【introduction】

Decomposition of water to produce hydrogen is recognized as a green, clean and efficient method, but its hydrogen evolution half reaction is a complex (H ⁺ ) -solid (catalyst) -gas (H 2 ) three-phase complex electrochemical process. At present, two-dimensional (2D) molybdenum disulfide, which has been widely used in solar cells, photocatalysis, lithium batteries and other fields, has gradually become a representative non-precious material for electrocatalytic hydrogen evolution reaction (HER) in water decomposition. However, to achieve more efficient catalytic performance, researchers still need to conduct multi-scale control and optimization of the structure and electronic properties of two-dimensional (2D) MoS 2 .

【Achievement Introduction】

Recently, Academician Bao Xinhe of Dalian Institute of Chemical Physics , Chinese Academy of Sciences and Associate Researcher (co-corresponding author) of Xiamen University Deng Dehui and others jointly reported the control strategies for the multiscale structure and electronic properties of 2D MoS 2 ; , Vertically oriented two-dimensional layer and Co-doped three-dimensional molybdenum disulfide show high hydrogen evolution activity and stability; compared with random oriented MoS 2 nanosheets (rNS-MoS 2 ), uniform mesoporous foam MoS 2 (MPF-MoS 2 ) significantly improves HER performance. Experiments and DFT calculations have proved that: Mesoporous foam MoS 2 (mPF-Co-MoS 2 ) with Co doping amount of 16.7% shows the highest HER activity; it also has the durability of more than 5000 cycles; at 10mAcm The overpotential at the current density of ² is only 156mV. Appropriate amount of Co doping can effectively adjust the adsorption of MoS 2 to H, while maintaining structural stability and promoting the HER activity to reach the optimal value. This article was published on Nature Communication under the name "Multiscale structural and electronic control of molybdenum disulfide foam for highly efficient hydrogen production".

【Graphic introduction】

Figure 1: Synthesis diagram of mesoporous foam MoS 2 material

Figure 2: Morphology and structure analysis of mesoporous foam MoS 2

(A, b) SEM image of mPF-MoS 2 .

(C, d) TEM image and corresponding HAADF-STEM image of mPF-MoS 2 in the same place.

(E) HAADF- STEM diagram and corresponding EDX diagram of mPF-MoS 2 .

(F) pore size distribution, and MoS-mpf 2 pair of N 2 adsorption - desorption isotherm type IV (inset).

(G) HRTEM image of mPF-MoS 2 , the inset shows obvious mesopores and the typical MoS 2 layer distance is 0.62nm.

(H) Comparison of XRD patterns of mPF-MoS 2 and rNS-MoS 2 .

(I) MoS-mpf 2 and MoS-RNS 2 K of ² comparing the weighted EXAFS spectra, MoS illustrations-RNS 2 and MoS-mpf 2 normalized one of Mo K- edge XANES spectra.

Proportions: (a) 500nm, (be) 100nm, (g) 5nm.

Figure 3: Electrocatalytic HER performance of mesoporous foam MoS 2

(A) a body MoS 2 , MoS RNS- 2 , 40% of Pt / C and MoS-mpf 2 a HER polarization curves.

(B) The superpotential graphs of rNS-MoS 2 , bulk MoS 2 and mPF-MoS 2 when the current density is 10, 20 and 50 mAcm ^-2 respectively .

(C) The durability test curve of mPF-MoS 2 ; first record the polarization curve, and 1000 scans between 0.1 and + 0.5V (relative to RHE) at 100mVs ^-1 . All HER measurements were performed in Ar-saturated 0.5MH 2 SO 4 electrolyte at 25 ° C.

Figure 4: Structure and electronic properties of various Co-doped mesoporous foam MoS 2 materials

(A) The HAADF-STEM image of mPF-Co-MoS 2 -16.7; and the corresponding EDX diagram of the orange area in the HAADF-STEM diagram, with a scale bar of 100 nm.

(B) Co K-edge XANES spectra of Co foil, CoS, Co 3 O 4 , and mPF-Co-MoS 2 series samples.

(C) Co K-edge k 2 -weighted EXAFS spectra of CoS, Co 3 O 4 , Co foil, and mPF-Co-MoS 2 series samples .

(D) Mo K-edge k ² -weighted EXAFS spectra of mPF-MoS 2 and a series of mPF-Co-MoS 2 samples .

(E) Raman spectra of mPF-MoS 2 and different mPF-Co-MoS 2 samples.

(F) XRD patterns of mPF-MoS 2 and mPF-Co-MoS 2 samples.

The numbers (1), (2), (3), (4), (5) and (6) represent mPF-Co-MoS 2 with Co doping content of 0, 3.4, 7.6, 16.7, 21.1 and 31.8%, respectively .

Figure 5: Effect of Co doping on the HER performance of mesoporous foam MoS 2

(A) HER polarization curves of mPF-MoS 2 , 40% Pt / C, and mPF-Co-MoS 2 with different Co doping contents .

(B) Current density curves of mPF-MoS 2 and mPF-Co-MoS 2 with different Co doping contents when the overpotentials are 150, 200 , and 250 mV, respectively .

(C) mPF-Co-MoS 2 -16.7 durability measurement curve. First record the polarization curve, and under 100mVs ^-1 , 1000 scans between 0.1 ~ + 0.5V (relative to RHE). All HER measurements were performed in Ar-saturated 0.5MH 2 SO 4 electrolyte at 25 ° C.

(D) Tafel diagrams of mPF-MoS 2 , mPF-Co-MoS 2 -16.7 and 40% Pt / C.

Figure 6: Theoretical calculation of the effect of Co doping content on the MoS 2 HER

(A) When the coverage is 1/4 ML and 1/12 ML, the average △ G H Vs Co of S atom

Doping content curve.

(B) Schematic diagram of the bonding of the H 1s orbital and the S 3p orbital (MoS 2 ), where the electron consumption of the S atom reduces the orbital position and enhances the HS bond.

(C) Different charge densities of Co-doped MoS 2 (Co-doped content is 13.3 wt%; Co: Mo atomic ratio is 1: 2). The red and green colors in the graph indicate electron accumulation and depletion, respectively. The isosurface level is 0.11e / Bohr ³ .

(D) △ G H Vs of S atoms. Bader charge curves of S atoms with different structures; insets are S bonded to three Co, two Co and one Mo, one Co and two Mo, and three Mo atoms, respectively Atomic configuration diagram. Green ball: Mo; yellow ball: S; pink ball: Co.

【summary】

This article introduces the rational adjustment of the multi-scale structure and electronic properties of MoS 2 to achieve efficient HER electrocatalysis. This control strategy has achieved: On the macro scale, a large number of uniform mesopores contribute to the transfer of H 3 O ⁺ (reactant) and H 2 (product); on the nano scale, the vertically oriented MoS 2 layer provides rich activity Edge sites; on the atomic scale, the introduction of chemical doping further improves the intrinsic catalytic activity of S atoms in mesoporous foam-like MoS 2 materials. The research results not only provide a novel and effective way for MoS 2 high-efficiency electrocatalysis HER, but also provide a way of thinking for the development and application of other similar 2D materials to a certain extent.

Literature link : Multiscale structural and electronic control of molybdenum disulfide foam for highly efficient hydrogen production ( Nature Communications , 2017, 8, 14430; DOI: 10.1038 / ncomms14430)

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