Multinuclear Transition Metal Sandwich-Type Polytungstate Derivatives for Enhanced Electrochemical Energy Storage and Bifunctional Electrocatalysis Performances

Bifunctional Electrocatalysis Performances

Article

Multinuclear Transition Metal Sandwich-Type Polytungstate

Derivatives for Enhanced Electrochemical Energy Storage and

Xinyue Ma, Kai Yu,* Jie Yuan, Liping Cui, Jinghua Lv,* Wenting Dai, and Baibin Zhou*

Cite This: https://dx.doi.org/10.1021/acs.inorgchem.0c00382

Read Online

ACCESS

Metrics & More

Article Recommendations

sı Supporting Information

ABSTRACT: Diﬀerent transition metal (TM) units are introduced into a trivacant Keggin cluster to form three sandwich

polytungstate derivatives, (H en)[{K(H O) } {K (H O) }{Ni(H O)(en) } {Ni (H O) (PW O ) }] (1), [Cu (Himi) -

0.5

III

{

As W O } ]·5H O (2), and (H btp) [Fe Fe (H O) (AsW O ) ]·4H O (3) (en = ethanediamine; imi = imidazole; btp =

34 2

,3-bis(1, 2, 4-triazol-1-yl) propane). Compound 1 is a 2,3,8-connected 3D network with {4 } {4 ·6 ·8 ·6 ·8}{6} topology based

2 2

on bisupported tetra-Ni sandwich phosphotungstate and two kinds of potassium connection units. Compound 2 is a dense 12-

connected 3D supramolecular network with {3 ·4 ·5 } topology based on hexa-Cu(imi) sandwiched arsenotungstate. Compound 3

represents the ﬁrst mixed valence tetra-Fe substituted sandwich arsenotungstate assembly. Compounds 1−3 show enhanced

supercapacitor performance (618.2, 603.4, and 504.6 F·g at a current density of 2.4 A·g with 91.5%, 89.3%, and 87.8% of cycle

eﬃciency after 5000 cycles, respectively) compared to their maternal polyoxometalates (POMs) and most reported POM-based

electrode materials, which suggests that the introduction of multinuclear TM into vacant POMs is an eﬀective method to improve

the energy storage performance of POMs. In addition, compounds 1 and 3 exhibit dual-functional electrocatalytic behaviors in the

reduction of iodate and the oxidation of dopamine for introduction of {Ni } and {Fe } units.

−

−1

INTRODUCTION

high theoretical speciﬁc capacity, wide voltage range, and

■

excellent conductivity and is the best and most promising

The rapid consumption of fossil energy and the deterioration

of ecological environment have given rise to the development

of advanced energy storage and conversion equipment.

Supercapacitors as novel energy storage devices have aroused

people’s interest and are widely used in portable electronics,

electric vehicles, and smart grids due to their long cycle

material. But the application of such materials has been

limited due to their scarce resources and high prices.

Therefore, the development of cheap supercapacitor materials

with good comprehensive performance is still an urgent issue.

Polyoxometallates (POMs) as a big class of nanometal

oxygen clusters composed of transition metals (Mo, W, and V

etc.) possess various structures, diﬀerent sizes, and excellent

−5

lifetime, rapid energy conversion, and high energy densities.

Pseudocapacitors (PCs) are Faraday capacitors which can

store energy through rapid reversible chemical adsorption,

desorption, or redox reactions on the electrode surface. The

quality of such supercapacitor devices mainly depends on the

performance of the electrode material itself. At present,

pseudocapacitance materials mainly include carbon-based

12−15

physicochemical characteristics,

which endows them with

wide applications in catalysis, photoelectric chemistry, and

16−19

pharmacochemistry.

In addition, POMs can engage in fast

Received: February 6, 2020

7,8

materials, conductive polymers,

and transition metal

However, the low capacitance and

,10

oxides/hydroxides.

high cost of new carbon-based materials, as well as poor cyclic

stability of conductive polymers, limit their practical

application. Among the transition metal oxides, RuO has

XXXX American Chemical Society

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

Table 1. Crystal Data and Structure Reﬁnements for Compounds 1−3

Compound

formula

C H K N Ni O P W

C H As Cu N O W

C H As Fe N O W

28 64 2 4 24 74 18

18 34

12 71 18

5428.54

5394.84

5603.57

Crystal size, mm³

Crystal system

Space group

a, Å

b, Å

c, Å

0.17 × 0.15 × 0.13

Triclinic

0.19 × 0.17 × 0.15

Cubic

Pa3

21.9385

0.18 × 0.16 × 0.14

Orthorhombic

Pbca

20.903(5)

19.772(5)

23.186(5)

12.27(3)

12.39(3)

16.48(5)

105.65(6)

91.29(6)

α, deg

β, deg

γ, deg

V (Å )

116.03(3)

2139(10)

4.213

25.711

9583(4)

3.884

22.892

10559.0(6)

3.394

D_c_a_l_c_d, kg m⁻

μ(Mo Kα), mm⁻

21.407

F(000), e

2408

9464

9976

θ range, deg

Reﬂections collected/unique/R_i_n_t

Data/restraints/parameters

2.601−24.999

13532/7353/0.0648

7353/962/587

0.0731/0.1873

1.073

3.080−24.986

12713/3098/0.0796

3098/324/215

0.0838/0.1772

1.066

2.442−27.670

114471/11166/0.0743

11166/277/680

0.0439/0.1387

1.051

R /wR [I ≥ 2σ(I)]

GoF (F )

R /wR (all data)

0.1181/0.1924

0.1111/0.1859

0.0749/0.1765

R1 = ∑(|F |- |F |)/∑Σ|F |; wR2 = {∑[w(|F | - |F | ) ]/∑[w(|F | ) ]}1/2_.

multielectron conversion without changing their own structure

due to their outstanding redox capacity and structural stability.

Thus, they have strong electrochemical energy storage capacity

property studies of sandwich polytungstate have been mainly

focused on magnetic behavior, catalytic properties, and

biological activity. The eﬀects of the introduction of transition

metal clusters on the energy storage performance and

electrochemical behavior of these compounds have not been

studied. Therefore, it is very meaningful and attractive to

explore the supercapacitor and electrocatalytic properties of

novel high-core sandwich polytungstate assemblies. Herein,

diﬀerent transition metal clusters are introduced into the

trivacant Keggin cluster to yield three novel multinuclear

20,21

and excellent electrocatalytic properties.

Recently, POMs

have received great attention as the active material of

2−33

supercapacitors.

However, the application of routine

POM materials in water system supercapacitors has been

hindered due to their poor electrical conductivity and great

solubility in aqueous solution. In order to overcome the above

shortcomings, many research groups combine POMs with

conductive polymers or immobilize POMs onto carbon-based

materials to prepare hybrid nanocomposites with composite

features and improved supercapacitor behavior. Representative

sandwich-type polytungstates, (H en)[{K(H O) } -

0.5 2

{

[

K (H O) }{Ni(H O)(en) } {Ni (H O) (PW O ) }] (1),

2 2 3 2 2 2 4 2 2 9 34 2

III

Cu (Himi) {As W O } ]·5H O (2), and (H btp) -

III

[Fe Fe (H O) (AsW O ) ]·4H O (3) via in situ hydro-

studies mainly include carbonnanotube/Cs-PMo hybrids,

2 2 2 2 9 34 2 2

thermal reaction of simple raw materials. The electrochemical

energy storage performance and electrocatalytic behavior after

the introduction of transition metals were studied for the ﬁrst

time. The result of our experiment reveals that the grafting of

multinuclear TM cluster into vacant POMs is an eﬀective

method to enhance the energy storage performance and

improve electrochemical properties of POMs.

POM adsorbed activated carbon materials, PMo -polyani-

line/graphene composites, polymeric ionic liquid connected

POM/reduced graphene oxide nanohybrids, and {Mo₁₃₂}-

rGO nanocomposites. However, the above synthesis

methods are complex, and it is necessary to prepare POM

precursors. In addition, the exact components of the

synthesized complexes are diﬃcult to be determined.

Fortunately, POM as an excellent molecular-based material

has outstanding tailoring properties. It can be connected with

transition metal, organic ligands, and metal−organic complexes

to form various hybrid materials and host−guest structures to

adjust the stability of the solution, the speciﬁc surface area, and

conductivity, so as to improve the supercapacitor perform-

EXPERIMENTAL SECTION

■

The details of general methods and materials, synthesis of compounds

1−3, X-ray crystallography, and preparation of the electrodes are

given in section 1 of the Supporting Information . Details of the

crystallographic data and structural determination for 1−3 are listed

in Table 1.

8−35

ances.

