Flexible Molecular Precursors for Selective Decomposition to Nickel Sulfide or Nickel Phosphide for Water Splitting and Supercapacitance

Article abstract of DOI:10.1002/chem.201904583

Herein, the synthesis of three nickel(II) dithiophosphonate complexes of the type [Ni{S₂P(OR)(4-C₆H₄OMe)}₂] [R=H (1), C₃H₇ (2)] and [Ni{S₂P(OR)(4-C₆H₄OEt}₂] [R=(C₆H₅)₂CH (3)] is described; their structures were confirmed by single-crystal X-ray studies. These complexes were subjected to surfactant/solvent reactions at 300 °C for one hour as flexible molecular precursors to prepare either nickel sulfide or nickel phosphide particles. The decomposition of complex 2 in tri-octylphosphine oxide/1-octadecene (TOPO/ODE), TOPO/tri-n-octylphosphine (TOP), hexadecylamine (HDA)/TOP, and HDA/ODE yielded hexagonal NiS, Ni₂P, Ni₅P₄, and rhombohedral NiS, respectively. Similarly, the decomposition of complex 1 in TOPO/TOP and HDA/TOP yielded hexagonal Ni₂P and Ni₅P₄, respectively, and that of complex 3 in similar solvents led to hexagonal Ni₅P₄, with TOP as the likely phosphorus provider. Hexagonal NiS was prepared from the solvent-less decomposition of complexes 1 and 2 at 400 °C. NiS (rhom) had the best specific supercapacitance of 2304 F g^?1 at a scan rate of 2 mV s^?1 followed by 1672 F g^?1 of Ni₂P (hex). Similarly, NiS (rhom) and Ni₂P (hex) showed the highest power and energy densities of 7.4 kW kg^?1 and 54.16 W kg^?1 as well as 6.3 kW kg^?1 and 44.7 W kg^?1, respectively. Ni₅P₄ (hex) had the lowest recorded overpotential of 350 mV at a current density of 50 mA cm^?2 among the samples tested for the oxygen evolution reaction (OER). NiS (hex) and Ni₅P₄ (hex) had the lowest overpotentials of 231 and 235 mV to achieve a current density of 50 mA cm^?2, respectively, in hydrogen evolution reaction (HER) examinations.

Full text of DOI:10.1002/chem.201904583

A Journal of
Accepted Article
Title: Flexible Molecular Precursors for Selective Decomposition
to Nickel Sulfide or Nickel Phosphide for Water Splitting and
Supercapacitance
Authors: Gwaza Eric Ayom, Dilshad Malik Khan, Tenzin Ingsel, Wang
Lin, Ram Gupta, Sizwe Zamisas, Werner Van Zyl, and
Neerish Revaprasadu
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To be cited as: Chem. Eur. J. 10.1002/chem.201904583
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10.1002/chem.201904583
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Flexible Molecular Precursors for Selective Decomposition to
Nickel Sulfide or Nickel Phosphide for Water Splitting and
Supercapacitance
Gwaza E. Ayom,a† Malik D. Khan,a† Tenzin Ingsel,b Wang Lin,b Ram K. Gupta,b Sizwe J. Zamisa,c
Werner E. van Zyl,c Neerish Revaprasadua*
Abstract: Herein, we synthesized three nickel(II) dithiophosphonate
complexes of the type [Ni{S2P(OR)(4-C6H4OMe)}2] [Me = Methyl; R =
H (1), C3H7 (2)] and [Ni{S2P(OR)(4-C6H4OEt}2] [Et = Ethyl; R =
(C6H5)2CH (3)], their structures confirmed by single crystal X-ray
studies. These complexes were subjected to surfactant/solvent
reactions at 300 ºC for one hour as flexible molecular precursors to
prepare either nickel sulfide or nickel phosphide particles. The
decomposition of complex 2 in TOPO/ODE, TOPO/TOP, HDA/TOP
and HDA/ODE yielded hexagonal NiS, Ni2P, Ni5P4 and
rhombohedral NiS, respectively. Similarly, the decomposition of
complex 1 in TOPO/TOP and HDA/TOP yielded hexagonal Ni2P and
Ni5P4 and that of complex 3 in similar solvents led to hexagonal
Ni5P4, with TOP as the likely phosphorus provider. Hexagonal NiS
was prepared from the solvent-less decomposition of complexes 1
and 2 at 400 ºC. NiS (rhom) had the best specific supercapacitance
of 2304 F/g at 2 mV/s scan rate followed by 1672F/g of Ni2P (hex).
Similarly, NiS (rhom) and Ni2P (hex) showed the highest power and
energy densities of 7.4 kW/kg, 54.16W/kg, 6.3kW/kg and 44.7W/kg,
respectively. Ni5P4 (hex) had the lowest recorded overpotential of
350 mV at a current density of 50 mA/cm2 among the samples
tested for the oxygen evolution reaction (OER). NiS (hex) and Ni5P4
(hex) had the lowest overpotentials of 231 and 235 mV to achieve a
current density of 50 mA/cm2, respectively, in hydrogen evolution
reaction(HER) examinations.
receive attention.[2] The drawback of this route to energy
production is the cost and scarcity of noble metals such as Pt, W
and Ru, usually employed as catalysts to increase the reaction
rate which in turn limits large scale production.[3] Research
endeavors are thus focused on developing electrochemical
devices that produce hydrogen energy at a scale and cost
competitive to that of carbon based fossil fuels.
Nickel sulfides and -phosphides have recently been explored
as cheap alternatives to these noble metals as catalysts in the
electrochemical splitting of water.[4] They are binary systems with
multiple compositions depending on the ratio of nickel to
sulfur/phosphorus in the system. For example, the nickel sulfide
system has compositions ranging from NiS (α-NiS and β-NiS),
NiS2, Ni3S4, Ni7S6, NiS5 and NiS8,[5] some of which were recently
explored as nano-catalysts in the hydrogen, and oxygen
evolution reactions (HER/OER).[6] The nickel phosphide system
similarly has multiple phases, including Ni3P, Ni2P, Ni5P2, Ni5P4
and Ni6P5 which have continued to receive attention due to their
potential electrocatalytic applications.
Single-source precursors of different types, such as
xanthates[7] and their pyridine adducts,[8] thio and dithiobiurets,[9]
dithiocarbamates,[10] and dithiophosphates[11] have been
explored to prepare nickel sulfide nanoparticles. On the other
hand, nickel phosphide is more scarce and usually prepared
using multiple sources which often requires, toxic reagents,
elevated temperature, prolonged reaction time and the
possibility of batch to batch variation cannot be avoided.[12]
There are only limited reports on the use of molecular
precursors for the synthesis of metal phosphide nanomaterials.
O’Brien et al. reported the use of nickel selenophosphinates for
the synthesis of nickel phosphide and nickel selenide
nanomaterials or thin films.[13] The same group also employed
Introduction
The environmental crisis arising from the growing
consumption of energy, sourced mostly from fossil fuels, has
elicited a growing search for cheap, clean and recyclable
alternatives to carbon based fossil fuels.[1] Hydrogen production
by water splitting via photo-catalysts as a clean, recyclable and
cheap alternative to traditional fossil fuels has continued to
dithiophosphinate
cobalt(II), [Co(Se2PR2)] (R
complexes
(dialkyldiselenophosphinato-
iPr, Ph and tBu), and di-t-
=
butyldithiophosphinatocobalt(II), [Co(S2PtBu2], (see C in Figure 1
for dithiophosphinate ligand) as single source precursors to
prepare cobalt phosphide, cobalt selenide or cobalt sulfide
nanoparticles.[14]
[a]
Dr. G. E. Ayom, Dr. M. D. Khan, Prof. N. Revaprasadu*
Department of Chemistry, University of Zululand, Private bag
X1001, Kwa-Dlangezwa 3880, South Africa. E-mail:
RevaprasaduN@unizulu.ac.za
Shanmugam et al. used di/triphenylphosphine complexes of
metal salts (Co, Fe and Ni) to prepare amorphous carbon
embedded metal phosphides by solvent-less pyrolysis, however,
a mixture of phases was obtained in all cases.[15] The phase
impurity, toxicity or high temperature treatment is primarily the
main reasons which limit the practical application of phosphides.
