S1

Supporting InformationA comprehensive approach providing a new synthetic route for bimetallic electrocatalysts via isopoly POMs [M/Rh(Cp*)4W8O32] (M = Rh(1) and Ir(2)

Vikram Singh,a Pengtao Ma,a Michael G. B. Drew,b Jingping Wang,*a Jingyang Niu*a

[a] Henan Key Laboratory of Polyoxometalate Chemistry, Institute of Molecular and Crystal Engineering, College of Chemistry and Chemical Engineering, Henan University, Kaifeng, Henan 475004 (P.R. China)[b] Department of Chemistry, The University of Reading, Whiteknights, Reading RG6 6 AD, U.K.

E-mail: jyniu@henu.edu.cn

Experimental

1. 1 Materials and Methods

1. 2 Single Crystal X-ray Crystallography

Table S1. Crystallographic parameters for complexes 1 and 2.

Table S2. Molecular dimensions, (distances, Å, angles deg) in 1 and 2.

Table S3. BVS calculations for 1 and 2.

Figure S1. ESI-MS spectra of compound 1 at different pH.

Figure S2. ESI-MS spectra of compound 2 at different pH.

Figure S3. 1H NMR of cluster 1 in CDCl3 at room temperature.

Figure S4. 13C NMR of cluster 1 in CDCl3 at room temperature.

Figure S5. 1H NMR of cluster 2 in CDCl3 at room temperature.

Figure S6. 13C NMR of cluster 2 in CDCl3 at room temperature.

Figure S7. Ball-stick and Polyhedral representation of 1.

Figure S8. (a) Intermolecular n∙∙∙π* interactions from the lone pair electrons of oxygen and the

π-electrons of methylcyclopentadiene rings in 2. (b) Wave like supramolecular network in 2.

Electronic Supplementary Material (ESI) for Dalton Transactions.This journal is © The Royal Society of Chemistry 2018

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Table S4. HER performance of some recently reported electrocatalyst @ NFs in different electrolytes.

Figure S 9. (a-f) SEM images of nanostructured 2 @ NF at different magnifications (g-j) EDX elemental mapping images of cross-sectional area of POM nanostructured surface 2 @ NF.

Figure S10. PXRD, IR and Raman spectra of 2 and 2 @ NF.

Figure S11. PXRD of derived nanohybrid materials 3 and 4.

Figure S12. (a) Rh 3d. (b)W4f and (c)Ni 3p xps spectra of 3.

Figure S13. (a, b) SEM and EDX of 3. (c-h) TEM at various cross-sectional areas and elemental mapping images of 3.

Figure S14. LSV changes of POM @ NFs (1 and 2) during 30 h of electrolysis at 1 M KOH

solution respectively.

Figure S15. PXRD of extracted samples, POM @ NFs (1 and 2) at various temperatures to their final conversion to 3 and 4.

Figure 16. ESI-MS spectra of cluster 1.

Figure S17. ESI-MS spectra of cluster 2.

Table S5. Peak assignments of the fragmented polyanion in the negative mode mass spectrum of

1 and 2.

Figure S 18. UV-Vis. spectra of 1 and 2 at 1 x 10-4 M aqueous solution.

Figure S 19.TGA curve of 1 and 2.

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Experimental

1.1 Materials and Methods. All chemical reagents were purchased from commercial sources

and used as such without any purification. Powder X-ray diffraction (PXRD) patterns were

recorded on a Bruker D8 ADVANCE diffractometer with Cu Kα ( = 1.54056 Å). The FT-

IR spectra were performed in the range 4000−450 cm−1 using KBr pellets on a Bruker

VERTEX 70 IR spectrometer. The C and H elemental analyses were obtained with a

PerkinElmer 2400−II CHNS/O elemental analyzer. Metal element analysis was conducted on

a PerkinElmer Optima 2100 DV inductively coupled plasma optical emission spectrometer.

