R–OH) is brought in vicinity of CdS
film surface, the thiol groups strongly react with the substrate,
and distort or fill-up the cavities near the rods yielding an
asymmetrically scattered rods all over the CdS surface. The
NPT treatment further, leads to the linking of dangling hy-
droxyl ions of TG to that of interactive ions of NPT. Presence of
NPT can be clearly seen in the form of spherical particles
(white colour) on the CdS surface as seen in Fig. 3(b). The
detection of Ti in EDS further validates the existence of linked
TiO2 nanoparticles over the CdS film surface. This adherent
NPT remains over the film even after washing of film in
solvent.
Fig. 3 e Schematic representation, EDS spectra and FESEM
images of (A) bare CdS photoanode; and (B) NPT modified
CdS photoanode.
t in nano-titania functionalized CdS photoanode for sustained2014), http://dx.doi.org/10.1016/j.ijhydene.2013.12.185
i n t e r n a t i o n a l j o u r n a l o f h yd r o g e n e n e r g y x x x ( 2 0 1 4 ) 1e1 1 5
This is in agreement with the earlier report [43] that S-
terminated CdS surface has affinity towards the thiol-group,
whereas TiO2 towards the hydroxyl group of TG. This study
demonstrates that we have achieved NPT modified nano-
structured CdS films. In order to, finally validate this model in
a quantitative manner; we further performed the XPS study
for the sake of completeness. The film surface studies (XPS
Fig. S.I.7eS.I.9) does confirm the proposed model (shown in
Figs. 1 and 3) and support the results of above section. Surface
studies clearly reveal the existence of Ti in the modified films.
3.3. Photoelectrochemical measurements of modifiedphotoanodes
The purpose of nanoparticle mediated surfacemodification of
CdS is to achieve an improved photoanode. Consequently, in
order to investigate the PEC behaviour of CdS and modified
CdS photoanodes, PEC characterization of respective photo-
electrodes was carried out. Fig. 4 shows the comparative
chronoamperometric curves for NPT modified CdS photo-
electrodes w.r.t. the bare CdS photoelectrode. An improve-
ment in the efficiency with the adsorption of NPT on CdS
surface is confirmed from the above studies.
Fig. 4 shows the effect of surface modification of CdS
photoanode with NPT on the PEC properties. As can be clearly
seen in case of NPT-d photoanode, the photocurrent increases
by 3.7 times than that generated by the bare CdS photoanode.
Above photocurrent improvement is evaluated using simple
differential function of I as defined by dI (dI¼ IModified film � IBare
Fig. 4 e Comparative study of photocurrent variation with
NPT treatment time for the NPT photo-electrodes with
respect to bare CdS, (dI [ IModified film e IBare CdS).
Please cite this article in press as: Pareek A, et al., Stabilizing effecthydrogen generation, International Journal of Hydrogen Energy (
CdS). The values of dI as shown in Fig. 4 clearly indicate an
enhancement in the photocurrent of modified photoelectrode
w.r.t. bare CdS photoelectrode. Similarly there is a systematic
increase in the efficiency for NPT-a, NPT-b and NPT-c photo-
anodes. This enhancement in the efficiency with TiO2 can be
attributed to the reduction of density of surface states on CdS
surface with the adsorption of NPT [36].
Electrochemical impedance spectroscopy was carried out
to understand the charge transfer mechanism between pho-
toelectrode/electrolyte interfaces. All themeasurements were
performed in dark conditions with an applied frequency of
10 kHz and ac small signal amplitude of 10mV Fig. 5 shows the
comparison of the Nyquist plots of CdS and NPT modified
photo-electrodes. A semicircle in the Nyquist plot clearly de-
picts that the charge transfer process at the CdS/electrolyte
interface is dominant and capacitive in nature [36]. The
experimental data were fitted using Z-View software. Fig. 5(d)
shows an equivalent circuit deduced from the analysis of
corresponding Nyquist plot.
In equivalent circuit, Rs represents an ohmic resistance of
electrolyte. Rt and Ct are the resistance and capacitance of the
electrode electrolyte interface. As can be seen in Fig. 5(a) the
diameter of the semicircle of Nyquist plot corresponding to
NPT modified photoelectrode is much greater than that of
bare CdS photoelectrode. It is important to note the recom-
bination time, which is equal to the product of resistance of
the solid interface and the capacitance (sr ¼ Rt � Ct) [36]. The
NPT modified photoanode shows much higher recombination
lifetime than bare CdS, implying reduction in the recombi-
nation process of charge carriers in modified electrodes.