Though the single-source molecular precursor route offers
advantages over multiple sources in the preparation of
nanomaterials,[16] it has rarely been used to prepare metal
sulfides and phosphides from a same molecular precursor.
[b]
[c]
T. Ingsel, W. Lin, Dr. R. K. Gupta
Department of Chemistry, Pittsburg State University, Pittsburg,
Kansas, USA.
S. J. Zamisa, Prof. W. E. van Zyl
School of Chemistry and Physics, University of KwaZulu-Natal
Private Bag X54001, Westville Campus, Durban, 4000
South Africa.
† Authors contributed equally.
Supporting information for this article is given via a link at the
end of the document.
1
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In this study, dithiophosphonate ligands which contain both
sulfur and phosphorus atoms were employed to prepare both
nickel sulfide and nickel phosphide nanomaterials by the
judicious control of reaction conditions. Dithiophosphonates (B),
which are far less studied within the phosphor-1,1-dithiolate
class of compounds,[17] can be considered an unsymmetrical
hybrid version of (A) and (C) in Figure. 1. They have rarely been
employed to prepare nickel sulfide or phosphide nanoparticles.
This is probably due to the greater challenge in the synthetic
route of the dithiophosphonate ligands, compared to the other
phosphor-1,1-dithiolate class of compounds.[17]
Figure 2. Molecular structures of 1, 2 and 3 drawn at 50% thermal ellipsoid
probability level. The default value of 1 was used as a scale factor for all bond
radii. Here 1 unit is 0.1 Å.
Figure 1. Different types of the phosphor-1,1-dithiolates showed in
deprotonated form with delocalization between the two P-S bonds. (A)
Dithiophosphate, (B) Dithiophosphonate (C) Dithiophosphinate (D)
Amidodithiophosphonate.
Table 1. Crystallographic data and structural refinement details for complexes
1, 2 and 3
In view of this, we formed three nickel(II) dithiophosphonate
complexes: [Ni{S2P(OR)(4-C6H4OMe)}2] [Me = Methyl; R = H (1),
C3H7 (2)] and [Ni{S2P(OR)(4-C6H4OEt)}2] (where Et = Ethyl; R =
(C6H5)2CH (3)) as precursors to prepare nickel sulfide and
phosphide nanomaterials by the hot injection method. The
solvent-less decomposition of all the precursors was also carried
out in order to observe the effect of capping agents on the phase
of the deposited nanomaterials. The synthesized complexes
were also investigated for their electrocatalytic performance.
Complex
1
2
3
Chemical
formula
C14H16NiO4P2S4
497.16
C20H28NiO4P2S4
581.31
C42H40NiO4P2S4
857.63
Mr
Crystal system,
space group
Orthorhombic,
Pbca
Triclinic, P-1
101
Triclinic, P-1
100
Temperature (K)
100
13.0145 (2),
6.1979 (1),
23.3552 (3)
6.3640 (5),
7.5640 (7),
13.5402 (13)
8.9611 (2),
9.5520 (2),
12.0497 (3)
Results and Discussion
a, b, c (Å)
Molecular structures
Complex 1 crystallizes in the orthorhombic space group
Pbca while complexes 2 and 3 crystallize in triclinic space group
P-1. A perspective view of complexes 1, 2 and 3 is given in
76.310 (3),
77.430 (3),
83.945 (4)
102.924 (1),
94.856 (2),
94.381 (3)
α, β, γ (°)
90, 90, 90
Figure 2, while Tables
1 and 2 give important X-ray
V (Å3)
1883.89 (5)
617.09 (10)
996.84 (4)
crystallographic data and selected bond parameters,
respectively. There has been a previous report[18] of a similar
Ni(II) molecular structure as 1, though as a hydrated ammonium
salt. We present a better well resolved model of molecular
structure of 2 earlier reported.[19] The crystal structure of
compounds 1, 2 and 3 contain half of the molecule in their
respective asymmetric units which consist of one
dithiophosphonate ligand and a Ni atom which resides on a
crystallographic inversion centre. The complete molecule of 1, 2
and 3 have the two dithiophosphonate ligands coordinated to the
Ni1 atom via S1 and S2 atoms in a κ2:S,S’ coordination mode as
shown in Figure 2. Furthermore, the anisyl (in 1 and 2), and
phenetolyl (in 3) moieties of the coordinated ligands are
arranged in a trans configuration which is similar to that
observed in closely related structures.[18-20] As a result, the metal
center in all the compounds adopted a distorted square planar
geometry with S—Ni—S bond angles between 81.820(4)° and
180° (Table 2).
Z
4
1
1
µ (mm−1
)
1.66
1.28
0.82
Crystal size
(mm)
0.28 × 0.24 ×
0.13
0.32 × 0.21 ×
0.12
0.31 × 0.12 ×
0.11
Tmin, Tmax
0.675, 0.746
0.650, 0.746
0.778, 0.927
No. of
measured,
independent and
observed [I >
2σ(I)] reflections
18495, 2376,
2066
11282, 3057,
2760
21970, 4870,
4486
Rint
0.033
0.672
0.025
0.669
0.027
0.675
(sin θ/λ)max (Å−1
)
R[F2 > 2σ(F2)],
wR(F2), S
0.024, 0.062,
1.08
0.031, 0.071,
1.06
0.027, 0.073,
1.08
2
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steric demand and electronic effects of different molecular
groups on the P atom.
No. of reflections
2376
117
3057
263
4870
242
Intermolecular hydrogen bonding patterns in the crystal
packing of 1, 2 and 3 are depicted in Figure 3, while selected
hydrogen bonding parameters are listed in Table 3. Classical
No. of
parameters
Δρmax, Δρmin (e
2( )
0.45, −0.26
0.75, −0.77
0.50, −0.43
O—H···S hydrogen bonds with graph-set notation 푅2 8 were
Å−3
)
observed in 1 between the H1 atom of the hydroxyl group and
the coordinated S2 atom of the neighboring molecule and form
Table 2. Selected bond lengths and angles for complexes 1, 2 and 3.
chains which extend along the crystallographic
b axis.
Furthermore, non-classical C—H···O hydrogen bonds between
H7C and O2 of neighboring anisyl moieties stitch the chains
together to form a corrugated, two-dimensional supramolecular
structure which propagates along the crystallographic ab plane.
C—H···O hydrogen bonds were also observed between
methylene H9A atom of the propyl group and O1A of the
neighboring anisyl moiety. Linking the molecules in this manner
results in the formation of a chain which extends diagonally with
respect to the crystallographic b and c axis. In 3, the C—H···S
hydrogen bonds between the H5A atom of the phenetolyl moiety
and the S1 atom of the neighboring molecule form a one-
dimensional supramolecular architecture that extends along the
crystallographic c axis.
