Amorphous PtNiP particle networks of different particle sizes for the electro-oxidation of hydrazine

Article abstract of DOI:10.1039/c5ra13774h

The design of alloy networks is an important fundamental and applied research challenge in the area of catalysis due to the high surface area, gas permeability and electrical conductivity of alloy network structures. Herein amorphous PtNiP particle networks were prepared via the NaBH₄ co-reduction process. Moreover, the reaction temperature control from 0 °C to 80 °C was shown to be a powerful tool for the 'tuning' of particle sizes. Electron microscopy, X-ray diffraction and selected area electron diffraction were used to show the morphology, the amorphous behavior and the changes in particle size of the particle networks. The results of the electrochemical performance showed that the amorphous PtNiP particle networks had better catalytic activity towards hydrazine oxidation compared to the Pt and PtNi networks. The electrocatalytic activity reached a peak value, 0.62 mA at -0.63 V, at a PtNiP-50 electrode. The correlation between the particle size of the amorphous PtNiP particle networks and their electrocatalytic activity for the hydrazine oxidation reaction provided the opportunity to develop highly active electrocatalysts for hydrazine fuel cells.

Full text of DOI:10.1039/c5ra13774h

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Amorphous PtNiP particle networks of different
particle sizes for the electro-oxidation of
hydrazine†
Cite this: RSC Adv., 2015, 5, 68655
a
a
b
b
Yuanyuan Ma, Hui Wang, Weizhong Lv, Shan Ji, Bruno G. Pollet,c Shunxi Lia
*
a
*
and Rongfang Wang
The design of alloy networks is an important fundamental and applied research challenge in the area of
catalysis due to the high surface area, gas permeability and electrical conductivity of alloy network
structures. Herein amorphous PtNiP particle networks were prepared via the NaBH4 co-reduction
process. Moreover, the reaction temperature control from 0 ꢀC to 80 ꢀC was shown to be a powerful
tool for the ‘tuning’ of particle sizes. Electron microscopy, X-ray diffraction and selected area electron
diffraction were used to show the morphology, the amorphous behavior and the changes in particle size
of the particle networks. The results of the electrochemical performance showed that the amorphous
PtNiP particle networks had better catalytic activity towards hydrazine oxidation compared to the Pt and
PtNi networks. The electrocatalytic activity reached a peak value, 0.62 mA at ꢁ0.63 V, at a PtNiP-50
electrode. The correlation between the particle size of the amorphous PtNiP particle networks and their
electrocatalytic activity for the hydrazine oxidation reaction provided the opportunity to develop highly
active electrocatalysts for hydrazine fuel cells.
Received 14th July 2015
Accepted 7th August 2015
DOI: 10.1039/c5ra13774h
www.rsc.org/advances
the solid ligaments due to their unique geometrical congura-
tion, low relative density, nanometer-scale ne pores etc.8–10
Introduction
Thus, porous Pt-based ordered networks (or nanosponges) with
narrow pore-size distributions are of particular interest for
electrocatalytic applications. For instance, PtNi11 and PtCo12
particle networks synthesized by the use of surfactants have
shown to exhibit good electrocatalytic activity towards methanol
and formic acid oxidation reactions. Furthermore, the effect of
the composition of porous PtNi and PtCo particle networks on
their catalytic activities was also studied. Porous PtPd alloy
nanosponges through template-free methods displayed supe-
rior electrocatalytic activity for ethanol oxidation reactions.13,14
However, to date no studies reported how a dened set of
reaction conditions can be tuned to yield particle network-like
structure with different particle sizes and the effect of the
particle size on its electrochemical performance.
