Energydocument	 is	 the	 Accepted	 Manuscript	 version	 of	 a	 Published	 Work	 that	 appeared	 in	
This	 &
final	 form	 in	 ChemSoc.Rev,	
Environmental copyright	 ©	 The	 Royal	 Society	 of	 Chemistry	 2017	 aGer	 peer	
review	and	technical	ediIng	by	the	publisher.	To	access	the	final	edited	and	published	work	
Science
see:	hKps://pubs.rsc.org/en/content/arIclelanding/2017/ee/c7ee01553d#!divAbstract
View Article Online

Published on 25 July 2017. Downloaded by Universitat Rovira I Vigili on 4/12/2019 2:11:47 PM.

COMMUNICATION

Cite this: Energy Environ. Sci.,
2017, 10, 1770
Received 6th June 2017,
Accepted 25th July 2017
DOI: 10.1039/c7ee01553d

View Journal | View Issue

Ternary Ni–Co–P nanoparticles as
noble-metal-free catalysts to boost the hydrolytic
dehydrogenation of ammonia-borane†
Chun-Chao Hou,‡ab Qiang Li, ‡c Chuan-Jun Wang,ab Cheng-Yun Peng,ab
Qian-Qian Chen,ab Hui-Fang Ye,ab Wen-Fu Fu,*ad Chi-Ming Che,e Nuria Lopez
´
´
and Yong Chen *ab

*c

rsc.li/ees

The development of high-efficiency and low-cost catalysts for
hydrogen release from chemical hydrogen-storage materials is

Broader context

essential for the hydrogen-economy paradigm. Herein, we report

The chemical storage and release of hydrogen under mild conditions are of
importance to the hydrogen-economy paradigm. Ammonia-borane (AB) has
been regarded as a competitive candidate for chemical hydrogen storage
because of its high hydrogen content, non-toxicity, and long-term stability
under ambient temperature. Fast hydrogen evolution from AB has been
achieved using noble metal nanoparticles (e.g. Rh and Pt) as the catalyst.
However, all non-noble metal catalysts (e.g. Fe, Co, Ni nanoparticles) still
display relatively poor catalytic activity; the TOF is usually less than 70 minÀ1 at
room temperature for these systems. Therefore, the development of highefficiency and noble-metal-free catalysts for hydrogen release is highly
desirable. Metal phosphides with partial charge transfer from metal to P
have been discovered to be promising catalysts for AB hydrolysis. However, the
specific mechanism regarding how the electronic structure of metal phosphide
influences the catalytic performance and why the presence of extra OHÀ can
dramatically improve the activity are unclear. In this work, ternary Ni–Co–P
nanoparticles with various metal elemental ratios and electronic structures are
firstly used as catalysts for AB hydrolysis. The incorporation of Co into Ni2P
effectively optimizes the electronic structures of Ni2ÀxCoxP catalysts to enhance
their interaction with AB and simultaneously facilitate the hydroxyl activation
of AB, resulting in the reduction of the reaction energy barrier and thus
substantial improvement of the catalytic rate.

a facile and controllable method to fabricate a series of Co-doped
nickel phosphides and their corresponding nanohybrids with graphene oxide (GO) as highly efficient, robust and noble-metal-free
catalysts for ammonia borane hydrolysis. The incorporation of
Co into Ni2P effectively optimizes the electronic structures of
Ni2ÀxCoxP catalysts to enhance their interaction with AB and
simultaneously facilitate the hydroxyl activation of AB, resulting in
the reduction of the reaction energy barrier and thus substantial
improvement of the catalytic rate.

Hydrogen, a renewable clean and abundant energy vector, is
well recognized as one of the most ideal candidates to replace
conventional fossil fuels in the future, but this prospect meets
some intractable obstacles including the storage, transportation
and release of hydrogen for practical application due to its low
boiling point and volumetric density under air conditions.1–4
The development of safe and efficient chemical storage and
release of hydrogen under mild conditions is thus necessary for
the sake of the well-known hydrogen-economy paradigm.5–9
Ammonia-borane (AB) which has the advantages of a low molecular
weight but high hydrogen content (19.6 wt%, 146 g LÀ1), long-term
stability under ambient temperature, and non-toxicity, is regarded
a

Key Laboratory of Photochemical Conversion and Optoelectronic Materials and
HKU-CAS Joint Laboratory on New Materials Technical Institute of Physics and
Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China.
E-mail: chenyong@mail.ipc.ac.cn
b
University of Chinese Academy of Sciences, Beijing 100049, P. R. China
c
Institute of Chemical Research of Catalonia, ICIQ. The Barcelona Institute of
¨sos Catalans, 16, 43007, Tarragona, Spain.
Science and Technology, Av. Paı
E-mail: nlopez@iciq.es
d
College of Chemistry and Engineering, Yunnan Normal University,
Kunming 650092, P. R. China. E-mail: fuwf@mail.ipc.ac.cn
e
State Key Laboratory of Synthetic Chemistry and Department of Chemistry,
The University of Hong Kong, Pokfulam Road, Hong Kong, P. R. China
† Electronic supplementary information (ESI) available. See DOI: 10.1039/c7ee01553d
‡ The authors contributed equally.