Hence, these electrodes show an improved PEC performance.
3.4. Photoelectrochemical stability studies of NPTmodified electrodes
Implementation of sustainable hydrogen energy for energy
applications necessitates achieving a stable and an efficient
photoanode. Stability remains one of the most important
factors that controls life of a photoanode, and ultimately even
of PEC cell. In general, stability depends on several physical,
chemical and other factors [48]. Accordingly, in order to,
quantitatively describe stability of a photoanode, we have
defined a new parameter (Sphotoelectrode) which is the function
of several dependent parameters (physical/chemical/others)
as described below:
Sphotoelectrode ¼ 4ðphysicalÞ+4ðchemicalÞ+4ðothersÞ (2)
Where, f (physical) e physical properties of electrodes
correlated to stability viz. crystal structure, orientation,
thickness, area, geometry.
f (chemical) e pH of electrolyte, electrolyte composition,
concentration of electrolyte.
f (others) e temperature, time, stirring and photocurrent
density.
It is imperative that stability (Sphotoelectrode) is multiple-
parameter dependent function involving various processes,
and thus it is difficult to describe it quantitatively. However, in
in nano-titania functionalized CdS photoanode for sustained2014), http://dx.doi.org/10.1016/j.ijhydene.2013.12.185
Fig. 5 e Electrochemical impedance studies of (a) bare CdS, NPT modified photoanode (b) only NPT modified photoanode (c)
bare CdS photoanode (d) equivalent circuit and corresponding values of charge transfer resistance and capacitance values.
Fig. 6 e Chronoamperometry of bare CdS and NPT treated
photoanodes for different adsorption time for 2.5 h under
470 nm filter (Pin w 40 mW/cm2). Inset shows the
chronoamperometric of bare CdS andmost stable electrode
NPT-b under solar simulator (Pin w 80 mW/cm2) for 9 h.
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y x x x ( 2 0 1 4 ) 1e1 16
order to simplify its quantitative estimation in present study,
we have considered the variation of photocurrent with time as a
means to estimate the time-dependent stability of a photo-
anode; accordingly, we propose “photoanode-stability” to be a
simple function of photocurrent density and illumination
time, assuming other parameters constant:
X
photoelectrode
% ¼ DCdS � Dmodified
DCdS� 100%
0Dmodified/DCdS;
Pphotoelectrode/0
Dmodified/0;P
photoelectrode/1
(3)
Where Dphotoelectrode is slope of “I vs. t” curve of the photo-
electrode, given by:
D ¼ vIvt
¼ Iðt2Þ � Iðt1Þt2 � t1
Here, I(t1) is photocurrent at time ‘t1’and I(t2) is photocur-
rent at time ‘t2’.
Accordingly, the slope of Iet curve for CdS (6CdS) and
modified photoanode (6modified) were calculated from Fig. 6.
Subsequently, stability (Ʃ) is estimated for each modified
photoanode w.r.t the bare CdS photoanode. It can be noted
that Fig. 6 displays the comparison of chronoamperometric
curves for various electrodes for the duration of 2.5 h, while
inset of Fig. 6 indicating the time-dependent photocurrent
generation from NPT-b for around 9 h, under simulated solar
radiation. Fig. 6 clearly demonstrates that the NPT-b is the
most stable photoanode, as it displays a stable photocurrent.
These curves clearly reveal that, if the decay in photocurrent
of photoanode is comparatively faster as in case of bare CdS, it
indicates a poor stability (Sphotoelectrode). However, if there is no
decay in the photocurrent as seen for themodified photoanode
(say NPT-b-red curve) then it indicates the photoanode has 100
% stability. It is noteworthy that in order to quantify slope
Please cite this article in press as: Pareek A, et al., Stabilizing effechydrogen generation, International Journal of Hydrogen Energy (
(6CdS), it is necessary to relate it with the angle subtended by
the decay curve with X-axis (as shown in Fig. S.I.11). This can
be shown as below.
