Decoration of Pd and Pt nanoparticles on a carbon nitride (C3N4) surface for nitro-compounds reduction and hydrogen evolution reaction

Article abstract of DOI:10.1039/c7nj01221g

Herein, we propose the synthesis of Pd and Pt monometallic nanoparticles on a carbon nitride (C₃N₄) surface for the reduction of nitro compounds as well as for electrocatalysis. For the synthesis of C₃N₄/Pd and C₃N₄/Pt, metal ions were initially adsorbed on the C₃N₄ surface and then subsequently reduced by NaBH₄. The as-synthesized heterostructures were authenticated by different characterization techniques: UV-vis, PXRD, XPS, TEM, FESEM, and EDS. Decorations of monometallic NPs on C₃N₄ not only improved the reduction efficiency of nitro-compounds but also enhanced the electrocatalytic activity in the hydrogen evolution reaction. C₃N₄/Pt proved to be an efficient electrocatalyst as it requires a potential of -0.339 V to attain a current density of 10 mA cm^-2; whereas, C₃N₄/Pd requires -0.371 V to reach a current density of 10 mA cm^-2vs. Ag/AgCl. Both C₃N₄/Pd and Pt heterostructures are better than bare C₃N₄, which needs -0.596 V to achieve a current density of 10 mA cm^-2vs. Ag/AgCl. On the other hand, C₃N₄/Pd showed a better performance in nitro-compound reduction compared to C₃N₄/Pt and bare C₃N₄. The kinetic study reveals that the rate constant using a C₃N₄/Pd catalyst is 6.7 × 10^-1 min^-1 for p-nitroaniline reduction, which is 101 times higher compared to bare C₃N₄ and 4.7 times higher in comparison to C₃N₄/Pt.

Full text of DOI:10.1039/c7nj01221g

View Article Online
View Journal
NJC
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: R. Nazir, P.
Fageria, M. Basu, S. Gangopadhyay and S. Pande, New J. Chem., 2017, DOI: 10.1039/C7NJ01221G.
Volume 40 Number
1
January 2016 Pages 1–846
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
NJC
New Journal of Chemistry
www.rsc.org/njc
A journal for new directions in chemistry
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1144-0546
PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
rsc.li/njc

Page 1 of 24
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ01221G
Decoration of Pd and Pt Nanoparticles on Carbon Nitride (C
3
N
4
) Surface for
Nitro- Compounds Reduction and Hydrogen Evolution Reaction
a
a
a
b
Roshan Nazir, Pragati Fageria, Mrinmoyee Basu, Subhashis Gangopadhyay, and Surojit
Pande*a
aDepartment of Chemistry, Birla Institute of Technology and Science, Pilani, Rajasthan, 333031,
India. E-mail: spande@pilani.bits-pilani.ac.in, surojitpande@gmail.com
Tel.: +91-1596 515709. Fax: +91-1596 244183
bDepartment of Physics, Birla Institute of Technology and Science, Pilani, Rajasthan, 333031,
India
1

New Journal of Chemistry
Page 2 of 24
View Article Online
DOI: 10.1039/C7NJ01221G
Abstract
Here, we propose the synthesis of Pd and Pt monometallic nanoparticles on carbon nitride
) surface for the reduction of nitro compounds as well as for electrocatalysis. For the
(
C
3
N
4
synthesis of C
subsequently reduced by NaBH
different characterization techniques, UV-vis, PXRD, XPS, TEM, FESEM, and EDS.
Decorations of monometallic NPs on C not only improve the reduction efficiency of nitro-
compounds but also enhanced the electrocatalytic activity in hydrogen evolution reaction.
/Pt proved efficient electrocatalyst as it requires -0.339 V potential to attain current density
3
N
4
/Pd and C
3
N
4
/Pt, metal ions were initially adsorbed on C
3
N
4
surface and then
4
. The as-synthesized heterostructures was authenticated by
3
N
4
C
3
N
4
2
2
of 10 mA/cm , whereas, C
Ag/AgCl. Both C /Pd and Pt heterostructures are better than bare C
to achieve 10 mA/cm current density vs. Ag/AgCl. On the other hand, C
performance in nitro-compound reduction as compared to C /Pt and bare C
study reveals that the rate constant using C /Pd catalyst is 6.7 ×10 min for p-nitroaniline
reduction, which is 101 times higher as compared to bare C and 4.7 times in comparison to
/Pt.
3
N
4
/Pd requires -0.371 V to reach 10 mA/cm current density vs.
, which needs -0.596 V
/Pd showed better
. The kinetic
3
N
4
3
N
4
2
3
N
4
3
N
4
3
N
4
-1
-1
3
N
4
3
N
4
C
3
N
4
Keywords: Metal nanoparticles, C
3
4
N substrate, Hydrogen evolution reaction, and Nitro-
compound reduction
2

Page 3 of 24
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ01221G
1
. Introduction
Now-a-days increasing global population demands for clean, affordable and reliable energy
1
source. Currently, fossil fuels have been dominating the global energy demands but increasing
concerns of global warming due to production of undesirable carbon-dioxide appeals for low
2
,3
pollutant emission and high efficient energy fuels. Over the years, hydrogen is a promising and
efficient energy source due to its high energy density, efficiency, and low pollutant emission.4
Hydrogen have been generated from sources like water, coal, biomass etc., but electrochemically
water splitting is widely investigated as a sustainable method to evolve H via hydrogen
2
evolution reaction (HER). Generation of hydrogen from water splitting is environmentally
friendly and globally accepted pathway.
In recent times noble metal nanoparticles (NPs) have attained a tremendous attention for
hydrogen evolution reaction, which is due to low resistance and excellent catalytic activity in
acidic media. Amongst all effective HER electrocatalysts, Pt based nanocomposites were proved
as an effective and efficient catalysts due to their low reduction overpotentials and fast kinetics.5-
7
However, limited sources and expensive availability of Pt based nanocomposites shifted the
research for an alternative. Recently, Pd NPs were investigated as an active electrocatalysts and a
good alternative for Pt NPs.8,9 Mostly monometallic Pd NPs have been reported on supported
material (e.g., carbon powder, Tungsten carbide (WC) etc.)10-12 but the durability of supported
1
3
catalyst is very low. Therefore, it is very important to produce a new support based catalyst
with high durability and superior electrocatalytic activity. One of the constructive strategy is
incorporation of a heteroatom in the solid support, e.g., nitrogen, which can coordinate with
metal NPs and overcomes the durability.14,15
Carbon nitride (C
photocatalyst. C has its unique layered structure and a characteristic electronic band structure
consists of valence band and conduction band.16 Porous matrix of C
surface can easily
functionalize with many organic/inorganic compounds with high reactivity.17,18 Synthesis of Pd
NPs on g-C surface for selective hydrogenation of phenol and its derivatives has been
reported by Antonietti and co-workers. Wang and co-workers reported Pd NPs loading on a
hybrid solid support consist of C and graphene for oxidation of formic acid and methanol
3
4
N ) is a polymeric semiconductor and used as visible light
3
N
4
3
N
4
3
N
4
1
9
3
N
4
20
electro-oxidation. The same group also reported oxidation of glycerol using Pd NP loaded
3

