Self-supported CoMoS nanosheet array as an efficient ...Self-supported CoMoS 4 nanosheet array as an...

Self-supported CoMoS4 nanosheet array as an efficientcatalyst for hydrogen evolution reaction at neutral pH

Xiang Ren1,§, Dan Wu1,§, Ruixiang Ge2, Xu Sun1, Hongmin Ma1, Tao Yan3, Yong Zhang1, Bin Du3, Qin Wei1 (),

and Liang Chen2 ()

1 Key Laboratory of Interfacial Reaction & Sensing Analysis in Universities of Shandong, School of Chemistry and Chemical Engineering,

University of Jinan, Jinan 250022, China 2 Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, China 3 School of Resources and Environment, University of Jinan, Jinan 250022, China § Xiang Ren and Dan Wu contributed equally to this work.

Received: 24 May 2017

Revised: 24 July 2017

Accepted: 22 August 2017

© Tsinghua University Press

and Springer-Verlag GmbH

Germany 2017

KEYWORDS

CoMoS4 nanosheet array,

hydrogen evolution

reaction,

anion exchange reaction,

neutral pH,

density functional theory

ABSTRACT

Development of earth-abundant electrocatalysts, particularly for high-efficiency

hydrogen evolution reaction (HER) under benign conditions, is highly desired,

but still remains a serious challenge. Herein, we report a high-performance

amorphous CoMoS4 nanosheet array on carbon cloth (CoMoS4 NS/CC), prepared

by hydrothermal treatment of a Co(OH)F nanosheet array on a carbon cloth

(Co(OH)F NS/CC) in (NH4)2MoS4 solution. As a three-dimensional HER electrode,

CoMoS4 NS/CC exhibits remarkable activity in 1.0 M phosphate buffer saline

(pH 7), only requiring an overpotential of 183 mV to drive a geometrical current

density of 10 mA·cm–2. This overpotential is 140 mV lower than that for Co(OH)F

NS/CC. Notably, this electrode also shows outstanding electrochemical durability

and nearly 100% Faradaic efficiency. Density functional theory calculations

suggest that CoMoS4 has a more favorable hydrogen adsorption free energy

than Co(OH)F.

1 Introduction

Drastic depletion of fossil fuel resources has triggered

urgent demand for clean and renewable energy sources

[1, 2]. As a high-energy density and abundant fuel

resource, hydrogen is regarded as an ideal candidate

for replacing non-regenerated energy resources in the

future [3]. Electrochemical water splitting is considered

to be a promising method for hydrogen production;

however, this process requires efficient electrocatalysts

to trigger proton reduction with minimal overpotential

and fast kinetics [4, 5]. Pt is the most effective catalyst

for the hydrogen evolution reaction (HER), although

it suffers from low abundance and high cost. Water

splitting in either strongly acidic [6] or basic [7, 8]

solutions not only causes severe corrosion issues

Nano Research 2018, 11(4): 2024–2033

https://doi.org/10.1007/s12274-017-1818-6

Address correspondence to Qin Wei, [email protected]; Liang Chen, [email protected]

www.theNanoResearch.com∣www.Springer.com/journal/12274 | Nano Research

2025 Nano Res. 2018, 11(4): 2024–2033

because of the extreme pH conditions, but also limits

the lifetime of the electrode materials, preventing

widespread application. Consequently, the development

of an efficient and earth-abundant HER catalyst is highly

desired, but remains challenging at neutral pH.