As, mathematically the slope is given by:
D ¼ tan j0j ¼ 0zstable photoelectrode
j ¼ 450zunstable photoelectrode
An ideal stable photoanode exhibits y¼ c behaviour in the I
vs. ‘t’ curve i.e. straight line with slope, D ¼ 0 (j ¼ 0). Deviation
from ideal behaviour leads to the reduction in the photocurrent,
which shows a deterioration of the photoanode due to the
photocorrosion process. This can be clearly understood from
t in nano-titania functionalized CdS photoanode for sustained2014), http://dx.doi.org/10.1016/j.ijhydene.2013.12.185
i n t e r n a t i o n a l j o u r n a l o f h yd r o g e n e n e r g y x x x ( 2 0 1 4 ) 1e1 1 7
the Fig. S.I.11 that shows angle j. On the basis of above pro-
posed theory, we have considered the analysis of I vs. ‘t’
characteristics as shown in Fig. 6. Table 3 summarizes the
variation in the stability (Sphotoelectrode) as deduced from
equation-3, for the modified photoanodes. It can be seen that
NPT-b shows significant stability (P
modified) than bare CdS
(P
CdS). This clearly shows a correlation of the stable NPT-b
behaviour with the maximum S of 100%.
Further, It can be noted NPT-b can be concluded as with
optimum loading, and not those with higher loading, say like
NPT-d. NPT-d shows a delayed equilibration with time,
possibly due to the fact that only few layers of NPT can be
adherent to CdS surface by getting linked to hydroxyl group of
TG. During electrochemical measurement extra TiO2 layers
comes out in the electrolyte with time until it reaches an op-
timum amount which can be adherent to CdS surface. This
leads to reduction in current up to a specific duration of time
and then it becomes stable.
After studying the stability of different NPT modified
electrodes under 470 nm filter for 2.5 h, further stability
studies were done for the most stable electrode i.e. NPT-b
under AM 1.5 solar simulator for 9 h as shown in inset of Fig. 6.
The above electrode is further found to be stable for 9 h,
without any deterioration in the electrode performance. Sta-
bility factor is calculated for NPT-b under solar simulator
measurements for 9 h as mentioned in Table 3 (NPT-b S).
Quantitative analysis of electrode and electrolyte was done
to further prove the suppression of photocorrosion. X-ray
photoelectron spectroscopy was performed for the analysis of
deterioration of photoelectrode by photocorrosion process.
In a PEC cell hydrogen is produced by photoelectrons
generated during illumination of photoelectrode given by
reaction:
2Hþ þ 2e�/H2 (4)
And holes generated are consumed to oxidize sulphide
ions into elemental sulphur. This process known as photo-
corrosion process given by reaction [49]:
S2� þ 2hþ/S (5)
This elemental sulphur combineswith sulphite ion present
in electrolyte (Na2S þ Na2SO3) and forms thiosulphate ion:
Sþ SO2�3 /S2O
2�3 (6)
Table 3 e Change in the photocurrent (I) with time (t) asslope-O, and stability (Sphotoelectrode) parameter asevaluated during the present study for differentphotoanodes.
Photoelectrode Dphotoelectrode � 10�3 aPphotoelectrode%
CdS bare 2.30 0
NPT-a 1.90 17
NPT-b 0.00 100
NPT-c 0.63 72
NPT-d 0.62 73
NPT-b S 0.00 100
a Pis estimated after 2.5 h of the PEC measurements for all elec-
trode except NPT-b S, Sphotoelectrode for NPT-b S was specifically
tested for longer time of 9 h.
Please cite this article in press as: Pareek A, et al., Stabilizing effecthydrogen generation, International Journal of Hydrogen Energy (
So the presence of thiosulphate on the electrode is the
evidence of photocorrosion reaction occurring during illumi-
nation of photoelectrode.
Keeping this in view, XPS analysis is carried out for
photoelectrode before and after 2.5 h of PEC measurements.
Fig. 7 shows the region wise XPS spectra of sulphur in CdS
and NPT coated CdS photoanodes before and after 2.5 h of
photoelectrochemical measurements. As shown in Fig. 7(a)
there is a thiosulphate peak observed at 163.3 eV after 2.5 h
of PEC measurements (highlighted with red colour in
Fig. 7(a) which is not seen before measurements in XPS
spectra. It clearly confirms photocorrosion reaction
occurred during measurements. Fig. 7(b) shows the XPS
spectra of NPT modified CdS photoelectrode before and after
9 h of PEC measurements. In Fig. 7(b) there is no thio-
sulphate peak observed after 2.5 h of PEC measurements.
This clearly demonstrates the suppression of photo-
corrosion reaction in NPT modified films. There is a peak at
164.2 eV in CdS-NPT electrodes before measurements which
corresponds to S of thiol group present in thioglycerol which
is absent in bare CdS as expected.