Parameter
1
2
3
Ni—S1/Å
2.22747(3)
2.2514(2)a
2.2163(2)b
2.22694(6)
Ni—S2/ Å
2.22389(2)
180.00(6)
88.6211(9)
2.2322(2)
180.00(5)
2.23177(6)
180.00(2)
88.492(2)
S1—Ni—S1i/ °
S1—Ni—S2/ °
90.464(4)a
81.820(4)b
S1—Ni—S2i/ °
P1—S1/ Å
91.3789(9)
1.9961(6)
89.536(4)a
98.180(4)b
91.508(2)
1.9992(4)
2.0928(2)a
1.8156(2)b
Table 3. Selected hydrogen bonding parameters observed in complexes 1, 2
and 3.
P1—S2/ Å
P1—O2/ Å
2.0239(6)
2.0083(2)
2.0051(5)
1.58148(3)
1.5532(1)a
1.7032(1)b
1.59703(4)
D—H···A
D—H
H···A
D···A
D—H···A
Compound
1
S1—P1—S2/ °
101.34(3)
101.807(4)a
99.133(4)b
101.96(2)
O1—
H1···S2i
P1—(S1—S2—
S1i—S2i plane)/
Å
0.287840(3)
0.019715(1)a
0.44232(3)b
0.46432(1)
0.84
0.98
2.43
2.54
3.267(1)
3.478 (2)
172
161
C7—
H7C···O2iii
Ni···P/ Å
2.84814(3)
2.8714(2)
2.80755(6)
Compound
2
Symmetry code: (i) −x, −y, −z
[a] Bond parameter involving disordered atoms in PART 1. [b] Bond parameter
involving disordered atoms in PART 2
C9A—
H9A···O1A
0.99
2.52
3.175(4)
123
The phosphorus atom in both 1 and 3 is marginally out of
plane with respect to the S1—S2—S1i—S2i plane by
0.287840(3) Å and 0.46432(1) Å, respectively. Furthermore, the
P—O bond distance in 1 (1.58148(3) Å) was found to be slightly
shorter than that observed in 3 (1.59703(4) Å) but the Ni···P
Compound
3
C5—
H5A···S1i
0.99
2.96
3.704(2)
133
contact distance is relatively shorter in
compared to 1 (2.84814(3) Å). These subtle differences in the
3 (2.80755(6) Å)
Symmetry codes for compound 1: (i) −x+2, −y+1, −z+1, (ii) x, −y+1/2, z+1/2,
(iii) −x+3/2, y+1/2, z. compound 3: (i) −x, −y, −z−1.
geometric parameters may also be due the difference of the
3
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4
gives
a
summary of nanoparticles formed from the
decomposition of the complexes under different reaction
conditions. The nature of surfactant and dispersing solvent used,
significantly influenced the composition of the phase. For
example, the TOPO/TOP mixture favors the formation of NiP-1,
while replacing TOPO with HDA yielded mainly the NiP-2 phase.
Similarly, replacing TOP with ODE as the dispersing solvent in
the decomposition of complex 2 gave hexagonal NiS in TOPO
herein referred to as NiS-1 and rhombohedral NiS in HDA,
herein referred to as NiS-2, respectively (Figure 4).
Figure 3. Intermolecular hydrogen bonding networks observed in the crystal
Table 4. Table Caption. Nickel sulfide or phosphide nanoparticles formed by
decomposing complexes 1, 2 and 3 in different coordinating solvents and
dispersion mediums at 300 °C for 1 hour.
packing of complexes 1,
2 and 3. O—H···S, C—H···O and C—H···S
hydrogen bonds are shown as dashed orange, green and blues lines,
respectively. The default value of 1 was used as a scale factor for all bond
radii. Here 1 unit is 0.1 Å.
Dispersing
Precursor
Surfactant
Phase formed
solvent
2
TOPO
TOPO
HDA
TOP
ODE
TOP
ODE
TOP
TOP
TOP
TOP
NiP-1
NiS-1
NiP-2
NiS-2
NiP-1
NiP-2
NiP-2
NiP-2
Nanoparticle formation by the hot injection route
Thermogravimetric analyses of the three complexes were
carried out under an argon atmosphere. Complexes 2 and 3
showed high thermal stability with decomposition setting in
above 200 °C unlike complex 1 where decomposition begins at
about 100 °C, which is due to the loss of water molecules.
Complexes 1 and 2 decomposed in multiple steps, unlike
complex 3 where decomposition was observed in a sharp single
step, all leading to a residue of about 18 to 40 % correlating to
NiS and Ni2P as shown in Figure S1.
Nickel sulfide and phosphide nanoparticles were synthesized
by the thermal decomposition of complex 2 in surfactant
solutions of TOPO or HDA and dispersing solvents of TOP or
ODE. The effect of the nature of surfactant and dispersion
medium was investigated. The decomposition of complex 2 in
TOPO/TOP or HDA/TOP yielded nickel phosphide nanoparticles,
while decomposition in TOPO/ODE or HDA/ODE produced pure
nickel sulfide nanoparticles, respectively. The powder X-ray
diffraction patterns of the nickel sulfide and phosphide
nanoparticles obtained by decomposition of molecular complex
HDA
1
3
TOPO
HDA
TOPO
HDA
Although both surfactants (i.e. TOPO and HDA) are neutral,
their binding interactions and passivating tendency differs
significantly. TOPO is branched and binds with nanoparticles
surface through the lone pair of electrons on the phosphine
oxide moiety forming a dative bond. By contrast, HDA has a
linear structure and the surface bonding is through the lone pair
of electrons present on the nitrogen atom. Furthermore, it has
been suggested by Yu et al. that the passivation of nanoparticles
surface by linearly shaped surfactants left some gaps while
arranging and in the packing process, which in turn allows
oxygen to reach the surface of the nanomaterials resulting in
surface oxidation.[21] Whilst, the branched structured surfactants
can protect the surface comparatively better resulting in
enhanced stability of the nanocrystals.
Following the observations on the effect of the surfactants
TOPO/HDA and the injection solvents TOP/ODE on the phase
and composition of nanoparticles formed from the
decomposition of complex 2, we further investigated the effect of
the alkyl (R) group on the phase or composition of nanoparticles
formed. In this case, complexes [Ni{S2P(OH)(4-C6H4OMe)}2] (1)
2
in different solvents are presented in Figure 4. The
decomposition of complex 2 in TOPO/TOP yielded phase pure
Ni2P, herein referred to as NiP-1 (Figure 4b), while the diffraction
pattern obtained by the decomposition of the same precursor in
HDA/TOP mixture can be indexed to phase pure Ni5P4, herein
referred to as NiP-2 (Figure 4c). Similar results were also
obtained by the decomposition of complexes 1 and 3 in
TOPO/TOP and HDA/TOP. This leads to the noteworthy
observation that although phosphorus is present in the complex,
the presence of TOP is necessary for the preparation of nickel
phosphide. Similar behavior was also observed for
i
dialkyldiselenophosphinatocobalt(II), [Co(Se2PR2)] (R = Pr, Ph
and tBu) complexes, where cobalt phosphide, cobalt selenide or
cobalt sulfide nanoparticles were obtained depending on the
surfactants used.[14] The study suggested that TOP, not the
dithiophosphinate molecular complexes, is the source of
phosphorus in the formed metal phosphides. In order to further
investigate the source of phosphorus, nickel(II) chloride was
used instead of the complexes and the reaction was performed
under similar conditions. Interestingly, heating nickel chloride in
TOPO/TOP mixture yielded the Ni2P phase (Supplementary
Figure 2), which confirms that TOP provides phosphorus in the
formation of metal phosphides. Furthermore, the type of the
phosphide phase formed depends on the surfactant used. Table
and [Ni{S2P(OR)(4-C6H4OEt)}2] (where Et
= Ethyl; R =
(C6H5)2CH) (3) were decomposed in TOPO/TOP or HDA/TOP
under similar conditions as used for the decomposition of
complex 2 for comparison and the results of the nanoparticles
formed by all complexes is shown in Table 4.