Co exhibits effective catalytic performance towards

hydrogen evolution [4, 6, 9–11]. Recently, a variety of

Co-based catalysts have been developed for HER,

such as CoP [9], FexCo1–xP [10], Mn-doped CoP [12],

CoO/CoSe2 [13], and Co-S [14]. Amorphous MoSx has

also received considerable attention as a hydrogen

evolution catalyst [15, 16]. It has been demonstrated

that Co acts as an effective promoter to enhance the

catalytic activity of MoSx [17]; however, such CoMoSx

catalyst film electrodeposited on a planar electrode

still requires an overpotential of 200 mV to drive

1.04 mA·cm–2. Recent studies have demonstrated that

the direct nanoarray growth of an active phase on a

current collector provides distinct advantages, including

higher electrode stability, lower series resistance,

exposure of more active sites, and easier electrolyte

and gas diffusion [18–31]. Thus, although it has not

been reported to date, the development of a CoMoSx

nanoarray as a three-dimensional (3D) catalyst elec-

trode is highly attractive for achieving high-efficiency

hydrogen evolution catalysis.

In this study, we report our recent effort toward

this direction in developing a CoMoS4 nanosheet array

on carbon cloth (CoMoS4 NS/CC) via topotactic hydro-

thermal conversion of a Co(OH)F nanosheet array on

carbon cloth (Co(OH)F NS/CC) in (NH4)2MoS4 solution.

Through the anion exchange reaction, the ions (OH–,

F–) escape from the Co(OH)F nanosheet array and Co2+

subsequently contacts with MoS42–, resulting in the

formation of an amorphous CoMoS4 nanosheet array

(Scheme 1) [32, 33]. CoMoS4 NS/CC shows superior

Scheme 1 Schematic diagram to illustrate the two-step hydro-thermal fabrication of CoMoS4 NS/CC.

activity as a 3D hydrogen-evolving catalyst electrode,

only requiring an overpotential of 183 mV to drive

a geometrical current density of 10 mA·cm–2 in 1.0 M

phosphate buffer saline (PBS). Notably, CoMoS4 NS/CC

also demonstrates strong long-term electrochemical

durability. Density functional theory (DFT) calculations

provide further theoretical insight into the enhancement

mechanism.

2 Experimental

2.1 Materials

Co(NO3)2·6H2O, NH4F, urea, and (NH4)2MoS4 were

purchased from Beijing Chemical Corp (China). Pt/C

(20 wt.% Pt on Vulcan XC-72R) was purchased from

Alfa Aesar (China) Chemicals Co. Ltd. Carbon cloth

(CC) was purchased from Hongshan District, Wuhan

Instrument Surgical Instruments business, and was

pretreated with HNO3 and then cleaned by sonication

in water and ethanol three times to remove surface

impurities. The ultrapure water used in all the

experiments was generated by a Millipore system.

All chemicals were used as received without further

purification.

2.2 Characterizations

The X-ray diffraction (XRD) patterns were obtained

from a Rigaku/MAX 2550 X-ray diffractometer with

Cu Kα radiation (40 kV, 30 mA) at a wavelength of

0.154 nm (RIGAKU, Japan). The scanning electron

microscopy (SEM), SEM mapping and energy-dispersive

X-ray (EDX) images were collected with a tungsten

lamp-equipped SU3500 scanning electron microscope

at an accelerating voltage of 20 kV (HITACHI, Japan).

The transmission electron microscopy (TEM) and high-

resolution transmission electron microscopy (HRTEM)

images were obtained from a Zeiss Libra 200FE

transmission electron microscope operated at 200 kV.

Inductively coupled plasma mass spectrometry (ICP-

MS) analysis was performed on Thermo Scientific

iCAP6300. The X-ray photoelectron spectroscopy (XPS)

measurements were performed on an ESCALABMK

II X-ray photoelectron spectrometer using Mg as the

excitation source.

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2026 Nano Res. 2018, 11(4): 2024–2033

2.3 Preparation of Co(OH)F NS/CC

Co(NO3)2·6H2O (2 mmol), NH4F (8 mmol) and urea

(10 mmol) were dissolved in 36 mL of ultrapure water

under magnetic stirring to produce a uniform solution.

Then, the pre-treated CC and the above solution were

transferred into a 50 mL Teflon-lined stainless-steel

autoclave and maintained at 373 K for 8 h. After cooling

to room temperature, the product was washed five

times with ultrapure water to obtain Co(OH)F NS/CC.