Amorphous alloys, a type of metastable materials with long-
range disordered but short-range ordered structure are rich in
low-coordination sites (terraces, steps, corner atoms) and
defects in their structures.15,16 It is well-documented and well-
known that the low-coordination sites play important roles in
catalysis, such as various types of hydrogenation reactions.17,18
In the eld of electrochemical catalysis, only limited number of
the amorphous Pt-based electrocatalysts prepared by ball-
milling has been reported.19,20 However, amorphous Pt-based
particle networks synthesized by chemical methods have
never been explored for electrocatalysis. For the rst time, we
present herein a method to prepare amorphous types of
As a member of the noble metals group (PGM – Platinum Group
Metals), platinum (Pt) exhibits superior catalytic and electrical
properties as well as outstanding corrosion resistance, which
makes it an ideal candidate as an electrocatalyst for both anodic
and cathodic electrochemical reactions in fuel cells and water
electrolysers.1,2 However its high price and scarcity are major
issues for the successful deployment of commercial fuel cell
systems.3,4 Thus, many efforts have been devoted to the
construction of functional Pt-based materials with designed
shape, size, composition and geometrical congurations in
view of achieving superior electrocatalytic properties and high
precious-metal utilisations.5–7
In comparison with solid and bulk counterparts, porous
frameworks consisting of various functional metals can not only
increase the active area but also provide efficient mass-transfer
for reactant molecules, as well as improving electron mobility in
aCollege of Chemistry and Chemical Engineering, Northwest Normal University,
Lanzhou 730070, China. E-mail: wrf38745779@126.com; wangrf@nwnu.edu.cn;
Fax: +86 931 7971533; Tel: +86 931 7971533
bCollege of Chemistry and Chemical Engineering, Shenzhen University, Shenzhen
518060, China. E-mail: sji@uwc.ac.za; Fax: +86 27 21 9599316; Tel: +86 27 21
9599316
cHySAFER, School of the Built Environment, University of Ulster, Shore Road,
Newtownabbey, Co. Antrim, BT37 0QB, UK
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c5ra13774h
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Pt-based particle networks and study their applications in 5 mm diameter glassy carbon disk, 2 mg of catalyst was
electrocatalysis. Herein, we also report a temperature-controlled dispersed ultrasonically in 0.4 mL Naon/ethanol (0.25%
reduction reaction strategy by NaBH4 to prepare amorphous Naon) solution, and 8 mL of the above solution was pipetted
PtNiP particle networks of various particle sizes. For and air dried on the glassy carbon surface. The electrode surface
completeness, the effect of the particle size on the electro- was electrochemically cleaned by repeatedly cycling the poten-
catalytic activity for hydrazine oxidation was investigated.
tial applied to the working electrode until a reproducible signal
was obtained. All experiments were conducted at the laboratory
temperature.
Experimental
Synthesis
Results and discussion
All reagents were of analytic grade (AR), and ultrapure water was
used throughout the experiments. By extending our previous
synthetic methods,21,22 the preparation of PtNiP alloy network
was as follows: 200 mg of NiCl2$6H2O and 150 mg of
NaH2PO2$H2O were dissolved in 30 mL of de-aerated ultrapure
water (bubbled continuously with N2) at controlled tempera-
Fig. 1a and b show low and high SEM images of PtNiP-20
respectively. PtNiP-20 clearly comprises of a wide-ranging
network-like structure of aligned nanoparticles, which is also
visible using TEM (Fig. 1c). TEM images show that most parti-
cles have elliptical morphology of ca. 10 nm diameter (Fig. 1d).
The EDS spectra as shown in the inset (Fig. 1c) indicates that Pt,
Ni, and P elements are present in PtNiP-20. SAED patterns
displayed in Fig. 1d indicates that the PtNiP-20 alloy is amor-
phous.23,24 Fig. 1e and f show the STEM images and the distri-
bution prole of elements Pt, Ni and P in a typical region i.e. the
red bar across Fig. 1e. Overall, the positions and widths of the
peaks of the three elements match with each other, indicating
that PtNiP-20 have uniform distribution of the three elements.
Using ICP analyses, the atomic ratio of Pt : Ni : P in the PtNiP-20
bulk is found to be 1 : 5.1 : 7.8.
In our previous work,21,22 it was shown that the composition
of the Pd-based particle networks can be tuned by adjusting the
precursor ratio. However as previously pointed out and from the
authors' knowledge, no investigations have reported whether
the particle size in particle network structure could be modied.
Moreover, it is well-known that metallic particle electrocatalysts
have particle size-dependent activities.25 Thus, the effect of the
particle size of PtNiP in PtNiP particle networks on the catalytic
performance for hydrazine oxidation was considered. In this
study, PtNiP particle networks with different particle sizes have
been successfully synthesized by controlling the reaction
ꢀ
tures of 0, 20, 50 and 80 C (using a thermostatic bath). Then
2.2 mL of 20 mg mLꢁ1 H2PtCl6$6H2O solution was rapidly
added to the solution; stirring continued for another 0.5 h.
