A novel and facile synthetic route to MMo (M = Ni or Co) bimetallic phosphides

Article abstract of DOI:10.1080/10426507.2019.1660657

A novel and facile route to bimetallic molybdenum phosphides was described. Both NiMoP and CoMoP phosphides were successfully prepared by a hexamethylenetetramine (HMT) route. Mixed-salt precursors containing HMT, M-HMT (M = Ni, Co or Mo) complexes, MMo-HMT (M = Ni or Co) complexes and P-containing species can be directly converted to bimetallic molybdenum phosphides under a flow of Ar at 800 °C. It was proposed that the bimetallic phosphides were formed via two possible reaction pathways: (i) MMo-HMT complexes/P→MMoP (M = Ni or Co) and (ii) M-HMT (M = Ni, Co or Mo) complexes/P→M₂P/MoP→MMoP (M = Ni or Co). Additionally, it was found that the dispersions and surface areas of NiMoP and CoMoP prepared by HMT route were higher than those of corresponding bimetallic phosphides prepared by traditional H₂ reduction method.

Full text of DOI:10.1080/10426507.2019.1660657

Phosphorus, Sulfur, and Silicon and the Related Elements
ISSN: 1042-6507 (Print) 1563-5325 (Online) Journal homepage: https://www.tandfonline.com/loi/gpss20
A novel and facile synthetic route to MMo (Mꢀ=ꢀNi
or Co) bimetallic phosphides
Zhiwei Yao, Meijun Dong, Yan Shi, Yue Sun & Qingyou Liu
To cite this article: Zhiwei Yao, Meijun Dong, Yan Shi, Yue Sun & Qingyou Liu (2019): A novel
and facile synthetic route to MMo (Mꢀ=ꢀNi or Co) bimetallic phosphides, Phosphorus, Sulfur, and
Silicon and the Related Elements, DOI: 10.1080/10426507.2019.1660657
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PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
https://doi.org/10.1080/10426507.2019.1660657
A novel and facile synthetic route to MMo (M ¼ Ni or Co) bimetallic phosphides
a
a
a
a
b
Zhiwei Yao
, Meijun Dong , Yan Shi , Yue Sun , and Qingyou Liu
a
College of Chemistry, Chemical Engineering and Environmental Engineering, Liaoning Shihua University, Fushun, People’s Republic of
b
China; Key Laboratory of High-temperature and High-pressure Study of the Earth’s Interior, Institute of Geochemistry, Chinese Academy of
Sciences, Guiyang, People’s Republic of China
ABSTRACT
ARTICLE HISTORY
A novel and facile route to bimetallic molybdenum phosphides was described. Both NiMoP and
CoMoP phosphides were successfully prepared by a hexamethylenetetramine (HMT) route. Mixed-
salt precursors containing HMT, M-HMT (M ¼ Ni, Co or Mo) complexes, MMo-HMT (M ¼ Ni or Co)
complexes and P-containing species can be directly converted to bimetallic molybdenum phos-
Received 30 May 2019
Accepted 23 August 2019
KEYWORDS
Bimetallic molybdenum
phosphide; NiMoP; CoMoP;
hexamethylenetetramine;
formation mechanism
ꢀ
phides under a flow of Ar at 800 C. It was proposed that the bimetallic phosphides were formed
via two possible reaction pathways: (i) MMo-HMT complexes/P!MMoP (M ¼ Ni or Co) and (ii) M-
HMT (M ¼ Ni, Co or Mo) complexes/P!M P/MoP!MMoP (M ¼ Ni or Co). Additionally, it was found
2
that the dispersions and surface areas of NiMoP and CoMoP prepared by HMT route were higher
2
than those of corresponding bimetallic phosphides prepared by traditional H reduction method.
GRAPHICAL ABSTRACT
[
21,22]
Introduction
MMo (M ¼ Ni or Co) bimetallic phosphides.
