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1 Supporting Information Formation of Hierarchical Heterostructured Cages as An Efficient Photocatalyst for Hydrogen Evolution Sibo Wang, Bu Yuan Guan, Xiao Wang, and Xiong Wen (David) Lou * School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore , Singapore * Corresponding author. xwlou@ntu.edu.sg Experimental details Synthesis of ZIF-67 polyhedrons: In a typical synthesis, two solutions were prepared by dissolving Co(NO3)2 6H2O (175 mg) and 2-methylimidazole (320 mg) in 40 ml of methanol. Afterward, the two solutions were mixed rapidly and aged for 6 h at room temperature. The produced ZIF-67 precipitate was washed with ethanol 2 times and then dispersed in 20 ml of ethanol for further use. Synthesis of Co9S8 dodecahedral cages: 10 ml of the obtained ZIF-67 mixture was added into 10 ml of an ethanol solution containing 50 mg of thioacetamide (TAA), and stirred for 2 min. Then, the resultant mixture was transferred into a Teflon-lined autoclave (40 ml in capacity) and maintained at a preheated oven at 180 C for 3 h. After cooling down to room temperature, the precipitate was washed with ethanol several times and dried at 60 C, yielding a cobalt sulfide S1

2 product (denoted as CoSx). The Co9S8 dodecahedral cages were produced by annealing the CoSx material in an argon flow at 550 C for 6 h with a heating rate of 5 C min -1. Synthesis of hierarchical Co9S8@ZnIn2S4 heterostructured cages: Growth of ZnIn2S4 nanosheets on the surface of the Co9S8 dodecahedral cages was achieved by a low-temperature solvothermal reaction. Typically, certain amounts of the Co9S8 cages (e.g., 6.3, 8.6 and 12.7 mg), 8 ml of H2O (ph = 2.5), and 2 ml of glycerol were added into a glass bottle (20 ml in capacity) and stirred for 30 min, followed by the addition of 27.2 mg of ZnCl2, 58.6 mg of InCl3 4H2O, and 30 mg of TAA. The obtained mixture was stirred for 5 min and then put into an oil bath at 80 C under stirring. After reaction for 2 h, the products were washed with ethanol three times and dried at 60 C in a vacuum. The obtained samples were denoted as 15%-Co9S8@ZnIn2S4, 20%-Co9S8@ZnIn2S4, and 30%-Co9S8@ZnIn2S4, respectively, where the prefixes indicated the theoretical weight percentage of Co9S8 in the Co9S8@ZnIn2S4 hybrids. Typically, the material used for characterizations and photocatalytic tests was the 20%-Co9S8@ZnIn2S4 sample (Co9S8@ZnIn2S4 for clarity) unless otherwise stated. For comparison, the nanosheet-assembled ZnIn2S4 particles were synthesized under the same reaction conditions without the addition of Co9S8 as the substrates. Synthesis of Co9S8 and Co9S8@ZnIn2S4 nanoparticles (NPs): The Co9S8 NPs were synthesized according to a modified method. 1 Typically, 0.5 mmol of Co(NO3)2 6H2O and 4 mmol of thiourea were added to 30 ml of H2O and stirred at room temperature for 10 min to achieve a homogeneous solution, which was then dried at 80 C to evaporate the solvent completely. The resultant product was thermally treated at 800 C for 1 h with a heating rate of 5 C min -1 under a N2 atmosphere, obtaining the Co9S8 NPs. The synthesis of the Co9S8@ZnIn2S4 NPs is similar to that of the 20%- S2

3 cages, but with the same amount of Co9S8 NPs to replace the Co9S8 cages. Materials characterization. The morphology and structure of the samples were examined by fieldemission scanning electron microscope (FESEM; JEOL-6700) and transmission electron microscope (TEM; JEOL, JEM-2010). The crystal phases of the samples were analyzed by X-ray diffraction (XRD) on a Bruker D2 Phaser X-Ray Diffractometer with Ni filtered Cu Kα radiation (λ = Å) at a voltage of 30 kv and a current of 10 ma. The compositions of the samples were analyzed by energy-dispersive X-ray spectroscopy (EDX) attached to the FESEM instrument. Elemental mapping images were recorded using EDX spectroscope attached to TEM (JEOL, JEM- 2100F). The chemical composition of the samples was analyzed by the X-ray photoelectron spectra (XPS, PHI Quantum 2000) with the reference of C1s peak (284.6 ev). N2 sorption isotherms were collected on an ASAP2020M apparatus. The samples were degassed in vacuum at 120 C for 4 h and then measured at 77 K to determine N2 sorption. UV-vis diffuse reflectance spectra (DRS) were obtained using a Varian Cary 500 UV-vis-NIR spectrometer equipped with an integrating sphere and BaSO4 was used as a reference. Photoluminescence (PL) spectra were acquired on Edinburgh Analytical Instruments FL/FSTCSPC920 coupled with a time-correlated single-photo-counting system at room temperature. For the measurement of PL lifetime, the used excitation wavelength (λex) was 350 nm and the maximum emission wavelength (λem) was 500 nm. The average lifetime (Ave. τ) is calculated according to τ = τ1 I1 + τ2 I2 + τ3 I3 (τi is the lifetime; Ii is the relative intensity). 2 Electrochemical impedance spectroscopy (EIS) measurements were carried out at the open circuit potential over the frequency range from 10-2 to 10 5 Hz. Mott-Schottky plots were collected on a BioLogic VSP-300 electrochemical system without any irradiation to obtain the S3

