Supporting Information Dynamic Interaction between Methylammonium Lead Iodide and TiO 2 Nanocrystals Leads to Enhanced Photocatalytic H 2 Evolution from HI Splitting Xiaomei Wang,, Hong Wang,, Hefeng Zhang,, Wei Yu, Xiuli Wang, Yue Zhao,, Xu Zong *, and Can Li * State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences; Dalian National Laboratory for Clean Energy, The Collaborative Innovation Center of Chemistry for Energy Materials (ichem), Zhongshan Road 457, Dalian 116023, China. University of Chinese Academy of Sciences, Beijing 100049, China. *Correspondence and requests for materials should be addressed to C. L. and X. Z. (email: canli@dicp.ac.cn, xzong@dicp.ac.cn). Page S1
Experimental Methods Chemicals and materials. PbI 2 (99.999%) was purchased from Sigma Aldrich. HI (7.6 mol L -1, 57 wt %, in water, unstabilized) was purchased from ACROS ORGANICS. Methylammonium iodine (MAI) was obtained from Luminescence Technology Corp. H 3 PO 2 (50 wt %, in water) was received from Alfa Aeasa. Commercial TiO 2 (P25) was obtained from Degussa. Nb 2 O 5 and methanol were received from Sinopharm Chemical Reagent Co., Ltd. Ta 2 O 5 was received from Shanghai Yuanji Chemical Reagent Co., Ltd. H 2 PtCl 6 6H 2 O was purchased from TCI Chemical. Synthesis of methylammonium lead iodide powder. Methylammonium lead iodide (MAPbI 3 ) was synthesized from aqueous solution by dissolving 0.645 mol L -1 of MAI and PbI 2 in 25 ml of aqueous HI. The aqueous HI was prepared by adding 50 wt % H 3 PO 2 to 57 wt % HI in a 4:1 volume ratio. The solution was heated at 100 o C for 1 h, then cooled to room temperature to obtain the saturated solution with MAPbI 3 precipitates. The MAPbI 3 precipitates were separated from the saturated solution by a centrifuge treatment and dried at 45 o C for 48 h in a vacuum oven. Preparation of Pt/TiO 2 (Ta 2 O 5, Nb 2 O 5 ). Pt/TiO 2 (Ta 2 O 5, Nb 2 O 5 ) was prepared with a photo-reduction deposition method using H 2 PtCl 6 as the precursor. In a typical procedure, 250 mg TiO 2 (Ta 2 O 5, Nb 2 O 5 ) sample was suspended in 60 ml deionized water. Desired amount of H 2 PtCl 6 solution and 15 ml CH 3 OH were added and the suspension was then irradiated by a 300 W Xe lamp (Ushio-CERMAXLX300) under constant stirring. After reaction for 4 h, the suspension was centrifuged five times in Page S2
deionized water and anhydrous ethanol, respectively, and dried at 60 o C for 12 h in a vacuum oven. Photocatalytic reactions. Photocatalytic reactions were performed in 5 ml saturated MAPbI 3 solution in HI in a homemade reactor with an exposed irradiation area of 1.82 cm 2. Typically, the saturated MAPbI 3 solution in HI was prepared as follows. First, 7.6 mol L -1 HI and H 3 PO 2 were mixed in a 4:1 volume ratio. Then, 10 ml of the reduced HI solution was mixed with 4.2 g of MAPbI 3 powder prepared in a HI solution under Ar atmosphere to prevent oxidation of the reduced HI solution. To saturate the reduced HI solution with MAPbI 3, stirring was continuously performed for 3 h under an Ar atmosphere in the dark. A 300 W Xe lamp (Ushio-CERMAXLX300) was used as the light source, and the irradiation spectrum was controlled using a 420 nm cutoff filter that passed wavelengths longer than 420 nm. The light intensity was fixed as 200 mw cm -2 in this case. Before irradiation, the reaction system was thoroughly purged with Ar thrice in order to drive off the air inside. In addition, for the additional preheat treatment systems, the reaction system was heated at 80 o C for 20 min, then cooled to the room temperature before irradiation. The amount of evolved H 2 was determined by gas chromatograph (Agilent, GC7890, TCD, Ar carrier). In particular, the photocatalytic reactions of Pt/MAPbI 3 and TiO 2 -Pt/MAPbI 3 were carried as follows. First, 10 mg of MAPbI 3 powder was added to 2 ml of saturated HI solution. Then, desired amount of H 2 PtCl 6 solution was mixed with the solution. Next, by using the 300 W Xe lamp with a 420 nm cutoff filter, photo-deposition was Page S3