Electrospray ionization mass spectrometric (ESI-MS) measurements were performed on an

AB SCIEX TRIPLE TOF spectrometer. For obtaining ESI-MS data, 10 μL samples were

dissolved in water and introduced into the ESI source through a Finningan surveyor auto

sampler. Mobile phase (H2O), flowed at a rate of 5 μL/min. The MS scans were run up to 2.5

min, and spectra obtained are averages of 8-10 scans. Electrochemical measurements were

made on a CHI 620c electrochemical analyzer. Corresponding work voltage and current is 40

kV and 100 mA, respectively. The morphology of the reduced hybrid product 3 and 4 was

confirmed by a high-resolution transmission electron microscope (HR-TEM, JEM-2100) at

an acceleration voltage of 200 kV. Raman scattering was collected on a Renishaw RW1000

confocal microscope with 514 nm line of Ar+ iron laser as the exciting light. Morphology

analysis was conducted on a scanning electron microscope (SEM, JSM-7600F) at an

acceleration voltage of 10 kV. Thermogravimetric-mass (TG-MS) analyses of the samples

were performed at the instrument NETZSCH STA 449 F5 analyzer. The samples were

observed in the temperature range of 30 to 1200 °C under nitrogen flow at the heating rate of

10 °C·min−1. The UV-Vis. absorption spectra were measured from 200 to 800 nm in 1 х 10-4

M aqueous solution on Hitachi UV-vis. spectrophotometer at room temperature. Elemental

mapping and energy dispersive X-ray spectroscopy (EDS) were recorded using JSM-5160

LV-Vantage typed energy spectrometer. The BET surface areas of the samples were tested

using a surface area and porosity analyzer (ASAP 2010). X-ray photoelectron spectroscopy

(XPS) was collected on scanning X-ray microprobe (PHI 5000 Verasa, ULAC-PHI, Inc.).

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1. 2. Single Crystal X-ray Crystallography

The X-ray data were collected on a Bruker Apex-II CCD diffractometer at 296(2) K with MoKα

monochromated radiation (λ= 0.71073 Å). The structures were solved using direct methods with

the Shelxs 97 program. The non-hydrogen atoms were refined with anisotropic thermal

parameters. The hydrogen atoms bonded to carbon were included in geometric positions and

given thermal parameters equivalent to 1.2 times those of the atom to which they were attached.

The hydrogen atoms on the water molecules were not located. The majority of water molecules

in the two structures were refined with reduced occupancy.The structures were refined using

Shelxl16-6 on F2.From the O…O distances it was likely that there were many hydrogen bonds

between water molecules though the hydrogen atoms could not be located. It was noticeable

however that there were very few close O…O distances between the water molecules and the

clusters in either structure. Details of the crystallographic data are summarized in Table S1 with

molecular dimensions in Table S2.

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Table S1. Crystallographic parameters for complexes 1 and 2.

Compound 1 2

Chemical formula C40H100O52Rh4W8 C40H104Ir4O55W8

Formula weight 3295.64 3704.82

Crystal system Monoclinic Monoclinic

Space group P21/n P21/n

a(Å) 12.461(2) 12.685(3)

b (Å) 15.509(3) 15.825(4)

c (Å) 22.269(4) 22.113(5)

Β 99.352(3) 94.964(4)

V (Å3) 4246.3(14) 4422.2(18)

Z 2 2

ρcalc(g cm-3) 2.578 2.782

µ (Mo Kα) (mm-1) 1632 16.44

F(000) 3056 3368

Reflections collected 25416 22662

Independent reflections 9603 7976

Reflections with I > 2σ(I) 7495 4701

Final indices[I>2σ(I) ]

R1, wR2

0.0403, 0.1017 0.05954, 0.1325

R1],wR2[ [all data] 0.0599, 0.1086 0..1204, 0.1535

GOF c 1.074 0.0911

Residual electron

Density, e/Å-3

1.862, -1.467 2.465, -2.704

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Table S 2. Molecular dimensions, (distances, Å, angles deg) in 1 and 2.

Compound 1 2

M=Rh M=Ir

W1-O13 1.704(7) 1.724(14)

W1-O6 1.726(8) 1.702(14)

W1-O3 1.935(6) 1.944(12)

W1-O15$1 1.960(6) 1.961(14)

W1-O9$1 2.123(6) 2.139(14)

W1-O10 2.140(6) 2.220(14)

W2-O2 1.728(7) 1.706(13)

W2-O12 1.773(7) 1.771(14)

W2-O15 1.849(6) 1.888(14)

W2-O4 1.995(6) 2.022(13)

W2-O1 2.052(6) 2.047(13)

W2-O7 2.190(6) 2.229(13)

W3-O16 1.731(6) 1.751(14)

W3-O11 1.760(7) 1.764(14)

W3-O3 1.867(7) 1.887(13)

W3-O4 2.009(6) 2.022(13)

W3-O8 2,055(6) 2.074(13)

W3-O7 2.208(6) 2.243(13)

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W4-O5 1.722(7) 1.722(14)

W4-O10 1.818(6) 1.801(14)

W4-O9 1.803(6) 1.821(13)