New Journal of Chemistry
Page 4 of 24
View Article Online
DOI: 10.1039/C7NJ01221G
2
1
hybrid C
3
N
4
and graphene system. Barman and co-workers described the synthesis of porous
Pd NPs-C
3
N
4
composite (Pd-CNx) for hydrogen evolution and hydrogen oxidation reactions in
acidic media.22 Porous Pd-CNx composite shows best catalytic activity towards HER than
commercial Pt/C and Pd/C. They also mentioned Pd-CNx composite showed high durability in
strongly acidic media, much higher than that of commercial Pt/C. Recently, our group also
reported the synthesis of mono- (Au and Pd) and bimetallic NPs using C
3
N
4
quantum dot under
the illumination of UV light for 4-nitrophenol reduction. The advantages of C as a support
for any catalytic and electrocatalytic reactions are manifold.22,23 First, strong interaction between
metal NPs with C provides large accessible active sites. Second, porous structure of C
allows reactant to reach active site or edge easily and quick formation of product on metal
surface. Third, synergistic effect between metal and C facilitates the rate of the catalytic
23
3
N
4
3
N
4
3
N
4
3
N
4
reaction. Therefore, based on the literature report it is quite evident that C
3
4
N supported Pd NPs
are durable and exhibit better electrocatalytic activity.
Being inspired from the above studies, we proposed a simple method for Pd and Pt
monometallic NPs synthesis on C surface for hydrogen evolution and nitrocompound
reduction. For the synthesis of C /Pd and Pt NPs, precursor metal ions were initially adsorbed
on C surface and then subsequently reduced by a reducing agent, NaBH . All the materials
3
N
4
3
N
4
3
N
4
4
were characterized by UV-vis, powder X-ray diffraction, scanning electron microscopy,
transmission electron microscopy, and X-rayꢀ photoelectron spectroscopy techniques. The as-
synthesized materials were used as an electrocatalyst for HER and heterogeneous catalyst for
reduction of nitro-compounds. For HER, best catalytic efficiency was achieved in case of
C
3
4
N /Pt. Pt NPs proved efficient catalyst in electrocatalysis as it requires potential of -0.339 V
vs. Ag/AgCl. While C
3
N
4
/Pd showed best performance in nitro-compound reduction with a rate
-1
-1
constant, k = 6.7 ×10 min for 4-nitroaniline reduction, which is 101 times higher than bare
C
3
N
4
. These results revealed that decoration of metal nanoparticles on C
improved the reduction kinetics of nitro-compounds but also enhanced the electrocatalytic
activity. The advantages for this work are manifold. First, syntheses of metal NPs on C
3
N
4
surface not only
3
N
4
surface, a stable support with better catalytic activity and high durability. Second, to develop a
good electrocatalyst for HER in acid medium, which is comparable with commercial Pt/C and
Pd/C.
4

Page 5 of 24
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ01221G
2
. Experimental Section:
Pure chemicals of analytical grade (AR) were used as such without any further purification.
PdCl and K PtCl were purchased from Alfa Aesar and extrapure urea from Sd-fine
K
2
4
2
4
chemicals, India. Sodium borohydride, p-nitroaniline, o-nitrobenzoic acid, nafion perfluorinated
resin, isopropyl alcohol, and sulfuric acid (HPLC grade) were purchased from Sigma Aldrich.
Ethanol was purchased from Merck and p-nitrophenol from Spectrochem, India. Throughout the
experiment DI water was used.
2
.1. Synthesis of C
3
N
4
: Bulk C
3
4
N was synthesized via poly-condensation reaction from urea,
which is reported elsewhere.18,24 In brief, thermal treatment was given in a silica crucible using a
compound, which is a rich source of carbon and nitrogen (e.g., urea). Firstly, 10 g urea was dried
°
at ~ 80-90 C to remove adsorbed moisture. Secondly, dried urea was transferred in a covered
°
silica crucible and placed in a muffle furnace for thermal treatment at 550 C for 2.5 h with a
°
-1
heating rate 10 C min . Thirdly, at room temperature condition the light yellow color product
°
was collected and washed with 0.1 M HNO
3
to remove extra impurities and dried at 80 C. 1.0 g
C
3
N
4
was exfoliated in 100 mL water using a sonicator for 5 h to obtain C
3
4
N nanosheet at a
-1
concentration of 10 mg mL .
Synthesis of C /Pd and Pt NPs: For the synthesis of C
nanosheet (19 mL) was taken and 1 mL of 10 M aqueous solution of K
the reaction mixture was stirred for 1 h and treated with NaBH
(1 mL of 1.0 M) to reduce Pd2+
ions and stirring was continued for another 2 h. After addition of NaBH , the brown color
3
N
4
3
N
4
/Pd, exfoliated C
3
N
4
-2
2
PdCl was added. Then
4
4
4
solution was changed into grey color due to the formation of palladium nanoparticles. Finally,
the product was washed with distilled water and ethanol to remove impurities and dried in air.
To synthesize C
used in place of K
.2. Characterization techniques
3
N
4
/Pt similar procedure for C
N
3 4
/Pd was followed except K
2
PtCl was
4
2
PdCl4.
2
Ultraviolet-visible light absorption spectra were recorded using a Jasco V-650
Spectrophotometer (UV-1800). Powder X-ray diffraction (PXRD) were recorded using a Rigaku
Mini Flex II diffractometer with Cu-Kα radiation at 25 °C. Room temperature FTIR analysis of
the powder samples (pellets in KBr, without moisture) were measured by using a Perkin Elmer
-1
2
000 infrared spectrometer in the range of 500-2000 cm . FESEM analysis was carried out using
Nova Nano Sem 450 operated from 0.5 kV to 30 kV. High-resolution transmission electron
5