As one of the branches of POMs, the trilacunary Keggin

9−

RESULTS AND DISCUSSION

[

XW O ] (X = P, As, Sb, and Bi) is an ideal building unit

■

that can combine a certain number of transition metals into the

vacant positions between two polyoxoanions to form sandwich

polytungstates with multinuclear clusters. The introduction of

diﬀerent transition metal units will play important roles in

Synthesis. In the process of exploring novel transition

metal substituted sandwich polytungstate assemblies, we try to

introduce copper, vanadium, iron, etc. into a {XW } (X = As,

P) system by a one-step hydrothermal method, as the high-

core sandwich unit mentioned above is relatively diﬃcult to be

incorporated into the trivacancy Keggin system. Many factors

8−42

43−47

regulating catalysis,

ties,

magnetism,

redox proper-

8−50

and medicinal activity of POMs.⁵¹⁻⁵⁴However,

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

1 b). The bond lengths of Ni −O and bond angle of O −Ni −O

Article

aﬀect the structure of the sandwich-type derivatives during

preparation. The addition of diﬀerent transition metals, organic

ligands, and mineralizers directly aﬀects the type, number of

substitutions, and ﬁnal spatial structure of sandwich-type

POMs. When the reaction of Na MoO ·2H O, NaAsO ,

Scheme 1. Relationship among the Structures of the

Sandwich-Type Polytungstates, Transition Metal Salts, and

Organic Ligands

FeCl , and 1,3-bis(1,2,4-triazol-1-yl) propane was conducted at

60 °C for 6 days at a pH range of 4−4.5, tetra-Fe-substituted

compound 3 was prepared. This inspired us to change

transition metal and build copper substituted arsenotungstate

derivatives under similar conditions. Unfortunately, when

copper salt is used to replace FeCl , no expected crystals

were obtained, which indicates that the introduction of a

multinuclear copper sandwich unit requires the assistance of

appropriate mineralizing agent. This may be the reason why

other transition metal hexasubstituted derivatives similar to

compound 2 have been reported as early as 2009, while

compounds with six-core copper have not yet been prepared.

NH VO as excellent mineralizer can eﬀectively activate POM

clusters, so it is added to the system. Because of the

simultaneous existence of copper and vanadium elements in

the system, the bonding competition between them and

linker {K (H O) }, two {K(H O)} cations, and one H en

ligand (Figure S1). Two {PW O } fragments and one

trivacant Keggin cluster {AsW } must be considered. When the

{Ni (H O) } unit connect each other via seven bridging O

4 2 2

rigid ligand imidazolium is added to the system to control the

temperature at 160 °C, the hexa-copper substituted arsen-

otungstate derivatives are synthesized. When imi ligands are

replaced by pz and phen and the reaction temperature is

reduced to 140 °C, the mixed hexa-TM (V^I^VCu O )

substituted arsenotungstate derivatives are obtained. It is

clear that the type of ligands and the temperature of reaction

are the key factors aﬀecting the coordination activity of

atoms of each polyoxoanion to form a tetra-Ni sandwiched

cluster {Ni (H O) (PW O ) }. In the central belt of the

34 2

sandwich structure, four 6-coordinated Ni atoms (Ni1 and

Ni3) are linked via a common edges mode to form a

centrosymmetric tetranuclear unit {Ni O (H O) } (Figure

vanadium and copper with {AsW } polyoxyanions. Higher

reaction temperature and the addition of imi ligands are

beneﬁcial to enhance the reaction activity of Cu and reduce the

reaction activity of vanadium in the {Cu/V/As/W} system.

The experimental results show that the introduction of

vanadium is a very diﬃcult project, which can only be

achieved with the aid of Cu²and two rigid ligands. This is the

main reason why few sandwich compounds with high nuclear

vanadium substitutions have been reported. In the strategy, Cu

with d conﬁguration and two complementary rigid ligands

are easy to form multicore complexes and further form a more

complex metal−organic network, which may induce V-

substituted sandwich clusters and their extended assembly. In

addition, we try to use the same one-step hydrothermal

method to prepare high-core transition metal substituted

sandwich-type phosphotungstate. Diﬀerent transition metals

and various organic ligands have been tried through a large

number of parallel experiments under the reaction conditions

of compound 3 by replacing sodium arsenite with phosphate

or hydrogen phosphate. The results show that only when the

transition metal nickel and organic ligand en are added into the

system can a 4-Ni substituted 3D highly connected derivative

be obtained. It is clear that phosphotungstate is not easy to be

synthesized by hydrothermal synthesis of simple raw materials.

On the contrary, a precursor method is more suitable for these

derivatives, which can be proved by the widely reported

methods of preparing for sandwich-type phosphotungstes. The

synthesis strategies of the three compounds are summarized in

Scheme 1.

Figure 1. (a) Polyhedral/ball and stick representation of the

[

(

{K(H O)} {K (OH) (H O) }{Ni(H O) } {Ni (H O) -

2 2 2 2 2 2 2 5 2 4 2 2

PW O ) }] cluster. (b) Coordination manner of the tetra-Ni

33 2

sandwich unit {Ni O (H O) } in compound 1.

are in the range of 2.02(2)−2.21(3) Å and 88.0(10)−

174.3(10)°, respectively. The distance between adjacent Ni···

Ni is 3.157 and 3.192 Å. Each Ni2 adopts hexacoordinated

octahedral geometry bonds and bonds to four N derived from

two en, one terminal oxygen atom of polyanion, and one water

molecule to form a complex unit {Ni(H O)(en) }. Each such

unit links with two symmetrical oxygen atoms of sandwich

polyanion to yield a biarm sandwich unit [{Ni(H O)(en) } -

Structure Descriptions of 1. Compound 1 belongs to the

2 2

spatial group of triclinic crystal system and contains two B-

{Ni (H O) (PW O ) }] (Figure 1a). The distances of Ni−O

34 2

α-type trivacant Keggin clusters {PW O }, one {Ni (H O) }

sandwich unit, two {Ni(H O)(en) } complexes, one binuclear

and Ni−N are in the range of 2.15(3)−2.24(3) Å and

2.05(4)−2.10(3) Å, respectively (Table S1).

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

Figure 2. (a) Polyhedral/ball and stick representation of a 2D layer of compound 1; (b) polyhedral/ball and stick representation of the 3D network

of 1; (c) view of the topology of the 2D layer; (d) view of the topology of the 3D network.

Two crystallographically independent potassium atoms

expand the sandwich cluster unit into an extended 3D open

skeleton. Each K1 cation exhibits a deformed octahedral

coordination environment with ﬁve O donors from three

sandwich clusters and one water molecule. The K2 displays a

distorted octahedral conﬁguration, which is deﬁned by two

terminal oxygen atoms of sandwich polyanion and four water

molecules. Two water molecules act as linkage unit connecting

two symmetrical K2 atoms into a binuclear bridge unit

{

K (H O) }. The average distance of K−O is 2.602. Each

biarmed sandwich building block links to six surrounding

K1(H O)} caions, while each {K1(H O)} cation connects

{

with three adjacent sandwich units. In this way, each biarmed

sandwich cluster bonds to six adjacent analogues via

Figure 3. Polyhedral/ball and stick representation of

III

{

Cu (imi) (As W O ) } cluster.

6 6 9 33 2

{

K1(H O)} linkers to result in a inﬁnite 2D layer (Figures

a and S2 ). The {K (H O) } segments of each sandwich

2 2 6

polyanion projecting from the layer bond with the O atom of

the sandwich cluster on the adjacent two layers to form a 3D

framework (Figure 2b). The overall structure of compound 1 is

sandwich unit {Cu (imi) (AsW O )}. The bond lengths of

Cu−O and bond angle of O−Cu−O are in the range of

2.038(18)−2.065(18) Å and 79.4(9)−147.8(14)°, respec-

tively. The Cu−N distance is 1.99(2) Å. The distance between

adjacent Cu···Cu is 3.118 Å (Table S2).

an extended (2,3,8)-connected 3D network with {4 } {4 ·6 ·

·6 ·8}{6} topology based on a 3,6-connected 2D layer in

view of considering {K (H O) } as 2-connected nodes,

{

K1(H O)} as 3-connected nodes, and sandwich cluster as

Each hexa-Cu substituted sandwich unit as basic building

block links six sandwich {Cu (imi) (AsW O )} clusters in

-connected nodes (Figure 2c and d).

Structure Descriptions of 2. Compound 2 crystallizes in

ABAB mode via the H-bond interaction (N1···O1 2.729)

the Pa3

spatial group of the cubic crystal system and consists

between the N of the central sandwich unit {Cu O N } and

of two trivacant Keggin B-α-{AsW O } polyoxoanions, one

the O atoms of ambient polyoxoanion clusters (Figure S4a ).