W4-O8 2.018(6) 2.053(13)

W4-O1 2.010(6) 2.063(13)

W4-O7 2.272(6) 2.259(12)

M6-O4 2.123(6) 2.145(14)

M6-O8 2.110(6) 2.135(14)

M6-O1 2.094(6) 2.138(12)

M6-C39 2.122(11) 2.12(2)

M6-C24 2.094(11) 2.13(2)

M6-C20 2.112(10) 2.13(2)

M6-C21 2.122(10) 2.17(2)

M6-C25 2.107(12) 2.18(2)

M5-O12 2.113(6) 2.116(15)

M5-O11 2.101(7) 2.111(15)

M5-O14 2.162(7) 2.167(13)

M5-C26 2.110(10) 2.11(2)

M5-C23 2.096(11) 2.08(2)

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M5-C30 2.087(10) 2.13(2)

M5-C32 2.106(10) 2.15(3)

M5-C35 2.088(10) 2.12(2)

O13-W1-O6 101.3(4) 102.1(7)

O13-W1-O3 96.6(3) 96.6(6)

O6-W1-O3 96.5(3) 95.9(6)

O13-W1-O15$1 95.0(3) 95.1(6)

O6-W1-O15$1 94.1(3) 94.3(6)

O3-W1-O15$1 162.4(3) 162.1(5)

O13-W1-O9$1 88.7(3) 89.2(6)

O6-W1-O9$1 169.8(3) 168.1(6)

O3-W1-O9$1 84.2(3) 84.4(5)

O15$1-W1-O9$1 82.9(3) 82.1(5)

O13-W1-O10 168.6(3) 168.0(6)

O6-W1-O10 90.0(3) 89.84(6)

O3-W1-O10 83.9(2) 83.8(5)

O15$1-W1-O10 82.1(2) 82.1(6)

O9$1-W1-O10 80.0(2) 78.9(5)

O2-W2-O12 103.4(3) 104.2(7)

O2-W2-O15 101.5(3) 102.3(7)

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O12-W2-O15 97.9(3) 99.8(6)

O2-W2-O4 99.8(3) 99.4(6)

O12-W2-O4 90.4(3) 89.2(6)

O15-W2-O4 154.6(3) 153.6(6)

O2-W2-O1 93.8(3) 94.0(6)

O12-W2-O1 160.5(3) 158.4(6)

O15-W2-O1 87.4(3) 87.3(5)

O4-W2-O1 77.5(2) 76.3(5)

O2-W2-O7 166.1(3) 166.1(6)

O12-W2-O7 88.7(3) 87.6(6)

O15-W2-O7 83.2(2) 82.6(5)

O4-W2-O7 73.0(2) 73.0(5)

O1-W2-O7 73.2(2) 73.0(5)

O16-W3-O11 103.4(3) 104.2(7)

O16-W3-O3 103.1(3) 102.6(7)

O11-W3-O3 98.5(3) 99.5(6)

O16-W3-O4 99.4(3) 99.2(7)

O11-W3-O4 88.7(3) 88.3(6)

O3-W3-O4 154.0(2) 154.1(5)

O16-W3-O8 94.8(3) 95.7(6)

O11-W3-O8 158.8(3) 157.0(6)

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O3-W3-O8 87.6(3) 87.0(6)

O4-W3-O8 77.6(2) 77.1(6)

O16-W3-O7 166.6(3) 167.1(6)

O11-W3-O7 87.3(3) 85.9(5)

O3-W3-O7 83.1(2) 83.3(5)

O4-W3-O7 72.4(2) 72.7(5)

O8-W3-O7 73.2(2) 73.0(5)

O5-W4-O10 102.4(3) 102.8(6)

O5-W4-O9 103.1(3) 104.0(6)

O10-W4-O9 98.0(3) 97.2(7)

O5-W4-O8 99.3(3) 97.7(6)

O10-W4-O8 87.2(3) 89.0(6)

O9-W4-O8 155.2(3) 155.4(6)

O5-W4-O1 98.2(3) 97.7(6)

O10-W4-O1 156.4(3) 156.5(6)

O9-W4-O1 88.4(3) 88.3(6)

O8-W4-O1 78.1(2) 77.3(5)

O5-W4-O7 168.3(3) 167.5(6)

O10-W4-O7 85.8(2) 85.7(6)

O9-W4-O7 83.7(3) 83.7(5)

O8-W4-O7 72.5(2) 73.0(5)

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O1-W4-O7 72.3(2) 72.1(5)

O4-M6-O8 74.0(2) 73.2(5)

O4-M6-O1 73.8(2) 71.9(5)

O1-M6-O8 74.1(2) 73.9(5)

O12-M5-O11 85.3(2) 81.7(5)

O12-M5-O14 86.1(3) 83.4(6)

O11-M5-O14 86.2(3) 83.2(6)

$1 Symmetry element 1-x, 1-y, -z

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Table S3. BVS calculations for 1.