New Journal of Chemistry
Page 6 of 24
View Article Online
DOI: 10.1039/C7NJ01221G
microscopy (HRTEM) analysis was carried out on a Bruker microscope operated at 200 kV. X-
ray photoelectron spectroscopy (XPS) was performed using a commercial Omicron spectrometer
equipped with an Mg-Kα x-ray source (1256.6eV). For all measurements, emission current of the
X-ray source was fixed at 15 mA for an anode voltage of 15 kV. High resolution XPS spectra
were collected using a pass energy of 20 eV, with a step size of 0.1 eV. The UHV chamber base
-9
pressure was maintained < 10 mbar throughout the measurements. XPS samples were prepared
by dropping 10 μL of the aqueous dispersed solution of C /Pd and Pt nanoparticles onto a
3
N
4
small pieces conducting carbon tape and dried under a dry nitrogen line. To compensate any kind
of charging effect, C 1s binding energy peak at 284.5 eV has been used as a reference. The
electrochemical measurements were performed on a potentiostat (CHI 604E, CH Instruments,
USA) using a three-electrode cell system. Glassy carbon electrode (GCE, 3 mm diameter), Pt
wire, and Ag/AgCl were used as working, counter, and reference electrode, respectively.
Aqueous solution of H
2
SO (10 mL of 0.5 M) was used during electrochemical measurements.
4
The linear-sweep voltammogram (LSV) of catalyst was obtained between 0.0 V to -0.6 V
potential ranges applying 50 mV/S scan rate.
2
.3. Catalysis in nitro-aromatic reduction: Nitro-aromatic reduction was carried out using
NaBH as a hydrogen donor and water as a solvent. For this reduction reaction aqueous solution
of p-nitroaniline (4-NA) (2.0 mL of 10 M) and 2.0 mL of 10 M NaBH
4
-3
-1
4
was added in 16 mL
water. Total volume of the solution was 20 mL. After that, in the reaction mixture 1.0 mg of
catalyst was added. To monitor the reduction reaction, 3.0 mL solution was taken from the
reaction vessel and UV-vis spectroscopy was measured. After UV-vis measurement 3.0 mL
solution was poured again in the reaction container so that the total volume remain unchanged.
All the as-synthesized catalysts (bare C
3
4
N , Pd, and Pt) were used for the reduction reaction.
In case of other nitro compound reduction similar method was followed except p-
nitrophenol and o-nitrobenzoic acid were used instead of 4-NA.
The percentage of conversion of the nitro-compound reduction can be calculated using:
%
Conversion = (A
and absorbance at time ‘t’ = A
.4. Catalysis in HER: preparation of ink: 4.0 mg catalyst and 20 μL of 5 wt% nafion
0
- A
t
)/A
0
× 100
where, initial absorbance = A
0
t
.
2
solution was dispersed in 200 μL of isopropanol by bath-sonication until a homogeneous
suspension was formed. Then, 5.0 μL of the above catalyst suspension was drop-casted onto a
6

Page 7 of 24
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ01221G
GCE and dried in air. Electrochemical impedance measurements were performed using GC as
working electrode and onset potentials of different catalysts were chosen as performing bias for
the measurement with the sweeping frequency from 50 KHz to 10 Hz with a 10 mV AC dither.
Pt and Ag/AgCl were used as counter and reference electrode.
3
. Results and Discussion
Synthesis of Pd and Pt monometallic NPs on C
In brief, first, K PdCl and K PtCl were dispersed on the surface of C
using NaBH as a reducing agent. All these materials were washed carefully and further used for
3
N
4
surface is mentioned in experimental section.
and then reduced
2
4
2
4
3
N
4
4
characterization and application purposes. In the following sections complete characterization,
mechanism of formation, and application will be discussed.
Fig. 1 shows UV-vis spectrum of bare C
seen from Fig. 1 that C shows strong absorption in visible region with absorption edge at ~
55 nm. Using classical Tauc approach, from the plot of (αhʋ) vs. photon energy (hʋ) the band
gap energy (E ) of C can be calculated (inset of Fig. 1). The calculated Eg value for C is ~
.8 eV, which is well matched with previous reports.16,18 Both C
/Pd and Pt shows comparable
3
N
4
and monometallic (Pd and Pt) NPs. It can be
N
3 4
1
/2
4
g
3
N
4
3
N
4
2
3
N
4
absorption in visible region and weak absorption in UV region with an absorption edge at ~ 455
nm.
Figure 1. UV-vis DRS for C
3
N
4 3
, C N
4
/Pd and C
3
N
4
/Pt, where, all the powder samples were mixed with BaSO
4
as
reference. From the UV-Vis spectrum of C
3
N
4
, inset shows (E plot for band gap (E ) calculation.
p
)2 vs. E
p
g
7

New Journal of Chemistry
Page 8 of 24
View Article Online
DOI: 10.1039/C7NJ01221G
The FTIR analysis result for C
case of C
stretching vibration at 1411, 1322, and 1240 cm are presented. Both the stretching vibration
represent aromatic modes of C ring. The out-of-plane bending vibration for heptazine rings is
experienced from the intense band at 809 cm . Pd and Pt monometallic NPs decorated on C
3
N
4
, C
3
N
4
/Pd and C
3
N
4
/Pt is shown in Fig. S1 (ESI). In
−1
3
N , C=N stretching vibration is observed at 1637 and 1571 cm , while, C–N
4
−1
3
N
4
-1
3
N
4
shows similar IR stretching frequencies for C=N and C-N stretching vibration without any
significant shift. Young and co-workers also reported similar IR characteristic features of Pt
loaded C
3
N
4
and in case of pure C
3
N
4
.25
The structural identity and phase purity of the as-synthesized metal NPs were studied by
PXRD analysis. It can be seen from the inset of Fig. 2 that bare C
3
4
N contains a characteristic
o
peak at 27.5 , which is associated with inter planar stacking of aromatic compounds. The PXRD
o
o
spectrum of C
3
N /Pd NPs shows two characteristics peak at 2θ = 39.9 and 46.2 for (111) and
4
(200) planes, respectively (JCPDS-46-1043). The presence of (111) and (200) planes represent
o
fcc structure of Pd along with a peak at 27.5 , which is due to presence of (002) plane of C
3
N
4
. It
o
o
o
o
can be seen from Fig. 2 that, the 2θ values are at 39.9 , 46.2 , 67.8 , and 81.8 for (111), (200),
(
220), and (311) planes, respectively, for C
3
N
4
/Pt NPs which represent fcc structure (JCPDS 04-
o
0
802) of Pt. In addition to those peaks, another peak at 2θ = 27.5 for (002) plane of C
3
4
N is also
present. Absence of any extra peak in the PXRD analysis of monometallic (Pd and Pt) NPs
confirms that the as-prepared compounds are pure and there is no remaining precursor salt.
Therefore, the decoration of metal NPs on C
3
4
N surface is further confirmed by the presence of
(
002) plane of C
3
4
N .
3 4 3 4 3 4
Figure 2. Powder X-ray diffraction patterns C N /Pd and C N /Pt. Inset shows the PXRD pattern of C N .
8