The detailed mechanism equation is as follows [34, 35]

Co2+ + F− → CoF+

CO(NH2)2 + H2O → 2NH3 + CO2

NH3 + H2O → NH4+ + OH−

CoF+ + OH− → Co(OH)F

2.4 Preparation of CoMoS4 NS/CC

CoMoS4 NS/CC was prepared by hydrothermal reaction.

In a typical synthesis, (NH4)2MoS4 (0.025 g) was dissolved

in 35 mL of water under vigorous stirring for 2 h.

The prepared Co(OH)F NS/CC was placed into the

(NH4)2MoS4 solution and transferred into a Teflon-lined

stainless autoclave (50 mL). The reaction was conducted

at 433 K for 8 h. After cooling down to room tem-

perature, the CoMoS4 NS/CC was removed and washed

thoroughly with water before vacuum drying.

2.5 Preparation of Pt/C electrode

To prepare the Pt/C electrode, 50 mg of Pt/C and 20 μL

of 5 wt.% Nafion solution and 280 μL of ethanol were

dispersed in 700 μL of water by sonication for 30 min

to form an ink. Then, 29.6 μL of catalyst ink was loaded

on bare CC (1 cm × 1 cm), with a catalyst loading of

1.48 mg·cm–2.

2.6 Electrochemical measurements

The electrochemical measurements were performed

on a CHI 660E electrochemical workstation (Chenhua,

Shanghai). A three-electrode system was used in the

experiment: A graphite rod was used as the counter

electrode; a saturated calomel electrode (SCE) was

used as the reference electrode; and the as-prepared

CoMoS4 NS/CC was used as the working electrode.

All the measurements were performed at 298 K in

1.0 M PBS solution. The reference electrode was

calibrated to the reversible hydrogen electrode (RHE)

scale: E(RHE) = E(SCE) + (0.242 + 0.059 pH) = E(SCE) +

0.655 V.

2.7 Turnover frequency calculation

To compare the activity of CoMoS4 NS/CC with other

non-noble metal catalysts, the turnover frequency

(TOF) for each active site was calculated by Eq. (1)

TOF = jA/2Fm (1)

where j is the current density (A·cm–2) at the defined

overpotential of the electrochemical measurement in

1 M PBS; A is the geometric area of the test electrode;

2 indicates the number of moles of electrons consumed

in the evolution of one mole of H2 from water; F is

the Faradic constant (96,485 C·mol–1); and m is the

number of active sites (mol). The latter can be extracted

from the linear relationship between the oxidation

peak current and scan rate by Eq. (2)

Slope = n2F2AΓ0/4RT (2)

where n is the number of electrons transferred; Γ0 is

the surface concentration of active sites (mol·cm–2); and,

R and T are the ideal gas constant and the absolute

temperature, respectively.

2.8 Faradaic efficiency determination

The Faradaic efficiency (FE) was calculated by com-

paring the measured amount of H2 generated by

cathodal electrolysis with the calculated amount of

H2 (assuming an FE of 100%). Gas chromatography

(GC) analysis was carried out on GC–2014C (Shimadzu

Co.), with a thermal conductivity detector and nitrogen

carrier gas. Pressure data during electrolysis were

recorded using a CEM DT-8890 differential air pressure

gauge manometer, with a sampling interval of 1 Hz.

2.9 Computations

Spin-polarized DFT calculations were performed using

the Vienna ab initio simulation package (VASP) [36–38].

