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. 2015 Aug 21;1(7):e1500259.
doi: 10.1126/sciadv.1500259. eCollection 2015 Aug.

Hierarchical Ni-Mo-S nanosheets on carbon fiber cloth: A flexible electrode for efficient hydrogen generation in neutral electrolyte

Jianwei Miao  1 , Fang-Xing Xiao  1 , Hong Bin Yang  1 , Si Yun Khoo  1 , Jiazang Chen  1 , Zhanxi Fan  2 , Ying-Ya Hsu  3 , Hao Ming Chen  3 , Hua Zhang  2 , Bin Liu  1
Affiliations

Hierarchical Ni-Mo-S nanosheets on carbon fiber cloth: A flexible electrode for efficient hydrogen generation in neutral electrolyte

Jianwei Miao et al. Sci Adv. .

Abstract

A unique functional electrode made of hierarchal Ni-Mo-S nanosheets with abundant exposed edges anchored on conductive and flexible carbon fiber cloth, referred to as Ni-Mo-S/C, has been developed through a facile biomolecule-assisted hydrothermal method. The incorporation of Ni atoms in Mo-S plays a crucial role in tuning its intrinsic catalytic property by creating substantial defect sites as well as modifying the morphology of Ni-Mo-S network at atomic scale, resulting in an impressive enhancement in the catalytic activity. The Ni-Mo-S/C electrode exhibits a large cathodic current and a low onset potential for hydrogen evolution reaction in neutral electrolyte (pH ~7), for example, current density of 10 mA/cm(2) at a very small overpotential of 200 mV. Furthermore, the Ni-Mo-S/C electrode has excellent electrocatalytic stability over an extended period, much better than those of MoS2/C and Pt plate electrodes. Scanning and transmission electron microscopy, Raman spectroscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and x-ray absorption spectroscopy were used to understand the formation process and electrocatalytic properties of Ni-Mo-S/C. The intuitive comparison test was designed to reveal the superior gas-evolving profile of Ni-Mo-S/C over that of MoS2/C, and a laboratory-scale hydrogen generator was further assembled to demonstrate its potential application in practical appliances.

Keywords: Carbon Fiber Cloth; Flexible Electrodes; Hierarchical Ni-Mo-S Nanosheets; Hydrogen Generation; Neutral Electrolyte.

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Figures

Fig. 1
Fig. 1. Synthesis processes of MoS2/C and Ni-Mo-S/C.
(A) Schematic illustration of syntheses of MoS2 and Ni-Mo-S on carbon fiber cloth. (B) Photographic image of freshly prepared Ni-Mo-S/C (1:1).
Fig. 2
Fig. 2. Low-magnification SEM images.
(A) Bare carbon fiber cloth. (B) NiSx/C. (C) Ni-Mo-S/C (3:1). (D) Ni-Mo-S/C (1:1). (E) Ni-Mo-S/C (1:3). (F) MoS2/C. All scale bars, 2 μm.
Fig. 3
Fig. 3. High-magnification SEM images.
(A) Ni-Mo-S/C (3:1). (B) Ni-Mo-S/C (1:1). (C) Ni-Mo-S/C (1:3). (D) MoS2/C. All scale bars, 500 nm.
Fig. 4
Fig. 4. TEM images.
(A and B) Low-magnification TEM images of (A) MoS2/C and (B) Ni-Mo-S/C (1:1). (C and D) HRTEM images of (C) MoS2/C and (D) Ni-Mo-S/C (1:1). Insets: Corresponding cross-sectional HRTEM images. Dashed circles in (D) indicate the structure defects of Ni-Mo-S/C (1:1).
Fig. 5
Fig. 5. XRD analysis.
XRD pattern of Ni-Mo-S/C (1:1) after subtraction of carbon fiber cloth signal. Inset: Original XRD pattern of Ni-Mo-S/C (1:1). a.u., arbitrary unit.
Fig. 6
Fig. 6. Raman spectroscopy.
Raman spectra of Ni-Mo-S/C (1:1) and MoS2/C. Inset: Schematic illustration of E2g1 and A1g vibrational modes in layered 2H-MoS2.
Fig. 7
Fig. 7. XPS.
(A) Survey XPS spectrum of Ni-Mo-S/C (1:1). (B to D) High-resolution scans of (B) Mo 3d, (C) S 2p, and (D) Ni 2p.
Fig. 8
Fig. 8. Electrochemical performances.
(A) Polarization curves of carbon fiber cloth, NiSx/C, MoS2/C, and different Ni-Mo-S/C in neutral electrolyte. GSA, geometric surface area. (B) Corresponding Tafel plots obtained using slow-scan rate polarization curves. (C) Electrochemical impedance spectra of different electrodes at −0.3 V versus RHE. Inset: Equivalent circuit used for data analyses. CPE, constant-phase element; ZW, Warburg impedance. (D) Plot of charge transport resistance of different samples.
Fig. 9
Fig. 9. Electrochemical hydrogen evolution tests.
(A) Onset comparison between MoS2/C and Ni-Mo-S/C (1:1). (B) Stability tests of Ni-Mo-S/C (1:1) and MoS2/C in neutral electrolyte. (C) LSV curves of Ni-Mo-S/C (1:1) before and after stability tests. (D) Comparison of the detected amount of evolved H2 and the theoretical value in Faraday efficiency measurement.
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