conducted under Ar atmosphere for 2 h. The sample consisting of 10 mg of MAPbI 3 powder with photo-deposited Pt and 2 ml of saturated HI solution was transferred into 3 ml of saturated HI solution in reactor and purged with Ar thrice for Pt/MAPbI 3, and additional 5 mg TiO 2 was added for the TiO 2 -Pt/MAPbI 3. The photocatalytic performance was analyzed using GC under a 300 W Xe lamp (200 mw cm -2 ) with a light filter that passes wavelengths longer than 420 nm over 6 h. The experimental error for the activity measurement is within 5%. Calculation of the efficiency. The photocatalytic HI splitting of the hybrid system was carried out under irradiation with a solar simulator (AM 1.5G 100 mw cm 2, XES-40S2-CE). The solar HI splitting efficiency, so-called solar-to-chemical (STC) conversion efficiency, is the ratio of solar light converted to break the chemical bonding of HI. Our calculation for HI splitting efficiency is based on the amount of evolved hydrogen. The HI splitting efficiency was determined as follows Solar HI splitting efficiency = [Evolved H 2 (mol) 6.02 10 23 2 0.330 (ev) 1.6 10-19 ]/[P sol. (W cm -2 ) Area (cm 2 ) time (s)] 100% For instance, in the case of the Pt (0.75 wt %)/TiO 2 (7.5 mg)-mapbi 3 (50 mg), 44.6 μmol of H 2 was evolved after 30 min of light irradiation at 100 mw cm -2. The light irradiation area was 1.82 cm 2, the solar HI splitting efficiency was calculated to be 0.86%. Where 0.330 ev was the total potential for the splitting of HI with a concentration of 6.06 mol L -1 of HI. The apparent quantum efficiency (AQE) of HI splitting reaction by Pt/TiO 2 -MAPbI 3 Page S4
hybrid system was measured under the same reaction conditions with incident light at 420 nm by using band-pass filter. The AQE was calculated as follows AQE (%) = 100 (number of evolved H 2 molecules 2)/(number of incident photons) Characterizations. The as-prepared samples were characterized by X-ray power diffraction (XRD) on a Rigaku D/Max-2500/PC powder diffractometer. The sample powder was scanned using Cu-Kα radiation with an operating voltage of 40 kv and a current of 200 ma. The scan rate of 5 o min -1 was applied to record the patterns. UV-visible (UV-vis) diffuse reflectance spectra were recorded on a UV-vis spectrophotometer (JASCO V-650) equipped with an integrating sphere. The morphologies were examined by scanning electron microscopy (SEM, Quanta 200 FEG) and transmission electron microscopy (TEM, HITACHI HT7700). The surface areas were measured on a NOVA 4200e adsorption analyzer by N 2 adsorption at 196 C using the BET method. Photoluminescence (PL) measurements. The MAPbI 3 and TiO 2 /MAPbI 3 samples were coated on the substrate of glass to obtain the PL spectra. The steady state PL spectra were obtained with Edinburgh Instruments FLS920 fluorescence spectrometer. Time-resolved photoluminescence (TRPL) spectra were acquired using the time-correlated single photon counting method with an Edinburgh Instruments FLS920 fluorescence spectrometer. The excitation source is a picosecond pulsed diode laser at 406.8 nm with the pulse width 64.2 ps. All decays were measured using a 4096-channel analyzer in ambient condition. Page S5
Results and Discussion Figure S1. X-ray diffraction (XRD) pattern of the as-prepared MAPbI 3 powder. Page S6
Figure S2. SEM images of the as-prepared MAPbI 3 powder with scale bar of (a) 200 μm and (b) 20 μm. Page S7