We used the Perdew–Burke–Ernzerhof (PBE) functional

for the exchange-correlation energy and projector-

augmented wave (PAW) potential [39–41]. The kinetic


2027 Nano Res. 2018, 11(4): 2024–2033

energy cutoff was set to 450 eV. Ionic relaxation was

performed until the force on each atom was less than

0.01 eV·Å–1. The k-points meshes were 3 × 3 × 1 with

Monkhorst–Pack method [42]. The DFT-D2 method

was used to calculate the adsorption energy; this is an

efficient method used to approximately account for

the long-range van der Waals interactions [43]. The

simulations were based on a CoMoS4 model structure,

with 16 Co, 16 Mo, and 56 S atoms, and a Co(OH)F

model containing 20 Co, 24 O, 24 H, and 20 F atoms.

To minimize the undesired interactions between

images, a vacuum of at least 15 Å was considered

along the z-axis. The free energy change for H*

adsorption on CoMoS4 and Co(OH)F surfaces (ΔGH)

was calculated using the following equation proposed

by Norskov and coworkers (Eq. 3) [44]

ΔGH = Etotal – Esur – EH2/2 + ΔEZPE – TΔS (3)

where Etotal is the total energy of the adsorption state;

Esur is the energy of the pure surface; EH2 is the energy

of H2 in gas phase; ΔEZPE is the zero-point energy

change; and ΔS is the entropy change.

3 Results and discussion

Figure 1(a) shows the XRD patterns of Co(OH)F

NS/CC and CoMoS4 NS/CC. It is observed that the

peaks at 20.8°, 32.3°, 33.5°, 34.8°, 38.8°, 39.9°, 51.9°,

52.8°, 57.0°, 59.1°, and 61.6° are indexed to the (110),

(310), (201), (400), (211), (410), (221), (420), (511), (002),

and (601) planes of Co(OH)F (JCPDS no. 50-0827),

respectively. The as-synthesized CoMoS4 NS/CC

only shows two peaks at 26° and 43° (CC: JCPDS no.

75-2078), indicating the formation of an amorphous

species. XPS is used to characterize the as-synthesized

CoMoS4. Figure S1 in the Electronic Supplementary

Material (ESM) is the XPS survey spectrum for CoMoS4

NS/CC, which illustrates the amorphous product

consisting of Co, Mo and S elements. The CoMoS4

catalyst may be superficially oxidized before the XPS

measurement [9], leading to a slight shift compared

with the pure product. In Fig. 1(b), the peaks at 779.6

and 794.7 eV correspond to Co 2p3/2 and Co 2p1/2,

respectively. Meanwhile, the binding energies (BEs)

at 783.1 and 801.0 eV with two shakeup satellites

Figure 1 (a) XRD patterns of Co(OH)F NS/CC and CoMoS4 NS/CC. XPS spectra of CoMoS4 nanosheet in the (b) Co 2p, (c) Mo 3d, and (d) S 2p regions.

(identified as “Sat.”) also correspond to Co2+/Co3+

[45, 46]. In Fig. 1(c), the BEs at 229.5, 232.9 and 236.1 eV

are well matched to Mo 3d5/2, Mo 3d3/2, and Mo6+,

respectively, indicating that Mo exists in its VI

oxidation state form, which is in accordance with that

of MoS42– [47–49]. S 2p3/2 and S 2p1/2 appear at BEs of

162.1 and 163.4 eV (Fig. 1(d)), respectively, suggesting

the existence of S2–. The ICP-MS analysis suggests an

atomic ratio of nearly 1:1:4 for Co:Mo:S, indicating

the formation of CoMoS4, which is consistent with

the XPS and EDX results (Table S1 in the ESM). Based

on the above characterizations, it has been proven that

Co(OH)F has been successfully converted to CoMoS4.

The SEM images (Fig. 2(a)) of Co(OH)F NS/CC show

the entire surface of CC is completely covered with

Co(OH)F nanosheet array. As observed in Fig. 2(b), the

anion-exchanged CoMoS4 maintains the nanosheet

morphology. The cross-section SEM images for

Co(OH)F NS/CC and CoMoS4 NS/CC (Fig. S2 in the

ESM) indicate that all the nano arrays are about 2.5 μm

in thickness, before and after anion exchange. Figure S3

in the ESM shows the TEM image of the CoMoS4

nanosheet, which is in accordance with Fig. 2(b).