Page 9 of 24
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ01221G
XPS technique was employed to investigate the surface chemical properties of the metal
NPs as well as their oxidation states. Successful formation of Pt and Pd nanoparticles has been
observed on C
existence of Pt 4f (74.4 eV and 71.1 eV) and Pd 3d (340 eV and 335 eV) doublets for the
Pt/C and Pd/C nanostructures, respectively, confirms the successful formation of metal
nanoparticles on the C surface. High resolution scans of C 1s and N 1s core level spectra with
their various deconvolution components are shown in Fig. 3a and 3b, respectively, for a clean
surface. The deconvoluted C 1s binding energy spectrum can be fitted with four peaks
centered at around 284.6 eV, 286.4 eV, 288.1 eV and 289.8 eV, which are attributed to C-C, C-N
or C-O), C=N and C=O, respectively (Fig. 3a). Similarly, the N 1s BE spectrum of C is also
3
N
4
surface as well as their oxidation states are also depicted in Fig. 3. A clear
3
N
4
3
N
4
3
N
4
C
3
N
4
(
3
N
4
deconvoluted into four peaks centering around 401 eV, 399.7 eV, 398.6 eV and 397 eV,
representing N-O (or N-H), N-(C)3, C-N-C, and C=N-C bonding, respectively (Fig. 3b). These
findings are in good agreement with earlier reported values of carbon nitrides.23 Both the
findings also indicate the formation of a high quality C
for the metal nanoparticles growth.
3
4
N layer which further acts as a substrate
Fig. 3c shows the high resolution scans of Pt 4f binding energy peaks along with its
deconvoluted spin orbit splitting components which is fitted with 4f 5/2 and 4f 7/2 doublet
centered at 74.4 eV and 71 eV, respectively. The spin orbit splitting of 3.4 eV with an intensity
ratio of about 0.76 have been observed. This finding is well matched with earlier reported values
0
26
of Pt oxidation state. Similarly, the deconvolution of Pd 3d high-resolution spectrum is shown
in Fig. 3d. Deconvolution data mainly appears with two sets of Pd 3d doublets with an intensity
ratio of about 2:3. One pair centered at 335.5 eV and 340.8 eV corresponds to the metallic Pd(0)
state of Pd 3d5/2 and Pd 3d3/2, respectively. A spin orbit splitting of about 5.3 eV with an intensity
ration of 0.69 has also been noticed which confirms the formation of metallic nanoparticles of
0
23
Pd oxidation state. Whereas, the other Pd doublet positioned at 337.2 and 342.4 eV can be
attributed to the Pd(I) oxidation state where we observed a spin orbit splitting of about 5.2 eV
and an intensity ration of 0.68, suggesting that the Pd surface is partially oxidized. A very similar
kind of oxidation phenomena of Pd nanoparticles has also been noticed23 for Au-Pd
nanoparticles on C
3
4
N surface. However, for a better understanding, details of all the
deconvoluted spectra are summarized in Table 1.
9

New Journal of Chemistry
Page 10 of 24
View Article Online
DOI: 10.1039/C7NJ01221G
(
a)
(b)
(
c)
(d)
Figure 3. High resolution XPS spectra of (a) C1s and (b) N1s spectra for C
3
N
4
and (c) Pt4f and (d) Pd3d for Pt/C
3
N
4
and Pd/C structure, respectively
3 4
N
1
0

Page 11 of 24
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ01221G
Table 1: Binding energy positions and relative intensities of deconvoluted C1s and N1s spectra for C
3 4
N and Pt4f
and Pd3d for Pt and Pd on C , respectively
3
N
4
Samples B E peaks Sub-peaks
O=C-O
Area
Position
12279.79 289.761
19435.63 288.052
C 1s
N=C-N
C-N or C-O 10759.05 286.352
C-C
12880.8 284.616
C
3
N
4
N-O or N-H
N-(C)3
3989.9 401.047
N 1s
10757.6
399.69
C-N-C
C=N-C
20052.3 398.555
3855.78 397.021
Pt 4f 5/2
Pt 4f 7/2
42976.07
56419.52
74.425
71.072
Pt/C
3
N
4
Pt 4f
Pd 3d3/2
5424.266 340.801
PdO 3d3/2 4112.645 342.417
7846.58 335.536
PdO 3d5/2 6035.727 337.165
Pd/C
3
N
4
Pd 3d
Pd 3d5/2
ꢀ
Fig. 4a and 4b exhibits FESEM images of C
is shown in Fig. S2 (ESI), which exhibits highly dense C
/Pd, where, Pd NPs are very small in size and homogeneously
surface. All the Pd NPs are spherical in shape and slightly aggregated. Fig.
b represents FESEM image of Pt NPs decorated on C surface. It can be seen from Fig. 4b
that Pt NPs are perfectly spherical and particle size-distributions are wide. Therefore, FESEM
analysis confirms the distribution and spherical nature of Pd and Pt NPs on C surface.
3
N
4
/Pd and C
3
N
4
/Pt NPs. FESEM image of bare
C
3
N
4
3
N
4
sheet like structures. Fig. 4a
shows FESEM image of C
3
N
4
distributed on C
3
N
4
4
3
N
4
3
N
4
1
1

New Journal of Chemistry
Page 12 of 24
View Article Online
DOI: 10.1039/C7NJ01221G
3 4 3 4
Figure 4. FESEM image of C N /Pd (a) and C N /Pt (b) NPs
Elemental mapping analysis of C
S5, ESI) confirms distribution of Pd and Pt on C
presence of C, N and Pd in case C /Pd while in C
analysis of C
formation of Pd and Pt on C
Fig. 5 and 6 represents TEM images of Pd and Pt nanoparticles on C
seen from Fig. 5a that Pd NPs are uniform and spherical in shape with an average particle size 8
1 nm and homogeneously distributed on C surface. HRTEM image of Pd NP is shown in
Fig. 5b, where the interplaner spacing (d) value is 0.21 nm, which corresponds to (111) plane of
Pd. Therefore, the growth of Pd cluster on C surface occurs through (111) plane. Shape of Pt
NPs is spherical and distributed on C surface, shown in Fig. 6a. Size of Pt NPs is 12 ± 1 nm
and the interplanar spacing value is 0.23 nm (Fig. 6b), which represents the growth of Pt
3
N
4
(Fig. S3, ESI), C
3
N
4
/Pd (Fig. S4, ESI), and Pt (Fig.
3
N
4
surface. EDS analysis substantiates the
/Pt confirms C, N and Pt. Line mapping
N
3 4
3
N
4
3
4
N /Pd and Pt also exhibits the existence of C, N, Pd and Pt, which authenticates the
3
4
N .
3
4
N surface. It can be
±
3
N
4
3
N
4
3
N
4
nanocrystal through (111) plane. Therefore, TEM analysis of Pd and Pt NPs on C
3
4
N surface is
well acquainted with their FESEM analysis.
1
2