The HDS
activity was found to be in the order of Ni P> MoP > NiMoP,
and the hydrodeoxygenation (HDO) activities decreased in the
2
After transition metal carbides and nitrides, transition metal
phosphides are another class of interstitial compounds receiving
much attention in recent years due to their widespread applica-
tions in various fields, such as electronics, photonics, magnetism,
[21,22]
sequence of Ni P> NiMoP > MoP.
However, the MMo
2
[
5,21–28]
(M ¼ Ni or Co) bimetallic phosphide systems
were still
[
1–4]
studied widely in recent years probably due to the interesting
bimetallic effects (e.g. regulating product distribution) for the
catalysis and so on.
In particular, metal phosphides (e.g.
MoP, Ni P and Co P) have been identified as potential catalysts
2
2
[27]
phosphide systems in various reactions.
for many reactions such as hydrogenation and hydrotreat-
[
5–10]
[11]
Unlike monometallic phosphides that can be prepared
using many methods including H -temperature programed
reduction (H -TPR) of phosphate, chemical vapor depos-
ition, phosphorization using red or white phosphorus,
ing,
dry reforming of methane,
NO dissociation
N H decompos-
2 4
[12,13]
[14]
2
ition,
and electrocatalytic reactions
2
including hydrogen evolution, oxygen reduction and evolution
[15–17]
reactions.
. To further improve the catalytic activities of
decomposition of high-boiling point tri-n-octylphosphine
phosphide catalysts, M-based (M ¼ Mo, Ni or Co) bimetallic
phosphides have been prepared and used as catalysts. Recently,
Zhang et al. investigated NiCo bimetallic phosphide catalyst for
hydrogen evolution reaction (HER), and found that the NiCo
bimetallic phosphide exhibited higher HER activity than their viz. H
(
TOP) or
P(SiMe3)3
reported in several recent
[
1,28,29]
reviews,
the synthetic method for MMo (M ¼ Ni or
Co) bimetallic phosphides was limited to only one approach,
[
5,21–27]
-TPR method.
Therefore, it was worthwhile to
monometallic counterparts. In addition, the synergistic effect develop novel and simple methods for the preparation of
2
[18]
between Ni and Co in the NiCo bimetallic phosphide system bimetallic phosphide catalysts.
was also found in hydrodesulfurization (HDS) and hydrazine
decomposition reactions.
In recent years, the main research focuses of our group
[19,20]
Unlike NiCo bimetallic phos- were on the preparation and catalytic activity of phos-
[
30–40]
phide, no synergistic effect was observed between two metals in phides.
We developed an original technique for the
CONTACT Qingyou Liu
liuqingyou@vip.gyig.ac.cn
Key Laboratory of High-temperature and High-pressure Study of the Earth’s Interior, Institute of
Geochemistry, Chinese Academy of Sciences, Guiyang, 550081, People’s Republic of China.
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/gpss.
Supplemental data for this article can be accessed on the publisher’s website.
ß 2019 Taylor & Francis Group, LLC

2
Z. YAO ET AL.
Figure 2. XRD patterns of the products of NiMoP-HMT-N (a) and CoMoP-HMT-N
b) thermal decomposition at different temperatures.
Figure 1. XRD patterns of the products of NiMoP-HMT (a) and CoMoP-HMT (b)
thermal decomposition at different temperatures.
(
synthesis of highly dispersed monometallic phosphides
Table 1. Phase structures of the solid products during decompos-
(
MoP, Ni P and Co P) by one-step decomposition of hex- ition processes.
2 2
amethylenetetramine (HMT)-containing precursors under NiMo sample
XRD phases
Amorphous
CoMo sample
XRD phases
Amorphous
[
39,40]
inert atmosphere.