According to the EDX mappings in Fig. 2(c), the Co,

Mo, and S elements in the amorphous product are

uniformly distributed on the CC. The HRTEM image

(Fig. 2(d)) presents a well-resolved lattice fringe

with an interplanar distance of 1.56 Å indexed to the


2028 Nano Res. 2018, 11(4): 2024–2033

Figure 2 SEM images of (a) Co(OH)F NS/CC and (b) CoMoS4 NS/CC (inset: high-magnification image). (c) SEM image and EDX elemental mapping images of Co, Mo, and S in CoMoS4 NS/CC. (d) HRTEM image and (e) SAED spectrum of the Co(OH)F nanosheet. (f) HRTEM image and (g) SAED spectrum of the amorphous CoMoS4 nanosheet.

(002) plane of Co(OH)F. The corresponding selected

area electron diffraction (SAED) spectrum shows a

discernible ring indexed to (002) plane of Co(OH)F

(JCPDS no. 50-0827), as shown in Fig. 2(e). Figures 2(f)

and 2(g) indicate that the CoMoS4 nanosheet array is

amorphous after anion exchange.

We further investigated the HER activity of CoMoS4

NS/CC (loading: ~ 1.48 mg·cm–2) using a typical

three-electrode system with a scan rate of 2 mV·s–1 in

1.0 M PBS. Owing to the direct reflection of the

intrinsic behavior of catalysts, the iR correction is

used to eliminate the effect of ohmic resistance unless

otherwise specified [50] and all potentials were reported

on a RHE scale. Commercial Pt/C on CC (loading:

~ 1.48 mg·cm–2) was examined for comparison.

Figure 3(a) shows the linear sweep voltammetry (LSV)

curves. As expected, Pt/C displays excellent HER acti-

vity, requiring an overpotential of only 59 mV to drive

a current density of 10 mA·cm–2. Co(OH)F NS/CC is

also capable of HER catalysis, requiring 323 mV to

drive 10 mA·cm–2. In sharp contrast, CoMoS4 NS/CC

exhibits superior HER activity compared to Co(OH)F

NS/CC, only requiring a much smaller overpotential

of 183 mV to drive 10 mA·cm–2; 140 mV lower than

that for Co(OH)F NS/CC. The overpotential of CoMoS4

NS/CC is lower than those reported for Co-based

HER catalysts under neutral conditions, including

Co-NRCNTs/glass carbon electrode (GCE) (η10 mA·cm–2 =

540 mV) [51], CoO/CoSe2/Ti (η10 mA·cm–2 = 337 mV) [13],

carbon nanofiber@CoS2/GCE (η10 mA·cm–2 = 360 mV) [52]

and CoMoS3/fluorine-doped tin oxide (FTO) (η5 mA·cm–2 =

206 mV) [53]. A more detailed comparison is provided

in Table S2 in the ESM. The performance of the

CoMoS4 NS/CC catalyst under acidic and alkaline

conditions was also assessed (Fig. S4 in the ESM).

The Tafel plots are well fitted by the following

equation: η = b·logj + a, where j is the current density

and b is the Tafel slope. In Fig. 3(b), the Tafel slopes

are 75, 116 and 193 mV·dec–1 for Pt/C, CoMoS4 NS/CC

and Co(OH)F NS/CC, respectively. This suggests

that the HER occurs on Co-based electrodes through

a Volmer rate-determining step mechanism [54, 55].

Figure 3(c) shows the multi-step chronopotentiometric

curve for CoMoS4 NS/CC in 1.0 M PBS, with the current

increasing from 16 to 52 mA·cm–2 (4 mA·cm–2 per 500 s).

