Supplementary Information

Synthesis of RuNi Alloy Nanostructures Composed of Multilayered Nanosheets for Highly Efficient

Electrocatalytic Hydrogen Evolution

Guigao Liu,1† Wei Zhou,3† Bo Chen,1 Qinghua Zhang,4 Xiaoya Cui,1 Bing Li,5 Zhuangchai Lai,1

Ye Chen,1 Zhicheng Zhang,1 Lin Gu4 and Hua Zhang1,2*

1Center for Programmable Materials, School of Materials Science and Engineering, Nanyang

Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore.

2Department of Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong

Kong, China

3Department of Applied Physics, Tianjin Key Laboratory of Low Dimensional Materials Physics,

Preparing Technology Faculty of Science, Tianjin University, Tianjin, 300072, PR China.

4Institute of Physics, Chinese Academy of Sciences and Beijing National Laboratory for

Condensed Matter Physics, Beijing 100190, China. Collaborative Innovation Center of Quantum

Matter, Beijing 100190, China. School of Physical Sciences, University of Chinese Academy of

Sciences, Beijing 100190, China.

5Institute of Materials Research and Engineering (IMRE), A*STAR (Agency for Science,

Technology and Research), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Singapore.

†These authors contributed equally to this work.

*Correspondence to: hua.zhang@cityu.edu.hk; hzhang@ntu.edu.sg

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Experimental section

Chemicals

Ruthenium(III) chloride hydrate (RuCl3·χH2O, ruthenium content: 40.00-49.00% ), nickel(II)

acetylacetonate (Ni(acac)2, 95%), tungsten hexacarbonyl (W(CO)6, 97%),

poly(vinylpyrrolidinone) (PVP, MW=40000), formaldehyde solution (HCHO, 36.5-38% in

H2O), benzyl alcohol (C6H5CH2OH; anhydrous, 99.8%), oleylamine (≥98%) and Nafion alcohol

solution (5 wt%) were purchased from Sigma-Aldrich. Ethanol (95%), acetone (Tech Grade) and

hexane were supplied by Aik Moh (Aik Moh Pt. Ltd Singapore). All the chemicals were used as

received without further purification. Ultrapure water (18.2 MΩ cm resistivity at 25 °C) was

used in all experiments.

Synthesis of the RuNi alloy nanostructures (RuNi NSs) composed of multilayered

nanosheets

RuNi NSs were synthesized through a one-pot solvothermal method. Typically, after 9.3 mg

of RuCl3·χH2O, 16.2 mg of Ni(acac)2 and 100 mg of PVP were added into 6 mL of benzyl

alcohol, this mixture was ultrasonicated for around 30 minutes to obtain a homogeneous

solution, followed by further addition of 0.6 mL of formaldehyde solution. After being

thoroughly mixed, this solution was transferred into a 22.0 mL Teflon-lined stainless steel

autoclave, which was then sealed, heated to 220 °C and kept for 12 h. Finally, the resulting

product, i.e. RuNi NSs, was collected by centrifugation, and washed with ethanol and acetone

thoroughly. The obtained RuNi NSs were dispersed in ethanol for further characterization.

Synthesis of Ru nanosheets

Ru nanosheets were prepared through a modified hydrothermal method.[1] Typically, 93.3 mg

of RuCl3·χH2O and 200 mg of PVP were dissolved in 15-mL water, followed by the addition of

0.5 mL of formaldehyde solution. Then the mixture solution was transferred into a 22.0-mL

Teflon-lined stainless steel autoclave and sealed. Subsequently, the autoclave was heated at 160

°C for 4 h. After cooled down to room temperature, the Ru nanosheets were collected by

centrifugation, and then washed with ethanol and acetone thoroughly.

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Synthesis of Ni nanosheets

Ni nanosheets were prepared through the previously reported method.[2] Briefly, 256.9 mg of

Ni(acac)2 and 105.6 mg of W(CO)6 were added to 8-mL oleylamine in a 50-mL round flask.

Then the mixture was heated to 60 °C and kept for 30 min under N 2 atmosphere with magnetic

stirring. After that, a clear solution was obtained, which was further heated to 170 °C. After

reaction for 10 min, the solution was immediately cooled down to room temperature. The Ni

nanosheets were collected by centrifugation and washed thoroughly with a mixed solution of

hexane and ethanol.

Characterization

The transmission electron microscopy (TEM) and high resolution TEM (HRTEM) images

were taken on JEOL-2010 and JEOL-2100F transmission electron microscopes operated at 200

kV. The high-angle annular dark-field scanning transmission electron microscope (HAADF-

STEM) and energy-dispersive X-ray spectroscopy (EDS) elemental mapping were conducted on

a JEOL-2100F TEM and a high resolution aberration corrected TEM (JEOL JEM-ARM200F).