Meanwhile, six other adjacent polyoxoanion clusters using the

N atoms (N1) of their sandwich unit connect the symmetric O

atoms (O1) of the central cluster via the same H-bonding

interaction in the same way (Figure S4b). In the above

connection ways, each polyoxoanion is connected with 12

surrounding analogues in the form of ABAB to result in a 3D

dense packing structure (Figures S4c and 4a). The simpliﬁed

structure of compound 2 is an extended 12-connected 3D net

{

Cu (imi) } sandwich unit, and solvent water molecules

6 6

(Figures 3 and S3). In structure 2, each Cu atom adopts a

pentacoordinated tetragonal pyramid conﬁguration to link four

O atoms derived from equatorial {WO } of two {AsW O }

clusters and one N donor of the imi molecule. Six {CuO N}

units are bonded together to generate a six-nuclear metal ring

{

Cu O N }. Two {AsW O } clusters are sandwiched by the

6 12 6 9 33

coplanar six-core unit {Cu O N } via 12 terminal O atoms of

two polyoxoanion clusters to yield a hexa-Cu substituted

with {3 ·4 ·5 } topology based on the fact that the 6-Cu

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

substituded sandwich cluster acts as a 12-connected node

ligands reinforce the 2D layer via four supramolecular

interactions (C9···O20 3.122, C12···O19 3.042, C18···O23

(Figure 4 b).

3.118, and C11···O11 3.151). The lattice water molecules link

the adjacent 2D plane into the 3D supramolecular net via a

pair of hydrogen bonds (O28 ···O2W 2.70(2) Å and O2W···

O11 2.74(2) Å) (Table S4 and Figure S8).

Compounds 1−3 were synthesized by adjusting the kinds of

transition metals and organic ligands under similar hydro-

thermal conditions, which are summarized in Scheme 1. The

bond valence calculation shows that all tungsten atoms are in

6 valence, the phosphorus, nickel, and potassium center in

compound 1 are in +5, +2, and +1, respectively, the arsenic

and copper atoms in compound 2 are in +3 and +5, and the

arsenic, Fe1, and Fe2 centers in compound 3 are +5, +3, and

2, respectively.

IR Spectroscopy. The IR spectra of 1−3 (Figure S9)

Figure 4. (a) Tightly stacked 3D networks of compound 2; (b) fcu/

exhibit the obvious vibration bands of trivacant Keggin

clusters.

cubic closest packing with 12-connected {3 ·4 ·5 } topology.

47,57

−1

The peaks at 1042, 933, 879, 756 cm in 1,

−

−1

872, 996, 804, 714 cm in 2, and 862, 982, 813, 706 cm in 3

Structure Descriptions of 3. Compound 3 belongs to the

Pbca space group of the orthorhombic crystal system, which is

composed of one 4-Fe substituted sandwich POM cluster

are indicative of the stretching vibration of v(P−O ) (1)/(As−

O ) (2 and 3), ν(WO ), ν(W−O ), and ν(W−O ),

respectively. The vibrational signals in the region of 1430−

III

{

Fe Fe (H O) (AsW O ) }, four biprotonated organic

−1

34 2

658 cm are attributed to the vibration of v(N−H) of

ligands H btp, and four water molecules (Figure S5). Two

−1

organic ligands in 1−3. The broad peaks at 3299−3581 cm

are ascribed to the stretching vibration ν(O−H) of water

molecules or ν(N−H) of protonated organic ligand.

trivacant Keggin polyoxoanion B-α-{AsW O } are bonded

together by mixed valence tetranuclear iron units

III

{

Fe Fe (H O) } via seven bridging O atoms of each

2 2 2 2

TG Analyses. The TG analyze curves (Figure S10) of

polyoxoanion to form a tetra-Fe sandwiched cluster

compounds 1−3 were depicted under a N atmosphere from

III

{

Fe Fe (H O) (AsW O ) }. The sandwich units of com-

2 2 2 2 9 34 2

0 to 900 °C. Two obvious weight losses can be detected in

pounds 3 and 1 are isostructural, and the coordination mode of

the TG curve of compounds 1−3. The ﬁrst weight losses of

III

iron in {Fe Fe O (H O) } is the same as that of nickel in

.67% (calcd 2.63%) at 225−330 °C for 1, 14.20% (calcd

3.77%) at 160−210 °C for 2, and 1.94% (calcd 1.89%) at

60−210 °C for 3 can be attributed to the removal of all water

{

Ni O (H O) } (Figure 5 ). The diﬀerence is that the

4 14 2 2

molecules. The second weight loss of 5.45% (calcd 5.41%) at

80−650 °C for 1, 6.14% (calcd 6.64%) at 385−650 °C for 2,

and 12.96% (calcd 12.91%) at 380−630 °C for 3 is attributed

to the losses of organic ligands en, Himi, and H btp,

respectively.

XRPD and X-ray Photoelectron Spectra Analyses. In

order to prove the purity and stability of compounds 1−3, the

samples before electrochemical test were selected and

immersed in 0.5 M sulfuric acid solution for 72 h. The X-ray

powder diﬀraction of samples before and after soaking were

tested, which are shown in Figure S11 . Compared with the

simulated PXRD diagram, the characteristic peaks of the

samples did not change before and after soaking, which are in

good agreement with that of the simulated XRD. The result

suggests that compounds 1−3 have good stability and purity.

The oxidation states of As and Cu of compound 2, as well as

As and Fe of compound 3, are further determined by XPS

tests, which were conducted in the energy area of As 3d5/2, As

3d3/2, Cu 2p3/2, Cu 2p1/2, Fe 2p3/2, and Fe 2p1/2 (Figure

6). The XPS spectrum of compound 2 exhibits two peaks at

39.0 and 43.2 eV in As 3d and two peaks at 933.7 and 953.8 eV

Figure 5. Polyhedral/ball and stick representation of

III

{

Fe Fe (H O) (AsW O ) } cluster in 3.

34 2

{

Fe^I^I^IFe O (H O) } is a mixed valence tetranuclear unit.

The bond lengths of Fe1 −O3 and Fe1−O4 are 1.906(10) and

.890(12), respectively (Table S3). The relatively shorter bond

length contribution between Fe1 and O atoms results in +III

valences of Fe1. The bond lengths of Fe2−O are in the range

of 2.078(11)−2.254(11) Å, which yields +II valences of Fe2.

The adjacent tetra-Fe sandwiched polyoxoanions with two

spatial orientations are aggregated together in an ABAB

manner via supramolecular interactions (O24··· O30 3.032)

between terminal O atoms of two sandwich-type anions to give

birth to 1D chains (Figure S6). The same supramolecular

interactions (O24···O30 3.032) extend adjacent 1D chains to

the 2D supramolecular plane (Figure S7). In addition, isolated

in the Cu 2p region, which are attributed to As (ref 58) and

Cu , respectively. Two peaks at 39.9 and 44.6 eV in the As

3d for compound 3 are ascribed to As . Additionally, four

peaks at 724.6, 711.2, 723.5, and 709.6 eV in Fe 2p are

attributed to Fe and Fe ions, respectively. The oxidation

number of all elements coincides with the calculated results of

the valence bond.

SEM and EDS Analyses. The element composition and

surface topography of compounds 1−3 were studied by

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

mV s are shown in Figure 8 . The CV curves of 1 −3 -GCE

Article

N, O, As, W, and Fe in compound 3 are detected and evenly

distributed from the ﬁgure of EDS mapping and microanalysis.

Capacitive Performance Compounds 1−3. The electro-

chemical performances of 1−3-based glassy carbon electrode

(

1−3-GCE) were carried out in a trielectrode system with 0.5

M sulfuric acid electrolyte. The cyclic voltammetry (CV)

curves of 1−3-GCE in the potential window range of −0.6−0.6

V (potentials vs Ag/AgCl) at scanning rates from 25 to 200

−

Figure 6. XPS spectrum of As (a), Cu (b) of compound 2 and As (c),

Fe (d) of compound 3.

scanning electron micrographs (SEM) and energy dispersive

spectroscopy (EDS). As shown in Figures 7 and S12 −S15,

compounds 1−3 are rectangular bulk crystals with a size of

about 130 × 80 × 15, 140 × 70 × 30, and 180 × 120 × 60

μm , respectively. The elements C, N, O, P, W, K, and Ni in

compound 1 , C, N, O, As, W, and Cu in compound 2 , and C,

Figure 8. Cyclic voltammograms (CV) curves of 1-GCE (a), 2-GCE

(

b), and 3-GCE (c) in 0.5 M sulfuric acid solution at 25, 50, 75, 100,

25, 150, 175, and 200 mV s (inset shows plots of the anodic and

−1

cathodic peak currents vs scan rates). (d) Comparative diagrams of

−

CV curves of 1-, 2-, and 3-GCE at 20 mV s . Potentials vs Ag/AgCl.

exhibit three pairs of reversible redox peaks with mean-peak

potentials E₁_/₂= (E_p_a+ E )/2, −115 (II−II′), −345 (III−

III′), and −585 (IV−IV′) mV for 1, −120 (II−II′), −333

(

III−III′), and −578 (IV−IV′) mV for 2, and −105 (II−II′),

−

325 (III−III′), and −529 (IV−IV′) mV for 3, which could

be assigned to continuous two-electron redox processes of W

atom in sandwich-type polytungstate clusters. The redox

reaction of the W center of compounds 1−3 is similar. The

transformation mechanism of compound 1 as a representative

can be described as the following:

0−

{

Ni (H O) (PW O ) } + 2e + 2H⁺

9 34 2

10−

↔

{H Ni (H O) (PW W O ) }

(1)

(2)

(3)

34 2

H Ni (H O) (PW W O ) } + 2e + 2H⁺

10−

34 2

10−

↔

{H Ni (H O) (PW W O ) }

34 2

H Ni (H O) (PW W O ) } + 2e + 2H⁺

10−

34 2

10−

↔

{H Ni (H O) (PW W O ) }

34 2

Additional quasi-irreversible peaks (I/I′) in 1−3-GCE with

395, 80, and 425 mV in the positive voltage direction

represent the characteristic peaks associated with the transition

metal Ni, Cu, and Fe redox couples, respectively.