At the initial current value, the potential immediately

levels off at –1.03 V and is unchanged for the remaining

500 s. The other steps exhibit similar results, indicating

the excellent conductivity and mass transportation

properties, as well as the mechanical robustness of

the 3D CoMoS4 NS/CC electrode [1, 56]. Meanwhile,

the stability of CoMoS4 NS/CC was also evaluated in

Figure 3 (a) LSV curves of Pt/C, Co(OH)F NS/CC and CoMoS4 NS/CC for HER. (b) Corresponding Tafel plots for Pt/C, Co(OH)F NS/CC and CoMoS4 NS/CC. (c) Multi-current process of CoMoS4 NS/CC. (d) LSV curves of CoMoS4 NS/CC before and after 1,000 cyclic voltammetry cycles and time-dependent current density curve of CoMoS4 NS/CC. All experiments were performed in 1.0 M PBS.


2029 Nano Res. 2018, 11(4): 2024–2033

this study (Fig. 3(d)). The LSV curves of CoMoS4 NS/CC

show no obvious changes after 1,000 cyclic voltammetry

(CV) cycles in 1.0 M PBS, suggesting that the catalytic

activity is fully retained, in accordance with the 25 h

long-term durability results.

The electrochemical double layer capacitance (Cdl)

of CoMoS4 NS/CC was tested to calculate electro-

chemical surface area by CV. In Figs. S5(a) and S5(b)

in the ESM, scan rates of 20, 40, 60, 80 and 100 mV·s–1

were used to evaluate the performance of the catalysts.

As shown in Figs. S5(c) and S5(d) in the ESM, Cdl of

18.6 and 0.975 mF·cm–2 is obtained for CoMoS4 NS/CC

and Co(OH)F NS/CC, respectively, suggesting that the

topotactic conversion of the anion exchange reaction

increases the surface roughness, which is beneficial

for enhancement of HER activity. The significantly

rougher catalyst surface [57, 58] and much higher

performance of the amorphous product [59, 60] indicates

higher electrochemical double-layer capacitance.

Meanwhile, electrochemical impedance spectroscopy

(EIS) was also performed to evaluate the performance

of the catalysts. EIS is considered to be a powerful

tool for studying electrode kinetics in a catalytic

reaction. CoMoS4 NS/CC possesses a smaller semicircle

radius than Co(OH)F NS/CC (Fig. S6 in the ESM), which

suggests lower charge-transfer resistance (Rct) and

more rapid catalytic kinetics when amorphous CoMoS4

is generated.

The TOF was calculated in this study to demonstrate

the HER activity of CoMoS4 NS/CC at a constant

overpotential. Figure S7 in the ESM shows the cyclic

voltammograms in the region of −1.0 to + 0.6 V vs.

SCE for CoMoS4 NS/CC at pH 7. As the product

evolution rate per mole of active sites, the TOF is

calculated to be 0.2 and 1.13 s–1 at overpotentials of 200

and 600 mV for CoMoS4 NS/CC, smaller than those for

reported amorphous MoS3 (~ 0.005 s–1, η = 200 mV) [15]

and Mo-oxo system (~ 0.3 s–1, η = 600 mV) [61].

The FE of CoMoS4 NS/CC was measured by GC

analysis, which was quantified with a calibrated pressure

sensor of a H-type electrolytic cell. The FE of the HER

process is calculated to be in approximate agreement

with the theoretical value (assuming 100% FE), which

suggests that nearly 100% FE is achieved by this

catalyst electrode (Fig. S8 in the ESM).

Generally, the hydrogen evolution activity of a

catalyst is related to ΔGH. In detail, a thermoneutral

ΔGH value of 0 eV can result in optimal HER activity,

with a balance between proton reduction and removal

of adsorbed hydrogen from the surface [44]. For further

understanding, the side-view structure of Co(OH)F

and CoMoS4 is shown in Figs. 4(a) and 4(b), respectively.

