Supplementary Materials for

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1 advances.sciencemag.org/cgi/content/full/3/3/e /dc1 Supplementary Materials for Bulk layered heterojunction as an efficient electrocatalyst for hydrogen evolution Changdeuck Bae, Thi Anh Ho, Hyunchul Kim, Seonhee Lee, Seulky Lim, Myungjun Kim, Hyunjun Yoo, Josep M. Montero-Moreno, Jong Hyeok Park, Hyunjung Shin This PDF file includes: Published 31 March 2017, Sci. Adv. 3, e (2017) DOI: /sciadv fig. S1. Schematic illustration of the deposition system. fig. S2. Sequential gas-phase reaction of MoS2 on Si wafers. fig. S3. Influence of tp of MoCl5 on the uniform growth zone. fig. S4. Elemental and structural analyses of thin MoS2 films. fig. S5. Elemental analysis of annealed CMS layers. fig. S6. High-resolution XPS spectra of the annealed CMS layers in Mo (3d), S (2p), Cu (2p), and Cl (2p) regions. fig. S7. Raman spectra of MoS2 (300 cycles) grown on Au. fig. S8. The Mott-Schottky measurement of MoS2 on an Au/Si substrate. fig. S9. The Hall effect measurements of MoS2 on 500-nm-thick SiO2/Si. fig. S10. Arrhenius plot of the resistivity from Hall effect measurements on ALDgrown MoS2/SiO2 (500 nm)/si. fig. S11. SEM images of the as-grown CMS layers. fig. S12. Thickness dependence of ALD films and Mo contents as a function of position. fig. S13. HER activities from the CMS samples with thickness gradient. fig. S14. Schematic illustration of the structural evolution of BLHJs upon annealing. fig. S15. Low-magnification TEM micrograph of our CMS layers upon annealing (500 C for ~1 hour under N2 flow) to give an overview of the structures that consist of layered MoS2 and the superstructures of Chevrel clusters (marked by yellow and blue arrows, respectively). fig. S16. XRD patterns of our CMS on Cu subjected to different thermal treatments.

2 fig. S17. EDX elemental analysis of our TiO2/CMS/Cu structures. fig. S18. EDX line scan results for the TiO2/CMS/Cu structures. fig. S19. Detailed elemental maps of our CMS layers shown in Fig. 1E (main text), indicative of the origin of local variations in the detected elements. fig. S20. HR-TEM image of annealed CMS to give an overview of the local surface termination. fig. S21. Schematic of our three electrode cell used for HER experiments. fig. S22. Surface morphology of TiO2-coated annealed CMS. fig. S23. Estimation of electrochemically active surface area of our CMS material by double-layer capacitance measurements. fig. S24. XPS analyses of CMS materials to check possible contamination of noble metals. fig. S25. Stability against scanning of the present CMS system (10,000 times). fig. S26. XPS analyses of TiO2/CMS after stability tests. fig. S27. Reproducibility tests in the electrocatalytic performance of CMS and NMS materials. fig. S28. Electrochemical analysis and HER of the CMS layers with a non-pt counter electrode (that is, graphite). fig. S29. UPS spectra. fig. S30. Optical absorption of amorphous TiO2 grown on quartz glass. fig. S31. Energy band diagrams and the corresponding circuit models of various structures. fig. S32. HER measurements of our 40-nm-thick TiO2 with different control samples. fig. S33. KPFM study of our CMS on Cu. fig. S34. Local transport study of our annealed CMS/Cu samples. fig. S35. Comparison between our CMS/TiO2 and various HER materials (32) in the electrocatalytic performance. fig. S36. TEM image of the NMS layer as prepared to give an overview of the structures that densely consist of layered MoS2. fig. S37. ALD cycle dependent HER performance of annealed CMS. fig. S38. HR-TEM image of a CMS layer annealed at 700 C. fig. S39. Linear sweep voltammetry of the CMS layers annealed at different temperatures. table S1. Summary of the catalytic performance of various materials for the hydrogen evolution reaction, reported in the literature. Reference (48)

3 fig. S1. Schematic illustration of the deposition system. a, Schematic of our deposition system for MoS2. b, Schematic flowchart showing a full deposition cycle of MoCl5 and H2S, separated by N2 purging (red-dotted box).