This HMT-based method produced NiMoP-HMT-500
CoMoP-HMT-500
CoMoP-HMT-600
CoMoP-HMT-700
CoMoP-HMT-800
NiMoP-HMT-600
Ni
2
P
2
Co P
CoMoP, Co
CO as major gas product rather than H O. The high disper-
sions and surface areas of as-prepared phosphides were NiMoP-HMT-800
2
NiMoP-HMT-700
NiMoP, Ni
NiMoP,
2
P
2
P
CoMoP,
Co P, MoP
2
Amorphous
Amorphous
CoMoP, Co2P
CoMoP
Ni
Amorphous
Ni P, Ni12P
5
2
P, MoP
achieved probably owing to the mitigation of hydrothermal
sintering. Based on the success with the HMT route to syn-
NiMoP-HMT-N-500
NiMoP-HMT-N-600
CoMoP-HMT-N-500
CoMoP-HMT-N-600
CoMoP-HMT-N-700
CoMoP-HMT-N-800
2
thesize monometallic phosphides, we decided to attempt NiMoP-HMT-N-700
NiMoP, Ni2P
NiMoP
NiMoP-HMT-N-800
whether this simple procedure can also be used to produce
bimetallic phosphides. In this work, both NiMoP and
CoMoP phosphides were successfully prepared by the HMT
route. Techniques of XRD, XPS, TEM, SEM and EDX elem-
ent mapping were adopted for the characterization of prod-
ucts and precursors, to give insights into the formation
mechanism of bimetallic phosphides.
NiMoP-HMT-600 and CoMoP-HMT-600 samples, respect-
ively. With a further increase of temperature to 700 C, an
ꢀ
additional new set of peaks for NiMoP (main diffraction
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
peaks at 2h ¼ 39.2 , 43.2 , 47.3 , 49.2 and 54.2 , PDF 71-
ꢀ
0
4
202) and CoMoP (main diffraction peaks at 2h ¼ 39.2 ,
ꢀ
ꢀ
ꢀ
ꢀ
0.8 , 41.6 , 42.9 and 47.0 , PDF 71-0478) appeared on the
NiMoP-HMT-700 and CoMoP-HMT-700 samples, respect-
ively. At the final temperature of 800 C, both NiMoP-
Results and discussion
ꢀ
Figure 1 shows the XRD patterns of the products of the
NiMoP-HMT and CoMoP-HMT precursors decomposition
at different temperatures. After decomposition at 500 C, the
HMT-800 and CoMoP-HMT-800 samples showed three
ꢀ
mixed phases of MoP (main diffraction peaks at 2h ¼ 27.9 ,
ꢀ
ꢀ ꢀ ꢀ
2.0 , 43.0 and 57.1 , PDF 65-6487), Ni P, NiMoP and
2
3
resulting samples NiMoP-HMT-500 and CoMoP-HMT-500 MoP, Co P and CoMoP, respectively.
2
were completely amorphous. When the temperature was
Figure 2 shows the XRD patterns of the products of the
ꢀ
increased to 600 C, there were poorly crystalline Ni P precursors with added NH ꢁ2H O (NiMoP-HMT-N and
2
ꢀ
3
2
ꢀ
ꢀ
ꢀ
(
main diffraction peaks at 2h ¼ 40.6 , 44.5 , 47.3 and 54.1 , CoMoP-HMT-N) decomposition at different temperatures.
PDF 65-1989) and Co P (main diffraction peaks at Like the products of MMoP-HMT decomposition at low
2
ꢀ
ꢀ
ꢀ
ꢀ
2
h ¼ 40.8 , 43.3 and 52.1 , PDF 32-0306) generated on the temperatures (500–700 C), the products of MMoP-HMT-N

PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
3
(
133.1–133.2 eV) were agreed with assignments by others to
2
þ
2þ/3þ
2þ
4þ
6þ
5þ
[41–43]
Ni , Co
respectively. The binding energies of the peaks at 853.0,
78.4, 227.7–227.8 and 129.3–129.5 eV were attributed to
/Co , Mo /Mo
and P
species,
7
aþ
bþ
dþ
rꢂ
[27,39]
Ni , Co , Mo and P in phosphide,
respectively.
The detection of these oxidized species was attributed to
surface oxidation of phosphides in the passivation pro-
[
42]
cess.