Rh5 2.22 O3 1.87 O11 1.77Rh6 2.24 O4 1.80 O12 2.16W4 6.77 O5 2.11 O13 1.68W7 6.24 O6 2.02 O14 1.59W2 6.22 O7 1.69 O15 1.80W3 6.40 O8 1.32O1 1.85 O9 1.32O2 1.96 O10 2.11

for 2

Ir5 2.68 O1 1.94 O10 1.87Ir6 2.65 O2 1.78 O11 2.103W1 6.23 O3 2.02 O12 2.10W2 5.93 O4 2.07 O13 1.67W3 6.09 O5 1.69 O14 0.52W4 6.28 O6 1.69 O15 2.04

O7 2.55 O16 1.59O8 1.90O9 1.86

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Figure S1. ESI-MS spectra of compound 1 at different pH.

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Figure S2. ESI-MS spectra of compound 2 at different pH.

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Figure S3. 1H NMR of cluster 1 in CDCl3 at room temperature.

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Figure S4. 13C NMR of cluster 1 in CDCl3 at room temperature.

S17

Figure S5. 1H NMR of cluster 2 in CDCl3 at room temperature.

S18

Figure S6. 13C NMR of cluster 2 in CDCl3 at room temperature.

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Figure S7. Ball-stick and Polyhedral representation of 1; Rhodium located at the corner of the

quasi-cubane structural core. Rh Orange, W blue, C black, O red. Hydrogen atoms not shown for

clarity. Solvent water molecules are also omitted.

Figure S8. (a) Intermolecular n∙∙∙π* interactions from the lone pair electrons of oxygen and the

π-electrons of methylcyclopentadiene rings in 2; (b) building wave like supramolecular network.

Ir green, W blue, C black, O red, H grey.

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Table S4. HER performance of some recently reported electrocatalyst @ NFs in different electrolytes.

Catalysts Electrolyte Overpotential (mV) @ 10

mAcm-2

Tafel Slope (mV dec-1) Reference

Ni0.6Ir0.4/WO3/NF 1M KOH 35 34 This work

Ni0.6Rh0.4/WO3/NF 1M KOH 67 56 This work

NiW/NF 1 M KOH 36 43 1

NiSe/NF 1 M KOH 80 50 2

WO3-x/NF 1 M KOH 175 110 3

Ir/MoO2/NF 1 M KOH 70 42 4

Rh/MoO2/NF 1 M KOH 125 63 4

W-doped NixP/NF 1 M KOH 160 @ 20 98 5

Ni59W41 1 M KOH 122 @ 20 5

Ni8P3/NF 1 M KOH 130 58.5 6

NiCo2S4/NF 1 M KOH 248 56.8 7

NiFe LDH/NF 1 M KOH 225 48.7 7

NiW-1/Cu 0.5 M

H2SO4

85 @1 43 8

W-30 CNF

W-20 CNF

W-10 CNF

0.5 M

H2SO4

185

227

300

89

121

110

9

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Figure S 9. (a-f) SEM images of nanostructured 2 @ NF at different magnifications (g-j) EDX

elemental mapping images of cross-sectional area of POM nanostructured surface 2 @ NF.

Figure S10. (a) PXRD, (b) IR and (c) Raman spectra of 2 and 2 @ NF.

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Figure S11. PXRD of derived nanohybrid materials 3 and 4.

Figure S12. (a) Rh 3d. (b) W4f and (c) Ni 3p xps spectra of 3.

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Figure S13. (a, b) SEM and EDX of 3. (c-h) TEM at various cross-sectional areas and elemental mapping images of 3.

Figure S14. LSV changes of POM @ NFs (1 and 2) during 30 h of electrolysis at 1 M KOH

solution respectively.

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Figure S15. PXRD of extracted samples, POM @ NFs (1 and 2) at various temperatures to their final conversion to 3 and 4.

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1.3 ESI-MS

ESI-MS studies have been extremely helpful in an attempt to establish the exact

composition and protonation phenomenon in POMs, as well as to investigate the

existence of other relatively stable species in the solution. The ESI mass spectra of 1 and

2 (Figs S16 and S17) were recorded in aqueous solution.