Powder X-ray diffraction (XRD) patterns were collected on an X-ray diffractometer (Shimadzu,

XRD-6000) with Cu Kα radiation. The surface chemical analysis of samples was performed by

an X-ray photoelectron spectroscopy (XPS) with a Theta Probe electron spectrometer (ESCA-

Lab-200i-XL, Thermo Scientific). The energy calibration in XPS spectra was performed by

using the main C1s peak at 285 eV as a reference.

Electrochemical measurements

All the electrochemical measurements were conducted in a three-electrode system using an

Autolab electrochemical workstation (PGSTAT12) at room temperature. A graphite rod and

Hg/HgO (1.0 M KOH) were used as counter and reference electrodes, respectively. The

electrolyte was 1.0 M KOH aqueous solution (purged by pure N2). The working electrode of

RuNi NSs was prepared by drop-casting 10 μL of the dispersion of RuNi NSs onto a glassy

carbon (GC) electrode (3 mm in diameter) with the Ru loading amount of 1.9 μg as measured by

the inductively coupled plasma-optical emission spectrometry (ICP-OES). The prepared

electrode was then irradiated by a UV lamp (10 W with emission of 185 and 254 nm) for 4 h to

remove the surfactant on RuNi NSs. Finally, 2 μL of Nafion solution (0.1 wt%) were dropped

S3

onto the electrode surface. After being dried, the electrode was used for the electrochemical

measurements.

Linear sweep voltammetry (LSV) curves were measured in the N2-saturated 1.0 M KOH

aqueous solution at a sweep rate of 5 mV s−1. The durability tests were performed by applying

the cyclic potential sweeps between 0.1 V and -0.1 V (versus reversible hydrogen electrode (vs.

RHE)) at scan rate of 100 mV s-1 for 10,000 cycles. Electrochemical impedance spectra (EIS)

were recorded over the frequency range from 100 kHz to 0.1 Hz with an amplitude of applied

voltage of 5 mV (Fig. S8). The Hg/HgO reference electrode used in the electrocatalytic

measurements was calibrated with respect to the RHE by testing LSV in the H2-saturated 1.0 M

KOH aqueous solution with Pt wires used as both working electrode and counter electrode (Fig.

S17). For comparison, the electrocatalytic hydrogen evolution activities of commercial Ru/C and

Pt/C catalysts were also tested.

DFT calculations

In this work, all calculations were performed based on the density-functional theory (DFT).[3]

The generalized gradient approximation (GGA) with PBE functional was used for the exchange-

correlation energy. The DFT-D2 functional was employed for van der Waals interaction. A

plane-wave expansion for the basis set with a cutoff energy of 450 eV was employed. The 5×5×1

Monk-horst k-point meshes were used for the Brillouin-zone integrations of supercell models.

All atoms were relaxed until the residual force was less than 0.01 eV/Å. To avoid the periodic

interaction along out-plane direction, a vacuum layer of 16 Å was used for the slab model.

Under standard conditions, the adsorption energy ΔE was calculated from the energy

difference between catalysts with and without adsorbent. Under standard conditions, the

adsorption Gibbs free energy of intermediate hydrogen on catalyst (ΔGH¿0 ) can be calculated as

follows:

ΔGH ¿0 =∆ EH+∆ EZPE−T ∆ SH (1)

where ΔEZPE and ΔSH are the differences in zero point energy and entropy between adsorbed

hydrogen and hydrogen gas, respectively.

S4

Additionally, the dissociation energy of water molecular was calculated from the energy

difference between water molecules adsorbed and splitting on the surface of the catalyst.

S5

Table S1. Comparison of catalytic performance of our synthesized RuNi NSs, the commercial

Ru/C, Pt/C and some recently reported representative HER electrocatalysts in alkaline solutions.

Catalysts

Catalyst loading

amount (mg cm-2)

Current density

(mA cm-2)

Overpotential at

corresponding J (mV)

Tafel slope (mV dec-1) Reference

RuNi NSs[a] 0.027[c] 10 15 28 This work

Commercial Ru/C[a] 0.027[c] 10 70 65 This work

Commercial Pt/C[a] 0.027[c] 10 54 41 This work

Ru@C2N[a] 0.082[c] 10 17 38 [4]

Pt3Ni2-NWs-S/C[a] 0.015[c] 10 42 - [5]

PtNi alloy nano-multipods[b] 0.008[c] 22 70 78 [6]

Co-substituted Ru[a] 0.153[c] 10 13 29 [7]

NiOx/Pt3Ni

Pt3Ni3-NWs[a]0.015[c] 10 40 - [8]