The use of TOP as the dispersing solvent in the
decomposition of complexes 1 and 3 in all cases gave nickel
phosphide nanoparticles which are in accordance with our
observations for the decomposition of complex 2 under similar
conditions. Unlike complexes 1 and 2, the decomposition of
complex 3 in both TOPO/TOP and HDA/TOP resulted only in the
4
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NiP-2 phase in both cases. This suggests that the nature of the
substituents (alkyl or aryl) may play a crucial role in determining
the composition of the phosphide nanoparticles, in addition to
the solvents used. On the other hand, the formation of NiP-1 and
NiP-2 in the decomposition of complexes 1 and 2 using
TOPO/TOP and HDA/TOP, respectively, indicates that
increasing the chain length of the alkyl group [R = H (1) and
C3H7 (2)] did not have an effect on the composition of the
phosphide nanoparticle formed.
Synthesis of nanoparticles by the solvent-less route
The decomposition of complexes 1, 2 and 3 were also
carried out via the solvent-less melt method. This method was
employed to look at the effect of the absence of a solvent on the
composition and phase formed. The effect of the alkyl group was
also observed with this method. The decomposition of
complexes 1 and 2 at 400 °C for 1 hour under N2, yielded NiS
(hex) nanoparticles in both cases, respectively, herein referred
to as NiS-3, while the decomposition of complex 3 under similar
conditions gave no crystalline particles. Complex 3 was also
heated at a higher temperature of 500 °C for a longer time of 2
hours but gave a non-crystalline product. Considering the earlier
observation that the likely source of phosphorus for the prepared
nickel phosphide nanoparticles is TOP and not directly derived
from the ligand, decomposition products of this solvent-less
route suggests that decomposition of phosphorus and sulfur
containing precursors in the absence of any solvent will likely
yield the metal sulfide nanoparticles rather than the phosphide.
Figure S3 gives the p-XRD patterns of the solvent-less
decomposition of complexes 1 and 2.
Figure 4. Powder XRD patterns of nickel sulfide and phosphide nanoparticles
obtained from decomposing complex 2 in (a) TOPO/ODE (b) TOPO/TOP (c)
HDA/TOP and (d) HDA/ODE at 300°C for 1 hour.
After investigating the decomposition behavior of molecular
precursors by the colloidal and solvent-less route, it can be
inferred that in the absence of TOP, nickel sulfide is always
formed, probably due to the presence of a pre-formed bond
between nickel and sulfur atoms in the molecular precursors.
Among P-S and S-Ni bonds, P-S bond is more susceptible to
thermal decomposition and NiS is formed by the cleavage of the
P-S bond. On the contrary, the presence of TOP, along with
TOPO or primary alkylamine, at an elevated temperature, results
in the catalytic decomposition of TOP which releases active
phosphorus which reacts with the nickel to form nickel
phosphide. Therefore, TOP as a source of phosphorus, is
necessary for the formation of nickel phosphide.
The morphology of Ni2P nanocrystals synthesized from
complex 2 in TOPO/TOP was determined by SEM and TEM
analysis. SEM images reveals formation of primarily spherical
nanoparticles with good monodispersity, as shown in Figure 5(a-
d). The crystallinity of the nanoparticles was confirmed by
HRTEM analysis, which shows well defined lattice fringes with
the d-spacing of 0.20 nm matching the (201) plane of Ni2P
(Figure 5(f)). The spherical morphology was further confirmed by
TEM analysis (Figure 5(e)) and examination of these
nanoparticles by energy-dispersive X-ray (EDX) analysis also
provided evidence of their purity as emissions were due
exclusively to nickel and phosphorus atoms. Moreover, the
presence of sulfur as an impurity was not observed (Figure 5(g)).
Figure 5. (a) NiP-1 (b) NiS-1 (c) NiP-2 (d) NiS-2 SEM images of hot injection
decomposition of complex 2; (e) TEM image, (f) HRTEM image and (g) EDX of
hot injection decomposition complex 2 (NiP-1).
The SEM micrographs of nanoparticles obtained by
decomposition of complex 2 in various solvents are shown in Fig.
5 (a-d). It was observed that NiP-1 and NiS-1 nanoparticles were
spherical with a narrow size distribution. The NiP-2 and NiS-2
nanoparticles synthesized in HDA were agglomerated,
confirming that TOPO served as a better capping agent in
controlling the size and shape of nanoparticles.
Electrochemical properties of NiS and NiP for
supercapacitor applications
The charge storage capabilities of the sample electrodes NiS
and NiP were determined by employing cyclic voltammetry (CV)
and galvanostatic charge-discharge (GCD) tests. In Figure 6, the
relationship between current density and the electric potentials
of the five samples in cyclic voltammetry tests are shown by
plotting curves at scan rates ranging from 2 mV/s to 300 mV/s.
5
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The area under the CV curves of electrode samples was
observed to increase under faster scan rates as shown in Figure
7 where NiS-2 exhibited the best specific capacitance of 2304
Figure 8. Galvanostatic charge-discharge characteristics of NiS-1 and NiP-
1 samples at various applied current density.
The NiS-3 and NiS-1 electrode samples recorded specific
capacitance of 1359 F/g and 1068 F/g, respectively, at 2 mV/s
scan rate. Both NiS-3 and NiS-1 exists in the same phase
however the sample synthesized by the solvent-less method
(NiS-3) showed better specific capacitance as compared to
sample (NiS-1) capped with the primary amine. Although the use
of a surfactant plays a crucial role in controlling the size and
shape of the nanomaterials, the surface passivation also has a
detrimental effect on the electrocatalytic properties of the
material.[23] Since, the surface of NiS-3 is free of any surface
passivation by a capping agent, it displayed a comparatively
higher specific capacitance than the surface capped NiS-1,
despite having
a
similar phase. Likewise, the specific
capacitance of NiP-1 and NiP-2 was compared against different
scan rates. NiP-1 showed a higher specific capacitance of 1672
F/g and NiP-2 displayed a specific capacitance of 1081 at 2
mV/s. The supercapacitance of a material is influenced by its
electrical conductivitity[24] and metal-rich phosphides (MxPy; x ˃
y) tend to show better electrical conductivity than their metal-
deficient analogues.[25] NiP-1 (Ni2P) has about 66.6% Ni in its
structure compared to NiP-2 (Ni5P4) with 55.55%. The higher
specific capacitance of NiP-1 compared to NiP-2 could be
attributed to its higher Ni content.
In Figure 8 galvanostatic charge-discharge graphs show
electric potential vs time charge-discharge characteristics of
NiS-1 and NiP-1 samples when different current densities were
applied. The discharge time is lower with increased current
densities applied to NiS-1 and NiP-1. The differing specific
capacitance of NiS-1, NiS-2, and NiS-3 with respect to different
current densities is shown in Fig. 9. NiS-2 i.e. millerite phase,
with 1153 F/g at a current density of 0.5 A/g exhibited the
highest specific capacitance among studied NiS electrodes.