In addition, the XPS of O 1s for the bimetallic
phosphide samples might be also of interests and the results
were shown in Supplemental Material, Figure S1. The region
of the O 1s spectra included three peaks. It was suggested
that peaks at 530.9–531.0 and 532.3–532.4 eV were due to
[
44,45]
metal oxides and POx,
respectively, and those at about
ꢂ
ꢂ
5
33.1 eV to adsorbed oxygen species such as O , OH
[
45]
or H O.
2
Subsequently, the morphologies of MMoP-HMT-N-800
(
M ¼ Ni or Co) samples were investigated by SEM and TEM.
It can be observed from SEM images (Figure 4) that the mor-
phologies of NMoP-HMT-N-800 and CoMoP-HMT-N-800
were similar and they were composed of nanoparticles with
size range of around 50–200 and 10–100 nm, respectively.
Additionally, it was obvious that these nanoparticles con-
nected with each other through thin plates or sheets. These
plates or sheets should be carbon deposits from HMT decom-
[
39]
position, as suggested before.
These results were in good
accordance with the observation of TEM images (Figure 5).
The insets in Figure 5 clearly showed the crystal lattices of
NiMoP (111) and CoMoP (201), which further proved the
existence of NiMoP and CoMoP in the NMoP-HMT-N-800
and CoMoP-HMT-N-800 samples, respectively. For the sake
of comparison, the morphologies of NiMoP and CoMoP pre-
pared by traditional H -TPR method were also characterized
by means of SEM. It can be seen from Supplemental
Material, Figure S2 that the NiMoP and CoMoP consisted of
2
Figure 3. XPS spectra of Ni 2p, Co 2p, Mo 3d and P 2p: (a) NiMoP-HMT-N-800;
b) CoMoP-HMT-N-800.
(
decomposition also showed a phase transformation: amorph- large aggregates of irregularly shaped particles, which was
[
46]
ous state!M phosphide!M phosphide and MMo phos- similar to the result reported by others.
It was clear that
phide mixture (M ¼ Ni or Co). Fortunately, however, unlike the dispersions of NiMoP and CoMoP prepared by HMT
MMoP-HMT-800 samples were mixed phases of MMo route were higher than those of corresponding bimetallic
bimetallic phosphides and their monometallic counterparts, phosphides prepared by H -TPR method (see Figure 4 and
2
the MMoP-HMT-N-800 samples demonstrated the single Supplemental Material, Figure S2).
phases of MMoP (M ¼ Ni or Co). For the sake of compari-
Finally, the textural properties and carbon contents of the
son, Table 1 summarizes the phase structures of the solid NiMoP and CoMoP samples obtained in this study were
products obtained during decomposition processes. It was listed in Table 3. It was found that the NiMoP and CoMoP
obvious from Table 1 that the addition of NH ꢁ2H O in the phosphides obtained by HMT method showed lower BET
3
2
precursor preparation was helpful for the formation of single surface areas 2 than monometallic phosphides Ni
P
2
ꢂ1
phases of MMoP (M ¼ Ni or Co).
(SBET¼191.7 m g and carbon content ¼ 32.5 wt%) and
2
ꢂ1
To further confirm the formation of MMoP, the MMoP- Co2P (S ¼43.6
BET
m
g
and carbon content
¼
[
39]
HMT-N-800 (M ¼ Ni or Co) samples were characterized by 25.3 wt%),
probably attributing to their lower carbon con-
XPS, SEM, TEM and so on. Figure 3 shows the XPS spectra tents. It was reported that the existence of a large amount of
of Ni 2p, Co 2p, Mo 3d and P 2p levels for the MMoP- carbon in phosphide materials can play a role in bonding of
HMT-N-800 (M ¼ Ni or Co) samples. Based on the curve nanoparticle aggregation, leading to the enhancement of sur-
[
47]
fitting, the binding energies of Ni 2p3 , Co 2p , Mo 3d
5/2
face area of phosphides.