Page 13 of 24
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ01221G
3 4
Figure 5. TEM (a) and HRTEM (b) image of C N /Pd NPs
3 4
Figure 6: TEM (a) and HRTEM (b) image of C N /Pt NPs
In this study C
Initially, C powder was sonicated for ~5 hour so that bulk C
exfoliation. In the exfoliated solution of C , K PdCl and K PtCl were added and stirred for 1
hour. Upon stirring Pd and Pt ions were adsorbed on C surface via weak van der Waals
interaction. Even, pi-conjugated electron cloud of C
also helpful for the adsorption of Pd2+
3
N
4
was used as a substrate, where, Pd and Pt NPs were decorated.
N
3 4
3
N
4
dispersed properly via
3
N
4
2
4
2
4
2
+
2+
N
3 4
3
N
4
1
3

New Journal of Chemistry
Page 14 of 24
View Article Online
DOI: 10.1039/C7NJ01221G
2
+
and Pt ions. After that a reduction reaction using NaBH
4
as a reducing agent was followed to
synthesize monometallic Pd and Pt nanoparticles on C
decorated uniformly on C
ions on C . Both Pd and Pt adsorb on porous C
XPS analysis. The overall synthesis of Pd and Pt on C
3
N
4
surface. Both the metal NPs were
2
+
2+
3
N
4
surface, which confirm the uniform distribution of Pd and Pt
surface strongly, which is confirmed from
surface is shown in Scheme 1.
3
N
4
3
N
4
0
0
3
N
4
3 4
Scheme 1. The mechanism of decoration of Pd and Pt nanoparticles on the surface of C N
4
4
. Applications in electrocatalysis and catalysis:
.1. Hydrogen evolution reaction using monometallic NPs: The preliminary catalytic activity
, C /Pd, and C /Pt catalysts towards hydrogen evolution reaction was studied using
linear sweep voltamograme (LSV) technique. 0.5 M aqueous H SO solution and 50 mV/s scan
of C
3
N
4
3
N
4
3
N
4
2
4
rate were used to conduct all the electrochemical measurements. Throughout the electrochemical
study Ag/AgCl electrode was used as reference electrode and the potentials are reported with
respect to Ag/AgCl. Cathodic polarization curves in Fig. 7a shows that after decoration of metal
nanoparticle on the surface of C
successive anodic shift in the onset potential compared to bare C
requires potential of -0.339 V, -0.371 V, and -0.596 V, respectively, vs. Ag/AgCl to reach
3
N
4
, there is remarkable increase in current density with
3
N
4
. C /Pt, C /Pd, and bare
3
N
4
3
N
4
C
3
N
4
2
current density of 10 mA/cm . Whereas, for pristine Pt (5% Pt on C) -0.307 V potential is
2
required to reach 10 mA/cm . From the observed result it is clear that C
3
4
N /Pt shows better
activity compared to C
3
N /Pd. The stability of catalysts (Pd and Pt) on electrode surface was
4
checked up to 3000 cycles and shown in Fig. S6a and b (ESI). It can be seen from Fig. 6a and b
that the catalyst are stable on electrode surface and there is no significant change before and after
3000 scan vs. Ag/AgCl.
1
4

Page 15 of 24
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ01221G
-
0.7
0.6
0.5
0.4
0.3
0.2
C N
3
4
C N /Pd
-
-
-
-
-
3
4
C N /Pt
3
4
5% Pt/C
A
-0.1
C
B
0.0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
2
log (j) mA/cm
3 4 3 4 3 4
Figure 7. LSV polarization curves of C N , C N /Pd, C N /Pt, and pristine Pt for hydrogen evolution reactions (a),
Tafel plot (b), and impedance measurement with Pd, Pt, and bare C
3
N
4
(c). Inset of c shows the magnified version of
4
/Pt NPs.
impedance measurement with C
3
N
The probable shortcomings of HER catalysts are low surface area, poor electron
transportation, and instability under different harsh operating conditions. The density and
reactivity of active sites also governs the performance of the catalyst.27-29 Incorporation of metal
nanoparticles on C
surface not only increases the number of active sites but also improves the electron transportation
through its porous surface. This superior activity of C /Pd and C /Pt as compared to bare
is attributed to the Gibbs free energy for hydrogen adsorption (ΔGH*).4 To be a better
3
N
4
overcomes these drawbacks to some extent. Metal NPs decorated on C
3
N
4
3
N
4
3
N
4
C
3
N
4
descriptor of the intrinsic activity of metal nanoparticles for HER, Gibbs free energy is proposed.
Mechanism of HER: HER reaction follows two mechanisms. First step is the discharge
+
step and also called as Volmer step where there is the electron transfer to proton or H
3
O and
+
+
-
lead to Hads. Hydronium cation (H
3
O ) is the proton source in acidic electrolytes. H
3
O + e
H
ads+ H O. Two different reaction pathways may follow in the second step. One way is
2
+
-
Heyrovsky process also called desorption reaction (Hads+ H
3
O + e
H
2
+ H O), i.e., transfer
2
of second electron to the Hads atom with simultaneously coupling of another proton to evolve
hydrogen gas. The other possibility is already adsorbed two hydrogen atoms combine on catalyst
surface to give H
2
gas. This third step is called as Tafel or recombination reaction (Hads + Hads
H
2
). The mechanism and rate-determining step are studied by the Tafel slope. Tafel slope is
an inherent and intrinsic property of material, which is useful to determine the effectiveness of a
catalyst. In order to calculate the Tafel slope the linear portion of the Tafel plots is to be fitted in
the Tafel equation (η = b log (j)+ a, where η = overpotential, b = Tafel slope, and J = current
1
5

