Defects Engineered Monolayer MoS2 for Improved Hydrogen ...
Defects Engineered Monolayer MoS2 for Improved Hydrogen Evolution Reaction Gonglan Ye 1, Yongji Gong 2,*, Junhao Lin 3,4, Bo Li 1, Yongmin He 1, Sokrates T. Pantelides 3,4, Wu Zhou 3, Robert Vajtai 1,*, Pulickel M. Ajayan 1,2,* 1 Department of Materials Science & NanoEngineering, Rice University, Houston, Texas 77005, USA 2 Department of Chemistry, Rice University, Houston, Texas 77005, USA 3 Materials Science & Technology Division, Oak Ridge National Lab, Oak Ridge, TN 37831, USA 4 Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235, USA
Figure S1. Set up of chemical vapor deposition (CVD) grown MoS2. Sulfur (S) and molybdenum oxide (MoO3) powder are used as the S and Mo precursor. Argon (Ar) is used as the carrier gas and the growth is carried on under atmospheric pressure and 750 ºC.
Figure S2. HER performance of monolayer MoS2 with different size. (a-d) Monolayer MoS2 with different size distribution but similar coverage and their corresponding HER performances (e). The MoS2 with smallest triangles shows the best performance among four different samples, while the largest MoS2 sample shows the worst HER performance.
Figure S3. Shift of Raman peaks of CVD grown MoS2 with oxygen plasma treatment. For A1g mode, the position shift was observed from 383.57 cm-1 to 381.62 cm-1 and 380.14 cm-1. For E12g mode, the position shift was observed from 405.85 cm-1 to 407.56 cm-1 and 409.26 cm-1. These shifts confirmed the lattice distortion caused by oxygen plasma exposure.
Figure S4. High resolution XPS analysis of the Mo atoms of the pristine CVD MoS2, H2 treated MoS2 and O2 plasma treated MoS2, where Mo-O bonding only forms in the O2 plasma treated sample.
Figure S5. The relationship between edge length and current density in the O2 plasma treated samples, where shows current density increases linearly with edge length. The edge length is normalized by pristine MoS2 sample and the current density is at -0.65 v vs RHE.
Figure S6. Comparison of the edge structure in the samples treated with oxygen plasma and
hydrogen annealing. (a-d) High resolution Z-contrast images shows the atomic structure of the open edges found in MoS2 treated by oxygen plasma (a, b) and hydrogen annealing (c, d). The edge structures are similar in the two samples, as indicated in the atomic structural model (e).
Figure S7. Histogram of the intensity of the atomic sites in the basal plane of MoS2 post-treated with oxygen plasma. Right: High resolution Z-contrast images of the hexagonal lattice of the basal plane of MoS2 posttreated with oxygen plasma. The image area is 12 nm×12nm. Left: Histogram of the intensity of each atomic sites through an atom-by-atom intensity quantification analysis. The dashed lines are Gaussian fit to the peaks. The concentration of S vacancies is estimated to be 1.9%. Similar sulfur vacancy concentration in the basal plane is also observed in the hydrogen annealing sample.
Figure S8. Electrochemical performance comparison of MoS2 treated by oxygen plasma exposure and hydrogen anneal.
Figure S9. Stability of the resultant defective MoS2. MoS2 treated by both oxygen plasma (A-B) and hydrogen anneal (C-D) shows good stability in air even after 30 days.
Figure S10. HER cycle performance to show the stability of the resultant defective MoS2. (A) MoS2 with 10 s plasma treatment (B) MoS2 annealed in hydrogen at 500 ˚C.
AUTHOR INFORMATION Corresponding Author *Yongji Gong, Robert Vajtai, Pulickel M. Ajayan *E-mail: [email protected], [email protected], [email protected]
Figure S1. Set up of chemical vapor deposition (CVD) grown MoS2. Sulfur (S) and molybdenum oxide (MoO3) powder are used as the S and Mo precursor. Argon (Ar) is used as the carrier gas and the growth is carried on under atmospheric pressure and 750 ºC.
Figure S2. HER performance of monolayer MoS2 with different size. (a-d) Monolayer MoS2 with different size distribution but similar coverage and their corresponding HER performances (e). The MoS2 with smallest triangles shows the best performance among four different samples, while the largest MoS2 sample shows the worst HER performance.
Figure S3. Shift of Raman peaks of CVD grown MoS2 with oxygen plasma treatment. For A1g mode, the position shift was observed from 383.57 cm-1 to 381.62 cm-1 and 380.14 cm-1. For E12g mode, the position shift was observed from 405.85 cm-1 to 407.56 cm-1 and 409.26 cm-1. These shifts confirmed the lattice distortion caused by oxygen plasma exposure.
Figure S4. High resolution XPS analysis of the Mo atoms of the pristine CVD MoS2, H2 treated MoS2 and O2 plasma treated MoS2, where Mo-O bonding only forms in the O2 plasma treated sample.
Figure S5. The relationship between edge length and current density in the O2 plasma treated samples, where shows current density increases linearly with edge length. The edge length is normalized by pristine MoS2 sample and the current density is at -0.65 v vs RHE.
Figure S6. Comparison of the edge structure in the samples treated with oxygen plasma and
hydrogen annealing. (a-d) High resolution Z-contrast images shows the atomic structure of the open edges found in MoS2 treated by oxygen plasma (a, b) and hydrogen annealing (c, d). The edge structures are similar in the two samples, as indicated in the atomic structural model (e).
Figure S7. Histogram of the intensity of the atomic sites in the basal plane of MoS2 post-treated with oxygen plasma. Right: High resolution Z-contrast images of the hexagonal lattice of the basal plane of MoS2 posttreated with oxygen plasma. The image area is 12 nm×12nm. Left: Histogram of the intensity of each atomic sites through an atom-by-atom intensity quantification analysis. The dashed lines are Gaussian fit to the peaks. The concentration of S vacancies is estimated to be 1.9%. Similar sulfur vacancy concentration in the basal plane is also observed in the hydrogen annealing sample.
Figure S8. Electrochemical performance comparison of MoS2 treated by oxygen plasma exposure and hydrogen anneal.
Figure S9. Stability of the resultant defective MoS2. MoS2 treated by both oxygen plasma (A-B) and hydrogen anneal (C-D) shows good stability in air even after 30 days.
Figure S10. HER cycle performance to show the stability of the resultant defective MoS2. (A) MoS2 with 10 s plasma treatment (B) MoS2 annealed in hydrogen at 500 ˚C.
AUTHOR INFORMATION Corresponding Author *Yongji Gong, Robert Vajtai, Pulickel M. Ajayan *E-mail: [email protected], [email protected], [email protected]