1770 | Energy Environ. Sci., 2017, 10, 1770--1776

as a competitive candidate for chemical hydrogen storage.10–12 Fast
hydrogen evolution from AB has been achieved using homogeneous
molecular systems and metallic nanoparticles (MNPs), especially Pt,
Ru-based noble metals and/or their alloys, as the catalyst.13–16
However, the exorbitant prices and global reserve scarcity of
these precious metals limit their extensive usage. It is highly
required to develop robust and noble-metal-free catalysts
with high and controllable activities which can operate under
ambient conditions.17–20
In this respect, Xu and co-workers reported that low-cost
MNPs (Ni, Co and Cu) immobilized on various supports with
ample surface areas showed good catalytic performances for AB
hydrolysis in 2006.21 Following this, they found that amorphous
Fe NPs generated in situ through reduction of FeSO4 by NaBH4
exhibited high catalytic activity, which overwhelmingly hinges on the
aspects of morphology, dispersion, size and electronic structure.22

This journal is © The Royal Society of Chemistry 2017

View Article Online

Published on 25 July 2017. Downloaded by Universitat Rovira I Vigili on 4/12/2019 2:11:47 PM.

Communication

Quite recently, Zhong, Lee and co-workers developed a nanostructured CuxCo1ÀxO/GO bi-metallic synergistic system to
verify that the catalytic activity largely depends on the electronic
structure changes in the metal nanoparticles (MNPs).23 Through
the in situ XAS experiments, they managed to find that by
screening the ratio of Cu–Co in the MNPs deposited on GO,
the B–N bond in AB could be weakened due to the interaction of
the modified surface of the catalysts with AB, which eventually
accelerates the hydrolysis of AB but is still suboptimal with
respect to widespread applications. It has become the general
trend, even though still a daunting challenge, to develop highly
efficient catalysts through regulation of their electronic structures
to facilely adsorb and weaken the B–N bonds.24–27
Recently, metal phosphide NPs with suitable charge transfer
from metal to P facilitating the Proton-Coupled Electron Transfer
(PCET) process have been widely used as photo- and electrocatalysts
for water splitting.28–31 In light of the above unique feature and
their high chemical stability over a wide range of pH 0–14, Ni2P
NPs were firstly applied to AB hydrolysis by our group and
achieved a moderate TOF at room temperature.32 However, the
specific mechanism regarding how the electronic structure of
metal phosphide influences the catalytic performance and why
the presence of extra OHÀ could dramatically improve the
activity was unclear. With this in mind, herein we firstly use
ternary Ni–Co–P nanoparticles with various metal elemental
ratios and electronic structures as catalysts for AB hydrolysis in
order to deeply understand the electronic structure–catalytic
activity relationship of metal phosphides and thus to further
promote their catalytic performance. Among the Ni2ÀxCoxP catalysts,
the optimized Ni0.7Co1.3P displays the best catalytic performance
with an initial TOF value of 58.4 mol(H2) mol(Ni0.7Co1.3P)À1 minÀ1 at
ambient temperature. Furthermore, when Ni0.7Co1.3P was uniformly
distributed on GO as a hybrid catalyst, an unprecedentedly high TOF
value of 153.9 mol(H2) mol(Ni0.7Co1.3P)À1 minÀ1 for AB hydrolysis
was achieved under ambient conditions. As far as we know, this
TOF value is the highest one ever reported for noble-metal-free
heterogeneous systems. This superior catalytic performance can
be ascribed to collective factors including the ternary Ni–Co–P
synergistic effect, high dispersibility, improved surface area and
the interfacial interaction between Ni0.7Co1.3P and GO. The
experimental results and mechanistic interpretation presented
here are expected to stimulate further research efforts on metal
phosphides for AB hydrolysis in the future.
The clean-surface Ni2ÀxCoxP NP catalysts were prepared
using a facile two-step strategy without addition of strong reducing
agents like NaBH4 and organic stabilizers (Fig. S1, ESI†). First,
the Ni1À0.5xCo0.5x(OH)2 precursors were obtained through a
co-precipitation method by virtue of the similar Ksp of Co(OH)2
and Ni(OH)2. Then, the precursors were converted into ternary
Co–Ni–P nanohybrids via a solid-state phosphorization reaction.
When Ni(OH)2 alone was used as the precursor, the XRD analysis
indicates the formation of the hexagonal phase of Ni2P (JCPDS
No. 65-3544) (Fig. S2 and S3, ESI†). With the increase of the
Co-doping content, the positions of the XRD peaks shift toward
higher diffraction angles corresponding to hexagonal NiCoP
(JCPDS No. 71-2336), suggesting successful Co-doping into the

This journal is © The Royal Society of Chemistry 2017

Energy & Environmental Science

Fig. 1 (a) TEM and (b) magnified TEM images of the as-prepared
Ni0.7Co1.3P nanoparticles. (c) The size distribution diagram. (d) The HRTEM
image, (e) the spacing of the crystal lattice, (f) the FFT pattern of the
corresponding area in (d), and (g) the corresponding EDX elemental
mapping of Co, Ni and P for the Ni 0.7Co1.3P.