New Journal of Chemistry
Page 16 of 24
View Article Online
DOI: 10.1039/C7NJ01221G
density).27,28 In case of bare Pt, it has very high Hads and it follows Volmer-Tafel mechanism and
the Tafel step i.e., the recombination step is the rate-determining step. Measured Tafel slope for
Pt is 30 mV/decade. If the rate-determining step is Heyrovsky step, Tafel slope value will be 40
mV/decade and if the Volmer step is the rate-determining step, then the Tafel slope will be 120
mV/decade. In our present study, Tafel slope of 5% Pt on C, C
74, 116 and 71 mV/decade, respectively (Fig. 7b). Tafel slope values suggest that for C
and C /Pt, HER reaction follows Volmer-Heyrovsky mechanism. Heyrovsky step is the rate
determining step for C /Pt and for C /Pd Volmer step is the rate determining. In case of Pt
decorated C , Tafel slope is lowest compared to others, which also indicates the superior
activity of Pt. A comparative study of HER activity with reported references is given in Table 2.
3
N
4
, C
3
N
4
/Pd, and C
3
N
4
/Pt, are 37,
1
3
N
4
/Pd,
3
N
4
N
3 4
3
N
4
3
N
4
It can be seen from Table 2 that our reported C
with reported literature.
3
4
N /Pd and Pt catalyst shows comparable activity
Table 2: Comparative study of HER activity of reported references
Material
Loading
amount
Medium
Overpotential to
generate 10
mA/cm current
Tafel slope
(mV/decade)
Reference
2
2
(
mg/cm )
0.043
0.14
density
3
Pd-C N
4
0.5 M H
0.5 M H
0.5 M H
2
2
2
SO
SO
SO
4
4
4
-55 mV
35
35
34
22
34
35
PdCu@Pd
nanocube
-5 mV (onset)
-3 mV (onset)
Pd on rGO
-
Pt dendrimer
on C
-
-
0.5 M H
0.5 M H
0.5 M H
2
SO
SO
SO
4
4
-16 mV (onset)
-26 mV (onset)
- 300 mV (at 60
42
58
-
36
36
37
Pt on GO
2
N-doped
CNTs
0.7
2
4
2
mA/cm )
supported Pd
Carbon
supported Pt
5 µg/cm2
10 µg/cm2
-
0.1 M HClO
0.1 M HClO
50 mV (at 2.4
mA/cm2
Anodic = 260
± 23
Cathodic =
38
38
39
4
4
1
33 ± 5
Carbon
supported Pd
70 mV (at 2.4
mA/cm2
Anodic = 260
± 23
Cathodic =
1
33 ± 5
Ultrafine
Pt/Pd on
0.5M H
2
SO
4
-0.21 V (onset)
38
1
6

Page 17 of 24
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ01221G
MWCNTs
Pd on C
Pt on C
3
N
4
1.056
1.056
0.5M H
0.5M H
2
SO
SO
4
4
-0.339 V vs.
Ag/AgCl
116
71
This work
This work
3
N
4
2
-0.371 V vs.
Ag/AgCl
To account the comparative electrocatalytic activity of C
3
N
4
, C
3
N
4
/Pt, and C
3
4
N /Pd
electrochemical impedance measurements were carried out. Electrochemical impedance study
gives information about the ease of charge transportation on different electrode surfaces.
Impedance measurements for C
onset potentials. Impedance curve for C
consisting resistance (Rs), Constant phase element (CPE) and Warburg constant (W
value of resistances are summarized in Table 3 (Fig. 7c). Observed RCT of C /Pt, C
are 15 Ω, 75 Ω, and 431 Ω, respectively. Lower charge transfer resistance of C
of Fig. 7c) reveals that C /Pt composite electrodes offer the least resistance to the electron
transportation followed by C /Pd and C . Pt nanoparticle decoration on the surface of C
successfully enhances the electrochemical activity.
3
N
4
/Pt, C
3
N
4
/Pd, and C
3
N
4
were measured at their respective
/Pt is fitted with the equivalent circuit
) and the
/Pd and
/Pt (inset
3
N
4
/Pd and C
3
N
4
S
3
N
4
3
N
4
C
3
N
4
3
N
4
3
N
4
3
N
4
3
N
4
3
N
4
3 4 3 4 3 4
Table 3: RCT values of bare C N , C N /Pd, and C N /Pt NPs
Materials used
RCT value (Ω)
C
3
N
4
431
75
C
3
N
4
/Pd
/Pt
C
3
N
4
15
4
.2. Nitrocompound reduction using Pd and Pt NPs:
To verify the activity of our as-synthesized catalysts (C
3
4
N /Pd and Pt) we have chosen
another reduction reaction. Reduction of nitro-compounds has raised considerable interest
because nitrophenol compounds are determined water pollutants and thus a serious global
concern. During the preparation of dyes, pigments, and polymers aromatic amines are important
intermediates and precursors, which makes reduction of nitro-compounds equally significant.30
Therefore, we have checked the catalytic activity of our as-synthesized catalyst (bare C
3
4
N , Pd,
1
7

New Journal of Chemistry
Page 18 of 24
View Article Online
DOI: 10.1039/C7NJ01221G
and Pt NPs) for p-nitroaniline (4-NA), p-nitrophenol (4-NP), and o-nitrobenzoic acid (2-NBA)
reduction reaction.
4
-NA exhibits a distinct absorption spectrum at 381 nm, which is shown in Fig. 8. When
a freshly prepared NaBH solution was added into 4-NA, there was slight decrease in the
4
absorption peak. In absence of any catalyst the peak intensity of 4-NA at 381 nm remains
unaffected with time, which verifies that the reduction reaction doesn’t occur. After addition of
catalyst (1.0 mg), the reduction of 4-NA was initiated, which can be visualized by gradual
decrease in absorption intensity of 4-NA at 381 nm, accompanying the appearance of new peaks
at ~307 nm and 240 nm. C
The UV-visible absorption spectra showed the reactant peak at 381 nm disappeared and the
product peak at 307 nm and 240 nm appeared with time. For C /Pd catalyst the reaction is
3
N
4
/Pd was used for reduction of 4-NA, which is shown in Fig. 8a.
3
N
4
very fast and ~ 98% conversion of 4-NA to 4-phenelenediammine (4-PDA) occurs within 6 min.
The conversion process is studied by UV-vis spectra at different time interval. The ratio of the
concentrations of 4-NA and 4-PDA at different time interval gives A
/A vs. t (min) shows exponential decay (Fig. 8b), which specify the pseudo first order kinetics.
Finally, linear plot of ln(A /A ) vs. t (min) (Fig 8c) confirms the pseudo-first order kinetic
reaction and the value of rate constant ‘k’ was determined from the slope using the following
t
/A
0
values. The plot of
A
t
0
t
0
-
1
-1
equation. The rate constant value using C
3
N
4
/Pd catalyst is 6.7×10 min .
ln(A /A )= kt
Similar catalytic conversion was also performed with C
both cases only 1.0 mg catalyst was used. C /Pt catalyst needs 25 mins for ~ 98% conversion
of 4-NA to 4-PDA, shown in Fig. S7a (ESI). It can be seen from Fig. S7b that the plot of A /A
vs. t (min) is exponential decay, which indicates pseudo-first order reaction. Furthermore, plot of
0
t
3
N
4
/Pt and bare C
3
N catalyst. In
4
3
N
4
t
0
-1
-1
ln(A
pseudo-first order kinetics, shown in Fig. S7c, ESI. Using bare C
proceeds slowly and gives ~57% conversion in 90 min (Fig. S8). The plot of ln(A
t
/A
0
) vs. t (min) shows linear nature and the rate constant (k) value is 1.4×10 min favors
the reduction reaction
/A ) vs. t (min)
shows linear nature and the rate constant (k) value is 6.6×10 min . Therefore, the order of rate
3
N
4
t
0
-3
-1
constant for 4-NA to 4-PDA conversion is kC3N4/Pd > kC3N4/Pt > kC3N4
.
1
8