Figure 16. ESI-MS spectra of cluster 1.

Clusters 1 and 2 show prominent envelopes at (3140.45, 3104.36 and 3068.39) and

(3497.69, 3461.65 and 3425.63) which establishes the solution stability of polyanionic

frameworks in 1 and 2 respectively (Table S5) and thus indicates that the two

isomorphous cluster compounds remains intact in solution in similar anionic fragments

but slightly differs in their degrees of hydration.

Furthermore, ESI-MS were also tested at variable pH condition which shows the same

fragmentation patterns, thus the two structures are quite stable in wide pH range in

aqueous medium.

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Figure S17. ESI-MS spectra of cluster 2.

Table S5. Peak assignments of the fragmented polyanion in the negative mode mass spectrum of

1 and 2.

1.4 Electrochemical measurements

Obsd. m/z Calcd. m/z charge Polyanion

3140.62 3140.45 -1 [H7(Cp*Rh)4W8O32]·11H2O (1)

3104.55 3104.45 -1 [H7(Cp*Rh)4W8O32]·9H2O (1)

3068.49 3068.39 -1 [H7(Cp*Rh)4W8O32]·7H2O (1)

3497.81 3497.69 -1 [H7(Cp*Ir)4W8O32]·11H2O (2)

3461.78 3461.65 -1 [H7(Cp*Ir)4W8O32]·9H2O (2)

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Electrochemical measurements were performed with a BAS100B electrochemical

workstation. A three-electrode configuration at room temperature was used, in which

POM @ NFs (1 and 2), 3 and 4, Pt and Hg/Hg2Cl2 (saturated KCl-filled) were used as the

work electrode, the counter electrode and the reference electrode, respectively. All the

potentials were recorded with respect to the reversible hydrogen electrode (RHE). A

platinum gauze electrode and a saturated calomel electrode (SCE) served as the counter

electrode and the reference electrode, respectively. Potentials were referenced to a

reversible hydrogen electrode (RHE): E (RHE) = E(SCE) + 0.242 + 0.059pH, after

calibration. Linear sweep voltammetry (LSV) was recorded in 1.0 M KOH at a scan rate

of 5 mV s-1 to obtain the polarization curves. The long-term stability tests were performed

by continuous LSV scans at a sweep rate of 20 mV s-1. The LSV curves were obtained by

nearly 2 mg of catalytic loading of prepared nanocatalysts i.e. POM @ NFs (1 and 2), 3

and 4, 20 % Pt/C on NF surface (1 x 1 cm2) via catalytic ink using microliter syringe.

1.5 UV-Vis. absorption spectra

The UV-vis. spectra of clusters 1 and 2 were measured in 1 х 10-4 M H2O solution. The

clusters 1 and 2 slightly differ in their absorption spectra as {Cp*Ir} substituted 2 shows a broad

absorption band at 450 nm whereas the structurally analogue {Cp*Rh} substituted 1 absorption

band appears at 410 nm, peaks which represent significant LMCT transitions in the cluster due to

n to π* in 1 and 2 respectively. Beside this, 1 and 2 show intense absorption bands (ε ˃ 104 M-

1Cm-1) in the ultraviolet region, centered at 260-290 nm which could be assigned to ligand

centered π-π* transitions within the polyoxometalate framework.

S28

Figure S 18. UV-Vis. spectra of 1 and 2 at 1 x 10-4 M aqueous solution.

Thermogravimetric Analysis of 1 and 2

Figure S 19.TGA curve of 1 and 2.

The thermal analysis of 1 and 2 has been investigated under nitrogen atmosphere between

temperature 30-1200 °C. The TG curve of 1 and 2 appears with similar weight loss steps thus

indicating isomorphous structural framework. Compounds 1 and 2 show three step mass losses in

the above temperature range on slow heating rate of 10 °C/min. The first weight loss of ~12 %

and 8 % in the temperature range of 40 ~ 100 °C can be ascribed due to the loss of 23 and 17

S29

H2O lattice molecules in 1 and 2 respectively, which are according to the calculated values in

both the compounds. The second step weight loss of ~16 % and 15 % in the temperature range of

200-320 °C could be observed due to the loss of organic Cp* from the cluster framework in 1 and

2 respectively. The next small weight loss of about ~ 2% although could not appears sharp but

may be anticipated due to the loss of two WO6 units in 1 and 2, which is followed by the final

decomposition of cluster framework.

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