Note that the surface areas of
/2
3/2
and P 2p3/2 and the distribution of these corresponding spe- NiMoP and CoMoP prepared by HMT route were higher
cies are listed in Table 2. It can be seen from Figure 3 and than those of corresponding bimetallic phosphides prepared
2
ꢂ1
Table 2 that the surface regions of the two samples were by traditional H -TPR method (S ¼8 m g for NiMoP
2
BET
[5]
2
ꢂ1
composed of oxidized species and phosphorized species. The and SBET¼5 m g for CoMoP).
binding energies of oxidized Ni (855.9 eV), Co (780.1 and
To understand the formation mechanism of NiMoP and
81.4 eV) Mo (228.7–228.8 and 232.3–232.4 eV) and P CoMoP phosphides, the MMoP-HMT and MMoP-HMT-N
7

4
Z. YAO ET AL.
Table 2. XPS results of Ni 2p, Co 2p, Mo 3d and P 2p for the single phases of NiMoP and CoMoP obtained in this study.
Binding energy (eV)
Mo 3d5/2
Ni 2P3/2
Co 2P3/2
P 2p3/2
dþ
4þ
6þ
aþ
2þ
bþ
2þ/3þ
2þ
rꢂ
5þ
Sample
NiMoP-
HMT-N-800
CoMoP-
HMT-N-800
Mo
Mo
Mo
Ni
853.0
Ni
855.9
Co
Co
Co
P
P
227.7
227.8
228.8
228.7
232.4
232.3
129.5
129.3
133.1
133.2
778.4
780.1
781.4
Figure 5. TEM images of (a) NiMoP-HMT-N-800 and (b) CoMoP-HMT-N-800. The
insets show the corresponding NiMoP (211) and CoMoP (111) crystal lattices.
Figure 4. SEM images of (a) NiMoP-HMT-N-800 and (b) CoMoP-HMT-N-800.
(
M ¼ Ni or Co) precursors were characterized by XRD and
decomposition/reduction of MP-HMT (M ¼ Ni, Co or Mo)
precursors (composed of M-HMT (M ¼ Ni, Co or Mo) com-
EDX element mapping. Figure 6 shows the XRD patterns of
these MMoP-HMT and MMoP-HMT-N (M ¼ Ni or Co)
precursors as well as HMT for comparison. It can be seen
from Figure 6 that the MMoP-HMT and MMoP-HMT-N
plexes, P-containing species and HMT) to produce Ni P,
2
[
39,40]
Co P and MoP,
it was reasonable to observe from
2
Figure 1 that the in situ decomposition/reduction of MMoP-
(
M ¼ Ni or Co) precursors contained unknown compounds
HMT precursors would yield mixtures of M P, MoP and
2
except M-HMT (M ¼ Ni, Co or Mo) complexes (the phases
MMoP (M ¼ Ni or Co). The formation temperatures of
ꢀ
shown in Supplemental Material, Figure S3 have been con-
Ni P and Co P (>600 C) were lower than that of MoP
2
2
[
30]
ꢀ
39,40]
firmed by our previous study)
and HMT itself. The
(
800 C), which agreed with the results of previous stud-
[
unidentified phases were likely to be MMo (M ¼ Ni or Co) ies.
It was reasonable to deduce that the MMoP should
And the lack be originated from the decomposition/reduction of MMo-
[
48]
complexes with HMT, as proved by others.
of P-containing phases on the XRD patterns of MMoP- HMT (M ¼ Ni or Co) complexes and P-containing species.
HMT and MMoP-HMT-N (M ¼ Ni or Co) precursors was Noticeably, in the case of the MMoP-HMT-N precursors
due to these P-containing compounds being fully amorph- (Figure 2), although there was the existence of M P inter-
2
[
39]
ꢀ
ous.