lattice of Ni2P. Note that the XRD profiles are exactly the same as
NiCoP when the x value is larger than 1.0. It has been reported
that Co–Ni–P solid solutions, NiCoP (ICDD No. 04-001-4562),
Co1.49Ni0.51P (ICDD No. 04-019-5182), Co1.4Ni0.6P (ICDD No.
04-005-5616) and others,33–35 all show very similar XRD patterns
probably due to their same crystal structures and very similar
lattice parameters.
TEM and magnified TEM images of Ni0.7Co1.3P (Fig. 1a and b)
reveal the formation of well-distributed sphere-shaped nanoparticles with a diameter of 5–7 nm. The HRTEM image taken
for one Ni0.7Co1.3P nanocrystal reveals distinct lattice fringes
with a spacing of about 0.230 nm corresponding to the (111)
plane of Ni0.7Co1.3P (Fig. 1d and e), which is consistent with the
SAED pattern (Fig. 1f). The presence of Ni, Co and P elements
is confirmed by energy-dispersive X-ray spectroscopy (EDX)
(Fig. S4, ESI†) and inductively coupled plasma-optical emission
spectroscopy (ICP-OES). The latter also enabled the accurate
elemental analysis of the as-prepared samples (Table S1, ESI†).
As evidenced by the corresponding EDX elemental mappings,
the Ni, Co and P elements are uniformly distributed throughout
the Ni0.7Co1.3P nanocrystals (Fig. 1g). The chemical states of Ni,
Co and P for Ni0.7Co1.3P are further characterized by X-ray
photoelectron spectroscopy (XPS). As shown in Fig. S5 (ESI†),
two peaks are apparent in the Ni (2p) region at 853.7 and
856.6 eV and the Co (2p) region at 779.0 and 781.9 eV,
respectively, along with another two peaks in the P (2p) region
at 129.7 and 133.7 eV. The peaks at 853.7, 779.0 and 129.7 eV
are attributed to the binding energies (BEs) for Ni, Co and P of
Ni0.7Co1.3P, respectively. The peaks at about 856.6, 781.9 and
133.7 eV are assigned to the oxidized Ni, Co and P species,
resulting from inevitable surface oxidation of Ni0.7Co1.3P.36–38
The H2-generating reaction by hydrolysis of AB with various
Ni–Co–P catalysts was carefully evaluated under ambient conditions
in a sealed home-made flask equipped with a magnetic stirrer.
Control experiments showed that in the absence of catalysts, the AB
aqueous solution has long-term stability without any H2 release.

Energy Environ. Sci., 2017, 10, 1770--1776 | 1771

View Article Online

Energy & Environmental Science

Communication

Published on 25 July 2017. Downloaded by Universitat Rovira I Vigili on 4/12/2019 2:11:47 PM.

As shown in Fig. 2a and b, the Ni0.7Co1.3P catalyst demonstrated
the highest activity for hydrogen release from AB amongst a
series of Ni–Co–P catalysts. The generated H2 gas was identified
using gas chromatography (Fig. S6, ESI†) and was monitored by
a water-filled burette. All the hydrolysis experiments approximately
generated 3 mole of H2 gas per mole of AB, indicating that
the decomposition of AB proceeded according to reaction (1)
(see ref. 39):
H3NBH3 + 4H2O - NH4+ + B(OH)4À + 3H2

(1)

This process was further confirmed by 1H NMR and 11B
NMR spectra before and after the reaction (Fig. S7–S10, ESI†).
Then the effects of Ni2ÀxCoxP catalysts, the amount of AB and
temperature on the hydrogen-generating rate were measured to
interpret the kinetics of AB hydrolysis. As shown in Fig. 2c and
Fig. S11–S13 (ESI†), upon varying the molar ratio of Ni0.7Co1.3P/AB
by changing either the catalyst or the AB concentration, we found
that the hydrogen-generating rate is dependent on [Ni0.7Co1.3P],
following first-order kinetics with respect to catalyst concentration
(Fig. S11, ESI†). In contrast, the reaction rate is much less
dependent on [AB] (Fig. S13, ESI†), but nevertheless it does not
follow zero-order kinetics due to the interactions between the
catalysts and OHÀ/H2O. The Ni0.7Co1.3P catalyst at an optimized
cat/AB molar ratio of 0.026 displays the highest catalytic activity

Fig. 2 (a) Stoichiometric hydrogen evolution in 0.5 M NaOH solution
(5 mL) containing 1.62 mmol AB catalyzed by Ni2P, NiCoP, Ni0.7Co1.3P and
Ni0.5Co1.5P nanoparticles at 298 K. (b) The corresponding TOFs. (c) The
relationship between the H2 generation rate and Ni0.7Co1.3P/AB ratios and
(d) temperature. (e) Recycling of the Ni0.7Co1.3P catalyst (10 mg) in 0.5 M
NaOH solution (5 mL), with addition of AB (1.62 mmol) to the system at
298 K in each cycle.