4 fig. S2. Sequential gas-phase reaction of MoS2 on Si wafers. a, Schematic of the growth chamber. b, The chamber is a flow-through-type reactor, which can accommodate wafers up to 6 inches in diameter. When layered materials such as MoS2 are grown, the non-uniform gas flow (red arrows, distinguished by zones I through III) affects the surface chemistry and results in non-uniform growth rates. c, Representative photograph of the MoS2 layers grown on a 4-inch Si wafer, where the Aucoated wafer contrasts the grown films against the substrate. d, Scanning electron microscopy (SEM) images of MoS2 observed at different zones (marked by column headers). The upper and lower rows show plan-view SEM images and cross-sectional views, respectively.

5 fig. S3. Influence of tp of MoCl5 on the uniform growth zone. a-d, Different tp were applied when growing MoS2 on Au-coated, 4-inch Si substrates, as marked in the upper right of each panel.

6 fig. S4. Elemental and structural analyses of thin MoS2 films. a, XPS survey scan showing the presence of Cl. b-d, High-resolution XPS spectra in Mo 3d, S 2p, and Cl 2p regions. e, EDX spectra showing the presence of Cl. f. High-magnification TEM image.

7 fig. S5. Elemental analysis of annealed CMS layers. EDX analysis of the annealed CMS layers (three different samples: a-c, annealed at 500 C for 1 hr). Left column, cross-sectional SEM images. Middle column, EDX spectra. Right column, quantified atomic percentage for the selected elements.

8 fig. S6. High-resolution XPS spectra of the annealed CMS layers in Mo (3d), S (2p), Cu (2p), and Cl (2p) regions. Quantified atomic percentage are S2p 2.04 %; Cl2p 2.59 %; Cu2p 4.97 %; Mo3d 0.07 % except for C and O contamination.

9 fig. S7. Raman spectra of MoS2 (300 cycles) grown on Au. The characteristic Raman modes (E 1 2g and A1g) are labelled, and the difference between the in-plane (E 1 2g) and out-of-plane (A1g) peaks indicates the bulk MoS /C 2 (10 6 F -2 cm 4 ) Potential (V vs RHE) fig. S8. The Mott-Schottky measurement of MoS2 on an Au/Si substrate. The calculated results indicate a flat-band potential of V vs RHE and an n-type doping density of cm -3 when measured at a frequency of 4.8 Hz under dark conditions.

10 fig. S9. The Hall effect measurements of MoS2 on 500-nm-thick SiO2/Si. a, The electron concentration and b, the conductivity at different temperatures, exhibiting typical semiconductor behaviours. fig. S10. Arrhenius plot of the resistivity from Hall effect measurements on ALD-grown MoS2/SiO2 (500 nm)/si.

11 fig. S11. SEM images of the as-grown CMS layers. a, Cross-sectional view at low-magnification. Plane-view images of b, the top surface and c, the bottom surface. fig. S12. Thickness dependence of ALD films and Mo contents as a function of position. Thicknesses of a, MoS2 and b, CMS layers plotted against the distance from the chamber inlet, indicative of the influence of the gas flow during reactions. c, The amounts of elemental Mo across the resulting CMS layers, showing the uniform incorporation of MoS2 in the bulk.

12 fig. S13. HER activities from the CMS samples with thickness gradient. a, Polarization curves for CMS samples with thickness gradient. b, The corresponding Tafel curves. fig. S14. Schematic illustration of the structural evolution of BLHJs upon annealing. a, Two chalcogenide systems prepared by spontaneous sulfidation that are thermodynamically immiscible at given temperatures. b, Formation of the Chevrel phase (marked by cyan) by local alloying at the interfaces.

13 fig. S15. Low-magnification TEM micrograph of our CMS layers upon annealing (500 C for ~1 hour under N2 flow) to give an overview of the structures that consist of layered MoS2 and the superstructures of Chevrel clusters (marked by yellow and blue arrows, respectively).