For further confirmation of inhibition of photocorrosion
and to know the extent of film dissolution in the electrolyte,
induced coupled plasma (ICP) elemental analysis is done. As
already known [44] during photocorrosion process, deterio-
ration of CdS photoelectrode takes place because of which
Cd2þ ions would be present in an electrolyte. So concentration
of Cd2þ ions in electrolyte is investigated before and after 2.5 h
of PEC measurements. The detection of concentration of Cd
ions in electrolyte is shown in Table 4.
Expectedly, negligible concentration of Cd2þ is observed in
electrolyte used for CdS-NPT photoanodes, rather than elec-
trolyte tested for bare CdS photoanodes. This shows stability
Fig. 7 e X-ray photoelectron spectroscopy of (a) bare CdS
electrode before (CdS-BM) and after (CdS-M); (b) CdS-NPT-b
electrode before (CdS/NPT-BM) and after (CdS/NPT-M)
taken after 2.5 h of PEC measurement.
in nano-titania functionalized CdS photoanode for sustained2014), http://dx.doi.org/10.1016/j.ijhydene.2013.12.185
Table 4 e Cd2Dion concentration detected in therespective electrolyte taken after the PECmeasurement ofrespective electrodes. ICP technique was used for thischaracterization.
Samplename
Measurement time (h) aConcentrationof Cd2þ ions(ppm) � 10�2
Stability
CdS 0 (Before measurement) 0.00 Unstable
2.5 (After measurement) 1.46
CdS/NPT 0 (Before measurement) 0.00 Stable
2.5 (After measurement) 0.81
a ICP measurement was also carried out for electrolyte before any
PEC measurement (as received), no Cd2þ was detected.
Fig. 8 e IPCE measurement of bare CdS and NPT-b photo
electrode.
Fig. 9 e Chronoamperometry of bare CdS and NPT-b
photoelectrode under AM 1.5 solar simulator at 0.2 V/SCE.
Inset shows JeV curves under same source.
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y x x x ( 2 0 1 4 ) 1e1 18
of CdS photoelectrode is much improved by the passivation of
its surface by making use of nano-TiO2 layer.
These results demonstrated by above quantitative
elemental analyses are inline with the estimated stability
factor specially described in this study. Thus the work clearly
confirms the achievement of highly stable and efficient CdS
photoelectrode attained by NPT modification.
3.5. Efficiency studies of stabilized electrode
3.5.1. Incident photon to current conversion efficiencyIt is interesting to note at this point that NPT modified
electrode not only show an increased stability but also
exhibit an improved photocurrent generation as shown by
NPT-b. This is well understood by efficiency studies on NPT-
b photo electrodes. Incident photon to current efficiency
(IPCE) is one of the most important characterizations for PEC
devices. It describes the photocurrent collected per incident
photon flux as a function of illumination wavelength. IPCE
was calculated for bare CdS and NPT-b modified electrodes
using the expression [50].
IPCE ¼ 1240 � JphðmAcm�2ÞPðmWcm�2Þ � lðnmÞ
Where Jph the photocurrent density in mA cm�2, P is power of
source in mW cm�2 and l is wavelength in nm.
IPCE calculated for NPT-b electrodes is found to be 22%
which is much enhanced than that of bare CdS photoanode
(w8%) at 470 nm as shown in Fig. 8. Greater IPCE of NPT-b
electrodes demonstrates its improved efficiency of convert-
ing incoming radiation into hydrogen from water, with an
assumption that all the electrons produced during illumina-
tion were used for the evolution of hydrogen.
3.5.2. Solar to hydrogen conversion efficiencyTo evaluate hydrogen generating performance of NPT-b elec-
trode under standard solar conditions, chronoamperometric
and Currentepotential (JeV) measurements were carried out
under AM 1.5 solar simulator as shown in Fig. 9. Solar to
hydrogen efficiency (STH) was calculated for bare CdS and the
most stable modified electrode (NPT-b) at 0.2 V/SCE using
following expression [51].
hð%Þ ¼�Vrev � Vapp
� � JpI0
� 100
Please cite this article in press as: Pareek A, et al., Stabilizing effechydrogen generation, International Journal of Hydrogen Energy (
Here Vrev is standard reversible potential i.e. 1.23 V, I0 is
power intensity of source i.e. 80 mW/cm2 and
Vapp ¼ Vmeas � Voc
Whereas, Voc is open circuit potential and Vmeas is the po-
tential at which photocurrent measurements are carried out
with respect to a reference electrode (SCE).