Diﬀerent from the rectangular shape of a dual-layer capacitor,

the above three compounds exhibit quasi-reversible multiple

pairs of oxidation−reduction peaks, which indicates that they

are typical pseudocapacitance active material. When the scan

Figure 7. EDS elemental mappings of W, O, Ni, P, N, K, and C for

compound 1.

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

GCE are depicted in Figure 10 a at a certain current density

Article

−

548.0, 513.6, and 493.2 F·g⁻¹for 2-GCE, and 504.6, 480.4,

speed gradually increases from 25 to 200 mV s , the shape of

the CV curve remains substantially constant but shows an

increase in current density, which illustrates the outstanding

Faraday process on the electrode surface and good rate

−

464.7, 444.2, and 424.9 F·g for 3-GCE at the current

−

densities of 2.4, 4.8, 9.6, 14.4, and 19.2 A·g . The areal

capacitances (C ) are 182.4, 175.0, 166.6, 163.9, and 151.2 mF·

cm for 1-GCE, 178.0, 176.0, 161.7, 151.5, and 145.5 mF·

33,65

−2

performance of sandwich-type polytungstates.

From the

−

CV curve, we can also see that the cathode peak and anode

peak move slightly in the direction of negative and positive

potential, respectively, which may be caused by the polar-

ization eﬀect of the electrode. As shown in the inset of Figure

, the linear relations between the current of all redox peaks

and sweeping rate demonstrates the kinetics of interfacial

cm for 2-GCE, and 147.4, 141.5, 102.6, 87.3, and 78.1 mF·

−

cm for 3-GCE at the same current density as above. In the

case of high current density (19.2), the C and C of 1-3-GCE

can still remain very large values (512.4 F·g and 151.2 mF·

−

−1

−2

−1

cm (1), 493.2 F·g and 145.5 mF·cm (2), 424.9 F·g and

−

8.1 mF·cm (3)), which reﬂects the prominent rate

29−35

capability of the sandwich-type polytungstate. With the

increase of current density, the sequential slight decrease of

the C and C values (Figure 9d) can be attributed to the loss

Faraday reaction and the rapid electron transfer speed.

The contrast diagrams of CV curves between 1−3-GCE and

their respective parents’ POM: Na [PW O ]·7H O-GCE

of eﬃciency of polytungstate in the redox process under large

(

{PW }-GCE), and Na [A-α-HAsW O ]-GCE ({AsW }-

9 8 9 34 9

29,34

current.

In addition, consistent with the results of CV area

GCE) in the voltage range of −0.6 −0.6 V at scanning rate

of 25 mV·s are recorded in Figure S16 . Compared with CV

of {PW }-GCE and {AsW }-GCE, CV curve of 1-GCE, 2-

−1

comparison, the C values of 1−3-GCE are higher than that of

their contrast compounds ({PW }-GCE and {AsW }-GCE),

which further illustrates that the C of synthetic derivatives can

GCE, and 3-GCE exhibit bigger encircled area than that of

their parent-GCE at the same scanning speed, which suggests

that they have larger capacitance than that of their parent

POMs. Extended CV area indicates enhanced capacitance

performance due to the introduction of multicore transition

metals cluster. In addition, as shown in Figure 8d, the CV area

of 1−3-GCE is in the order of: 1-GCE > 2-GCE> 3-GCE,

indicating that compounds 1 and 2 have a larger capacitance

than that of compound 3. As a result, the introduction of the

transition metal complex and the construction of the 3D

channel assembly can also improve the supercapacitors

performance of sandwich-type polytungstate to some extent.

The galvanostatic charge−discharge at diﬀerent current

densities of 1−3-GCE was conducted in the potential range of

be increased by introducing multinuclear transition metals into

vacancy POM clusters. The C values of 1−3-GCE are higher

than that of amorphous POM-based nanocomposites, such as

carbonnanotube/Cs-PMo hybrids, POM adsorbed acti-

vated carbon materials, PMo -polyaniline/graphene compo-

sites, polymeric ionic liquid connected POM/reduced

graphene oxide nanohybrids, and {Mo₁₃₂}-rGO nano-

composite. The higher speciﬁc capacitance of compounds

−3 may be related to the ordered arrangement of the internal

structure of the crystal, which can lead to more rapid and

eﬃcient transfer of the electrons on the electrode surface.

Meanwhile, the C values of 1−3-GCE are also higher than that

29−37

of most reported POMs crystal materials (Table S5).

The

superiority of the capacitance performance may be due to the

introduction of transition metal cluster units, which leads to

more abundant redox reactions in multicore sandwich-type

POMs clusters.

−

0.6−0.6 to further evaluate the electrochemical energy

storage performance of synthetic compounds. As shown in

Figure 9, the GCD curves of 1−3-GCE exhibit the voltage

platform corresponding to the CV shape, which indirectly

reﬂects the Faraday redox behavior derived from tungsten and

the transition metal clusters of sandwich-type polytung-

The cycle stability of GCD is the key parameter to evaluate

the durability and lifetime of a supercapacitor electrode. The

cycling performances of 1−3-GCE, {PW }-GCE, and {AsW }-

9−35

state.

The speciﬁc capacitance (C ) values are 618.2,

−

93.2, 564.8, 555.6, and 512.4 F ·g for 1 -GCE, 603.4, 586.8,

Figure 10. Capacitance degradation of 1-GCE, 2-GCE, and 3-GCE

−

during 3000 cycles at a current density of 2.4 mA·cm . (b) EIS

contrast spectra of 1-GCE, 2-GCE, 3-GCE, and parent POM:

{

AsW O } and {PW O } (Inset: the magniﬁcation part of the high

9 33 9 34

frequency range for the EIS spectra).

−

(

2.4 A·g ) and voltage range (−0.6−0.6 V). After 1000 cycles,

the C values of 1−3-GCE decreased by approximately 7.56%,

.33%, and 10.72%, respectively, and then by a small amount

as the number of cycles increased. The capacitance retention

rates of 1−3-GCE are 91.5%, 89.3%, and 87,8%, respectively,

while those of {PW }-GCE and {AsW }-GCE are only 82.1%

Figure 9. GCD curves of 1-GCE (a), 2-GCE (b), and 3-GCE (c) at

current densities of 2.4, 4.8, 9.6, 14.4, and 19.2 Ag . (d) Comparison

−

of speciﬁc capacitance of 1−3-GCE and parent POM: {AsW O }

and {PW O } at diﬀerent current densities.

and 83.4% after 5000 cycles. Compounds 1−3 show better

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

concentration, the anodic peak current of the Ni(II) and

Article

Figure 11. EIS control spectra of 1-GCE (a), 2-GCE (b), and 3-GCE (c) before and after circulation (Inset: the magniﬁcation part of the high

frequency range for the EIS spectra).

cyclic stability than their maternal POM, suggesting that the

grafting of multinuclear transition metal units into trivacant

Keggin cluster improves the stability and cycle life of

polytungstate. In addition, compared with the cyclic stability

of compounds 1−3, it is found that the highest capacitance

retention rate of compound 1 is more than 90%, which can be

ascribed to its spatial structure characteristics. Compound 1 is

a complicated high-connected 3D framework based on tetra-Ni

substituted sandwich-type phosphotungstate. A large number

of covalent bonds in its structure reinforce the skeleton of

polytungstate, eﬀectively alleviate the volume changes caused

by Faraday redox reaction, and thus improve the cyclic stability

of electrode materials during charge and discharge.

conﬁrm the outstanding cyclic stability and reversible redox

performance of compounds 1−3.