Figure S3. Dissolution process of MAPbI 3 film that was deposited on TiO 2 film in saturated MAPbI 3 solution in HI. (a) Saturated MAPbI 3 solution in HI. (b) MAPbI 3 film that was deposited on TiO 2 film. The photograph of the MAPbI 3 film immersed in the saturated solution for (c) 0, (d) 2, (e) 3.5, and (f) 9 min. The MAPbI 3 film that was deposited on TiO 2 film completely dissolved in saturated HI solution over 9 min. Page S8
Figure S4. Photographs of the Pt/TiO 2 -MAPbI 3 hybrid powder in saturated HI solution. (i) Without preheat treatment, MAPbI 3 powders precipitated on the bottom of the reactor while Pt/TiO 2 can disperse well in the solution. (ii) MAPbI 3 powders dissolved completely after additional preheat treatment at 80 o C for 20 min. (iii) Improved dispersion of MAPbI 3 powders in the solution was observed upon re-precipitation at room temperature. Page S9
Figure S5. The UV-vis spectra of Pt (0.5 wt %)/TiO 2 solution with different concentrations of Pt/TiO 2. The absorption/scattering of light became more prominent with the increase of the concentration of Pt/TiO 2. Page S10
Figure S6. The time courses of photocatalytic H 2 evolution over Pt/MAPbI 3. Reaction conditions: 10 mg of Pt (0.375 wt %)/MAPbI 3, irradiation wavelengths λ > 420 nm. Page S11
Figure S7. TEM images of Pt/TiO 2 with various loading amounts of Pt. (a) 0 wt %, (b) 0.25 wt %, (c) 0.5 wt %, (d) 0.75 wt %, and (e) 1.0 wt %. Page S12
Figure S8. XRD patterns of Pt/TiO 2 with various loading amounts of Pt. Page S13
Figure S9. UV-vis spectra of Pt/TiO 2 with various loading amounts of Pt. Page S14
Figure S10. Influence of the amount of MAPbI 3 on the mass specific activity of MAPbI 3 for H 2 evolution. Reaction conditions: 10 mg of MAPbI 3, 5 mg of Pt (0.5 wt %)/TiO 2, irradiation wavelengths λ >420 nm, irradiation time 6 h, additional preheat treatment was performed at 80 o C for 20 min. Page S15
Figure S11. Influence of irradiation wavelengths on the rate of H 2 evolution. Reaction conditions: 10 mg of MAPbI 3, 5 mg of Pt (0.75 wt %)/TiO 2, additional preheat treatment was performed at 80 o C for 20 min. Page S16
Figure S12. The rate of H 2 evolution over Pt/TiO 2 -MAPbI 3 catalyst under 4 cycles of stability test. Reaction conditions: 10 mg of MAPbI 3, 5 mg of Pt (0.75 wt %)/TiO 2, irradiation wavelengths λ > 420 nm, additional heat treatment was performed at 80 o C/ 20 min. Page S17
Figure S13. XRD patterns of commercial Ta 2 O 5 and Pt (0.75 wt %)/Ta 2 O 5. Page S18
Figure S14. UV-vis spectra of commercial Ta 2 O 5 and Pt (0.75 wt %)/Ta 2 O 5. Page S19
Figure S15. TEM images of (a) commercial Ta 2 O 5 and (b) Pt (0.75 wt %)/Ta 2 O 5. Small dots corresponding to the Pt nanoparticles on Ta 2 O 5 were indicated in the blue circle. Page S20
Figure S16. XRD patterns of commercial Nb 2 O 5 and Pt (0.75 wt %)/Nb 2 O 5. Page S21
Figure S17. UV-vis spectra of commercial Nb 2 O 5 and Pt (0.75 wt %)/Nb 2 O 5. Page S22
Figure S18. TEM images of (a) commercial Nb 2 O 5 and (b) Pt (0.75 wt %)/Nb 2 O 5. Small dots corresponding to the Pt nanoparticles on Nb 2 O 5 were indicated in the blue circle. Page S23
Figure S19. The time courses of photocatalytic H 2 evolution on Pt (0.75 wt %)/Ta 2 O 5 -MAPbI 3 and Pt (0.75 wt %)/Nb 2 O 5 -MAPbI 3. Reaction conditions: 10 mg of MAPbI 3, 5 mg of Pt (0.75 wt %)/Ta 2 O 5 or Pt (0.75 wt %)/Nb 2 O 5, irradiation wavelengths λ > 420 nm, additional heat treatment was performed at 80 o C/ 20 min. Page S24
Figure S20. Schematic energy band diagrams of MAPbI 3 and Ta 2 O 5. Page S25
Figure S21. Schematic energy band diagrams of MAPbI 3 and Nb 2 O 5. Page S26
Figure S22. SEM images of (a) commercial TiO 2 and (b) Ta 2 O 5 nanoparticles used in the presence study. Page S27
Table S1. PL decay lifetime of the MAPbI 3 and TiO 2 /MAPbI 3 samples. Samples τ ave (ns) τ 1 (ns) A 1 (%) τ 2 (ns) A 2 (%) MAPbI 3 231.52 77.56 15.61 260.00 84.39 TiO 2 /MAPbI 3 131.51 58.90 51.80 209.55 48.20 Page S28