Open circuit potential for bare CdS and NPT-b electrode is
found to be �0.7 eV and �0.4 eV respectively as measured
using J-V curves without illumination (Fig. S.I. 10). Corre-
spondingly STH efficiencies calculated for bare CdS and NPT-b
photoanodes are found to be 0.2% and 0.7% respectively.
3.6. Stable and efficient hydrogen evolution frommodified photoanode
Finally in order to validate stability and efficiency of modified
CdS photoanode w.r.t hydrogen production, following studies
were carried out. Accordingly, accumulated hydrogen was
detected for bare CdS as well as for NPT-b electrodes at
different time intervals. Expectedly, NPT-b shows a very high
t in nano-titania functionalized CdS photoanode for sustained2014), http://dx.doi.org/10.1016/j.ijhydene.2013.12.185
Fig. 10 e The evolved hydrogen with reaction time
demonstrates that the modified photoanode (NPT-b) stably
generates 25 times higher hydrogen gas under simulated
solar radiation (AM 1.5) as compared to the unmodified
CdS.
i n t e r n a t i o n a l j o u r n a l o f h yd r o g e n e n e r g y x x x ( 2 0 1 4 ) 1e1 1 9
hydrogen evolution than bare CdS. Fig. 10 clearly demon-
strates that themodified photoanode (NPT-b) stably generates
25 times higher hydrogen gas under simulated solar radiation
(AM 1.5) as compared to the unmodified CdS. It is interesting
to note that during first 20 min, modified electrode generates
noticingly higher hydrogen gas as compared to the bare CdS
electrode. However, for longer accumulation times, very high
magnitude of hydrogen gas is evolved. The comparison of the
time dependent behaviour of CdS and modified photoanode
reveals that during the initial phase of PEC reaction, photo-
corrosion of the bare CdS was seemingly very less significant.
During later part of the PEC reaction both photocorrosion
and hydrogen productions are competitive processes, as
correlated from the detected Cd/S and generated photocur-
rent as well as evolved hydrogen gas. Thus in the case of bare
CdS, photocorrosion was found to be dominating process as
shown in earlier section (Fig. 7 & Table 3). This leads to bare
CdS yielding negligibly low hydrogen. In contrast, in case of
the modified photoanodes the photocorrosion was inhibited,
and at the same time photocurrent generation was domi-
nating process as supported by elemental analysis (Fig. 7 &
Table 4) and time dependent photocurrent measurement
(Fig. 6 & Table 3). Consequently in line with our earlier dis-
cussion a reduced charge-recombination is the main param-
eter that is responsible for yielding higher efficiency for
modified photoanodes. This behaviour was consistent even
for longer time of PEC reaction. Hence, modified NPT-b comes
out to be an efficient and a stable photoelectrode for hydrogen
generation via. cleavage of water molecule. This is one of the
desired achievements for CdS photoelectrode, which has been
specifically demonstrated, in present work.
4. Conclusions
Very stable CdS photoanodes have been fabricated by spray
pyrolysis film deposition technique. The modification of
Please cite this article in press as: Pareek A, et al., Stabilizing effecthydrogen generation, International Journal of Hydrogen Energy (
“aligned rod-like nanostructured CdS” bare electrodes by
adsorption of TiO2 (5 nm) nanoparticles yields 3.7 times
enhanced photocurrent generation than bare CdS electrode.
Themodified electrode generated 25 timesmore hydrogen gas
than the bare CdS. An enhanced IPCE of 22%has been reported
for TiO2 modified photoanode rather than bare CdS (w8%).
Modified photoanode shows improved STH of 0.7% than that
of bare CdS (w0.2%). Enhancement in photocurrent displayed
by nanoparticle TiO2 modified CdS photoanode is attributed to the
reduction in the electronehole recombination process. Spe-
cifically, photochemical-stability is studied by quantitative
elemental analysis using XPS and time dependent photocur-
rent. Stability factor (P
) that has been defined for the first time
has been quantified for the bare and the modified electrodes.
It is found thatP
modified(100%) achieved is much better thanPCdS (72%) when tested for a typical duration of 2.5 h of PEC
reaction time. Thus, obtainedP
-factor for modified electrode
demonstrates an improved stability for nano-TiO2 modified
photoelectrode. Such high efficiency and stability is attributed
to its passive behaviour over photo-corrosive CdS surface.