Bifunctional Electrocatalytic Properties. Dopamine

(DA) is a substance widely existing in the human body that

can transmit neural information. Whether DA in the brain

maintains balance is of great signiﬁcance to regulate the

uncertain mood of the human body. Lack of DA can cause

increased muscle tone and sluggish movement, including

quiescent tremors, which can lead to depression, Parkinson’s

disease, or heart disease. Therefore, it is of great signiﬁcance

to monitor its content in the human body by an electro-

chemical method to assist in clinical diagnosis of related

−

diseases. In addition, the exploration of iodate (IO ) content

is also of great signiﬁcance in medicine and the food industry.

So the organic biomolecule DA and inorganic IO₃⁻were

selected as substrates for redox reactions to further study the

electrocatalytic behavior of sandwich derivatives formed by the

introduction of diﬀerent transition metals.

As depicted in Figure 12, with the increase of DA

To further evaluate the relationship between capacitive

performance and the resistance of the polytungstate electrode

materials, the EIS spectra of compounds 1−3 and two control

compounds were tested and shown in Figure 10b. As shown in

the insertion diagram, the intercept between the Nyquist curve

of 1−3-GCE and the X axis in the high frequency domain is

.83, 4.20, and 4.35, respectively. The values are smaller than

those of {PW }-GCE and {AsW }-GCE, which means that

they have smaller ohmic resistance (R ) than their parent

POM. In addition, the radius of their curved semicircle is also

smaller than that of the two control compounds indicating that

they have lower charge transfer resistance (R ) than their

parent POM. Meanwhile, the slope of 1−3-GCE in the low

frequency region is larger than control compounds, suggesting

that compounds 1−3 have lesser ion diﬀusion resistance (Z )

than their mother POM. The results of comparison among

compounds 1−3 show that the order of three resistance values

s ct w

Figure 12. Cyclic voltammograms of 1-GCE (a) and 3-GCE (b) in

(R , R , Z ) is 1-GCE < 2-GCE < 3-GCE, suggesting that

.5 M H SO solution containing DA at diﬀerent concentrations

2 4

compounds 1 and 2 have smaller internal and diﬀusion

resistance than compound 3. The above EIS analysis results

can be interpreted as follows: (1) The introduction of the

multinuclear transition metal endows the obtained sandwich-

type derivative with a more abundant electron transfer process,

which enhances Faraday reaction and reduces the inherent

electrodes of three electrode materials. (2) The introduction of

(from bottom to top: bare-GCE, 0, 0.5, 1.0, 1.5, 2.0 mM; Scan rate:

−1

0 mV·s ). Potentials vs Ag/AgCl.

Fe(III) waves of 1-GCE and 3-GCE increased sharply,

illustrating the catalytic activities of 1-GCE and 3-GCE for

the oxidation of DA. It can be seen from the insertion ﬁgure

that there is a linear relationship between the added DA

concentration and anode peak (I) current, reﬂecting nearly

equal current stride and each addition of DA, which further

demonstrates the stability and eﬀective electrocatalytic activity

metal complexes (Ni(en) and Cu(imi)) in compounds 1 and

provides a rich π electron system and accelerates the electron

transfer in the electrode materials. (3) The 3D channel

structure of compound 1 allows rapid diﬀusion of the

electrolyte and provides a site for eﬃcient conversion of

ions/electrons. The EIS contrast diagrams before and after

of 1-GCE and 3-GCE to oxidation of DA. On the contrary,

with the addition of DA, the Cu peak of 2-GCE is almost

unchanged suggesting that it has no catalytic eﬀect on the

oxidation of DA (Figure S17 ). The above results indicate that

the transition metal summit due to the introduction of

multicore TM improves the oxidation capacity of polytung-

state, and the eﬀects of diﬀerent transition metals on the

oxidation capacity are also diﬀerent.

000 cycles of 1−3-GCE are shown in Figure 11. The Warburg

resistance (Z ) and R values of three compounds increase

slightly after 5000 cycles, while the shape of the Nyquist plots

was basically the same before and after cycles, so the R values

hardly changed much after 5000 cycles. These results further

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

concentration, the anode peak current of all W decreases and

Article

−

As shown in Figure 13a−c, with the increase of IO

GCEs have better catalytic stability and the catalytic activity

could be well maintained during repeating electrocatalytic

reactions.

CONCLUSION

■

In conclusion, diﬀerent TM units are introduced into trivacant

Keggin POMs to yield tetra-Ni, hexa-Cu, and tetra-Fe

substituted sandwich-type polytungstate derivatives. Synthetic

compounds exhibit better supercapacitor performance than

their parent POMs and most reported POM-based electrode

materials, which suggests that the introduction of multinuclear

transition metal into vacant POMs is an eﬀective method to

improve electrochemical supercapacitor performance of

POMs. In addition, compounds 1 and 3 are potential dual-

functional electrochemical sensing materials and exhibit

excellent catalytic behavior in the reduction of inorganic

iodate and the oxidation of organic biological molecules

dopamine for introduction of {Ni } and {Fe } units. This work

not only enriches the types of sandwich-type POMs but also

provides a useful strategy for enhancing the energy storage

performance and improving the electrocatalytic oxidation

ability of POMs.

Figure 13. Cyclic voltammograms of 1-GCE (a), 2-GCE (b), and 3-

GCE (c) in 0.5 M H SO solution containing IO₃⁻at diﬀerent

concentrations (from top to bottom: bare-GCE, 0, 0.5, 1.0, 1.5 mM;

−

ASSOCIATED CONTENT

sı Supporting Information

The Supporting Information is available free of charge at

https://pubs.acs.org/doi/10.1021/acs.inorgchem.0c00382.

Scan rate: 30 mV·s ). Potentials vs Ag/AgCl. (d) Histogram of the

■

−

CAT vs concentration of IO or DA for 1−3-GCE. (I values of

−

cathodic peak VI for IO and anodic peak I for DA at a scan rate of

−

0 mV·s .)

Experimental Section, structural ﬁgures (Figures S1−

S8), structural data (Tables S1−S5), physical character-

ization (Figures S9−S19), and electrocatalytic reaction

mechanism of 3-GCE (PDF)

the cathode peak current increases correspondingly. In

addition, the same linear relationship between IO₃⁻concen-

tration and cathode peak (II’, III’, and IV’) current indicates

stable and eﬀective electrocatalytic activity of 1-3-GCE for the

−

Accession Codes

reduction of IO . In contrast, no obvious response was

−

observed for the reduction of IO₃and oxidation of DA at a

CCDC 1945872−1945874 contain the supplementary crys-

tallographic data for this paper. These data can be obtained

free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by

emailing data_request@ccdc.cam.ac.uk, or by contacting The

Cambridge Crystallographic Data Centre, 12 Union Road,

Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

bare-GCE without active materials (Figures 12 and 13). The

−

reaction mechanism of 3-GCE on DA and IO₃as a

representative can be deduced and shown in the ﬁve sections

of the Supporting Information.

The catalytic eﬃciencies (CAT) of 1-3-GCE were computed

via the CAT formula. The bar chart of CAT% for 1-3-GCE

vs concentrations of DA or IO₃⁻is shown in Figure 13d. The

order of CAT of 1-3-SCE for iodate reduction and DA

oxidation is 3-GCE > 1-GCE > 2-GCE, which suggests that

the catalytic performance of tetra-Fe substituted arsenotung-

state is better than that of tetra-Ni substituted phosphotung-

state and 6-Cu substituted arsenotungstate. It can be seen from

the comparison results that the implantation of metal

complexes in compounds 2 and 3D structural advantages of

compound 1 are not reﬂected in the electrocatalytic eﬃciency,

which indirectly reﬂects that the diﬀerence in electrocatalytic

performance of three sandwich-type derivatives is mainly

determined by the types of TM sandwich unit. The

electrocatalytic advantage of compound 3 can be attributed

to the higher redox peak position of Fe center and the better

synergistic eﬀect between the mixed valence tetranuclear iron

AUTHOR INFORMATION

Corresponding Authors

■

Kai Yu − Key Laboratory for Photonic and Electronic Bandgap

Materials, Ministry of Education, School of chemistry and

chemical engineering and Key Laboratory of Photochemical

Biomaterials and Energy Storage Material, Heilongjiang

Province, Harbin Normal University, Harbin 150025, P. R.

China; orcid.org/0000-0002-6662-3724 ; Phone: (+86)

0451-88060334; Email: hlyukai188@163.com; Fax: (+86)

451-8806-0653

Jinghua Lv − Key Laboratory for Photonic and Electronic

Bandgap Materials, Ministry of Education, School of chemistry

and chemical engineering, Harbin Normal University, Harbin

150025, P. R. China ; Phone: (+86) 0451-88060334;

Email: wlljh1964@163.com ; Fax: (+86) 451-8806-0653

Baibin Zhou − Key Laboratory for Photonic and Electronic

Bandgap Materials, Ministry of Education, School of chemistry

and chemical engineering and Key Laboratory of Photochemical

Biomaterials and Energy Storage Material, Heilongjiang

Province, Harbin Normal University, Harbin 150025, P. R.