Likewise, when NiP-1 and NiP-2 were compared, NiP-1 provided
a higher specific capacitance of 1043 F/g at 0.5 A/g. Rani at
el.[26] recently investigated a nickel sulfide-based nanocomposite
for its electrochemical performance and recorded a specific
capacitance of 428 F/g at 10 mV/s while our NiS-2 sample gave
a specific capacitance of 1441 F/g at 10 mV/s. This indicates
approximately 3-fold increase in the charge storage capacity of
our orthorhombic NiS sample. Additionally, Sahoo at el.[27]
Figure 6. CV curves of NiS and NiP samples in 3 M KOH electrolyte.
F/g at 2 mV/s amongst all the NiS samples. Rhombohedral NiS
(NiS-2), also known as millerite, displays metallic behavior due
to its unique structure.[22] Millerite phase has Ni atoms that are
arranged in 3-membered cyclic rings resulting in the formation of
Ni3S9 clusters, where Ni-Ni atoms are linked by S atoms. The
coordinating sulfur atoms of these Ni3S9 clusters further
interconnects to form a framework of Ni-S. NiS-2 also has good
conductivity and electron transport which can be attributed to its
Ni(d)-S(p) charge transfer interactions. There can also be
hopping of electrons from d-orbitals of one Ni3 ring to another via
the p-type orbitals of the coordinating S atoms inducing electron
transfer between the adjacent metallic three membered Ni rings.
The specific capacitance of NiS-2 could therefore be due to its
strong metallic and electronic qualities.
synthesized
a
nickel sulfide-based supercapacitor by
incorporating carbon quantum dots. A specific capacitance of
880 F/g at a current density of 2 A/g was reported which is much
lower than our synthesized NiS-2 sample which showed a
specific capacitance of 1149 F/g at a current density of 2 A/g.
Figure 7. Variation of specific capacitance versus scan rate for NiS and NiP
samples in 3 M KOH electrolyte.
The data clearly show
a vastly improved electrocatalytic
performance of nickel sulfide samples synthesized in this work.
6
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Similarly nickel diselenide grown over titanium plate showed an
overpotential of 295 mV.[31]
LSV plots showcasing OER electrocatalytic performances of
NiP-1 and NiP-2 electrodes were compared against each other
in Figure 11. NiP-2 exhibited a lower overpotential (350 mV)
than NiP-1 (379 mV) at a current density of 50 mA/cm2. Liu et
al.[32] carried out a facile dispersion of a ternary system-NiFeP by
controlling the exposure of active sites for the promotion of
highly effective water electrolysis oxidation. The NiFeP
electrocatalyst showed an overpotential of 270 mV at a current
density of 10 mA/cm2. Read et al[33] used a scalable synthesis
method to deposit transition metal phosphide films on
Figure 9. Variation of specific capacitance versus current density for NiS
and NiP samples in 3M KOH electrolyte.
commercially available metal foils via
a
vapor phase
Additionally, the power and energy densities of all the samples
were calculated using galvanostatic charge-discharge data.
The variation of power and energy densities for all the
samples is shown in Figure 10. The graph shows NiS-2 has the
highest power and energy densities of 7.4 kW/kg and 54.16
Wh/kg, respectively. On the other hand, for our NiP materials,
NiP-1 displayed the highest power and energy densities of 6.3
kW/kg and 44.7 Wh/kg, respectively. Li et al.[28] have used the
electrodeposition method to deposit nickel sulfide on graphene-
decomposition of organophosphine reagents. An overpotential of
339, 367 and 390 mV were required to generate 10 mA/cm2 of
current for Ni2P, Co2P, and Fe2P samples, respectively. These
studies indicate that our work recorded lower or comparable
overpotentials for OER tests.
The electrochemical stability of NiS-1 was studied. The
polarization curves for NiS-1 at 1st and 1000th cycles of LSV are
shown in Figure 11 for comparison. A minimal difference of
about 5 mV was observed between 1st and 1000th cycles at 50
mA/cm2 suggests superior electrochemical stability of the
synthesized NiS samples tested. NiP-2 sample showed superior
electrochemical stability under similar conditions. Among the NiP
samples examined, a negligible (1 mV) potential difference
during the 1st and 1000th cycles of polarization study was
observed. The low overpotential and high electrochemical
stability of these materials support their applications as
electrocatalysts for oxygen evolution reactions.
covered cotton for supercapacitor applications.
A specific
capacitance of 775 F/g at 0.5 A/g was reported with power and
energy densities of 1.008 kW/kg and 11.2 Wh/kg, respectively.
Also a nanocomposite of nickel sulfide and graphene oxide
synthesized using a hydrothermal process showed a specific
capacitance of 800 F/g at 1 A/g with energy and power densities
of 111.1 Wh/kg and 499.5 W/kg, respectively.[29] Our materials
thus compare well with, or far exceed results of other studies.
Figure 10. Plot of power density versus energy density for NiS and NiP
samples in 3 M KOH electrolyte.
NiS and NiP particles for water splitting applications
Electrocatalytic performance for the oxygen evolution
reaction (OER) of the synthesized nickel sulfide and nickel
phosphide electrodes was analyzed by carrying out linear scan
voltammetry (LSV). The polarization curves for all the samples
are shown in Figure 11. When the LSV plots of the three
different NiS electrodes were compared against each other, NiS-
1 was observed to have the lowest overpotential of 371 mV
while NiS-2 and NiS-3 recorded an overpotential of 389 mV at a
current density of 50 mA/cm2. Recently, Wang et al.[30] have
Figure 11. LSV curves of (a) NiS samples, (b) NiP samples, (c) 1st and 1000th
LSV curves for NiS-1 sample, and (d) 1st and 1000th LSV curves for NiP-2
sample.
synthesized
a nanostructure of a Ni-based metal-organic
framework (MOF) modified Ni3S2/NiS hollow nanoparticle for
OER application. The MOF shell and hollow Ni3S2/NiS displayed
an overpotential of 298 mV at 10 mA/cm2, which is close to what
we observed for our NiS-1 sample (300 mV at 10 mA/cm2).
The electrocatalytic activities of the synthesized samples
were also studied for hydrogen evolution reactions. The
polarization curves for the nickel sulfides and phosphides are
shown in Figure 12. Amongst the prepared nickel sulfide
7
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samples, NiS-1 showed the lowest overpotential of 231 mV Conclusions
while NiS-2 and NiS-3 displayed an overpotential of 273 and 259
mV to achieve a current density of 50 mA/cm2, respectively.
We synthesized three nickel dithiophosphonate complexes and
determined their X-ray crystal structures. The complexes were
subsequently studied for the first time as single-source
precursors via the hot injection method to prepare either nickel
sulfide or nickel phosphide materials. The decomposition of 2 in
TOPO/TOP and HDA/TOP formed NiP-1 and NiP-2, respectively.
NiS-1 and NiS-2 were however prepared from the
decomposition of 2 in TOPO/ODE and HDA/ODE. Similarly, the
decomposition of 1 in TOPO/TOP and HDA/TOP yielded
hexagonal NiP-1 and NiP-2. Hexagonal NiP-2 was prepared
from the decomposition of 3 in TOPO/TOP and HDA/TOP. TOP
is therefore suggested as the phosphorus source of the
nanoparticles rather than the phosphorus containing ligands
which was confirmed with NiCl2.6H2O replacing the complexes in
the reaction route used. The solvent-less melt method was used
to prepare NiS (hex) from the decomposition of 1 and 2
suggesting that the decomposition of phosphorus and sulfur
containing precursors in the absence of any solvent will likely
yield the metal sulfide nanoparticles rather than the phosphide.