Page 19 of 24
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ01221G
Figure 8. UV-vis spectra of (a) reduction of 4-NA in presence of C
3
N
4
/Pd NPs (b) A
t
/A
0
vs. time (min) plot (c) ln
-
4
(
A
t
/A
0
) vs. time (min) plot. Conditions: [NA] = 10 M and amount of catalyst = 1.0 mg. In all cases water was used
as reference solution.
It can be seen from Fig. 9 that the comparative study of the catalysts towards reduction of
4
-NA to 4-PDA shows C
/Pd is 4.7 times higher as compared to C
better activity for C /Pd is presumably due to proper adsorption of nitro-compounds on
/Pd surface. To overcome the kinetic barrier, C /Pd and C /Pt can catalyze the
3
N
4
/Pd is a better catalyst than C
3
N
4
/Pt and bare C
3
N
4
. Rate constant (k)
of C
3
N
4
3
N
4
/Pt and 101 times better than bare C
3
N
4
. The
3
N
4
C
3
N
4
3
N
4
3
N
4
reduction of nitro-compounds by acting as an electron relay system where, electrons are initially
-
group) and then passed to acceptor (nitro group).31,32 In case of 4-NA
received from donor (BH
4
-
to 4-PDA reduction, the reaction follows two steps. First, 4-NA and BH
4
are chemically
adsorbed on porous catalyst surface and electrons are transferred followed by 4-PDA formation.
Second, the desorption of 4-PDA from the catalyst surface. Esumi and co-workers also reported
3
3
higher activity of Pd NPs towards nitro-compound reduction. Recently, our group reported the
-1
-1
reduction of 4-NP using Au, Pd and AuPd NPs, where Pd shows 1.5×10 min rate constant
value, which is comparable with this study.23
As an advantage of heterogeneous catalyst, C
3
4
N /Pd was used to check reusability for 4-
st
NA reduction reaction. After 1 cycle of the reaction the catalyst was centrifuged and washed
thoroughly with distilled water. The reduction of 4-NA to 4-PDA was repeated four times and
the corresponding results shows 98%, 96%, 92%, and 88% conversion. Therefore, the catalyst is
highly stable up to fourth cycle, which is shown in Fig. 10. After fourth cycle of the catalytic
1
9

New Journal of Chemistry
Page 20 of 24
View Article Online
DOI: 10.1039/C7NJ01221G
reaction the morphology of C
3
4
N /Pd NP was confirmed with the help of FESEM analysis (Fig.
S9, ESI), which shows similar morphology of Pd NP as discussed in FESEM analysis.
3 4
Figure 9. Comparative Study of reduction of 4-NA in presence of C N /Pd NPs
To check the catalytic activity of the as-synthesized C
3
N
4
/Pd, C
3
N
4
/Pt, and bare C
N
3 4
catalyst few other nitro-compounds (4-NP and 2-NBA) were used using similar experimental
condition for 4-NA reduction. A significant absorption peak at 290 nm was appeared in pure 4-
NP (Fig. S10, ESI). When a freshly prepared NaBH (0.1 M) solution was added into 4-NP, the
4
absorption peak was shifted to 400 nm, analogous to the 4-nitrophenolate ions where,
-
nitrophenolate ion behaves as an oxidant and BH
4
as a reductant. After addition of a catalyst, the
reduction of 4-NP was initiated, which can be visualized by monitoring the decrease in
absorption intensity of 4-nitrophenolate ions at 400 nm, accompanying the appearance of a new
peak of 4-aminophenol (4-AP) at 300 nm. In absence of any catalyst the peak intensity of 4-
nitrophenolate ion at 400 nm remains unaffected with time, which verifies the importance of
catalyst for this reduction reaction. For C
conversion, whereas, for C /Pt, 99% conversion occurs at ~6 min (Fig. S10a and S10b, ESI).
However, for bare C the reaction proceed very slowly and after 2 h only 55% converted into
-AP (Fig. S10c, ESI). Therefore, the rate of the reaction is lowest with bare C and almost
similar with Pd and Pt decorated C catalyst.
3
4
N /Pd catalyst, ~7 min was required for 99%
3
N
4
3
N
4
4
3
N
4
3
N
4
2
0

Page 21 of 24
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ01221G
th
3 4
Figure 10. Re-usability curve showing the efficiency of catalyst up to 4 cycle after 6 min using C N /Pd NPs
It can be seen from Fig. S11 (ESI) that 2-NBA shows a significant absorption peak at 266
nm. In absence of any catalyst the peak intensity of 2-NBA at 266 nm remains unaffected. Upon
addition of a catalyst, the reduction of 2-NBA was initiated, which can be visualized by
appearing a new peak of anthranilic acid at 300 nm. For C
required for complete conversion, whereas, for C /Pt conversion into anthranilic acid is
possible within 10 mins. However, for bare C the reaction is very slow. Therefore, the rate of
the reaction follows similar trend, C /Pd is a better catalyst than C /Pt and C only. The
/Pt, and bare C catalysts is
3
4
N /Pd, very less time (~5 min) is
3
N
4
3
N
4
3
N
4
3
N
4
3
N
4
conversion of 2-NBA to anthranilic acid using C
shown in Fig. S11a, b, and c (ESI).
3
N
4
/Pd, C
3
N
4
3
N
4
Conclusion:
Monometallic (Pd and Pt) nanoparticles can be successfully decorated on C
using NaBH as a reducing agent. Decoration of both Pd and Pt NPs on C surface improved
both the catalysis and electrocatalysis in reduction of nitro-compounds and hydrogen evolution
3
4
N surface
4
3
N
4
reaction. Pt NPs decorated on C
3
N
4
surface proved efficient electrocatalyst as it requires -0.339
2
V potential to reach current density of 10 mA/cm vs. Ag/AgCl, which is comparatively better
than Pd NPs. Using the value of Tafel slope it is suggested that for C
3
N
4
/Pd, and C
3
4
N /Pt, HER
2
1