China; orcid.org/0000-0001-8304-5092 ; Phone: (+86)

0451-88060334; Email: zhou_bai_bin@163.com;

Fax: (+86) 451-8806-0653

III

cluster {Fe Fe (H O) } and the W center in the POM

cluster. In summary, compounds 1 and 3 show dual-functional

electrocatalytic behavior for reduction of IO₃⁻assigned to W

centers and oxidation of DA attributed to Ni/Fe centers, which

are new potential bifunctional electrocatalytic sensor materials.

The electrocatalytic stability studies have shown that after 60

cycles, the CVs of reduced IO ₃⁻and oxidized DA have hardly

changed (Figures S18 and S19), which indicates that 1-3-

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Greatly Improved Surface Reactivity for High Performance

Article

Authors

Pseudocapacitors. Adv. Mater. 2017, 29, 1604167−1604174.

Xinyue Ma − Key Laboratory for Photonic and Electronic

Bandgap Materials, Ministry of Education, School of chemistry

and chemical engineering and Key Laboratory of Photochemical

Biomaterials and Energy Storage Material, Heilongjiang

Province, Harbin Normal University, Harbin 150025, P. R.

China

(10) Lin, J.; Liang, H.; Jia, H.; Chen, S.; Guo, J.; Qi, J.; Qu, C.; Cao,

J.; Fei, W.; Feng, J. In situ encapsulated Fe O nanosheet arrays with

graphene layers as an anode for high-performance asymmetric

supercapacitors. J. Mater. Chem. A 2017, 5, 24594−24601.

(11) Dubal, D. P.; Gund, G. S.; Holze, R.; Jadhav, H. S.; Lokhande,

C. D.; Park, C. J. Solution-based binder-free synthetic approach of

Jie Yuan − Harbin Medical University Daqing Campus, Daqing

RuO thin films for all solid state supercapacitors. Electrochim. Acta

63319, Heilongjiang, China

(

013, 103, 103−109.

Liping Cui − Key Laboratory for Photonic and Electronic

Bandgap Materials, Ministry of Education, School of chemistry

and chemical engineering and Key Laboratory of Photochemical

Biomaterials and Energy Storage Material, Heilongjiang

Province, Harbin Normal University, Harbin 150025, P. R.

China

Wenting Dai − Key Laboratory for Photonic and Electronic

Bandgap Materials, Ministry of Education, School of chemistry

and chemical engineering and Key Laboratory of Photochemical

Biomaterials and Energy Storage Material, Heilongjiang

Province, Harbin Normal University, Harbin 150025, P. R.

China

12) Xu, X.; Li, H. L.; Xie, S. S.; Mei, L.; Meng, R. R.; Chen, L. J.;

Zhao, J. W. Double-Oxalate-Bridging Tetralanthanide Containing

Divacant Lindqvist Isopolytungstates with an Energy Transfer

Mechanism and Luminous Color Adjustablility Through Eu /Tb

Codoping. Inorg. Chem. 2020, 59, 648−660.

(13) Li, Y. M.; Li, H. L.; Jiang, J.; Chen, L. J.; Zhao, J. W. Three

Types of Distinguishing l-Alanine-Decorated and Rare-Earth-

Incorporated Arsenotungstate Hybrids Prepared in a Facile One-

Step Assembly Strategy. Inorg. Chem. 2019, 58, 3479−3491.

(14) Wang, Z.; Su, H. F.; Tung, C. H.; Sun, D.; Zheng, L. S.

Deciphering synergetic core-shell transformation from [Mo O @

Ag ] to [Mo O @Ag ]. Nat. Commun. 2018, 9, 4407.

(15) Liu, J. C.; Han, Q.; Chen, L. J.; Zhao, J. W.; Streb, C.; Song, Y.

Complete contact information is available at:

https://pubs.acs.org/10.1021/acs.inorgchem.0c00382

F. Aggregation of Giant Cerium −Bismuth Tungstate Clusters into a

3D Porous Framework with High Proton Conductivity. Angew. Chem.,

Int. Ed. 2018, 57, 8416−8420.

(16) Sun, M.; Zhang, J. Z.; Putaj, P.; Caps, V.; Lefebvre, F.; Pelletier,

Notes

J.; Basset, J. M. Catalytic Oxidation of Light Alkanes (C1 −C4) by

The authors declare no competing ﬁnancial interest.

Heteropoly Compounds. Chem. Rev. 2014, 114, 981−1019.

(17) Li, J. S.; Tang, Y. J.; Liu, C. H.; Li, S. L.; Li, R. H.; Dong, L. Z.;

ACKNOWLEDGMENTS

■

Dai, Z. H.; Bao, J. C.; Lan, Y. Q. Polyoxometalate-based metal −

organic framework-derived hybrid electrocatalysts for highly efficient

hydrogen evolution reaction. J. Mater. Chem. A 2016, 4, 1202−1207.

This work was supported the National Natural Science

Foundation of China (Grants Nos. 21771046 and

(18) Zhang, S. M.; Chen, H. B.; Zhang, G. H.; Kong, X. P.; Yin, S.

1571044) and the Natural Science Foundation of Heilong-

Y.; Li, B.; Wu, L. X. An ultra-small thermosensitive nanocomposite

with a Mo ₁ ₅ ₄ -core as a comprehensive platform for NIR-triggered

photothermal-chemotherapy. J. Mater. Chem. B 2018, 6, 241−248.

jiang Province (JC2016001 and B2017007).

REFERENCES

1) Dubal, D. P.; Ayyad, O.; Ruiz, V.; Gom

energy storage: the merging of battery and supercapacitor chemistries.

■

(19) Schwarz, B.; Forster, J.; Goetz, M. K.; Yucel, D.; Berger, C.;

Jacob, T.; Streb, C. Visible-Light-Driven Water Oxidation by a

ez-Romero, P. Hybrid

Molecular Manganese Vanadium Oxide Cluster. Angew. Chem., Int.

Ed. 2016, 55, 6329−6333.

Chem. Soc. Rev. 2015, 44, 1777−1790.

(20) Ji, Y. C.; Huang, L. J.; Hu, J.; Streb, C.; Song, Y. F.

2) Liu, C.; Li, F.; Ma, L. P.; Cheng, H. M. Advanced Materials for

Energy Storage. Adv. Mater. 2010, 22, E28−E62.

Polyoxometalate- functionalized nanocarbon materials for energy

conversion, energy storage and sensor systems. Energy Environ. Sci.

(

3) Lukatskaya, M. R.; Mashtalir, O.; Ren, C. E.; Agnese, Y. D.;

Rozier, P.; Taberna, P. L.; Naguib, M.; Simon, P.; Barsoum, M. W.;

Gogotsi, Y. Cation Intercalation and High Volumetric Capacitance of

Two-Dimensional Titanium Carbide. Science 2013, 341, 1502−1505.

21) Zhou, W. L.; Peng, J.; Zhang, Z. Y.; Ding, Y. H.; Khan, S. U.

015, 8, 776−789.

Bifunctional electro-catalysts based on the Keggin/Dawson-type

polyoxotungstates and Cu-tris(imidazolyl) complexes. Electrochim.

Acta 2015, 180, 887−893.

4) Zhang, G. X.; Xiao, X.; Li, B.; Gu, P.; Xue, H. G.; Pang, H.

Transition metal oxides with one-dimensional/one-dimensional-

analogue nanostructures for advanced supercapacitors. J. Mater.

Chem. A 2017, 5, 8155−8186.

(

22) Cuentas-Gallegos, A. K.; Martínez-Rosales, R.; Baibarac, M.;

Gom

ez-Romero, P.; Rincon, M. E. Electrochemical supercapacitors

5) Zuo, W. H.; Li, R. Z.; Zhou, C.; Li, Y. Y.; Xia, J. L.; Liu, J. P.

based on novel hybrid materials made of carbon nanotubes and

Battery-supercapacitor hybrid devices: recent progress and future

prospects. Adv. Sci. 2017, 4, 1600539.

polyoxometalates. Electrochem. Commun. 2007, 9, 2088−2092.

23) Ruiz, V.; Suarez-Guevara, J.; Gomez-Romero, P. Hybrid

(

6) Zhu, Y. W.; Murali, S.; Stoller, M. D.; Ganesh, K. J.; Cai, W. W.;

electrodes based on polyoxometalate −carbon materials for electro-

Ferreira, P. J.; Pirkle, A.; Wallace, R. M.; Cychosz, K. A.; Thommes,

M.; Su, D.; Stach, E. A.; Ruff, R. S. Carbon-based supercapacitors

produced by activation of graphene. Science 2011, 332, 1537−1541.

chemical supercapacitors. Electrochem. Commun. 2012, 24, 35 −38.