14 fig. S16. XRD patterns of our CMS on Cu subjected to different thermal treatments.

15 fig. S17. EDX elemental analysis of our TiO2/CMS/Cu structures. a, Schematic depiction. b, Scanning TEM micrograph. c-f, The corresponding elemental maps as specified at the bottom of each figure.

16 fig. S18. EDX line scan results for the TiO2/CMS/Cu structures.

17 fig. S19. Detailed elemental maps of our CMS layers shown in Fig. 1E (main text), indicative of the origin of local variations in the detected elements.

18 fig. S20. HR-TEM image of annealed CMS to give an overview of the local surface termination. TEM micrographs of a, the CMS surfaces and b, the CMS/TiO2 interface to provide an information of local surface termination either by the MoS2 flakes or the Chevrel clusters marked by blue and yellow arrows, respectively. fig. S21. Schematic of our three electrode cell used for HER experiments. The structures are crosssectioned to show the detailed interior design. The system was designed to be gastight with a quartz window.

19 fig. S22. Surface morphology of TiO2-coated annealed CMS. a-b) Plane-view SEM of our annealed CMS after ALD coating of TiO2 layers at different magnifications. The inset shows the cross-sectional view. c) Three-dimensional reconstruction of an AFM height image of our CMS materials, indicative of a root mean squared roughness (RRMS) of 5 to 8 nm. fig. S23. Estimation of electrochemically active surface area of our CMS material by double-layer capacitance measurements. It resulted in a low roughness factor to be ~ 1.3 (equivalent planer surfaces, not porous) which is consistent with the AFM height image.

20 fig. S24. XPS analyses of CMS materials to check possible contamination of noble metals. XPS of our CMS material (a-b) as-grown, (c-d) annealed, and (e-f) with TiO2. (a, c and e) XPS survey scans. (b, d, and f) High resolution scans for checking possible contamination of the noble metals (the Ir4d/Pt4d/Ru3d region). The peak at ev is the expected C1s major peak (C-C) and the left-side shoulder, the C- O-C and O-C=O associated ones for adventitious carbon. No other peaks were detected in this region.

21 fig. S25. Stability against scanning of the present CMS system (10,000 times). The results exhibit that the performance did not degrade and rather stabilized upon initial surface activations. fig. S26. XPS analyses of TiO2/CMS after stability tests. XPS of our CMS system upon HER measurements (a-b) of 10,000 cycles and (c-d) for 100 hr. (a, c) XPS survey scans. (b, d) High resolution scans for checking possible contamination of the noble metals (the Ir4d/Pt4d/Ru3d region). The peak at ev is the expected C1s peak for adventitious carbon by detecting its decreased intensity after etching of 2~3 nm-thick surfaces. The contamination issue should be ruled out by observing no other peaks in this region.

22 fig. S27. Reproducibility tests in the electrocatalytic performance of CMS and NMS materials. Polarization curves for our (a) TiO2/CMS/Cu and (b) NMS/Ni electrocatalysts obtained from different batches, indicative of the prepared HER catalysts outperforming comparable Pt in a reproducible manner. The CMS/TiO2 systems displayed broader scattering in the performance than the cases of NMS. We believe that this pertains the variation by flow of in the MoS2 growing processes (as described in fig. S2). The non-ideal growth mode operates when layered materials such as MoS2 are deposited by ALD on planar surfaces. This was an open question, in the ALD community, on how ALD of layered materials works if a directional component predominates over the others. Two modes are possible: Highly textured in-plane growth via van der Waals (vdw) attachments when growing layered materials by ALD; a vertical growth mode where the layer-by-layer growths along the basal plane with strong covalent bonding of MoS2 is common if vdw secondary nucleation does not take place. In the case of NMS, the growth was less influenced by flow during ALD as a result of the presence of Ni forms. As a result, both showed the differences in performance.