Therefore, it can be deduced that the MMoP-HMT mediates at temperatures below 700 C, the final products
and MMoP-HMT-N (M ¼ Ni or Co) precursors should be were phase-pure MMoP (M ¼ Ni or Co). Moreover, there
composed of M-HMT (M ¼ Ni, Co or Mo) complexes, was no formation of MoP phase when the MMoP-HMT-N
ꢀ
MMo-HMT (M ¼ Ni or Co) complexes, P-containing species (M ¼ Ni or Co) precursors were heated at 800 C. Therefore,
and HMT.
it was possible that the MoP can be reacted with M P to
2
In view of the fact that the formation mechanism of form MMoP (M ¼ Ni or Co). To further confirm this fact,
monometallic phosphides was proposed as the in situ the mechanical mixtures of M P (M ¼ Ni or Co) and MoP
2

PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
5
Table 3. Textural properties and carbon contents of the NiMoP and CoMoP
samples obtained in this study.
2
ꢂ1
3
ꢂ1
Sample
S
BET (m g
)
D
P
(nm)
V
P
(cm g
)
Carbon (wt%)
NiMoP-HMT-N-800 12.8
CoMoP-HMT-N-800 22.3
12.9
28.3
0.03
0.05
1.9
5.3
S
BET¼BET surface area; D
P
¼average pore diameter; V ¼total pore volume.
P
Figure 7. XRD pattern of mechanical mixture of Ni
2
P and MoP (Ni:Mo ¼ 1:1)
ꢀ
treated in H
2
at 800 C for 1 h. The patterns of Ni
2
P and MoP are also shown
for comparison.
Figure 6. XRD patterns of MMoP-HMT and MMoP-HMT-N (M ¼ Ni or Co) precur-
sors as well as HMT for comparison.
ꢀ
were heated in H at 800 C and the resulting samples were
2
characterized by XRD (Figures 7 and 8). It was found that
the MoP can indeed react with Ni P/Co P to form
2
2
[
49]
Ni Mo P
4
(main diffraction peaks at 2h ¼ 40.3 , 44.3 and
x
y
7.3 )/CoMoP. The solid–solid reactions were not complete,
judging by the observed ratio of peaks intensities, which was
probably due to weak interaction between solids formed in a
simple mechanical mixing process. Thus, we proposed that treated in H at 800 C for 1 h. The patterns of Co P and MoP are also shown
Figure 8. XRD pattern of mechanical mixture of Co
2
P and MoP (Co:Mo ¼ 1:1)
ꢀ
2
2
for comparison.
the in situ decomposition/reduction of MMoP-HMT and
MMoP-HMT-N precursors to produce MMoP (M ¼ Ni or
Co) via two possible reaction pathways: (i) MMo-HMT
complexes/P!MMoP (M ¼ Ni or Co) and (ii) M-HMT
therefore reasonable that the transformation (M P/
2
MoP!MMoP) was suppressed during decomposition/reduc-
tion of MMoP-HMT precursors, which led to the formation
complexes (M ¼ Ni, Co or Mo)/P!M P/MoP!MMoP
2
of mixtures of MMoP, M P and MoP (M ¼ Ni or Co). In
(
M ¼ Ni or Co). In the case of monometallic phosphides,
2
contrast, the MMoP-HMT-N (M ¼ Ni or Co) precursors
containing higher dispersed M-HMT (M ¼ Ni, Co or Mo)
complexes can be converted into phase-pure MMoP by the
the NH ꢁ2H O was not necessary in the preparation of
3
2
[
39]
phase-pure Ni P and Co P via HMT route.
Although the
2
2
NH ꢁ2H O was added in the preparation of MoP in our pre-
3
2
[
40]
strong interaction between M P and MoP (M ¼ Ni or Co).