Aerwards, 40 mL of 0.2 mol Lꢁ1 NaBH4 aqueous solution was
added slowly into the mixture to react for 4 h. The resultants
denoted as PtNiP-0, PtNiP-20, PtNiP-50, and PtNiP-80 were
collected by ltration, washed with a 6 mol Lꢁ1 ammonia
solution, then washed with ultrapure water several times and
kept in an ethanol solution. It should be noted that PtNiP-0 was
kept in an ethanol solution at 0 ꢀC. For the synthesis of Pt and
PtNi, the reaction conditions were similar to the preparation of
PtNiP-20 but without the presence of Ni or P.
Characterization
X-ray diffraction (XRD) patterns were recorded on a Shimadzu
XD–3A (Japan) using ltered Cu-Ka radiation (l ¼ 0.15418 nm)
generated at 40 kV and 30 mA. Scanning electron microscopy
(SEM) images were obtained using a Carl Zeiss Ultra Plus.
Transmission electron micrographs (TEM) and selected area
electron diffraction (SAED) pattern of the catalysts were taken
on a JEOL (JEM-2000 FX) microscope operating at 200 kV, which
was coupled to the energy dispersive X-ray spectroscopy (EDS).
The average chemical compositions of the catalysts were
determined using an IRIS advantage inductively coupled
plasma atomic emission spectroscopy (ICP-AES) system
(Thermo, USA).
ꢀ
temperature. As shown in Fig. 2a, PtNiP-0 prepared at ca. 0 C
was composed of the accumulation of spheres, and the
The specic surface area (SBET) was determined by Bru-
nauer–Emmett–Teller (BET) method, and the pore size distri-
bution was calculated by the density functional theory (DFT)
method on Quantachrome Autosorb-1 volumetric analyzer.
Before measurements were made, the samples were degassed at
room temperature under vacuum for 24 h.
Electrochemical measurements
Electrochemical measurements were carried out using an elec-
trochemical work station (CHI 650D, CH Instruments,
Shanghai). A common three-electrode electrochemical cell was
used for the measurements. The counter and reference elec-
trodes were a platinum wire and an Ag/AgCl (3 mol Lꢁ1 KCl)
Fig. 1 (a and b) SEM and (c and d) TEM images, (e) SAED pattern, (f)
electrode respectively. The working electrode was prepared on a STEM image, and (g) line-scan EDX spectrum of PtNiP-20.
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characterization of particle network was not obvious. For the
PtNiP-20, PtNiP-50, and PtNiP-80 samples, the particle network
structures were clearly observed. When the temperature
ꢀ
ꢀ
increased from to 20 C and 80 C, the particle size decreased.
In the process for the formation of PtNiP alloys, it is possible
that the increase of the reaction temperature may enhance the
diffusion of the reaction as well as the reaction rate. Meanwhile,
the growth from the nuclei into the particles needs a relative
slow deposition process. There is not enough time to deposit
onto the formed nuclei for some of the continuously generated
PtNiP. Subsequently, these generated PtNiP would/could
become the new nuclei and grow, resulting in further parti-
cles being formed. Thus in this case, the particle size decreased.
Fig. 3a shows the XRD patterns of the obtained products. For
comparison purposes, the XRD patterns of Pt and PtNi samples
whose SEM images are presented in Fig. S1,† were also shown.
As observed, the Pt and PtNi samples display the characteristics
of the face-centred cubic (fcc) crystallite Pt (JCPDS#04-0802) for
planes (111), (200), (220), (311) and (222) situated at ca. 40ꢀ, 46ꢀ,
68ꢀ, 81.5ꢀ and 86ꢀ respectively.26 In addition, two very weak
peaks at ca. 33.4ꢀ and 59.3ꢀ appear, which could be related to
the formation of Ni(OH)2.27 The average crystalline size and
lattice constant of Pt and PtNi samples was calculated based on
the all peaks by MDI Jade 6.5 soware. Before obtaining the
results, the XRD patterns were treated with the process of theta
calibration of whole pattern, deducting background, smooth
and tting prole. The average crystalline size of Pt and PtNi is
6.0 nm and 15.4 nm respectively. The obtained lattice constants
Fig. 3 (a) XRD patterns of the Pt, PtNi, and four PtNiP samples; (b) the
enlarged region between 30ꢀ and 55ꢀ for PtNiP samples.
˚
˚
for Pt and PtNi samples are 3.9118 A and 3.9108 A respectively.