Acknowledgement
The authors wish to thank Mr. K. Ramesh Reddy, and L.
Venkatesh, for their help during film characterization.
Permission granted by Director, ARCI to publish the work is
also gratefully acknowledged.
Appendix A. Supplementary data
Supplementary data related to this article can be found at
http://dx.doi.org/10.1016/j.ijhydene.2013.12.185.
r e f e r e n c e s
[1] Gratzel M. Photoelectrochemical cells. Nature 2001;414:51e9.[2] Kim HG, Borse PH, Choi W, Lee JS. Photocatalytic nanodiodes
for visible light photocatalysis. Ang Chem 2005;44:4585e9.[3] Hong SJ, Jun H, Borse PH, Lee JS. Size effects of WO3
nanocrystals for photooxidation of water in particulatesuspension and photoelectrochemical film systems. Int JHydrogen Energy 2009;34:3234e42.
[4] Kim HG, Borse PH, Jang JS, Jeong ED, lee JS. Enhancedphotochemical properties of electron rich W dopedPbBi2Nb2O9 layered pervoskite material under visible lightirradiation. Mater Lett 2008;62:1427e30.
[5] Kim HG, Borse PH, Jang JS, Ahm CW, Jeong ED, Lee JS.Engineered nanorod pervoksite film photocatalysts toharvest visible light. Adv Mater 2011;23:2088e92.
[6] Lee WJ, Shinde PS, Go GH, Ramasamy E. Ag grid inducedphotocurrent enhancement in WO3 photoanode and theirscale up performance towards photoelectrochemical H2
generation. Int J Hydrogen Energy 2011;36:5262e70.[7] Li Y, Hu Y, Peng S, Lu G, Li S. Synthesis of CdS nanorods by an
ethylene diamine assisted hydrothermal method forphotocatalytical hydrogen evolution. J Phys Chem2009;113:9352e8.
in nano-titania functionalized CdS photoanode for sustained2014), http://dx.doi.org/10.1016/j.ijhydene.2013.12.185
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y x x x ( 2 0 1 4 ) 1e1 110
[8] Tak Y, Hong SJ, Lee JS, Yong K. Fabrication of ZnO/CdS core/shell nanowire arrays for efficient solar energy conversion. JMater Chem C 2009;19:5945e51.
[9] Meissner D, Benndorf P, Memming R. Photocorrosion ofcadmium sulphide: analysis by photoelectron spectroscopy.Appl Surf Sci 1987;27:423e6.
[10] Liao M, Feng J, Luo W, Wang Z, Zhang J, Li Z, et al. Co3O4
nanoparticle as robust water oxidation catalysts towardsremarkably enhanced photostability of a Ta3N5 photoanode.Adv Funct Mater 2012;22:3066e74.
[11] Inoue T, Watanabe T, Fujishima A, Honda K, Kohsyakawa K.Suppression of surface dissolution of cadmium sulphidephotoanode by reducing agents. J Electrochem Soc1977;124:719e22.
[12] Calza P, Minero C, Pelizzetti E. Photocatalytictransformations of chlorinated methanes in the presence ofelectron and hole scavengers. J Chem Soc Faraday Trans1997;93:3765e71.
[13] Fujishma A, Suguyama E, Honda K. Photosensitive electrodereactions. Bull Chem Soc Jpn 1971;44. 304e304.
[14] Darwent JR, Porter G. Photochemical hydrogen productionusing cadmium sulphide suspensions in aerated water. JChem Soc Chem Commun 1981;4:145e6.
[15] Memming R. The role of energy levels in semiconductor-electrolyte solar cells. J Electrochem Soc 1978;125:117e23.
[16] Wilson JR, Park SM. Photoanodic dissolution of n-cadmiumsulphide studied by rotating ring-disk electrodes. JElectrochem Soc 1982;129:149e54.
[17] Kalyanasundaraman K, Boragarello E, Duonghong D,Gratzel M. Cleavage of water by visible-light irradiation ofcolloidal CdS solutions; inhibition of photocorrosion by RuO2.Angew Chem 1981;20:987e8.
[18] Minoura H, Tsuiki M. Anodic reactions of several reducingagents on illuminated cadmium sulphide electrode.Electrochim Acta 1978;23:1377e82.