The energy storage capacity of the materials was examined with
NiS-2 having the best specific supercapacitance of 2304 F/g at a
2 mV/s scan rate. Similarly, NiS-2 showed the highest power
and energy densities of 7.4 kW/kg and 54.16 wh/kg, respectively.
Hexagonal NiP-2 recorded the lowest overpotential of 350 mV to
achieve a current density of 50 mA/cm2 among the samples
tested for oxygen evolution reaction (OER) with high cycling
stabilities in 1000 cycles. For the hydrogen evolution reaction
(HER) evaluation, NiS (hex) had the lowest overpotential of 231
needed to attain a current density of 50 mA/cm2. These results
indicate a positive future framework for exploration in energy
storage and generation devices.
Overall a lower overpotential of NiS-1 sample, both in OER and
HER, is indicative of its comparatively better efficiency, unlike
charge storage performance, where the sample with millerite
phase (NiS-2) was the most efficient one. The electrochemical
results indicate that, if
a particular phase indicates high
efficiency for energy storage application, the same phase may
not necessarily perform well for energy generation applications
as well. On the other hand, NiP-1 and NiP-2 samples showed
overpotential of 235 and 256 mV to deliver a current density of
50 mA/cm2, respectively. Comparatively, the Nickel-rich phase
(Ni2P), is
a suitable bifunctional material and has better
efficiency in both energy storage and generation applications,
than Ni5P4 phase. Qin et al.[34] have provided composition-
dependent catalytic activities of NiS/Ni3S4 for hydrogen evolution
reactions. The HER performance of these samples depends on
their composition ratio. The sample with 1 molar ratio of
NiS/Ni3S4 displayed the lowest overpotential and charge-transfer
resistance. An overpotential of 221 mV was required to drive 10
mA/cm2 of current. Our best sample showed
a lower
overpotential of approximately 150 mV to deliver a current
density of 10 mA/cm2. In a reported study, NiS2 deposited on
carbon cloth was used as an electrocatalyst for HER
applications.[35] The prepared electrode required overpotential of
243 mV to deliver a current density of 10 mA/cm2. The HER
performance of our samples thus compared well or exceeded
results of other studies.
The durability of the synthesized samples was also studied
using continuous cyclic voltammetry scans at 100 mV/s. The
LSV curve after 1000 continuous CV cycles were recorded and
compared with a pristine LSV curve. A small potential difference
of 14 and 27 mV was observed for NiS-1 and NiP-2 samples,
respectively, at 50 mA/cm2 of current density (Figure 12).
Figure 12. LSV curves of (a) NiS samples, (b) NiP samples, (c) 1st and
1000th LSV curves for NiS-1 sample, and (d) 1st and 1000th LSV curves for
NiP-2 sample.
8
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heated to 500 °C for 1 and 2 hours, which in all cases yielded a black
solid.
Experimental Section
Characterization: 1H NMR spectra were recorded on a Bruker
Advance 400 MHz instrument with TMS as an external reference at
room temperature. Thermogravimetric analyses were performed using
a Mettler-Toledo TGA/DSC at a nitrogen gas flow rate of 10 mL per
min. X-ray diffraction was performed using a Bruker D8 Discover
Diffractometer using CuKα radiation (λ = 1.54178 Å) in the 2θ range
from 10° to 70°. The data collected were used to determine the lattice
parameters and crystal phase. Crystal evaluation and data collection
were done on a Bruker Smart APEX2 diffractometer with Moκα
radiation (λ = 0.71073 A) using the APEXII[37] program suite. X-ray
diffraction data was collected at 100(1) K using an Oxford Cryostream
low-temperature apparatus. The structures were solved by the direct
method using the SHELXS[38] program. Scanning electron microscopy
(SEM) was carried out using a Philips XL30 FEG-SEM. Energy-
dispersive X-ray (EDX) spectroscopy was performed using a DX4
detector. All samples were carbon coated using an Edwards coating
system E306A prior to SEM analysis. TEM and HRTEM analysis of
the synthesized nanoparticles were performed using a JEOL 1400
TEM and JEOL 2100 HRTEM, respectively. Materials were prepared
by placing a drop of the diluted particle solution on Formvar-coated
grids (150 mesh) for TEM, and holey carbon grids for HRTEM. These
prepared samples were allowed to dry completely at room
temperature, viewed for TEM and HRTEM at accelerating voltages of
120 and 200 kV, respectively. Acquired images were using iTEM
software (TEM) and Gatan software (HRTEM). XRD analysis was
performed on a Bruker AXS D8 diffractometer employing a nickel-
filtered Cu Kα radiation (λ=1.5418Å) at 40 kV, 40 mA. Scans were
recorded in 2θ range of 10-80º at a scan speed of 0.5 sec. The
surface morphology of the particles was analyzed by a Zeiss Ultra
Plus FEG Scanning Electron Microscope (SEM) equipped with an
Oxford detector at 20 kV which in turn employs an Aztec software for
elemental analysis. The electrochemical examinations of the prepared
nanomaterials were recorded employing a Potentiostat having a
three-electrode system. Working electrodes were prepared by making
Materials: Hexadecylamine (HDA) 98%, tri-n octylphosphine (TOP)
90%, tri-octylphosphine oxide (TOPO) 90%, 1-octadecene (ODE)
90%, diphenylmethanol (DPM), nickel chloride hexahydrate, Celite,
chloroform and acetone were purchased from Sigma Aldrich and used
without further purification. Diethyl ether, THF, toluene and hexane
were distilled under dinitrogen over a Na wire with the formation of a
benzophenone ketyl indicator. Dichloromethane was distilled over
P4O10. Methanol was distilled from I2/Mg turnings.
Preparation of complexes: (a) [Ni{S2P(OR)(4-MeOC6H4)}2] (where
Me = Methyl; R = H (1), C3H7 (2)) The synthesis of complexes 1 and
2 was carried out by slight modification of the established literature
procedure.[18, 36] The procedure requires refluxing of P2S5 in anisole
for 6 hours using standard Schlenk techniques, cooling and filtration
to form (4-C6H4OMeP(S)S)2, commonly referred to as the
Lawesson’s reagent (LR). LR and water or alcohol [deionized H2O (1)
or C3H7OH (2)] in the right stoichiometric amounts were stirred in
THF in an inert atmosphere until the cloudy mixture went clear.
Stoichiometric amounts of NiCl2.6H2O were added in solid form into
the clear THF solutions, yielding immediate purple precipitates which
were filtered and washed with deionized water to remove any excess
NiCl2.6H2O. Compound 1: 1H-NMR (400 MHz, DMSO, ppm): δ 3.57
(3.0H, s, OCH3), 3.70 (1.0H, s, OH), 6.82 (2.0H, d, Ar-CH), 7.44
(2.0H, d, Ar-CH), 7.95 (1.0H, d, Ar-CH). Compound 2: 1H-NMR (400
MHz, CDCl3, ppm): δ 1.02 (6.0H, t, PrO-CH3), 1.80 (4.0H, m, PrO-
CH2), 3.87 (6.0H, s, Ar-OCH3), 4.31 (4.0H, q, Pr-OCH2), 7.00 (4.0H,
dd, Ar-CH2), 8.01 (4.0H, dd, Ar-CH2). (b) [Ni{S2P(OR)(4-C6H4OEt)}2]
[Et = Ethyl; R = (C6H5)2CH (3)] The synthesis of complex 3 was
similar to the procedure in (a) above. In this case P2S5 was refluxed
with phenetole and isolated as the phenetole analogue of LR.