1772 | Energy Environ. Sci., 2017, 10, 1770--1776

with an initial TOF value of 58.4 mol(H2) mol(Ni0.7Co1.3P)À1 minÀ1 at
ambient temperature.
As shown in Fig. 2d and Fig. S14 (ESI†), we also investigated
the temperature dependence of the catalytic reaction in the
range of 278–333 K. The activation energy is estimated to be
43.2 kJ molÀ1 through an Arrhenius plot. This value is favourably
comparable to those of Ru-based bimetallic catalysts.40,41 The
durability of this catalyst is further tested under ambient
atmosphere at 298 K. As depicted in Fig. 2e, the Ni0.7Co1.3P
catalyst retained 95.2% of its initial activity even after 7 cycles
and still kept good activity after 10 cycles, demonstrating its
good recyclability. The slight drop in activity might be ascribed
to the aggregation of NPs, degraded crystallinity and inevitable
surface oxidation during repeated experimental operations
(Fig. S15, ESI†).
To get an in-depth understanding of the improved catalytic
performance of ternary Ni–Co–P catalysts, X-ray photoelectron
spectroscopy (XPS) and X-ray absorption fine structure spectroscopy (XAFS) measurements were performed. Fig. S16 (ESI†)
shows XPS spectra of Ni2ÀxCoxP in the Co 2p, Ni 2p and P 2p
windows. It is clear that the BEs of both Ni 2p and Co 2p
positively shift with the increase of Co-doping concentration,
whereas the one of P 2p shifts negatively. These findings indicate
that more charge transfer from metal to P centres occurred. The
variation of electronic states can be further corroborated by the
XAFS results. As shown in Fig. 3a, the Ni K-edge XANES spectra
of all Ni–Co–P solid solutions are broadly similar to a distinct
pre-edge peak that is characteristic of metal phosphides and
differs from the pure Ni foil or NiOx.42–44
However, with the increase of Co-doping content into Ni2P,
both the Ni absorption edge of XANES (Fig. 3a and b) and the
Co K-edge (Fig. S17, ESI†) slightly shifted toward higher energy,
indicating a change in the average Ni and Co oxidation state
to a higher value. Furthermore, the arrow in Fig. 3b shows a
clear shift in absorption intensity (mt) with the increase of
Co-doping.45–47 As the white line is indicative of the unoccupied
electronic states, the increment of the white line peak at about
8350 eV indicates the increase of unoccupied electronic states,
which could be achieved by weak oxidation and in other words,
electron transfer occurs from Ni to P centres. A similar situation
is also observed in Co K-edge XANES spectra as shown in
Fig. S17 (ESI†). Based on the above discussions, we are convinced
that charge transfer from metal to P centres occurred. Indeed the
DFT calculations show a P charge in the range of À0.35 to À0.42 |eÀ|
(see Table S2, ESI†).
The Ni K-edge extended XAFS (EXAFS) k3w(k) oscillation
curve for the Ni0.7Co1.3P is comprised of an oscillation region
in 2.5–8 ÅÀ1 due to the Ni–P contribution and another one
beyond 8 ÅÀ1 assigned to the Ni–Ni contribution (Fig. 3c). This
profile reveals a noticeable difference in comparison to that of
Ni2P, implying the structural difference in the coordination
environment surrounding the Ni atoms.42–44 A similar situation
can be found for a Co atom (Fig. S16, ESI†), which coordinately
provides evidence for the successful Co-incorporation. The R
space plot for the Ni–Co–P NPs is characterized by two main
peaks centred at 1.78 Å and 2.20 Å, which roughly correspond to

This journal is © The Royal Society of Chemistry 2017

View Article Online

Published on 25 July 2017. Downloaded by Universitat Rovira I Vigili on 4/12/2019 2:11:47 PM.

Communication

Fig. 3 (a) Ni K-edge and (b) magnified XANES spectra of Ni2P, NiCoP,
Ni0.7Co1.3P and Ni0.5Co1.5P nanocatalysts. (c) Ni K-edge EXAFS k3w(k) oscillation
functions of the Ni2P and Ni0.7Co1.3P NPs and (d) the corresponding FT curves
of Ni2P, NiCoP, Ni0.7Co1.3P, Ni0.5Co1.5P NPs and pure Ni foil for comparison
(inset: the magnified curves of the Ni–Co–P solid solution).

the Ni–P and neighbouring Ni–Ni configurations, respectively.
Compared to Ni foil, the Ni–Co–P NPs all showed decreased
intensity, which was ascribed to the nano-size effect. As for
Co-doping, the phase-shift-free Fourier transform (FT) showed
an increased intensity of Ni–P and a decrease in the Ni–Ni
feature together with slight phase changes, implying that the
Co-doping induces a relatively higher coordination number of
Ni–P and a smaller coordination number of the second pair
(Ni–Ni).48 All of these results revealed that Co was successfully
incorporated into the crystal lattice of Ni2P and occupied
partially the initial place of Ni atoms, implying the formation
of a Co–P bond with decreasing long-range order.
The aforementioned results provide strong evidence for the
promotion of electron transfer from metal to P centres in these
ternary Ni–Co–P solutions, finally resulting in strong adsorption
of AB, which can effectively activate the B–N bonds in AB,
therefore decreasing the reaction energy barrier and accelerating
hydrogen evolution. This point was further corroborated by
DFT modeling with the PBE functional.49 The specific details
are provided in the ESI† and Tables S3–S6. In view of the basic
reaction conditions where the reaction takes place, an SN2
mechanism where surface OH* attacks the adsorbed BH3NH3
was found (Fig. 4, Scheme S1 and Table S4, ESI†). As shown in
the energy profile, the reaction starts from both AB and H2O
adsorbed on the surface of the catalyst. This adsorption process
is exothermic by 1.75 eV for NiCo2P2, and only 1.23 eV for Ni3P2,
indicating the stronger interaction between them (solvent
contributions would reduce adsorption by about 0.65 eV).50
The results are consistent with XPS and XAFS results.
Following the SN2 reaction in which surface OH* attacks the
BH3 group, B–N bond breaking is induced (OH* + BH3NH3* BH3OH* + NH3*, see video SN2.avi, ESI†). This reaction is exothermic
on Ni3P2 and NiCo2P2 by À0.20 and À0.62 eV, respectively, showing
that the doped system is more thermodynamically favourable.
From the kinetic point of view, the reaction barrier on the doped