2
vious study,
this study result (not shown) indicated that
the NH ꢁ2H O was not essential for the synthesis of phase-
3
2
pure MoP via HMT method. It was worthy to note that the
Experimental
NH ꢁ2H O was crucially important to obtain phase-pure
3
2
Sample preparation
MMo (M ¼ Ni or Co) bimetallic phosphides in this study. It
was therefore interesting to investigate the effect of the add-
The HMT precursors were prepared by dissolving
ition of NH ꢁ2H O on the precursors in the preparation of
3
2
Ni(NO ) ꢁ6H O or Co(NO ) ꢁ6H O, (NH ) Mo O ꢁ4H O,
3
2
2
3 2
2
4 6
7
24
2
MMo (M ¼ Ni or Co) bimetallic phosphides.
(
NH ) HPO and HMT (N (CH ) ) with a fixed mole ratio
4 2 4 4 2 6
Figure 9 shows the SEM images and EDX element map-
ping images of the MMoP-HMT and MMoP-HMT-N
of M:Mo:P:HMT ¼ 1:1:1:6 (M ¼ Ni or Co). The solutions
with some precipitate were kept under stirring at room tem-
(
M ¼ Ni or Co) precursors, which confirmed the presence of
ꢀ
perature (RT) for 1 h and then dried at 110 C. The resulting
samples were designated as NiMoP-HMT and CoMoP-
HMT, respectively. Additionally, to dissolve the precipitate,
M (M ¼ Ni or Co), Mo and P elements, in agreement with
the XPS results (Figure 3). Furthermore, it was clear that
these elements were more uniformly distributed in the pre- a few drops of ammonium hydroxide (NH ꢁ2H O) were
3
2
cursors with added NH ꢁ2H O than in the ones without added in the solutions, and after stirred and dried the result-
3
2
added NH ꢁ2H O. The results suggested that the dispersions ing samples were designated as NiMoP-HMT-N and
3
2
of M-HMT (M ¼ Ni, Co or Mo) complexes in the MMoP- CoMoP-HMT-N, respectively. The decomposition of precur-
HMT (M ¼ Ni or Co) precursors was lower than those in sors was carried out in a quartz reactor under a flow of Ar
ꢂ1
the MMoP-HMT-N (M ¼ Ni or Co) precursors. It was (50 mL min ). The temperature was raised linearly at a rate

6
Z. YAO ET AL.
Figure 9. SEM images and the corresponding Ni, Co, Mo and P element mapping images of NiMoP-HMT (a–d), CoMoP-HMT (i–l), NiMoP-HMT-N (e–h) and CoMoP-
HMT-N (m–p) precursors.
ꢀ
ꢂ1
of 10 C min and kept at a given value for 1 h, followed analyzer (NOVA4200). Carbon content of the samples was
by cooling to RT under Ar flow, and then passivated at RT determined by a Heraeus CHN-O-Rapid analyzer.
in a flow of 1%O /Ar for 2 h. A series of samples were
2
ꢀ
obtained from heating at 500, 600, 700 and 800 C, desig-
Conclusions
nated as MMoP-HMT-T and MMoP-HMT-N-T (M ¼ Ni or
Co, T ¼ 500, 600, 700 and 800).
In summary, phase-pure NiMoP and CoMoP phosphides
were successfully prepared by in situ decomposition/reduc-
tion of mixed-salt precursors containing HMT, M-HMT
Sample characterizations
(
M ¼ Ni, Co or Mo) complexes, MMo-HMT (M ¼ Ni or
X-ray diffraction (XRD) was carried out on an X-ray dif- Co) complexes and P-containing species under a flow of Ar
ꢀ
fractometer (X’Pert Pro MPD) equipped with a Cu Ka at 800 C. The investigation of the formation process showed
source. X-ray photoelectron spectroscopy (XPS) investigation that the bimetallic phosphide phases were formed via two
was conducted using a Kratos Axis ultra (DLD) equipped possible reaction pathways: (i) MMo-HMT complexes/
with Al Ka X-ray source. Charging effects were corrected by P!MMoP (M ¼ Ni or Co) and (ii) M-HMT (M ¼ Ni, Co or
means of adventitious carbon (284.6 eV) referencing. The Mo) complexes/P!M P/MoP!MMoP (M ¼ Ni or Co). It
2
morphology of the samples was characterized by scanning was worthy to note that the addition of NH ꢁ2H O into the
3
2
electron microscopy (SEM, Hitachi S-4800) and transmission precursors favored dispersing M-HMT (M ¼ Ni, Co or Mo)
electron microscopy (TEM, Philips Tecnal 10). The energy complexes and P-containing species, which can promote the
dispersive X-ray spectroscopy (EDX) element mapping formation of NiMoP and CoMoP via the second pathway.