Pt3Ni frames/Ni(OH)2/C[b] ~0.014[c] 4 ~60 - [9]

Ru/C3N4/C[b] 0.204 10 79 ~69 [10]

Pt NWs/SL-Ni(OH)2

[a] 0.016[c] 4 85.5 - [11]

CoNx/C[b] 2 10 170 75 [12]

CoMoSx[b] 0.050 5 ~158 - [13]

Co(OH)2/Pt(111)[b] - 10 248 - [14]

MoCx nano-octahedrons[a] 0.800 10 151 59 [15]

NiFeOx/CFP[a] 1.600 10 88 150 [16]

NiO/Ni-CNT[a] 0.28 10 ~86 82 [17]

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Ni0.33Co0.67S2[a] 0.3 10 88 118 [18]

Co-P film[a] - 10 94 42 [19]

MoP[a] 0.84 10 169 70 [20]

α-Mo2C[a] 0.102 10 176 58 [21]

MoB[a] 2.3 10 220 59 [22]

[a]The electrolyte is 1.0 M KOH solution.[b]The electrolyte is 0.1 M KOH solution.[c]Pt or Ru loading amount (mg cm-2).

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Figure S1. Statistical analysis of (a) layer number and (b) diagonal size of RuNi NSs, obtained

from 130 RuNi NSs measured by TEM. Inset in (b): Schematic illustration of one Ru NS with

diagonal size marked.

Figure S2. (a) TEM image of RuNi NSs. The arrow shows one RuNi NS vertically standing on

the TEM copper grid. (b) Statistical analysis of the thickness of RuNi NSs, obtained from 100

RuNi NSs measured by TEM.

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Figure S3. EDS mappings of an individual RuNi NS. From the figure, it is clearly observed that

the distributions of Ru and Ni are uniform over the nanostructure.

Figure S4. EDS spectrum of RuNi NSs. The signal of Si comes from the EDS detector. Inset

table summarizes the element ratios of Ru and Ni in RuNi NSs.

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Figure S5. TEM image of the product prepared without the addition of Ni precursor.

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Figure S6. (a, b) LSV curves of RuNi NSs with different loading amount of Ru in 1.0 M KOH

solution normalized by the geometric surface area of the electrode (a), and the mass of Ru loaded

on the electrode (b). The optimal Ru loading amount for HER is ~1.90 µg.

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Figure S7. TEM images of (a) Ru/C, (b) Pt/C, (c) Ru nanosheets, and (d) Ni nanosheets.

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Figure S8. EIS spectra of (a) RuNi NSs, (b) Ru/C, (c) Pt/C, (d) Ru nanosheets, and (e) Ni

nanosheets.

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Figure S9. Comparison of overpotentials at the current density of 10 mA cm-2 for RuNi NSs,

commercial Ru/C, Pt/C as well as the recently reported representative electrocatalysts in 1.0 M

KOH solutions. The data were also summarized in Table S1.

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Figure S10. (a, b) TEM images of RuNi NSs after the electrocatalytic stability test, i.e. 10,000

sweeping cycles. Inset in (b): The corresponding SAED pattern of an individual RuNi NS shown

in (b). Scale bar in the inset of (b) is 5 1/nm. It can be seen that the morphology and the hcp

phase structure of RuNi NSs were maintained after the HER durability test.

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Figure S11. I-t curves of RuNi NSs at different current densities.

As shown in Figure S11, the current densities remained stable during the test, indicating the good

stability of RuNi NSs for HER in alkaline solution.

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Figure S12. CO stripping voltammetry of (a) Ru/C, (b) Pt/C and (c) RuNi NSs in 1.0 M KOH

solution. The scan rate is 10 mV s-1. The corresponding solid curves indicate the stripping of a

monolayer of CO in the first scan cycle, and the dash curves indicate the second scan cycle after

the stripping of CO. (d) Charges of CO stripping for Ru/C, Pt/C and RuNi NSs, which were

integrated from the CO stripping peaks in (a), (b) and (c), respectively.

CO stripping experiments were performed using the previously reported method.[4,23-25]

The CO adsorption was conducted in 1.0 M KOH aqueous solution with bubbling CO for 20

min. After that, the electrolyte was saturated with N2 by bubbling N2 for 15 min to remove the

dissolved CO in the electrolyte. During all the aforementioned procedures, the potential was

maintained at 0.1 V vs. RHE. The CO stripping method has been widely used for quantifying the

number of active sites and the electrochemically active surface area (ECSA) of catalysts.[23-25]

S17

In this method, the number of active sites was calculated on basis of the CO stripping charge

(QCO) with the following equation:

n = Qco/(2Fm) (2)

where F is the Faraday constant (96485 C mol-1), and m is the metal mass loading (1.9 × 10-6 g).