This journal is © The Royal Society of Chemistry 2017

Energy & Environmental Science

Fig. 4 Energy profiles of AB hydrolytic dehydrogenation on Ni3P2(0001)
and NiCo2P2(0001) surfaces with the same initial hydroxyl concentration.
The 3D models in the upper panels denote transition states, while those at
the bottom correspond to the intermediates.

surface is also favoured as the barrier on NiCo2P2 (0.87 eV) is
0.21 eV lower than that on Ni3P2 (1.08 eV). The product, BH3OH*
has been widely regarded as the key intermediate in borohydride and ammonia borane oxidation reactions.51 After B–N
bond scission, one of the hydrides leaves the B atom with small
barriers (0.36 and 0.32 eV) (BH3OH* - BH2OH* + H*, see video
B–H bond-breaking.avi, ESI†) on both surfaces and this is then
followed by the almost barrierless B–N bond regeneration
(0.04 and 0.12 eV) (BH2OH* + NH3* - HOBH2–NH3*, see video
B–N regeneration.avi, ESI†). A second SN2 cycle was calculated,
HOBH3* + OH* - BH2 (OH)2* + H*, and the higher barrier
required (1.01 eV) shows that this step cannot compete with the
direct B–H bond breaking from BH3OH*. In the B–N bond
formation step, electrostatic interaction between B and N atoms
would contribute to the low B–N bond regeneration barrier.
Bader charge analysis52 (Table S5, ESI†) shows that B and
N atoms are positively and negatively charged by 1.26 and
1.20 |eÀ| in BH2OH and NH3. Possible side reactions were also
calculated (Table S4, ESI†) but they cannot compete with this
step. The hydride group on the surface can then attack H2O to
generate H2 (see video H2O splitting.avi, ESI†). The barriers of
this step are close to each other for the two surfaces (0.83 and
0.87 eV), and the process is slightly more exothermic (by 0.17 eV)
on the Co-containing one. The last step concerns H2 desorption
which is slightly easier on Ni2P but the energies for desorption
are low and will be surpassed by the molecular entropy gain.
After one reaction cycle (BH3NH3 + H2O - HOBH2NH3 + H2),
when the species left on the surface are HOBH2–NH3, it will
repeat the previous steps twice and produce two more H2
molecules from BH2(OH)2* and BH(OH)3*. These species and
their importance in reaction mechanisms have been proposed
by Chatenet et al. via in situ Fourier transform infrared spectroscopy studies on borohydride53 and ammonia borane oxidation
reactions.54 Our mechanism based on DFT matches well with
these results. We should note that the SN2 step is the ratelimiting step in AB hydrolytic dehydrogenation, which could
rationalize the common phenomenon that the presence of OHÀ

Energy Environ. Sci., 2017, 10, 1770--1776 | 1773

View Article Online

Published on 25 July 2017. Downloaded by Universitat Rovira I Vigili on 4/12/2019 2:11:47 PM.

Energy & Environmental Science

Fig. 5 (a) The photograph of Ni0.7Co1.3P/GO dispersed in water. (b) XRD
patterns. The TEM images of (c) GO and (d) the Ni0.7Co1.3P/GO nanohybrid.
(e) The magnified TEM and (g) HRTEM images of Ni0.7Co1.3P/GO. (f) The
size distribution. (h) The single NPs, (i) the FFT pattern of the corresponding
area in (h) and (j) the spacing of the crystal lattice.