First-principles DFT was used to calculate ΔGH for

the (110) surface of the catalyst, in order to illustrate

the superior HER activity of CoMoS4. Figure 4(c) shows

the free energy diagram for HER on Pt, Co(OH)F and

CoMoS4 surfaces. Pt, the most active HER catalyst,

presents a ΔGH of approximately –0.09 eV. With regard

to the Co(OH)F catalyst, it has been found that both

the Co top- and O-sites can accommodate H atoms,

whereas H adsorption on top of the F site is not

stable. The strong interactions between the H and O

ions yield an undesirable ΔGH of –0.773 eV. In sharp

contrast, the Co sites are well matched with the OH

and F coordinates, and bind H quite loosely, so that

ΔGH shifts from 0 to 0.576 eV. Furthermore, the same

chemical environments exist between the exposed Mo

and Co sites of CoMoS4 and the Co ions of Co(OH)F.

As a result, these sites also bind H weakly, yielding

large ΔGH values of 0.755 and 0.514 eV for the Mo

and Co sites, respectively. Meanwhile, the exposed S

atoms, which act as the stable binding sites, can also

accommodate hydrogen. Note that the S sites, which

have lower electronegativity than the O sites, can

interact moderately with H, leading to a favorable

ΔGH. In addition, the ΔGH of the S site is calculated to

be 0.191 eV, which is significantly closer to zero than

Figure 4 Side view of (a) Co(OH)F and (b) CoMoS4 model structures. The purple, blue, yellow, red, light blue and white balls represent Mo, Co, S, O, F and H atoms, respectively. (c) Free energy diagram for HER on Pt, Co(OH)F and CoMoS4 surfaces.


2030 Nano Res. 2018, 11(4): 2024–2033

any of the other sites. Considering that the catalyst is

amorphous, we also calculated the ΔGH values for the

(001) and (111) faces of CoMoS4. The calculated ΔGH

values for the (001) and (111) faces are –0.11 and 0.63 eV,

respectively. However, the amorphous transition metal

compound possesses more defects or vacancies that

can serve as active sites for enhanced water splitting

[59, 60, 62]. Thus, the amorphous product exhibits

higher activity than the crystal structure. In the

calculation steps, the crystalline CoMoS4 based on

different faces exhibits excellent activity, indicating

that the amorphous CoMoS4 has superior performance.

4 Conclusions

In summary, the self-supported CoMoS4 nanosheet

array on carbon cloth has been successfully derived

in situ from a Co(OH)F nanosheet array on carbon cloth

through hydrothermal anion exchange in (NH4)2MoS4

solution. As a 3D non-noble metal electrode, this

catalyst shows superior activity towards hydrogen

evolution, with a geometrical current density of

10 mA·cm–2 at an overpotential of only 183 mV in

1.0 M PBS (pH 7). This electrode also demonstrates

excellent long-term electrochemical durability and a

high TOF (1.13 s–1, η = 600 mV) for HER. This study

not only provides an attractive earth-abundant catalyst

for efficient HER, but also paves a new way to the

rational design and scalable self-templating fabrication

of metallic thiomolybdate nanoarrays for a wide range

of applications [63–66].

Acknowledgements

This work was supported by the National Key Scientific

Instrument and Equipment Development Project of

China (No. 21627809), the National Natural Science

Foundation of China (Nos. 21375047, 21377046, 21405059,

21575137, 21575050, and 21601064), Natural Science

Foundation of Shandong Province (Nos. ZR2016JL013

and ZR2016BQ10), Graduate Innovation Foundation

of University of Jinan (No. YCXB15004), and the

Special Foundation for Taishan Scholar Professorship

of Shandong Province (No. ts20130937).

Electronic Supplementary Material: Supplementary

Material (experimental section; SEM and TEM images;

XPS spectrum; CVs; LSV curves; capacitive current vs.

scan rate plots; EIS spectra; oxidation peak current

vs. scan rate plots; Faradaic efficiency; Tables S1 and

S2) is available in the online version of this article at

https://doi.org/10.1007/s12274-017-1818-6.

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