4 intrinsic features of the flat-band potentials. The frequencies were 0.5, 1.0, and 1.5 khz. Prior to all measurements, the electrolyte (0.2 M Na2SO4 aqueous solution) was purged with N2. An Agilent 7890B gas chromatograph (GC) equipped with a thermal conductivity detector (TCD) and a packed column (TDX-01) was utilized to analyze and quantify the H2 gas produced from the reaction system. Argon was used as the carrier gas. Photocatalytic H2 evolution. Typically, 4 mg of the photocatalyst, 1 ml of triethanolamine (TEOA), and 5 ml of H2O were added into a gas-closed glass reactor (80 ml in capacity). 3-5 A 300W Xe lamp with a 400 nm cutoff filter was used as the light source. During the photocatalytic process, the reaction system was vigorously stirred by a magnetic stirrer, and the reaction temperature was controlled by circulating cooling water. After each reaction, the generated H2 were sampled and quantified by an Agilent 7890B GC. All the determined H2 amounts were the average data of three samples. S4

5 Figure S1. (a-c) FESEM images and (d) TEM image of ZIF-67 dodecahedrons. Figure S2. (a) XRD pattern and (b) EDX spectrum of ZIF-67. S5

6 Figure S3. (a) XRD pattern and (b) EDX spectrum of CoSx.. Figure S4. (a,b) FESEM images, (c) TEM image and (d) SAED pattern of CoSx cages. S6

7 Figure S5. (a) XRD pattern and (b) EDX spectrum of Co9S8. Figure S6. (a,b) FESEM images, (c) TEM image and (d) SAED pattern of Co9S8 cages. S7

8 Figure S7. (a) N2 sorption isotherms and (b) the corresponding pore size distribution of Co9S8 cages. Figure S8. (a) XRD pattern and (b) EDX spectrum of Inset in (b) is the corresponding atomic percentages of the elements. S8

9 Figure S9. (a) FESEM image, (b) SAED pattern, (c) FESEM image and (d) TEM image of cages, (e) HRTEM image of the shell of a single Co9S8@ZnIn2S4 cage. S9

10 Figure S10. XPS spectra of (a) survey spectrum and high-resolution XPS spectra of (b) S 2p, (c) Zn 2p and (d) In 3d. The survey spectrum gives the signal peaks of Co, Zn, In and S elements, consistent with the results of EDX. In the high-resolution XPS spectrum of S 2p, the peaks located at and ev are assigned to the S 2p1/2 and S 2p3/2 orbitals of divalent sulfide ions (S 2- ), respectively, which is in line with the formation of ZnIn2S4. 6,7 The other two peaks of S 2p centered at and ev are attributed to S 2p1/2 and S 2p3/2 of Co-S bondings, in agreement with the results of previous works on Co9S8. 8,9 In the Zn 2p XPS spectrum, two peaks with the binding energy values of (Zn 2p1/2) and ev (Zn 2p3/2) are observed, which indicates the Zn(II) oxidation state of ZnIn2S4. 7,10 The In 3d high resolution XPS spectrum shows two peaks at ev (In 3d5/2) and ev (In 3d3/2), corresponding to the In cation with a valence of +3. 6,7 S10

11 Figure S11. Pore size distribution curve of S11

12 Figure S12. (a-c,e-g,i-k,m-o) FESEM images and (d,h,l,p) TEM images of the hierarchical heterostructured cages collected at different reaction times: (a-d) 10 min, (e-h) 20 min, (i-l) 30 min, and (m-p) 40 min. S12

13 Figure S13. (a,b) FESEM images and (c,d) TEM images of cages. Figure S14. (a) XRD pattern and (b) EDX spectrum of Inset in (b) is the corresponding atomic percentages of the elements. S13

14 Figure S15. (a,b) FESEM images and (c,d) TEM images of cages. Figure S16. (a) XRD pattern and (b) EDX spectrum of Inset in (b) is the corresponding atomic percentages of the elements. S14

15 Figure S17. XRD pattern of ZnIn2S4 particles. Figure S18. (a,b) FESEM images of nanosheet-assembled ZnIn2S4 particles. S15

16 Figure S19. XRD patterns of (a) Co9S8 and (b) NPs. Figure S20. (a,b,d,e) FESEM images and (c,f) TEM images of (a-c) Co9S8 and (d-f) NPs. S16

17 Figure S21. UV-Vis DRS spectra of Co9S8, 30%- and ZnIn2S4. Figure S22. Band gap energies of Co9S8 and ZnIn2S4. S17

18 Figure S23. Mott-Schottky plots of (a) Co9S8 and (b) ZnIn2S4. Figure S24. The separation and transfer processes of photogenerated electrons (e - ) and holes (h + ) in the Co9S8@ZnIn2S4 heterostructure for H2 evolution. S18

19 Figure S25. (a) XRD patterns of before and after photocatalytic H2 evolution reactions. (b) FESEM image of after photocatalytic H2 evolution reactions. S19

20 Table S1. Comparison of photocatalytic H2 generation performance. Catalyst CdS/Co9S8 ZnIn2S4/MoSe2 O-doped ZnIn2S4 BP/CN Phosphorene/g-C3N4 ZnIn2S4 layers CTF-HUST-2 PCN CCTs CTF-1 (C8N2H4) HM-TiPPh MIL-125-(SCH3)2 N2-COF Hole scavenger Cocatalyst TEOA / Na2S-Na2SO3 / Lactic acid / Na2S-Na2SO3 / Methanol / Lactic acid / Lactic acid Pt TEOA Pt TEOA Ni Methanol Pt TEOA-Methanol Pt TEOA Pt TEOA Pt TEOA chloro(pyridine)cobaloxime H2 evolution rate (μmol h -1 g -1 ) 6250 Ref. This work S20

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