The decrease of the lattice constant of PtNi related to that of Pt
suggests the insertion of Ni atoms into the Pt cubic lattice.28
In the curves of the PtNiP-0 sample, a clear broad peak
located at about 45ꢀ appears, without any trace of sharp peaks
related to the periodic lattice, suggesting that a typical amor-
phous structure is formed in the four PtNiP samples.29 This
nding is consistent to the previous SAED result, and suggests
that the presence of P plays an important role in the formation
of amorphous structure. The amorphous structure of PtNiP-20,
PtNiP-50, and PtNiP-80 was further proven by the broad peaks
located at 45ꢀ, indicating that the reaction temperature did not
inuence the amorphous structure. On the other hand, as
shown in Fig. 3b, the broad peak shied toward the lower 2q
value at ca. 0.7ꢀ, from the PtNiP-0 to the PtNiP-80 sample. The
amorphous structure is a short-range order with a long-range
disorder. When the ambient temperature increases, the atoms
would rearrange, leading to the increase of the order range.30
We therefore infer that, with the enhancement of the reaction
temperature, the order range lengthen, in other words, the
order degree of the atomic arrangement in the structure
increases, resulting in the negative shi of the broad peak from
PtNiP-0 to PtNiP-80 sample.
The porous structure of PtNiP samples was investigated by
N2 adsorption–desorption isotherms (Fig. S2†). The lowest
relative pressure in the curves is 1.0 ꢂ 10ꢁ5. For the four
samples, the isotherms can be classied as type I isotherms in
the low relative pressure, which can be ascribed to the well-
known Langmuir adsorption.31 No clear uptakes appear in the
low relative pressure in the isotherm curves, suggesting no
micropores exist in the PtNiP samples.32 At high relative pres-
sure, the isotherms can be classied as type II isotherms, which
is named as the sigmoid isotherm.31 A distinct hysteresis loop in
the larger range of ca. 0.45–1.0 P/P0 in the four isotherm curves
indicated an amount of mesopores.26 By the DFT theory method
based upon QSDFT equilibrium model, the pore size distribu-
tions were estimated. The high tting degree suggests that the
shape of the pores in the four samples is slit. These slit pores
derived of the gap among the particles of the network structure.
Fig. 2 SEM images of (a) PtNiP-0, (b) PtNiP-20, (c) PtNiP-50, and (d)
PtNiP-80 samples.
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The results were inserted in the isotherm proles. As seen could be ascribed to two effects: (i) an ‘electron effect’ – when Pt
Fig. S2,† the pores are in the mesoporous range between 3.4 nm alloys with Ni, the electron structure of Pt atoms may change
and 38 nm for the four samples, supporting the judgement from thus inuence the catalytic activity;29 (ii) the presence of Ni
the shape of the isotherms. No maximum distribution appears atoms around Pt atoms signicantly weakens the hydrogen
for each samples. From PtNiP-0 to PtNiP-80, the pore size adsorption/desorption, taking advantage of the hydrazine
distribution did not emerge a trend of change. The results could oxidation reaction.
be The BET surface areas of the four samples are shown in
Fig. 4. As observed, the BET surface areas increase with a gure, the hydrogen adsorption/desorption peaks and the metal
decrease in particle sizes from PtNiP-0 to PtNiP-80. oxidation peak, as well as the oxidation/reduction peaks related
CVs on PtNiP electrode are presented in Fig. 5c. From the
The surface electrochemical properties of Pt, PtNi and PtNiP to the transformation between Ni(OH)2 and NiOOH, can hardly
were investigated by Cyclic Voltammetry (CV) which is regarded be seen from the CV (in 0.1 mol Lꢁ1 KOH solution), indicating
as a powerful electrochemical technique for surface analysis.33 that the introduction of P atoms efficiently inhibits the occur-
For comparison, we also performed CV experiments of Pt and rence of these reactions. Aer the addition of N2H4 into the
PtNi in 0.1 mol Lꢁ1 KOH solution at a scan rate of 50 mV sꢁ1. As electrolyte, a clear hydrazine oxidation peak situated at about
shown in Fig. 5a, the CV of Pt electrode in 0.1 mol Lꢁ1 KOH ꢁ0.745 V vs. Ag/AgCl arose. On the basis of the current of
solution in the absence of N2H4 displays the typical features of
metallic Pt. The peaks in the low potential region correspond to
the hydrogen adsorption (Hads)/desorption (Hdes) and the broad
peaks in the high potential region relates to the oxidation/
reduction of Pt. In the presence of N2H4 in the electrolyte, the
reaction of both the hydrogen adsorption/desorption and
oxidation/reduction of Pt did not change drastically (no major
changes in the shapes of all peaks). However the oxidation peak
current increased, indicating that the hydrazine oxidation
occurred and no new peaks emerged, suggesting that the peak
of hydrazine oxidation overlapped with that of the hydrogen
desorption peak. This nding suggests that, on the Pt surface,
the hydrogen desorption competed with the hydrazine oxida-
tion, implying that pure Pt as electrocatalysts for hydrazine
oxidation with the conditions in this work is poor. On the PtNi
electrode (Fig. 5b), the peaks related to both hydrogen
adsorption/desorption and the oxidation/reduction of Pt in
0.1 mol Lꢁ1 KOH solution in the absence of N2H4 were weak,
and the oxidation/reduction peaks at the highest potential
within the whole potential range could be ascribed to Ni(OH)2
oxidation to NiOOH and the reduction of NiOOH to Ni(OH)2.21
In the 0.1 mol Lꢁ1 KOH + 0.1 mol Lꢁ1 N2H4 solution, an
oxidation peak at ca. ꢁ0.743 V vs. Ag/AgCl was observed, indi-
cating that hydrazine oxidation occurred on PtNi electrode.