Diphenylmethanol (C6H5)2CHOH) (0.50 g, 2.71 mmol) and the
phenetole LR (0.59 g, 1.36 mmol) were stirred in THF using standard
Schlenk techniques until dissolution of all solids. NiCl2.6H2O (0.028 g,
0.12 mmol) was then added as a solid to the clear THF solution
yielding an immediate purple colored solution. All the THF was then
removed under reduced pressure to yield a sticky solid. The Ni
complex was then extracted into 50 mL of DCM, filtered over Celite
and concentrated to yield a purple free flowing powder. 1H-NMR (400
MHz, CDCl3, ppm): δ 1.47 (6.0H, t, Ar-CH3), 4.13 (4.0H, Ar-OCH3),
7.01 (6.0H, Ar-CH2), 7.35 (10.0H, Ar-CH2), 7.45 (7.6H, t, Ar-CH2),
8.05 (4.0H, q, Ar-CH2
a
paste of the prepared nanomaterial (80 wt%), polyvinylidene
difluoride (PVDF, 10 wt.%), and acetylene black (10 wt.%) in N-methyl
pyrrolidinone (NMP) onto Ni foam. Calomel electrode and a
a
platinum wire were employed as a counter and reference electrodes
in 3M KOH. Charge storage capacities of samples were recorded
using cyclic voltammetry (CV) and galvanostatic charge-discharge
(CD) at different scan rates and current densities, respectively.
Electrocatalytic properties of the prepared electrodes were studied
using linear sweep voltammetry (LSV), cyclic voltammetry and
chronoamperometry (CA) at Princeton Applied Research, USA (STAT
electrochemical workstation). LSV was performed at a scan rate of 2
mV/s for both HER and OER examinations.
Preparation of nanoparticles by the hot injection method: (a)
Nickel sulfide Nickel sulfide nanoparticles were prepared by the
thermolysis of complex 2 with TOPO or HDA as surfactants and ODE
as the dispersing solvent. In a typical procedure, HDA or TOPO (5.0
g) were heated under N2, up to 300 °C. Complex 2 (0.2 g, 0.33 mmol),
dispersed in ODE (5.0 mL), was injected quickly into the hot solution,
yielding an immediate black solution. The reaction temperature
dropped to about 270 °C upon injection, and the reaction mixture was
heated up again to 300 °C. The temperature was maintained for 1
hour after which the reaction mixture was cooled down to about 70 °C.
Methanol/acetone (10 mL, 1:1) mixture was then added to the cooled
black solution and the precipitate was separated by centrifugation.
The precipitate was washed with a mixture of chloroform and acetone
(10 mL, 1:4 ratio), then finally with acetone (10 mL) and dried in air to
give a black precipitate. (b) Nickel phosphide The preparation of
nickel phosphide nanoparticles followed a similar procedure as (a)
above, except that TOP replaced ODE as the dispersing solvent.
Acknowledgements
The authors are grateful to the National Research Foundation
(NRF) South African Research Chairs Initiative (SARChI) and
Royal Society DFID Africa Capacity Building Initiative
programme for financial support.
Keywords: Energy storage • Energy generation • Hydrogen
evolution reaction • Oxygen evolution reaction •
Supercapacitance
Solvent-less decomposition of the complexes: Complexes 1 or 2
(0.2 g) was placed in a ceramic combustion boat which was placed in
a glass tube and heated slowly to 400 °C in a carbolite furnace under
N2 flow. The temperature was kept at 400 °C for 1 hour, after which it
was cooled down to the room temperature under N2 to give a black
powder. Complex 3 was heated at 400 °C for 2 hours and further
[1]
aA. Pandiyan, A. Uthayakumar, R. Subrayan, S. W. Cha, S. B.
K. Moorthy, Nanomaterials and Energy 2019, 1-21; bN. A.
Bahari, W. N. R. W. Isahak, M. S. Masdar, Z. Yaakob,
International Journal of Energy Research 2019.
aT. Takata, K. Domen, ACS Energy Letters 2019; bZ. Wang, C.
Li, K. Domen, Chemical Society Reviews 2019; cT. Di, Q. Xu,
W. Ho, H. Tang, Q. Xiang, J. Yu, ChemCatChem 2019, 11,
1394-1411.
[2]
9
This article is protected by copyright. All rights reserved.

10.1002/chem.201904583
Chemistry - A European Journal
FULL PAPER
[3]
aH. Yoshida, R. Yamada, T. Yoshida, ChemSusChem 2019;
[25]
[26]
[27]
[28]
[29]
[30]
[31]
[32]
[33]
[34]
[35]
[36]
R. B. Wexler, J. M. P. Martirez, A. M. Rappe, Chemistry of
Materials 2016, 28, 5365-5372.
B. Jansi Rani, N. Dhivya, G. Ravi, S. S. Zance, R. Yuvakkumar,
S. I. Hong, ACS Omega 2019, 4, 10302-10310.
S. Sahoo, A. K. Satpati, P. K. Sahoo, P. D. Naik, ACS Omega
2018, 3, 17936-17946.
bH. Wang, H. Liu, Y. Ji, R. Yang, Z. Zhang, X. Wang, H. Liu,
Chemical Communications 2019; cK. U. Calvinho, A. B.
Laursen, K. M. Yap, T. A. Goetjen, S. Hwang, N. Murali, B.
Mejia-Sosa, A. Lubarski, K. M. Teeluck, E. S. Hall, Energy &
Environmental Science 2018, 11, 2550-2559; dL. Bu, Q. Shao,
B. E, J. Guo, J. Yao, X. Huang, Journal of the American
Chemical Society 2017, 139, 9576-9582.
Y. Li, K. Ye, K. Cheng, J. Yin, D. Cao, G. Wang, Journal of
Power Sources 2015, 274, 943-950.
[4]
aG. Qu, Y. Zhao, G. Zhao, Y. Zhou, S. Cai, Y. Kang, C. Xu,
Electrochimica Acta 2019, 298, 943-949; bQ. Yan, X. Chen, T.
Wei, G. Wang, M. Zhu, Y. Zhuo, K. Cheng, K. Ye, K. Zhu, J.
Yan, D. Cao, Y. Li, ACS Sustainable Chemistry & Engineering
2019; cX. Hao, Z. Jiang, X. Tian, X. Hao, T. Maiyalagan, Z.-J.
Jiang, Journal of Alloys and Compounds 2019; dX. Xu, X. Tian,
Z. Zhong, L. Kang, J. Yao, Journal of Power Sources 2019,
424, 42-51; eJ. Joo, T. Kim, J. Lee, S. I. Choi, K. Lee,
Advanced Materials 2019, 1806682; fS. Deng, K. Zhang, D. Xie,
Y. Zhang, Y. Zhang, Y. Wang, J. Wu, X. Wang, H. J. Fan, X.
Xia, Nano-Micro Letters 2019, 11, 12; gJ. Ding, S. Ji, H. Wang,
H. Gai, F. Liu, V. Linkov, R. Wang, International Journal of
Hydrogen Energy 2019, 44, 2832-2840.
A. Wang, H. Wang, S. Zhang, C. Mao, J. Song, H. Niu, B. Jin,
Y. Tian, Applied Surface Science 2013, 282, 704-708.
F. Cao, R. Liu, L. Zhou, S. Song, Y. Lei, W. Shi, F. Zhao, H.
Zhang, Journal of Materials Chemistry 2010, 20, 1078-1085.