[19] Buchler N, Meier K, Reber JF. Photochemical hydrogenproduction with cadmium sulphide suspensions. J PhysChem 1984;88:3261e8.
[20] Sato K, Tachibana Y, Hattari S, Chiba T, Kuwabata S.Polyacrylic acid coating of highly luminescent CdSnanocrystals for biological labelling applications. J ColloidInterface Sci 2008;324:257e60.
[21] Zhao H, Chaker M, Ma D. Effect of CdS shell thickness on theoptical properties of water-soluble, amphiphilic polymer-encapsulated PbS/CdS core/shell quantum dots. J MaterChem 2011;21:17483e91.
[22] Peng R, Zhao D, Baltrusaits J, Hu CM, Koodali RT. Visible lightdriven photocatalytic evolution of hydrogen from water overCdS encapsulated MCM-48 materials. RSC Adv2012;2:5754e67.
[23] Deng S, Lu J, Yao X, Huang Y, Lin D, Ju H. Synthesis and low-potential electrogenerated chemiluminescence of surfacepassivated phenol formaldehyde resin@CdS quantum dots. JMater Chem C 2013;1:299e306.
[24] Navarro RM, Valle FD, Fierro JLG. Photocatalytic hydrogenevolution from CdSeZnOeCdO system under visible lightirradiation: effect of thermal treatment and presence of Ptand Ru cocatalyst. Int J Hydrogen Energy 2008;32:4265e73.
[25] Kannaiyan D, Kim E, Won N, Kim KW, Jhang YH, Cha MA,et al. On the synergistic coupling properties of compositeCdS/TiO2 nanoparticle arrays confined in nanopatternedhybrid thin films. J Mater Chem 2010;20:677e82.
[26] Jhang SK, Ji SM, Bae SW, Son HC, Lee JS. Optimization of CdS/TiO2 nanobulk composite photocatalysts for hydrogenproduction from Na2S/Na2SO3 aqueous electrolyte solutionsunder visible light (l � 420 nm). J Photochem Photobiol A2007;188:112e9.
Please cite this article in press as: Pareek A, et al., Stabilizing effechydrogen generation, International Journal of Hydrogen Energy (
[27] FujiH, InataK,OhtalaM,EguchiK,AraiH.SynthesisofTiO2/CdSnanocomposite via TiO2 coating on CdS nanoparticles bycompartmentalized hydrolysis of Ti alkoxide. J Mater Sci2001;36:527e32.
[28] Mitzithra C, Kaniaris V, Hamilakis S, Kordatos K, Kollia C,Loizos Z. Development and study of new hybridsemiconducting systems involving Cd chalcogenide thinfilms coated by fullerenes. Mater Lett 2011;65:1651e4.
[29] Hu J, Jiang H, Chen Z, Sun Y, Bande Y, Sekiguchi T. Uniform,thin and continuous graphitic carbon tubular coatings onCdS nanowires. J Mater Chem 2009;19:1093e7.
[30] Hou J, Wang Z, Kan W, Jiao S, Zhu H, Kumar RV. Efficientvisible-light-driven photocatalytic hydrogen productionusing CdS@TaON coreeshell composites coupled withgraphene oxide nanosheets. Sol Energy 2012;22:7291e9.
[31] Li C, Yuan J, Han B, Jiang L, Shangguan W. TiO2 nanotubesincorporated with CdS for photocatalytic hydrogenproduction from splitting of water under visible lightirradiation. Int J Hydrogen Energy 2010;35:7073e9.
[32] Qian S, Wang C, Liu W, Zhu Y, Yao W, Liu X. An enhancedCdS/TiO2 photocatalyst with high stability and activity: effectof mesoporous substrate and bifunctional linking molecule. JMater Chem 2011;21:4945e52.
[33] Chen Y, Wang L, Liu G, Yao X, Guo L. Nanoparticlesenwrapped with nanotubes: a unique architecture of CdS/titanate nanotubes for efficient photocatalytic hydrogenproduction from water. J Mater Chem 2011;21:5134e41.
[34] Jang JS, Kim HG, Borse PH, Lee JS. Simultaneous hydrogenproduction and decomposition of H2S dissolved in alkalinewater over CdSeTiO2 composite. Int J Hydrogen Energy2007;32:4786e91.
[35] Aliev ASh, Mamedov MN, Abbasov MT. Photoelectrochemicalproperties of TiO2/CdS heterostructures. Inorg Mater2009;45:965e7.