(24) Cui, Z. M.; Guo, C. X.; Yuan, W. Y.; Li, C. M. In situ

synthesized heteropoly acid/polyaniline/ graphene nanocomposites

to simultaneously boost both double layer-and pseudo-capacitance for

supercapacitors. Phys. Chem. Chem. Phys. 2012, 14, 12823−12828.

(

7) Yang, M.; Hong, S. B.; Yoon, J. H.; Kim, D. S.; Jeong, S. W.; Yoo,

D. E.; Lee, T. J.; Lee, K. G.; Lee, S. J.; Choi, B. G. Fabrication of

Flexible, Redoxable, and Conductive Nanopillar Arrays with

Enhanced Electrochemical Performance. ACS Appl. Mater. Interfaces

(25) Yang, M. H.; Choi, B. G.; Jung, S. C.; Han, Y. K.; Huh, Y. S.;

Lee, S. B. Polyoxometalate-coupled Graphene via Polymeric Ionic

Liquid Linker for Supercapacitors. Adv. Funct. Mater. 2014, 24, 7301−

7309.

(26) Dong, Y. N.; Chen, L.; Chen, W. L.; Zheng, X. T.; Wang, X. L.;

Wang, E. B.; GO, r. Functionalized with a Highly Electronegative

Keplerate-Type Polyoxometalate for High-Energy-Density Aqueous

Asymmetric Supercapacitors. Chem. - Asian J. 2018, 13, 3304−3313.

8) Chen, Y.; Han, M.; Tang, Y.; Bao, J.; Li, S.; Lan, Y.; Dai, Z.

016, 8, 22220−22226.

Polypyrrole −polyoxometalate/reduced graphene oxide ternary nano-

hybrids for flexible, all-solid-state supercapacitors. Chem. Commun.

9) Zhai, T.; Wan, L.; Sun, S.; Chen, Q.; Sun, J.; Xia, Q.; Xia, H.

015, 51, 12377−12380.

Phosphate Ion Functionalized Co O Ultrathin Nanosheets with

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

27) Li, D. D.; Ma, P. T.; Niu, J. Y.; Wang, J. P. Recent advances in

(42) Sartorel, A.; Carraro, M.; Scorrano, G.; Bassil, B. S.; Dickman,

M. H.; Keita, B.; Nadjo, L.; Kortz, U.; Bonchio, M. Iron-Substituted

Polyoxotungstates as Inorganic Synzymes: Evidence for a Biomimetic

Pathway in the Catalytic Oxygenation of Catechols. Chem. - Eur. J.

2009, 15, 7854−7858.

transition-metal-containing Keggin-type polyoxometalate-based coor-

dination polymers. Coord. Chem. Rev. 2019, 392, 49−80.

(

Z. M.; Lan, Y. Q. A highly stable polyoxometalate-based metal-organic

framework with an ABW zeolite-like structure. Chem. Commun. 2017,

28) Li, X. X.; Shen, F. C.; Liu, J.; Li, S. L.; Dong, L. Z.; Fu, Q.; Su,

(43) Zheng, S. T.; Yang, G. Y. Recent advances in paramagnetic-

TM-substituted polyoxometalates (TM = Mn, Fe, Co, Ni, Cu). Chem.

Soc. Rev. 2012, 41, 7623−7646.

29) Wang, G. N.; Chen, T. T.; Li, S. B.; Pang, H. J.; Ma, H. Y. A

3, 10054−10057.

coordination polymer based on dinuclear (pyrazinyl tetrazolate)

copper(II) cations and Wells-Dawson anions for high-performance

supercapacitor electrodes. Dalton Trans. 2017, 46, 13897−13902.

(44) Li, B.; Zhao, J. W.; Zheng, S. T.; Yang, G. Y. Combination

Chemistry of Hexa-Copper-Substituted Polyoxometalates Driven by

II ‑

the Cu Polyhedra Distortion: From Tetramer, 1D Chain to 3D

(

30) Du, N. N.; Gong, L. G.; Fan, L. Y.; Yu, K.; Luo, H.; Pang, S. J.;

Framework. Inorg. Chem. 2009, 48, 8294−8303.

45) Mialane, P.; Marrot, J.; Riviere, E.; Nebout, J.; Herve, G.

Gao, J. Q.; Zheng, Z. W.; Lv, J. H.; Zhou, B. B. Nanocomposites

Containing Keggin Anions Anchored on Pyrazine-Based Frameworks

for Use as Supercapacitors and Photocatalysts. ACS Appl. Nano Mater.

Structural Characterization and Magnetic Properties of Sandwich-

Type Tungstoarsenate Complexes. Study of a Mixed-Valent V 2^/^V

Heteropolyanion. Inorg. Chem. 2001, 40, 44−48.

(

019, 2, 3039−3049.

(46) Kortz, U.; Nellutla, S.; Stowe, A. C.; Dalal, N. S.; Rauwald, U.;

31) (a) Chai, D. F.; Hou, Y.; O ’Halloran, K. P.; Pang, H. J.; Ma, H.

Danquah, W.; Ravot, D. Sandwich-Type Germanotungstates:

Y.; Wang, G. N.; Wang, X. M. Enhancing Energy Storage via TEA-

Dependent Controlled Syntheses: Two Series of Polyoxometalate-

Based Inorganic-Organic Hybrids and their Supercapacitor. Chem-

ElectroChem 2018, 5, 3443−3450. (b) Chai, D. F.; Xin, J. J.; Li, B.;

Pang, H. J.; Ma, H. Y.; Li, K. Q.; Xiao, B. X.; Wang, X. M.; Tan, L. C.

Mo-based crystal POMOFs with high electrochemical capacitor

performance. Dalton Trans. 2019, 48, 13026−13033.

Structure and Magnetic Properties of the Dimeric Polyoxoanions

2 ‑

[

M (H O) (GeW O ) ] (M = Mn , Cu , Zn , Cd ). Inorg.

4 2 2 9 34 2

Chem. 2004, 43, 2308−2317.

(47) Zhao, J. W.; Shi, D. Y.; Chen, L. J.; Cai, X. M.; Wang, Z. Q.;

Ma, P. T.; Wang, J. P.; Niu, J. Y. Two organic −inorganic hybrid 1-D

and 3-D polyoxotungstates constructed from hexa-Cu substituted

sandwich-type arsenotungstate units. CrystEngComm 2012, 14, 2797−

(

32) Roy, S.; Vemuri, V.; Maiti, S.; Manoj, K. S.; Subbarao, U.;

(

806.

Peter, S. C. Two Keggin-Based Isostructural POMOF Hybrids:

Synthesis, Crystal Structure, and Catalytic Properties. Inorg. Chem.

48) Lisnard, L.; Mialane, P.; Dolbecq, A.; Marrot, J.; Clemente-

Juan, J. M.; Coronado, E.; Coronado, B.; Oliveira, P. D.; Nadjo, L.;

SEcheresse, F. Effect of Cyanato, Azido, Carboxylato, and Carbonato

Ligands on the Formation of Cobalt (II) Polyoxometalates:

Characterization, Magnetic, and Electrochemical Studies of Multi-

nuclear Cobalt Clusters. Chem. - Eur. J. 2007, 13, 3525−3536.

(

018, 57, 12078−12092.

33) Chai, D. F.; Gomez-García, C. J.; Li, B.; Pang, H. J.; Ma, H. Y.;

Wang, X. M.; Tan, L. C. Polyoxometalate-based metal-organic

frameworks for boosting electrochemical capacitor performance.

Chem. Eng. J. 2019, 373, 587−597.

(49) Zhang, Z. M.; Li, Y. G.; Wang, E. B.; Wang, X. L.; Qin, C.; An,

34) Wang, K. P.; Yu, K.; Lv, J. H.; Zhang, M. L.; Meng, F. X.; Zhou,

H. Y. Synthesis, Characterization, and Crystal Structures of Two

Novel High-Nuclear Nickel-Substituted Dimeric Polyoxometalates.

Inorg. Chem. 2006, 45, 4313−4315.

B. B. A Host −Guest Supercapacitor Electrode Material Based on a

Mixed Hexa-Transition Metal Sandwiched Arsenotungstate Chain

and Three-Dimensional Supramolecular Metal −Organic Networks

with One-Dimensional Cavities. Inorg. Chem. 2019, 58, 7947−7957.

(50) Al-Oweini, R.; Bassil, B. S.; Palden, T.; Keita, B.; Lan, Y. H.;

Powell, A. K.; Kortz, U. The manganese(III)-containing tungstophos-

35) Wang, G. N.; Wang, T. T.; Wang, X. M.; Ma, H. Y.; Pang, H. J.