23 fig. S28. Electrochemical analysis and HER of the CMS layers with a non-pt counter electrode (that is, graphite). a, Linear sweep voltammetry. b, Tafel curves. c, Onset HER potentials. d, Reproducibility obtained from different samples. e, Stability against cyclic voltammetry scanning of the present CMS system 1000 times.

24 fig. S29. UPS spectra. a, UPS spectra and b, the corresponding work functions of MoS2, Cu2S, asgrown CMS/Cu, annealed-cms/cu, and TiO2/annealed-CMS/Cu. c-d, Enlarged graphs of panel (a) at the specific spectral ranges.

25 fig. S30. Optical absorption of amorphous TiO2 grown on quartz glass. a, Optical absorption spectra of our TiO2 grown on quartz glass by ALD. The resulting Tauc plots constructed under the assumption that the resulting amorphous titania layers enable either b, indirect transition, or c, direct transition.

26 fig. S31. Energy band diagrams and the corresponding circuit models of various structures. a,b, Cu2S/Cu, c,d, MoS2/Cu, e,f, annealed-cms/cu and g,h, TiO2/annealed-CMS/Cu.

27 fig. S32. HER measurements of our 40-nm-thick TiO2 with different control samples. Polarization curves and the corresponding Tafel plots, respectively of a,b, Cu foil, c,d, Cu2S, e,f, MoS2, g,h, asgrown CMS.

28 fig. S33. KPFM study of our CMS on Cu. a-b, AFM height images at different magnifications. c, The corresponding surface potential map. d, The line profile results on the white solid line of panels b and c, i.e., A through A. fig. S34. Local transport study of our annealed CMS/Cu samples. a, AFM height image. b-f, The corresponding conduction maps at different loading forces of -1, -2, -3, -5, and -7 nn, respectively, and at a sample bias of -0.5 V.

29 table S1. Summary of the catalytic performance of various materials for the hydrogen evolution reaction, reported in the literature. Materials Current η Tafel, Onset Long-term Electrolyte References density, (mv) mv/dec potential, stability ma/cm 2 E vs RHE TiO 2 /CMS V ~0 ~ 10 days 1 M H 2 SO 4 This work NMS V~0 ~ 10 days 1 M KOH This work Pt 3 Ni nanoframes /C ,000 cycles 0.1 M KOH 9 Pt/C N.A. 0.1 M KOH 9 NiFe LDH/Ni foam hours 1 M NaOH 48 Cu 100-x Ti x ,000 cycles 0.1 M KOH 12 Nitrogen-doped hexagonal carbon hours; 10,000 cycles 0.5 M H 2 SO 4 14 Hybrid nanomaterial of Pt ,000 seconds 1 M KOH 11 NWs/SL-Ni(OH) 2 NiO/Ni-CNT hours 1 M KOH 13 Li + -Ni(OH)2-Pt ~130 - ~20-30 hours 0.1 M KOH 10 MoS 2 /CoSe 2 hybrid mv 24 hours 0.5 M H 2 SO 4 21 BiPt surface alloy V N.A. 0.5 M H 2 SO 4 7 Footnotes LDH (layered double hydroxide) NW (nanowires) SL (single-layered) CNT (carbon nanotubes)

30 fig. S35. Comparison between our CMS/TiO2 and various HER materials (32) in the electrocatalytic performance. Upon its longer activation (~24 hr), the present system successfully showed the highest performance in terms of both the overpotential and the stability without porosity. fig. S36. TEM image of the NMS layer as prepared to give an overview of the structures that densely consist of layered MoS2.

31 fig. S37. ALD cycle dependent HER performance of annealed CMS. a, Linear sweep voltammetry and b, Tafel curves of the CMS layers prepared by varying the pulse number. fig. S38. HR-TEM image of a CMS layer annealed at 700 C. The checkerboard-like clusters indicate the Chevrel phase of Cu2.76Mo6S8 and were densely formed in the matrix when compared with those annealed at 500 ºC (fig. S15).

32 fig. S39. Linear sweep voltammetry of the CMS layers annealed at different temperatures. The results of the control materials are also shown for comparison.