New Journal of Chemistry
Page 22 of 24
View Article Online
DOI: 10.1039/C7NJ01221G
reaction follows Volmer-Heyrovsky mechanism. Heyrovsky step is the rate determining step for
/Pt and for C /Pd Volmer step is the rate determining. On the other hand, Pd NPs
decorated on C shows excellent catalytic activity in reduction of 4-NA with higher rate
constant, k = 6.7 ×10 min as compared to Pt and bare C
Various nitro-compounds have been used to verify the catalytic efficiency and C
better activity as compared to others. Therefore, this study leaves an avenue for the decoration of
various mono- and bimetallic NPs on C surface.
C
3
N
4
3
N
4
3
N
4
-1
-1
3
N
4
and pseudo-first order kinetics.
/Pd shows
3
N
4
3
N
4
Acknowledgements: SP thank the following funding agencies for the financial support for this
work: Department of Science and Technology (DST) Science and Engineering Research Board
(SERB) Fasttrack (SB/FT/CS-042/2012) grant, University Grants Commission (UGC) special
assistance program, DST-FIST program, Government of India. MB thankfully acknowledges
financial support from Department of Science and Technology (DST) Inspire
(DST/INSPIRE/04/2015/00039) program. The instrumental support for TEM and XPS
measurements from the Material Research Center (MRC), MNIT Jaipur is highly acknowledged.
We also thank to the Department of Physics, BITS Pilani for assistance with powder X-ray
diffraction studies (DST-FIST sponsored).
2
2

Page 23 of 24
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ01221G
References
1
2
3
4
5
6
. S. Chu, A. Majumdar, Nature, 2012, 488, 294.
. M. S. Dresselhaus, I. L. Thomas, Nature, 2001, 414, 332.
. J. A. Turner, Science, 1999, 285, 687.
. C. G. M. Guio , L. A. Stern, X. Hu, Chem. Soc. Rev. 2014, 43, 6555.
. Z. Peng, H. Yang, Nano today, 2009. 4, 143.
. V. R. Stamenkovic, B. S. Mun, M. Arenz, K. J. J. Mayrhofer, C. A. Lucas, G. Wang, P. N.
Ross, N. M. Markovic, Nat. Mater., 2007, 6, 241.
7
8
1
9
. N. Furuya, S. Motoo, J. Electroanal. Chem., 1978, 88, 151.
. F. Li, P. Bertoncello, I. Ciani, G. Mantovani , P. R. Unwin, Adv. Funct. Mater., 2008, 18,
685.
. F. Li, I. Ciani, P. Bertoncello, P. R. Unwin, J. Zhao,C. R. Bradbury and D. J. Fermin, J. Phys.
Chem. C, 2008, 112, 9686.
1
3
1
0. S. N. Pronkin, A. Bonnefont, P.S. Ruvinskiy, E. R. Savinova, Electrochim. Acta, 2010, 55,
312.
1. H.-Y. Park, I.-S. Park, B. Choi, K.-S. Lee, T.-Y. Jeon, Y.-E. Sung, S. J. Yoo, Phys. Chem.
Chem. Phys., 2013, 15, 2125.
1
1
1
2. S. Han, D. H. Youn, M. H. Lee, J. S. Lee, ChemCatChem, 2015, 7, 1483.
3. K. H. Kangasniemi, D. A. Condit, T. D. Jarvi, J. Electrochem.Soc., 2004, 151, E125.
4. L. Perini, C. Durante, M. Favaro, V. Perazzolo, S. Agnoli, O. Schneider, G. Granozzi, A.
Gennaro, ACS Appl. Mater. Interfaces, 2015, 7, 1170.
1
1
1
1
1
2
2
2
2
5. V. D. Noto, E. Negro, S. Polizzi, F. Agresti, G. A. Giffin, ChemSusChem, 2012, 5, 2451.
6. Y. Zhang, T. Mori, J. Ye, Sci. Adv. Mater., 2012, 4, 282.
7. Z. Zhao, Y. Sun, F. Dong, Nanoscale, 2015, 7, 15.
8. P. Fageria, R. Nazir, S. Gangopadhyay, H. C. Barshilia, S. Pande., RSC Adv., 2015, 5, 80397.
9. Y. Wang, J. Yao, H. Li, D. Su, M. Antonietti, J. Am. Chem. Soc., 2011, 133, 2362.
0. W. Zhang, H. Huang, F. Li, K. Deng, X. Wang, J. Mater. Chem. A, 2014, 2, 19084.
1. H. Wang, L. Thia, N. Li, X.Ge, Z. Liu, X. Wang, ACS Catal., 2015, 5, 3174.
2. T. Bhowmik, M. K. Kundu, S. Barman, ACS Catal., 2016, 6, 1929.
3. P. Fageria, S. Uppala, R. Nazir, S. Gangopadhyay, C.-H. Chang, M. Basu, S. Pande,
Langmuir, 2016, 32, 10054.
2
3

New Journal of Chemistry
Page 24 of 24
View Article Online
DOI: 10.1039/C7NJ01221G
2
2
2
2
2
4. Y. Zhang, J. Liu, G. Wu, W. Chen, Nanoscale, 2012, 4, 5300.
5. W.-J. Ong, L.-L. Tan, S.-P. Chai, S.-T. Yong, Dalton Trans., 2015, 44, 1249.
6. S. Pande, M. G. Weir, B. Zaccheo, R. M. Crooks, New J. Chem., 2011, 35, 2054.
7. T. Shinagawa, A. T. Garcia-Esparza, K. Takanabe, Sci. Rep., 2015, 5, 13801.
8. A. Behranginia, M. Asadi, C. Liu, P. Yasaei, B. Kumar, P. Phillips, T. Foroozan, J.
C.Waranius, K. Kim, J. Abiade, R. F. Klie, L. A. Curtiss, A. Salehi-Khojin, Chem. Mater., 2016,
2
2
3
3
3
8, 549.
9. S. Trasatti, Electrochim. Acta, 1984, 29, 1503.
0. P. S. Rathore, R. Patidar, T. Shripati, S. Thakore, Catal. Sci. Technol., 2015, 5, 286.
1. Z. Jiang, J. Xie, D. Jiang, X. Wei, M. Chen, CrystEngComm, 2013, 15, 560.
2. S. Panigrahi, S. Basu, S. Praharaj, S. Pande, S. Jana, A. Pal, S. K. Ghosh, T. Pal, J. Phy.
Chem. C, 2007, 111, 4596.
3
3
3. K. Esumi, R. Isono, T. Yoshimura, Langmuir, 2004, 20, 237.
4. J. Li, F. Li, S.X. Guo, J. Zhang, J. Ma, Appl. Mater. Interfaces, 2017, 9, 8151.
3
3
3
3
3
5. J. Li, P. Zhou, F. Li, J. Ma, Y. Liu, X. Zhang, H. Huo, J. Jin, J. Ma, J. Power Sources, 2016, 302, 343.
6. B. Devadas, T. Imae, Electrochem. Commun., 2016, 72, 135.
7. S. U. B. Ramakrishna, D. S. Reddy, S. S. Kumar, Int. J. Hydrogen Energy, 2016, 41, 20447.
8. J. Durst, C. Simon, F. Hasche, H. A. Gasteiger, J. Electrochem. Soc., 2015, 162, F190.
9. M. Xiao, X. Liang, W. Li, Y. Yang, Y. Miao, J. Electrochem. Soc., 2015, 162, H415.
2
4