could dramatically improve the catalytic properties and shorten
the induction period. The lower barrier on the Co-containing
surface explains why TOF values are higher for these materials.
The observed improvement in the catalytic activity implies the
fine tuning of the electronic structure at the Ni–Co surface as
can be inspected from the d-band center position (see Table S6,
ESI†). In the Ni–Co system the Ni centres are slightly more
reactive than the Ni-only counterpart while the Co d-states are
slightly less reactive than the Co-only compound. Thus the
formation of the intermetallic bond is crucial for adjusting
the chemical properties of the surface.
In an effort to further improve the catalytic activity, a
Ni0.7Co1.3P/GO nanohybrid material was prepared according
to a modified procedure (see the ESI†). As displayed in the TEM
images in Fig. 5 and Fig. S18–S20 (ESI†), Ni0.7Co1.3P NPs with a
size of about 5 nm is uniformly deposited on the surface of GO
due to the anchoring effect of the oxide-GO. The formation of
the hybrid material is further confirmed by XRD, ICP-OES,
XPS and BET (Fig. S21, S22 and Table S7, ESI†) etc. Then the
catalytic activity of the Ni0.7Co1.3P/GO in the hydrolysis of AB
was evaluated under the same conditions. Control experiments
showed that pure GO has no catalytic activity for AB hydrolysis,
while the Ni0.7Co1.3P/GO sample exhibited exceedingly higher
catalytic performance compared to the single Ni0.7Co1.3P alone.
The dramatically improved activity can be attributed to the
good dispersion and hence the enlarged surface area of nanoparticles on the GO surface with good electrical activity, therefore,
creating an additional synergistic effect between the connection.55–58
The interaction between Ni0.7Co1.3P and GO was confirmed by
XAFS (Fig. 6). The rising edge of the Ni0.7Co1.3P/GO sample
shifts to a higher energy, implying slight electron transfer may
occur from Ni0.7Co1.3P to the GO, which was also corroborated
by XPS (Fig. S21, ESI†). Both experimental results indicate a
bonding relationship between the two materials.

1774 | Energy Environ. Sci., 2017, 10, 1770--1776

Communication

Fig. 6 (a) Stoichiometric hydrogen evolution in 0.5 M NaOH solution
(5 mL) containing 1.62 mmol AB catalyzed by pure GO, Ni0.7Co1.3P and the
Ni0.7Co1.3P/GO nanohybrid at 298 K. (b) The relationship between the H2
generation rate and various amounts of the Ni0.7Co1.3P/GO nanocatalyst.
(c) Ni K-edge XANES spectra and (d) the corresponding FT curves of the
Ni0.7Co1.3P NPs and Ni0.7Co1.3P/GO nanohybrid.

The stability of the Ni0.7Co1.3P/GO sample is also probed by
the recycling experiment. As shown in Fig. S23 (ESI†), the
Ni0.7Co1.3P/GO sample maintains 93.0% of its initial activity
after 5 cycles. It is worth mentioning that the recovered sample
in the second cycle demonstrates an extraordinary activity with
a TOF value of about 153.9 mol(H2) mol(Ni0.7Co1.3P)À1 minÀ1,
which is much higher than that in the first cycle (TOF =
93.3 mol(H2) mol(Ni0.7Co1.3P)À1 minÀ1). Such a phenomenon is
also observed for the pure Ni0.7Co1.3P sample and for other
metal phosphides reported in our previous studies.32,59 This
can be reasonably explained by the in situ reduction of some
surface oxidized Ni–Co–P species in this reductive NH3BH3
system. As far as we know, this achieved TOF of 153.9
(109.4 based on the total mole number of metal) represents
one of the highest values ever reported for all noble-metal-free
based catalysts (Table S8, ESI†).

Conclusions
In summary, we have successfully achieved a feasible, viable
and scalable way to synthesize Co-doped nickel phosphide NPs
and their nanohybrid with graphene oxide (GO) as excellent
catalysts for hydrolysis of AB. Benefitting from the ternary
Ni–Co–P synergistic effect, high dispersibility, improved surface
area and the interfacial interaction between Ni0.7Co1.3P and GO,
the Ni0.7Co1.3P/GO shows a high initial turnover frequency
(TOF) of up to 153.9 mol(H2) mol(Ni0.7Co1.3P)À1 minÀ1 at ambient
temperature, which is an unprecedented value higher than
those ever reported for noble-metal-free catalytic systems, and
a good sustainability maintaining 93.0% activity after 5 cycles.
The promotion is rationalized through Density Functional
Theory indicating that hydroxyl activation of the AB bond is
enhanced when Co is present. These findings not only enrich

This journal is © The Royal Society of Chemistry 2017

View Article Online

Communication

the family of noble-metal-free catalysts for AB hydrolysis, but
also provide significant and promising insights into modulating
the electronic structures of metal phosphides for hydrogen
storage and related applications.

Published on 25 July 2017. Downloaded by Universitat Rovira I Vigili on 4/12/2019 2:11:47 PM.

Acknowledgements
The financial support from the National Key Basic Research
Program of China (973 Program 2013CB834800 and 2013CB632403)
and the Strategic Priority Research Program of the Chinese Academy
of Sciences (XDB17030300) are deeply acknowledged. This work was
partially supported by the Natural Science Foundation of China
(21371175) and CAS-Croucher Funding Scheme for Joint
Laboratories. Y. C. is thankful of support from the Chinese
Academy of Sciences (100 Talents Program). Q. L. and N. L. are
grateful to MINECO (CTQ2015-68770-R) for financial support
´
´
and to the Centro de Supercomputacion y Visualizacion de
´
Madrid, Universidad Politecnica de Madrid for providing the
computational resources through the BSC-RES. We also thank
BSRF for synchrotron beamtime.