The turnover frequency (TOF, H2 s-1) can be estimated by using the following equation:

TOF = I/(2Fnm) (3)

where I is the current (A) during the LSV measurement. The factor, 2, is the number of electron

transferred, because two electrons are required to form one H2 molecule.

Assuming a value of 420 μC cm-2 for a saturated CO monolayer formation on active metal

sites, the ECSA can be calculated as follows:

ECSA = QCO/(m × 420 μC cm-2) (4)

S18

Table S2. Comparison of QCO, ECSAs, the number of active sites and TOF values (at the

overpotential of 50 mV) of our synthesized RuNi NSs, the commercial Rh/C and Pt/C catalysts.

Catalysts QCO (mC) ECSA (m2 g-1)Number of active

sites (10-3 mol g-1)

TOF at the

overpotential of

50 mV (H2 s-1)

RuNi NSs 1.23 154.1 3.35 1.60

Commercial Ru/C 0.64 80.2 1.75 0.67

Commercial Pt/C 0.49 61.4 1.34 1.35

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Table S3. Comparison of ECSAs of our synthesized RuNi NSs, the commercial Ru/C, Pt/C and

recently reported representative electrocatalysts.

Catalysts ECSA (m2 g-1Ru or Pt)

Method for the measurement Reference

RuNi NSs 154.1 CO stripping This work

Commercial Ru/C 80.2 CO stripping This work

Commercial Pt/C 61.4 CO stripping This work

Pt3Ni nanoframes 67.2 CO stripping [9]

PtPb/Pt core/shell nanoplates 55.0 Hydrogen underpotential

adsorption/deposition [26]

Jagged Pt nanowires 123.9 CO stripping [27]

Cubic Pt nanocages 46.8 Hydrogen underpotential adsorption/deposition [28]

Mo-doped Pt3Ni/C 83.9 CO stripping [29]

PtNiCo nanowires/C 82.2 Hydrogen underpotential adsorption/deposition [30]

Sphere PtNi/C 47 CO stripping [31]

Ru@C2N 16.6 CO stripping [4]

Rh-doped Pt nanowires/C 86.4 Hydrogen underpotential

adsorption/deposition [32]

Ru/C3N4/C 45.5 Cu underpotential deposition [10]

PtNi alloy nano-multipods 27.3 Hydrogen underpotential

adsorption/deposition [6]

Pt-Ni anisotropic superstructures 20.4 CO stripping [33]

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Figure S13. The numbers of active sites of Ru/C, Pt/C and RuNi NSs, which were calculated

based on the data of CO stripping.

S21

Table S4. Comparison of TOF values of our synthesized RuNi NSs, the commercial Ru/C, Pt/C

and recently reported representative HER electrocatalysts in alkaline solutions.

Catalysts Potential (mV vs. RHE)TOF at the

corresponding potential (H2 s-1)

Reference

RuNi NSs -50 1.60 This work

Commercial Ru/C -50 0.67 This work

Commercial Pt/C -50 1.35 This work

Ru@C2N -50 1.66[a] [4]

Ni-Mo catalysts -100 0.05[b] [34]

Ni5P4 -100 0.79[c] [35]

γ-Mo2N -250 0.07[d] [21]

α-Mo2C -176 0.5[d] [21]

[a]The TOF value of Ru@C2N was calculated based on the number of active Ru atoms.[b]The TOF value of Ni-Mo catalysts was calculated based on the number of surface Ni and Mo atoms.[c]The TOF value of Ni5P4 was calculated based on the number of total Ni atoms.[d]The TOF values of γ-Mo2N and α-Mo2C were calculated based on the number of surface Mo atoms.

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Figure S14. (a) Hydrogen adsorption free energies calculated on the surfaces of Ru(0001),

Pt(111) and RuNi(0001). (b-d) Hydrogen adsorption configurations on the surfaces of (b)

Ru(0001), (c) Pt(111) and (d) RuNi(0001).

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Figure S15. (a) Water adsorption energies calculated on the surfaces of Ru(0001), Pt(111) and

RuNi(0001). (b-d) Water adsorption configurations on the surfaces of (b) Ru(0001), (c) Pt(111)

and (d) RuNi(0001).

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Figure S16. (a) Water dissociation energies calculated on the surfaces of Ru(0001), Pt(111) and

RuNi(0001). (b-d) Water dissociation configurations on the surfaces of (b) Ru(0001), (c) Pt(111)

and (d) RuNi(0001).

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Figure S17. LSV curve recorded in the H2-saturated 1.0 M KOH solution for the calibration of

Hg/HgO electrode with respect to RHE. In this test, both the working and counter electrodes are

Pt wires.

S26

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