[36] Zhong M, Shi J, Xiong F, Zhang W, Li C. Enhancement ofphotoelectrochemical activity of nanocrystalline CdSphotoanode by surface modification with TiO2 for hydrogenproduction and electricity generation. Sol Energy2012;86:756e63.
[37] Robel I, Subramanian V, Kuno M, Kamat PV. Quantum dotsolar cells. Harvesting light energy with CdSe nanocrystalsmolecularly linked to mesoscopic TiO2 films. J Am Chem Soc2006;128:2385e93.
[38] Kongkanand A, Tvrdy K, Takechi K, Kuno M, Kamat PV.Quantum dot solar cells. Tunning photoresponse throughsize and shape control of CdSeeTiO2 architecture. J AmChem Soc 2008;130:4007e15.
[39] Dibbell RS, Watson DF. Distance-Dependent electrontransfer in tethered assemblies of CdS quantum dots andTiO2 nanoparticles. J Phys Chem C 2009;113:3139e49.
[40] Dibbell RS, Youker DG, Watson DF. Excited state electrontransfer from CdS quantum dots to TiO2 nanoparticles viamolecular linkers with phenylene bridges. J Phys Chem C2009;113:18643e51.
[41] Bora DK, Rozhkova EA, Schrantz K, Wyss PP, Braun A,Graule J, et al. Functionalization of nanostructured hematitethin-film electrodes with the light-harvesting membraneprotein C-phycocyanin yields an enhanced photocurrent.Adv Funct Mater 2012;22:490e502.
[42] Pareek A, Hebalkar N, Borse PH. Fabrication of a highlyefficient and stable nano-modified photoanode for solar H2
generation. RSC Adv 2013;3:19905e8.[43] Kamat PV, Tvrdy K, Barker DR, Radich JG. Beyond
photovoltaics: semiconductor nanoarchitecture for liquidjunction solar cells. Chem Rev 2010;110:6664e88.
[44] Yan X, Liu G, Wang L, Wang Y, Zhu X, Zou J, et al.Antiphotocorrosive photocatalysts containing CdS
t in nano-titania functionalized CdS photoanode for sustained2014), http://dx.doi.org/10.1016/j.ijhydene.2013.12.185
i n t e r n a t i o n a l j o u r n a l o f h yd r o g e n e n e r g y x x x ( 2 0 1 4 ) 1e1 1 11
nanoparticles and exfoliated TiO2 nanosheets. J Mater Res2010;25:182e8.
[45] Pareek A, Dom R, Borse PH. Fabrication of large area nanorodlike structured CdS photoanode for solar H2 generation usingspraypyrolysis technique. Int JHydrogenEnergy2013;38:36e44.
[46] Borse PH, Kankate LS, Dassenoy F, Wogel W, Urban J,Kulkarni SK, et al. Synthesis and investigation of rutile phasenanoparticles of TiO2. J Mater Sci Mater Elect 2002;13:553e9.
[47] Paola A Di, Bellardita M, Palmisano L. TiO2 photocatalystsprepared by thermo hydrolysis of TiCl4 in aqueous solutions.Surf Sci Catal 2010;175:225e8.
[48] Hodes G, Manassen J. Effect of surface etching andmorphology on stability of CdSe/Sx photoelectrochemicalcells. J Electrochem Soc 1981;128:2325e30.
Please cite this article in press as: Pareek A, et al., Stabilizing effecthydrogen generation, International Journal of Hydrogen Energy (
[49] Jang JS, Ham DJ, Lakshmi N, Choi WY, Lee JS. Role ofplatinum like tungsten carbide as cocatalyst of CdSphotocatalyst for hydrogen production under visible lightirradiation. Appl Catal A Gen 2008;346:149e54.
[50] Chen Z, Jaramillo TF, Deutsch TG, Shwarsctein AK,Forman AJ, Gaillard N, et al. Accelerating materials anddevelopment for photoelectrochemical hydrogenproduction. Standards for methods definitions and reportingprotocols. J Mater Res 2010;25:3e16.
[51] Kumari S, Tripathi C, Singh AP, Chauhan D, Shrivastav R,Dass S, et al. Characterization of Zn doped hematite thinfilms for photoelectrochemical splitting of water. Curr Sci2006;91:1062e4.
in nano-titania functionalized CdS photoanode for sustained2014), http://dx.doi.org/10.1016/j.ijhydene.2013.12.185