images were taken on the Hitachi S-4800 SEM unit. BET In addition, the dispersions and surface areas of as-prepared
surface area of the samples was measured by a surface area NiMoP and CoMoP were superior to those of corresponding

PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
7
bimetallic phoshides prepared by traditional H -TPR
Reforming of Methane. Catal. Sci. Technol. 2016, 6, 7996–8004.
DOI: 10.1039/C6CY00836D.
12] Zheng, M.; Shu, Y.; Sun, J.; Zhang, T. Carbon-Covered
Alumina: A Superior Support of Noble Metal-like Catalysts for
Hydrazine Decomposition. Catal. Lett. 2008, 121, 90–96. DOI:
2
method. The advantages of the resulting NiMoP and
CoMoP bimetallic phosphide nanomaterials were worthwhile
for further exploration.
[
[
[
[
[
[
[
10.1007/s10562-007-9300-9.
13] Cheng, R.; Shu, Y.; Zheng, M.; Li, L.; Sun, J.; Wang, X.; Zhang,
T. Molybdenum Phosphide, a New Hydrazine Decomposition
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Disclosure statement
No potential conflict of interest was reported by the authors.
2
49, 397–400. DOI: 10.1016/j.jcat.2007.04.007.
14] Yao, Z.; Dong, H.; Shang, Y. Catalytic Activities of Iron
Phosphide for NO Dissociation and Reduction with Hydrogen.
J. Alloys Compd. 2009, 474, L10–L13. DOI: 10.1002/chin.
Funding
200925019.
The work was supported by the National Natural Science Foundation
of China (No. 21978125), the Project of Liaoning Province Department
of Education (No. L2017LZD003), the Program for Liaoning
Innovative Talents in University (No. LR2018070), the Liaoning
Province Natural Science Foundation (No. 20180551272) and the
Public Welfare Project of Guizhou Province (No. 2016-09-1).
15] Lv, Y.; Wang, X. Nonprecious Metal Phosphides as Catalysts
for Hydrogen Evolution, Oxygen Reduction and Evolution
Reactions. Catal. Sci. Technol. 2017, 7, 3676–3691. DOI: 10.
1039/C7CY00715A.
16] Popczun, E. J.; Read, C. G.; Roske, C. W.; Lewis, N. S.; Schaak,
R. E. Highly Active Electrocatalysis of the Hydrogen Evolution
Reaction by Cobalt Phosphide Nanoparticles. Angew. Chem.
2
014, 126, 5531–5534. DOI: 10.1002/anie.201402646.
17] Feng, L.; Vrubel, H.; Bensimon, M.; Hu, X. Easily-Prepared
Dinickel Phosphide (Ni P) Nanoparticles as an Efficient and
ORCID
2
Robust Electrocatalyst for Hydrogen Evolution. Phys. Chem.
Chem. Phys. 2014, 16, 5917–5921. DOI: 10.1039/c4cp00482e.
18] Zhang, R.; Wang, X.; Yu, S.; Wen, T.; Zhu, X.; Yang, F.; Sun,
Zhiwei Yao
Qingyou Liu
http://orcid.org/0000-0002-2535-9808
http://orcid.org/0000-0002-5630-7680
2 x
X.; Wang, X.; Hu, W. Ternary NiCo P Nanowires as pH-
Universal Electrocatalysts for Highly Efficient Hydrogen
Evolution Reaction. Adv. Mater. 2017, 29, 1605502. DOI: 10.
1002/adma.201605502.
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