Meanwhile, the oxidation peak at the highest potential became
strong, maybe resulting from the oxidation of produced inter-
mediates. The enhanced catalytic activity of PtNi compared to Pt
Fig. 5 CV curves of (a) Pt, (b) PtNi, and (c) PtNiP-20 electrodes in the
Fig.
4
BET surface areas of PtNiP-0, PtNiP-20, PtNiP-50, and 0.1 mol Lꢁ1 KOH without or with 0.1 mol Lꢁ1 N2H4 solution at a scan
PtNiP-80 samples.
rate of 50 mV sꢁ1
.
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hydrazine oxidation peak, the catalytic activity of PtNiP catalyst
was much better than that of Pt and PtNi catalysts. Here, the
onset potential of hydrazine oxidation on the three electrodes
was not compared due to the overlap of the hydrogen desorp-
tion and hydrazine oxidation on Pt and PtNi electrodes. The
improved performance of PtNiP catalyst could be related to the
‘electron effect’29 and the inhibition for the hydrogen
adsorption/desorption on Pt atoms due to the presence of Ni
and P atoms. In addition, the amorphous structure could be a
factor inuencing the catalytic activity of PtNiP-20. Over the past
few years, our group has carefully studied the electrocatalytic
activity of amorphous electrocatalysts.28,30,34–39 We have found
that the defects in particle structure of amorphous electro-
catalysts can act as active sites for catalysis, moreover, the
improvement of crystallization degree may lead to the decrease
of the defects, thus reducing the catalytic activity of the elec-
trocatalysts. We then infer that the defects in amorphous
structure of PtNiP could also enhance its catalytic activity. To
further elucidate this statement, the study focused on a series of
PtNiP samples prepared at various reaction temperatures for
which their catalytic activities were determined.
Fig. 6 shows a series of CVs of PtNiP-0, PtNiP-20, PtNiP-50
and PtNiP-80 electrodes in hydrazine solution. As observed,
there is a specic trend in which the current peak of hydrazine
oxidation increases with the reaction temperature, and reaches
a value of +0.626 mA (recorded for the PtNiP-50 catalyst), and
then decreases (PtNiP-80 catalyst). At this point, it is thus
necessary to discuss the reason(s) caused by this observed
trend: based on the same composition for the four catalysts, the
particle size was rstly considered because the smaller the
particle size is, the larger the surface area is, then the larger the
number of active sites are for electrocatalysis. As shown by SEM
and BET data, from PtNiP-0 to PtNiP-80, the particle size
decreased and the BET surface area increased which should
lead to a continuous improvement in the catalytic activity of the
samples. On the other hand, the increase of the reaction
temperature from PtNiP-0 to PtNiP-80 made the order-range in
PtNiP structure become longer, implying an increase in the
crystalline degree. The number of the defects which acts as the
active sites deduced, resulting in the decrease of the catalytic
activity for hydrazine oxidation. When the effect of the particle
size balances the effect of the crystalline degree, the catalytic
activity of PtNiP catalyst would reach a maximum value. The
PtNiP-50 catalyst was best among the four catalysts resulting
from the balance between the particle size effect and the effect
of the crystalline degree. In addition, the results also evidenced
that the defects in amorphous structure of PtNiP samples acted
as the active sites for catalysis.
Fig.
6
CV curves of PtNiP-0, PtNiP-20, PtNiP-50, PtNiP-80
electrodes in the 0.1 mol Lꢁ1 KOH with 0.1 mol Lꢁ1 N2H4 solution at a
scan rate of 50 mV sꢁ1
.