Notes and references
1 Q.-L. Zhu and Q. Xu, Energy Environ. Sci., 2015, 8, 478–512.
¨
¨
2 O. Metin, V. Mazumder, S. Ozkar and S. H. Sun, J. Am. Chem.
Soc., 2010, 132, 1468–1469.
3 F. A. de Bruijn, ChemSusChem, 2008, 1, 782–783.
4 J. Yang, A. Sudik, C. Wolverton and D. Siegel, Chem. Soc.
Rev., 2010, 39, 656–675.
5 J. Wang, X. B. Zhang, Z. L. Wang, L. M. Wang and Y. Zhang,
Energy Environ. Sci., 2012, 5, 6885–6888.
6 J. Wang, Y. L. Qin, X. Liu and X. B. Zhang, J. Mater. Chem.,
2012, 22, 12468–12470.
7 J. M. Yan, X. B. Zhang, T. Akita, M. Haruta and Q. Xu, J. Am.
Chem. Soc., 2010, 132, 5326–5327.
8 J. M. Yan, X. B. Zhang, H. Shioyama and Q. Xu, J. Power
Sources, 2010, 195, 1091–1094.
9 J. M. Yan, X. B. Zhang, S. Han, H. Shioyama and Q. Xu,
J. Power Sources, 2009, 194, 478–481.
10 S. K. Singh, A. K. Singh, K. Aranishi and Q. Xu, J. Am. Chem.
Soc., 2011, 133, 19638–19642.
11 H.-L. Jiang, S. K. Singh, J.-M. Yan, X.-B. Zhang and Q. Xu,
ChemSusChem, 2010, 3, 541–549.
12 Q. Xu and M. Chandra, J. Alloys Compd., 2007, 446–447, 729–732.
13 W. Chen, J. Ji, X. Duan, G. Qian, P. Li, X. Zhou, D. Chen and
W. Yuan, Chem. Commun., 2014, 50, 2142–2144.
¨
14 M. Zahmakiran and S. Ozkar, Top. Catal., 2013, 56, 1171–1183.
15 M. Rakap, Appl. Catal., A, 2014, 478, 15–20.
16 S. Wang, D. Zhang, Y. Ma, H. Zhang, J. Gao, Y. Nie and
X. Sun, ACS Appl. Mater. Interfaces, 2014, 6, 12429–12435.
17 T. J. Clark, G. R. Whittell and I. Manners, Inorg. Chem., 2007,
46, 7522–7527.
18 J.-M. Yan, X.-B. Zhang, S. Han, H. Shioyama and Q. Xu,
Inorg. Chem., 2009, 48, 7389–7393.
19 Z.-H. Lu, H.-L. Jiang, M. Yadav, K. Aranishi and Q. Xu,
J. Mater. Chem., 2012, 22, 5065–5071.