Z. Pu, Y. Luo, A. M. Asiri, X. Sun, ACS applied materials &
interfaces 2016, 8, 4718-4723.
Z. Liu, G. Zhang, K. Zhang, H. Liu, J. Qu, ACS Sustainable
Chemistry & Engineering 2018, 6, 7206-7211.
C. G. Read, J. F. Callejas, C. F. Holder, R. E. Schaak, ACS
applied materials & interfaces 2016, 8, 12798-12803.
Z. Qin, Y. Chen, Z. Huang, J. Su, Z. Diao, L. Guo, The Journal
of Physical Chemistry C 2016, 120, 14581-14589.
C. Tang, Z. Pu, Q. Liu, A. M. Asiri, X. Sun, Electrochimica Acta
2015, 153, 508-514.
aW. E. Van Zyl, J. P. Fackler, Phosphorus, Sulfur, and Silicon
and the Related Elements 2000, 167, 117-132; bI. P. Gray, A.
M. Z. Slawin, J. D. Woollins, Dalton Transactions 2004, 2477-
2486.
[5]
aG. K. a. A. Yund, Journal of petrology 1962, 3; bJ. Barry, S.
Ford, Journal of Materials Science 2001, 36, 3721-3730; cK.
Ramasamy, M. A. Malik, P. O’Brien, J. Raftery, M. Helliwell,
Chemistry of Materials 2010, 22, 6328-6340; dM. V. Swain,
Journal of Materials Science 1981, 16, 151-158.
[6]
[7]
[8]
[9]
[10]
X. Zheng, X. Han, Y. Zhang, J. Wang, C. Zhong, Y. Deng, W.
Hu, Nanoscale 2019.
P. Musetha, N. Revaprasadu, M. Malik, P. O'Brien, MRS
Online Proceedings Library Archive 2005, 879.
N. Alam, M. S. Hill, G. Kociok-Kꢀhn, M. Zeller, M. Mazhar, K. C.
Molloy, Chemistry of Materials 2008, 20, 6157-6162.
A. L. Abdelhady, M. A. Malik, P. O’Brien, F. Tuna, The Journal
of Physical Chemistry C 2012, 116, 2253-2259.
N. Hollingsworth, A. Roffey, H.-U. Islam, M. Mercy, A. Roldan,
W. Bras, M. Wolthers, C. R. A. Catlow, G. Sankar, G. Hogarth,
Chemistry of Materials 2014, 26, 6281-6292.
[37]
[38]
S. a. S. Bruker. APEX2, Brucker AXS Inc., Madison, WI, USA
2012.
G. M. Sheldrick, Acta Cryst 2008, A64 339-341.
[11]
[12]
R. Yadav, A. K. Singh, Y. Waghadkar, G. Kociok-Köhn, A.
Kumar, R. Chauhan, S. Rane, S. Gosavi, New Journal of
Chemistry 2017, 41, 1327-1333.
aY. Ni, K. Liao, J. Li, CrystEngComm 2010, 12, 1568-1575; bH.
Li, S. Lu, J. Sun, J. Pei, D. Liu, Y. Xue, J. Mao, W. Zhu, Z.
Zhuang, Chemistry–A European Journal 2018, 24, 11748-
11754.
[13]
aW. Maneeprakorn, C. Q. Nguyen, M. A. Malik, P. O'Brien, J.
Raftery, Dalton Transactions 2009, 2103-2108; bA.
Panneerselvam, M. A. Malik, M. Afzaal, P. O'Brien, M. Helliwell,
Journal of the American Chemical Society 2008, 130, 2420-
2421.
[14]
[15]
[16]
W. Maneeprakorn, M. A. Malik, P. O'Brien, Journal of Materials
Chemistry 2010, 20, 2329-2335.
S. Shanmugam, A. Sivanantham, M. Matsunaga, U. Simon, T.
Osaka, Electrochimica Acta 2019, 297, 749-754.
aJ. A. Adekoya, M. D. Khan, N. Revaprasadu, RSC Advances
2019, 9, 35706-35716; bM. D. Khan, M. A. Malik, N.
Revaprasadu, Coordination Chemistry Reviews 2019, 388, 24-
47; cC. Gervas, M. D. Khan, S. Mlowe, C. Zhang, C. Zhao, R.
K. Gupta, M. P. Akerman, P. Mashazi, T. Nyokong, N.
Revaprasadu, ChemElectroChem 2019, 6, 2560-2569; dM. D.
Khan, M. Akhtar, M. A. Malik, N. Revaprasadu, P. O'Brien,
ChemistrySelect 2018, 3, 2943-2950; eS. A. Saah, M. D. Khan,
P. D. McNaughter, J. A. Awudza, N. Revaprasadu, P. O’Brien,
New Journal of Chemistry 2018, 42, 16602-16607; fM. D. Khan,
M. Aamir, M. Sohail, S. Bhoyate, M. Hyatt, R. K. Gupta, M.
Sher, N. Revaprasadu, Dalton Transactions 2019, 48, 3714-
3722; gM. D. Khan, J. Akhtar, M. A. Malik, N. Revaprasadu,
ChemistrySelect 2016, 1, 5982-5989.
[17]
[18]
[19]
[20]
[21]
[22]
W. E. van Zyl, J. D. Woollins, Coordination Chemistry Reviews
2013, 257, 718-731.
T. J. Ajayi, M. N. Pillay, W. E. van Zyl, Phosphorus, Sulfur, and
Silicon and the Related Elements 2017, 192, 1205-1211.
Y. ÖZCAN, S. Ide, M. KARAKU, H. YILMAZ, Analytical
sciences 2002, 18, 1285-1286.
S. Sewpersad, W. E. Van Zyl, Acta Crystallographica Section
E: Structure Reports Online 2012, 68, m1457-m1457.
W. W. Yu, Y. A. Wang, X. Peng, Chemistry of Materials 2003,
15, 4300-4308.
aS. Krishnakumar, N. Shanthi, D. Sarma, Physical Review B
2002, 66, 115105; bG. Gibbs, R. T. Downs, C. Prewitt, K. M.
Rosso, N. Ross, D. F. Cox, The Journal of Physical Chemistry
B 2005, 109, 21788-21795.
[23]
[24]
aS. Wang, L. Kuai, Y. Huang, X. Yu, Y. Liu, W. Li, L. Chen, B.
Geng, Chemistry–A European Journal 2013, 19, 240-248; bD.
A. Henckel, O. Lenz, B. M. Cossairt, ACS Catalysis 2017, 7,
2815-2820.
D. Wang, L. B. Kong, M. C. Liu, Y. C. Luo, L. Kang, Chemistry–
A European Journal 2015, 21, 17897-17903.
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10.1002/chem.201904583
Chemistry - A European Journal
FULL PAPER
Entry for the Table of Contents
FULL PAPER
Gwaza Eric Ayom, Malik Dilshad Khan,
Tenzin Ingsel, Wang Lin, Ram K. Gupta,
Sizwe J. Zamisa, Werner E. van Zyl and
Neerish Revaprasadu*
Page No. – Page No.
Flexible Molecular Precursors for
Selective Decomposition to Nickel
Sulfide or Nickel Phosphide for Water
Splitting and Supercapacitance
Text for Table of Contents
Molecular precursors were used to prepare selectively, nickel phosphide or nickel sulfide. Different phosphide and sulfide
phases were prepared by controlling reaction parameters and performance of different phases was investigated for energy
storage and energy generation applications.
11
This article is protected by copyright. All rights reserved.