O-coordinated W-Mo dual-atom catalyst for pH-universal electrocatalytic hydrogen evolution

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Science Advances  05 Jun 2020:
Vol. 6, no. 23, eaba6586
DOI: 10.1126/sciadv.aba6586
  • Fig. 1 Synthesis of W1Mo1-NG DAC.

    (A) Schematic illustration of the synthetic procedure. (B) The proposed chemical mechanism. The pairing of σ (*) and π (•) localized electrons at the zigzag sites is indicated.

  • Fig. 2 Morphology characterization of W1Mo1-NG.

    (A) SEM image. (B) TEM image. (C and D) AC HAADF-STEM images. The image clearly displays paired W-Mo atoms (white circles). (E) Statistical W-Mo diatomic distance in AC HAADF-STEM images. (F) Intensity profiles obtained in areas 1 to 3 and the corresponding schematics show different W-Mo projection distances on the visual plane. For top, middle, and bottom schematics, tilt angles of NG plane relative to the visual plane are 0°, 25°, and 90°, respectively. Atom colors: royal blue, W; cyan, Mo; dark gray, C; blue, N; red, O. (G) HAADF-STEM image and corresponding EDS elemental mapping images.

  • Fig. 3 Compositional characterization.

    (A) Raman spectra of W1Mo1-NG and NG. The two-dimensional (2D) peak is obviously enhanced in W1Mo1-NG, demonstrating that the number of graphene layers is reduced compared to raw NG. The appearance of D + G band at 2922 cm−1 declares the increased structure disorder. a.u., arbitrary units. (B) N2 adsorption-desorption isotherm; inset is pore size distribution diagram. (C) XRD patterns. The weak diffraction peaks at 14.6° and 43.1°, respectively, demonstrate the presence of oxygen-containing functional groups and a short-range order in stacked graphene layers. (D) XPS survey spectra. The W is absent in Mo2-NG, and Mo is absent in W2-NG. Inset is the percentages of W, Mo, N, O, and C in W1Mo1-NG measured by XPS and ICP-MS. High-resolution (E) Mo 3d and (F) W 4f XPS spectra. (G) O 1s spectra of Mo2-NG, W1Mo1-NG, and W2-NG. The fitted peak at 533.2 eV can be assigned to C─O bond. (H) High-resolution N 1s spectra of W1Mo1-NG, Mo2-NG, and W2-NG.

  • Fig. 4 X-ray absorption characterization.

    (A) XANES and (B) k3-weight FT-EXAFS spectra of W1Mo1-NG, Mo2-NG, and the reference samples at Mo K-edge. (C) XANES and (D) FT-EXAFS spectra of W1Mo1-NG, W2-NG, W powder, and WO3 at W L3-edge. The W ions in WO3 are in a [WO6] octahedron environment. WT-EXAFS of W1Mo1-NG, Mo2-NG, W2-NG, and the references at (E) Mo K-edge and (F) W L3-edge. (G and H) The corresponding Mo K-edge and W L3-edge EXAFS fitting curves for W1Mo1-NG at R-space and k-space, respectively. (I) The corresponding Mo K-edge EXAFS fitting curve for Mo2-NG at R-space. (J) The corresponding W L3-edge EXAFS fitting curve for W2-NG at R-space. The insets of (G), (I), and (J) are the schematic models of W1Mo1-NG, Mo2-NG, and W2-NG, respectively. Atom colors: royal blue, W; cyan, Mo; dark gray, C; blue, N; red, O.

  • Fig. 5 HER performance.

    The polarization curves and the corresponding Tafel plots of Mo2-NG, W1Mo1-NG, W2-NG, NG, and Pt/C in (A and B) 0.5 M H2SO4 and (C and D) 1.0 M KOH, respectively. (E) Comparison of the η10 in 0.5 M H2SO4 and 1.0 M KOH solutions for W1Mo1-NG and reported W- and Mo-based HER electrocatalysts. (F) Cyclic voltammetry (CV) cycles for W1Mo1-NG with varying scan rates from 20 to 300 mV s−1; the inset is Cdl measurement in 1.0 M KOH. (G) Turnover frequency (TOF) values of Mo2-NG, W1Mo1-NG, and W2-NG in 0.5 M H2SO4 and 1.0 M KOH solutions, respectively. (H) Polarization curves recorded from W1Mo1-NG catalyst before and after 50,000 potential cycles in 0.5 M H2SO4. (I) Galvanostatic responses recorded on W1Mo1-NG and Pt/C at a cathodic current density of 10 mA cm−2 under acidic and alkaline solutions.

  • Fig. 6 HER mechanism.

    Optimized geometries and possible active sites for H adsorption on (A) W1Mo1-NG, (B) Mo2-NG, and (C) W2-NG systems. Atom colors: cyan, Mo; royal blue, W; dark gray, C; blue, N; red, O; orange, H. (D) ΔGH diagrams of W1Mo1-NG, Mo2-NG, and W2-NG. The differential charge density maps of heteronuclear W1Mo1-NG system from (E) (100) and (F) (010) sections. The white dash line is the position of NG plane. The differential charge density maps of homonuclear (G) Mo2-NG and (H) W2-NG. The orange and aquamarine regions indicate electron depletion and accumulation, respectively. (I) Projected density of states (PDOS) of metal and O atoms in W1Mo1-NG, Mo2-NG, and W2-NG, the zero energy corresponds to the vacuum level. (J) pCOHP of the H adsorption on terminal O atoms for the W1Mo1-NG, Mo2-NG, and W2-NG models.

Supplementary Materials

  • Supplementary Materials

    O-coordinated W-Mo dual-atom catalyst for pH-universal electrocatalytic hydrogen evolution

    Yang Yang, Yumin Qian, Haijing Li, Zhenhua Zhang, Yuewen Mu, David Do, Bo Zhou, Jing Dong, Wenjun Yan, Yong Qin, Li Fang, Renfei Feng, Jigang Zhou, Peng Zhang, Juncai Dong, Guihua Yu, Yuanyue Liu, Xianming Zhang, Xiujun Fan

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