III

9 ‑

phate [Mn (H O) (A-a-PW O ) ] . Polyhedron 2013, 52, 461−

34 2

High-Performance Supercapacitor Afforded by a High-Connected

Keggin-Based 3D Coordination Polymer. Eur. J. Inorg. Chem. 2017,

466.

(51) Zhao, H. X.; Tao, L.; Zhang, F. M.; Zhang, Y.; Liu, Y. Q.; Xu,

36) Du, X. Q.; Ding, Y.; Song, F. Y.; Ma, B. C.; Zhao, J. W.; Song, J.

017, 5350−5355.

Efficient photocatalytic water oxidation catalyzed by polyoxometalate

H. J.; Diao, G. W.; Ni, L. B. Transition Metal Substituted Sandwich-

Type Polyoxometalates with Strong Metal −C(imidazole) Bond as

Anticancer Agents. Chem. Commun. 2019, 55, 1096 −1099.

7 −

[

Fe (H O) (OH) (W O ) (α -SbW O ) ]

based on abundant

metals. Chem. Commun. 2015, 51, 13925−13928.

37) Du, X. Q.; Zhao, J. L.; Mi, J. Q.; Ding, Y.; Zhou, P. P.; Ma, B.

33 6 2

(52) Karimian, D.; Yadollahi, B.; Mirkhani, V. Dual functional

hybrid- polyoxometalate as a new approach for multidrug delivery.

Microporous Mesoporous Mater. 2017, 247, 23−30.

(

^C ^.^;^Z ^h ^a ^o ^,^J ^.^W ^.^;^S ^o ⁿ ^g ^,^J ^.^E ^f ^f ⁱ ^c ⁱ ^e ⁿ ^t ^p ^h ^o ^t ^o ^c ^a ^t ^a ^l ^y ^t ⁱ ^c ^H 2 evolution

catalyzed by an unprecedented robust molecular semiconductor

Fe } nanocluster without cocatalysts at neutral conditions. Nano

Energy 2015, 16, 247−255.

(

(53) Wang, L.; Yu, K.; Zhu, J.; Zhou, B. B.; Liu, J. R.; Yang, G. Y.

Inhibitory effects of different substituted transition metal-based krebs-

type sandwich structures on human hepatocellular carcinoma cells.

Dalton Trans. 2017, 46, 2874−2883.

{

38) Huang, Z. Q.; Luo, Z.; Geletii, Y. V.; Vickers, J. W.; Yin, Q. S.;

(54) Wang, L.; Zhou, B. B.; Yu, K.; Su, Z. H.; Gao, S.; Chu, L. L.;

Wu, D.; Hou, Y.; Ding, Y.; Song, J.; Musaev, D. G.; Hill, C. L.; Lian,

T. Q. Efficient Light-Driven Carbon-Free Cobalt-Based Molecular

Catalyst for Water Oxidation. J. Am. Chem. Soc. 2011, 133, 2068−

Liu, J. R.; Yang, G. Y. Novel Antitumor Agent, Trilacunary Keggin-

Type Tungstobismuthate, Inhibits Proliferation and Induces

Apoptosis in Human Gastric Cancer SGC-7901 Cells. Inorg. Chem.

(

071.

39) Car, P. E.; Guttentag, M.; Baldridge, K. K.; Alberto, R.; Patzke,

55) Zhao, Z. F.; Zhou, B. B.; Zheng, S. T.; Su, Z. H.; Wang, C. M.

013, 52, 5119−5127.

G. R. Synthesis and characterization of open and sandwich-type

polyoxometalates reveals visible-light-driven water oxidation via

POM-photosensitizer. Green Chem. 2012, 14, 1680−1688.

Hydrothermal synthesis, crystal structure and magnetic character-

ization of three hexa-M substituted tungstoarsenates (M = Ni, Zn and

Mn). Inorg. Chim. Acta 2009, 362 , 5038 −5042.

40) Yu, L.; Du, X. Q.; Ding, Y.; Chen, H. L.; Zhou, P. P. Efficient

(56) Brown, I. D.; Altermatt, D. Bond-valence parameters obtained

from a systematic analysis of the inorganic crystal structure database.

Acta Crystallogr., Sect. B: Struct. Sci. 1985, B41, 244−247.

visible light-driven water oxidation catalyzed by an all-inorganic

copper-containing polyoxometalate. Chem. Commun. 2015, 51,

(

7443−17446.

(57) Muller, A.; Shah, S. Q. N.; Bogge, H.; Schmidtmann, M.

41) Vickers, J. W.; Lv, H. J.; Sumliner, J. M.; Zhu, G.; Luo, Z.;

Molecular growth from a Mo to a Mo cluster. Nature 1999, 397,

176 248

Musaev, D. G.; Geletii, Y. V.; Hill, C. L. Differentiating Homogeneous

and Heterogeneous Water Oxidation Catalysis: Confirmation that

48−50.

(58) Zhang, Y. P.; Li, L. L.; Sun, T.; Liu, B.; Hu, H. M.; Xue, G. L. A

10 ‑

11 ‑

[

Co (H O) (α -PW O ) ]

Is a Molecular Water Oxidation

Cagelike Polyanion with a Ag Enwrapped, [AgAs Mo O ] . Inorg.

2 15 54

Catalyst. J. Am. Chem. Soc. 2013, 135, 14110−14118.

Chem. 2011, 50, 2613−2618.

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Xue, G. L. An unusual fan-type polyanion with a silver cation located

Article

(

59) Ma, Y.; Xue, Q.; Min, S. T.; Zhang, Y. P.; Hu, H. M.; Gao, S. L.;

III

11 ‑

at the axial center, [AgAs (As As Mo O (OH) ) ] . Dalton

2 3

Trans. 2013, 42, 3410−3416.

(

60) Biesinger, M. C.; Payne, B. P.; Grosvenor, A. P.; Lau, L. W. M.;

Gerson, A. R.; Smart, R. S. C. Resolving surface chemical states in

XPS analysis of first row transition metals, oxides and hydroxides: Cr,

Mn, Fe, Co and Ni. Appl. Surf. Sci. 2011, 257, 2717−2730.

(

61) Sha, J. Q.; Liang, L. Y.; Sun, J. W.; Tian, A. X.; Yan, P. F.; Li, G.

M.; Wang, C. Significant Surface Modification of Polyoxometalate by

Smart Silver-tetrazolate Units. Cryst. Growth Des. 2012, 12, 894 −901.

62) Wang, X. L.; Luan, J.; Lin, H. Y.; Xu, C.; Liu, G. C. Three

multifunctional three-dimensional metal −organic frameworks based

on a flexible N,N ′-bis(3- pyridinecarboxamide)-1,6-hexane and 3-

nitrophthalate: Syntheses, structures and properties. Inorg. Chim. Acta

(

013, 408, 139−144.

63) Fu, H.; Li, Y. G.; Lu, Y.; Chen, W. L.; Wu, Q.; Meng, J. X.;

Wang, X. L.; Zhang, Z. M.; Wang, E. B. Polyoxometalate-Based Metal-

Organic Frameworks Assembled under the Ionothermal Conditions.

Cryst. Growth Des. 2011, 11, 458−465.

64) Zhang, C. D.; Sun, C. Y.; Liu, S. X.; Ji, H. M.; Su, Z. M. An

equatorial tri-iron substituted Wells −Dawson type tungstophosphate

with magnetic and bifunctional electrocatalytic properties. Inorg.

Chim. Acta 2010, 363, 718−722.

65) Fu, W.; Wang, Y.; Han, W.; Zhang, Z.; Zhang, H.; Xie, E.

Construction of hierarchical ZnCo O @NixCo (OH) core/shell

nanowire arrays for high-performance supercapacitors. J. Mater. Chem.

A 2016, 4, 173−182.

66) Cheng, H. M.; Qiu, H. X.; Zhu, Z. W.; Li, M.; Shi, Z.

Investigation of the electrochemical behavior of dopamine at

electrodes modified with ferrocene-filled double-walled carbon

nanotubes. Electrochim. Acta 2012, 63, 83−88.

(

67) Yu, Y.; Ma, H. Y.; Pang, H. J.; Li, S. B.; Yu, T. T.; Liu, H.; Zhao,

C. Y.; Zhang, Z. F. Two novel zipper-like compounds of the usual and

bivanadyl capped Keggin clusters connected by propeller-shaped

complexes. New J. Chem. 2014, 38, 1271−1276.

68) Li, C. X.; Zhang, Y.; O ’Halloran, K. P.; Ma, H. Y.

Electrochemical behavior of an inorganic −organic hybrid based on

isopolymolybdate anions and ethylenediamine. J. Appl. Electrochem.

2009, 39, 1011−1015.