Fig. 8 shows the effect of hydrazine concentration on the
catalytic activity of PtNiP-50 catalyst. As it can be seen that the
peak current increased signicantly with the increase of
hydrazine concentration, conrming that the oxidation
currents were indeed caused by the electrooxidation of hydra-
zine, and the hydrazine oxidation on PtNiP-50 electrode was
controlled by a diffusion process.40
To study the mechanism for the oxidation of hydrazine in
alkaline solution, the inuence of KOH concentration in the
alkaline hydrazine solutions on the potential and current of the
hydrazine oxidation peak was performed. As shown in Fig. 9, the
current of the hydrazine oxidation peak was increased and the
potential of the hydrazine oxidation shied towards low value
with increasing the KOH concentration in the electrolyte. Based
on the view of Karim-Nezhad and co-workers,41 the rst inter-
mediate of hydrazine oxidation in alkaline solution was
[HO–H2N]NH2–OH]2ꢁ. The hydrazine oxidation process can
be proposed as following:
N2H4 + 2HOꢁ / [HO–H2N]NH2–OH]2ꢁ
[HO–H2N]NH2–OH]2ꢁ / N2H2* + 2H2O + 2eꢁ
N2H2* + 2HOꢁ / N2 + * + 2H2O + 2eꢁ
To investigate the durability of the PtNiP samples, chro-
noamperometry (CA) measurements were carried out (Fig. 7). For
the four samples, the potentiostatic current decreased rapidly in
the initial period of time which can be due to the formation of
intermediate species during the electro-oxidation of hydrazine.
Aer 1000 s, the electro-oxidation current of hydrazine on PtNiP-
50 electrode was higher than that of other PtNiP catalysts, indi-
cating that PtNiP-50 catalysts appear to be more durable than
other PtNiP catalysts in the hydrazine oxidation reaction.
Fig. 7 Chronoamperometry curves of the four PtNiP samples in
0.1 mol Lꢁ1 KOH + 10 mmol Lꢁ1 N2H4 solution at ꢁ0.7 V vs. Ag/AgCl.
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Pt atoms due to the presence of Ni and P atoms, and the defects
in amorphous structure of PtNiP acting as the active sites for
catalysis.
(3) Compared to PtNiP-0, PtNiP-20 and PtNiP-80, PtNiP-50
exhibited the highest catalytic activity, resulting from the
balance between the decrease of particle size and the decrease
of the number of the defects.
(4) The hydrazine oxidation on PtNiP-50 electrode was
controlled by a diffusion process. The catalytic activity of PtNiP
would be enhanced by increasing the concentration of KOH.
Acknowledgements
Fig. 8 CV curves of PtNiP-50 electrode in the 0.1 mol Lꢁ1 KOH with
The authors acknowledge the National Natural Science Foun-
dation of China (21163018, 21363022, and 51362027) and
JCYJ20140418095735600 for providing funding for this
research.
0.006, 0.008, 0.010, 0.012, 0.014 and 0.016 mol Lꢁ1 N2H4 solution at a
scan rate of 50 mV sꢁ1
.
Notes and references
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Conclusions
In this study, the physical characterization results elucidated
the changes of the particle size and the amorphous structure of 14 X. Y. Liu, Y. Zhang, M. X. Gong, Y. W. Tang, T. H. Lu,
PtNiP particle networks as a function of the reaction tempera-
ture. The following conclusions can be drawn:
Y. Chenab and L. Jong-Min, J. Mater. Chem. A, 2014, 2,
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(1) The increase in the reaction temperature from 0 ꢀC to 15 W. Y. Wong, W. R. W. Daud, A. B. Mohamad,
80 ꢀC resulted in the decrease of the particle size and the defects
in PtNiP amorphous structure.
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(2) The current of hydrazine oxidation on PtNiP-20 electrode 16 K. Wang, H. Wang, R. Wang, J. Key, V. Linkov and S. Ji, S. Afr.
was 0.62 mA at ꢁ0.63 V, higher than that of the crystalline Pt J. Chem., 2013, 66, 86–91.
and PtNi catalysts, which could be associated to the electron 17 Y. Wang, X. Chen, B. Yue and H. He, Top. Catal., 2012, 55,
effect, the inhibition for the hydrogen adsorption/desorption on
1022–1031.
68660 | RSC Adv., 2015, 5, 68655–68661
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