This journal is © The Royal Society of Chemistry 2017

Energy & Environmental Science

20 X. Ma, Y.-X. Zhou, H. Liu, Y. Li and H.-L. Jiang, Chem.
Commun., 2016, 52, 7719–7722.
21 Q. Xu and M. Chandra, J. Power Sources, 2006, 163, 364–370.
22 J.-M. Yan, X.-B. Zhang, S. Han, H. Shioyama and Q. Xu,
Angew. Chem., Int. Ed., 2008, 47, 2287–2289.
23 K. Feng, J. Zhong, B. Zhao, H. Zhang, L. Xu, X. H. Sun and
S.-T. Lee, Angew. Chem., Int. Ed., 2016, 55, 11950–11954.
24 M. Mahyari and A. Shaabani, J. Mater. Chem. A, 2014, 2,
16652–16659.
25 J. Hu, Z. Chen, M. Li, X. Zhou and H. Lu, ACS Appl. Mater.
Interfaces, 2014, 6, 13191–13200.
26 Y.-Z. Chen, Q. Xu, S.-H. Yu and H.-L. Jiang, Small, 2015, 11,
71–76.
27 H. Zhang, X. Wang, C. Chen, C. An, Y. Xu, Y. Huang,
Q. Zhang, Y. Wang, L. Jiao and H. Yuan, Int. J. Hydrogen
Energy, 2015, 40, 12253–12261.
28 D. R. Weinberg, C. J. Gagliardi, J. F. Hull, C. F. Murphy,
C. A. Kent, B. C. Westlake, A. Paul, D. H. Ess, D. G. McCafferty
and T. J. Meyer, Chem. Rev., 2012, 112, 4016–4093.
29 J. Q. Tian, Q. Liu, A. M. Asiri and X. P. Sun, J. Am. Chem. Soc.,
2014, 136, 7587–7590.
30 Q. Liu, J. Q. Tian, W. Cui, P. Jiang, N. Y. Cheng, A. M. Asiri
and X. P. Sun, Angew. Chem., Int. Ed., 2014, 53, 6710–6714.
31 S. Cao, Y. Chen, C. J. Wang, P. He and W. F. Fu, Chem.
Commun., 2014, 50, 10427–10429.
32 C. Y. Peng, L. Kang, S. Cao, Y. Chen, Z. S. Lin and W. F. Fu,
Angew. Chem., Int. Ed., 2015, 54, 15725–15729.
33 Z. Wang, X. Q. Cao, D. Liu, S. Hao, G. Du, A. M. Asiri and
X. P. Sun, Chem. Commun., 2016, 52, 14438–14441.
34 W. Li, X. F. Gao, X. G. Wang, D. Xiong, P. Huang, W. G. Song,
X. H. Bao and L. F. Liu, J. Power Sources, 2016, 330, 156–166.
35 W. Li, D. Xiong, X. F. Gao, W. G. Song, F. Xia and L. F. Liu,
Catal. Today, 2017, 1, 122–129.
36 J. Q. Li, M. Yan, X. M. Zhou, Z.-Q. Huang, Z. M. Xia,
C.-R. Chang, Y. Y. Ma and Y. Q. Qu, Adv. Funct. Mater.,
2016, 37, 6785–6796.
37 J. Yu, Q. Q. Li, Y. Li, C. Y. Xu, L. Zhen, V. P. David and
J. S. Wu, Adv. Funct. Mater., 2016, 26, 7644–7651.
38 P. Zhang, Y. Chen, M. Wang, Y. Yang, J. Jiang, B. Zhang,
L. Duan, Q. Daniel, F. Li and L. C. Sun, J. Mater. Chem. A,
2017, 5, 7564–7570.
39 W. Y. Chen, D. Li, Z. J. Wang, G. Qian, Z. J. Sui, X. Z. Duan,
X. G. Zhou, I. Yeboah and D. Chen, AIChE J., 2017, 1, 60–65.
40 G. Chen, S. Desinan, R. Rosei, F. Rosei and D. Ma,
Chem. – Eur. J., 2012, 18, 7925–7930.
41 N. Mohajeri, A. T-Raissi and O. Adebiyi, J. Power Sources,
2007, 167, 482–485.
42 Y. K. Lee and S. T. Oyama, J. Catal., 2006, 239, 376–389.
43 T. Kawai, K. K. Bando, Y. K. lee, S. T. Oyama, W. J. Chun and
K. Asakura, J. Catal., 2006, 241, 20–24.
44 H.-R. Seo, K.-S. Cho and Y.-K. Lee, Mater. Sci. Eng., B, 2011,
176, 132–140.
45 S. T. Oyama, T. Gott, K. AsaKura, S. TakaKusagi, K. Miyazaki,
Y. Koike and K. K. Bando, J. Catal., 2009, 268, 209–222.
46 Y. Chen, C. Li, J. Zhou, S. Zhang, D. Rao, S. He, M. Wei,
D. G. Evans and X. Duan, ACS Catal., 2015, 5, 5756–5765.

Energy Environ. Sci., 2017, 10, 1770--1776 | 1775

View Article Online

Published on 25 July 2017. Downloaded by Universitat Rovira I Vigili on 4/12/2019 2:11:47 PM.

Energy & Environmental Science

47 L. Zhou, M. Shao, C. Zhang, J. Zhao, S. He, M. Rao,
M. Wei, D. G. Evans and X. Duan, Adv. Mater., 2016,
1604080.
48 K. Xu, H. Ding, H. F. Lv, P. Z. Chen, X. Lu, H. Cheng,
T. Zhou, S. Liu, X. J. Wu, C. Z. Wu and Y. Xie, Adv. Mater.,
2016, 28, 3326–3332.
49 J. P. Perdew and K. Burke; M. Ernzerhof, Phys. Rev. Lett.,
1996, 77, 3865–3868.
´
´
50 M. Garcia-Rates and N. Lopez, J. Chem. Theory Comput.,
2016, 12, 1331–1341.
51 T. Maiyalagan and V. S. Saji, Electrocatalysts for Low
Temperature Fuel Cells: Fundamentals and Recent Trends,
John Wiley & Sons, 2017.
´
52 G. Henkelman, A. Arnaldsson and H. Jonsson, Comput.
Mater. Sci., 2006, 36, 254.

1776 | Energy Environ. Sci., 2017, 10, 1770--1776

Communication

53 B. Molina Concha, M. Chatenet, F. Maillard, E. A. Ticianelli,
F. H. B. Lima and R. B. de Lima, Phys. Chem. Chem. Phys.,
2010, 12, 11507–11516.
54 B. Molina Concha, M. Chatenet, F. H. B. Lima and
E. A. Ticianelli, Electrochim. Acta, 2013, 89, 607–615.
55 P. Xi, F. Chen, G. Xie, C. Ma, H. Liu, C. Shao, J. Wang, Z. Xu,
X. Xu and Z. Zeng, Nanoscale, 2012, 4, 5597–5601.
56 L. Yang, N. Cao, C. Du, H. Dai, K. Hu, W. Luo and G. Cheng,
Mater. Lett., 2014, 115, 113–116.
¨
¨
57 K. Gungormez and O. Metin, Appl. Catal., A, 2015, 494, 22–28.
¨
58 N. S. Ciftci and O. Metin, Int. J. Hydrogen Energy, 2014, 39,
18863–18870.
59 Z. C. Fu, Y. Xu, S. L. F. Chan, W. Wang, F. Li, F. Liang,
Y. Chen, Z. S. Lin, W. F. Fu and C.-M. Che, Chem. Commun.,
2017, 53, 705–708.

This journal is © The Royal Society of Chemistry 2017