Polymer Semiconductors for Artificial Photosynthesis: Hydrogen Evolution by Mesoporous Graphitic Carbon Nitride with Visible Light

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1 Polymer Semiconductors for Artificial Photosynthesis: Hydrogen Evolution by Mesoporous Graphitic Carbon Nitride with Visible Light Xinchen Wang*, Kazuhiko Maeda, Xiufang Chen, Kazuhiro Takanabe, Kazunari Domen*, Yidong Hou, Xianzhi Fu*, and Markus Antonietti Supporting Information Methods Synthesis of. To prepare /r (r refers to the initial silica/cyanamide mass ratio), cyanamide (3 g, 72 mmol; Aldrich) was dissolved in different amounts of a 4% dispersion of 12-nm SiO 2 particles (Ludox HS4,Aldrich) in water (1.5, 3.75, 7.5, g Ludox for the r=.2.5,1,1.5,) with stirring at 333 K overnight. The resulting transparent mixtures were then heated at a rate of 2.3 K/min over 4 h to reach a temperature of 823 K and then tempered at this temperature for another 4 h. The resulting brown-yellow powder was treated with a 4M NH 4 HF 2 for 24 h to remove the silica template. The powders were then centrifuged and washed three times with distilled water and twice with ethanol. Finally the powders were dried at 343 K under vacuum for overnight. The yield of /1 is ~68.5% based on carbon. To prepare bulk g-c 3, cyanamide was directly heated to 823 K and then tempered at this temperature for another 4 h. Characterizaiton. The XRD patterns were collected in a Bruker D8 Advance X-ray diffractometer (Cu Kα 1 irradiation). N 2 -sorption analysis was collected using Micromeritics ASAP 21 equipment. Transmission electron microscopy (TEM) and high-resolution TEM were recorded on a FEI Tecnai 2 microscope. PL and time-resolved PL spectra were obtained using an Edinburgh Analytical Instruments FL/FSTCSPC92 coupled with a time-correlated single-photo counting system at 298K. Optical diffuse reflectance spectra were collected at room temperature with a UV-VIS diffuse reflectance spectrometry (DRS; V-56, Jasco). A white standard of BaSO 4 was used as a reference. Absorption spectra were calculated from the reflectance data with the Kubelka-Munk function. Preparation of electrode. The working electrode was prepared on fluoride-tin oxide (FTO) glass plates (Solems, France, 1 Ω per square). The FTO glass pieces with a size of 3 1. cm were sonicated in acetone and ethanol, and then rinsed with millipore water and dried in an air stream. 5 mg of the powder was ground in a porcelain mortar with 1 ml of water to produce slurry. The obtained slurry was used for spreading onto the FTO glass substrate, whose side part was previously protected using Scotch tape. After air drying, the electrode was fired at 35 o C for 6 min in air to improve adhesion. A copper wire was connected to the side part of the FTO glass using a conductive tape. Uncoated parts of the electrode were isolated with epoxy, and the exposed area of the electrode under illumination was.25 cm 2. Photocurrent measurements. Visible light photocurrent measurements were measured using a standard two electrodes photoelectrochemical cell. The working electrode was immersed in a sodium sulfate electrolyte solution (.5 M) with a platinum-gauze counter electrode. The working electrode was irradiated from the back side (substrate/semiconductor interface) in order to minimize the S1

2 influence of thickness of the semiconductor layer. The electrode were excited by the chopped (.25 Hz) emission of an Oriel 1W xenon lamp with an UV (42 nm) cut-off filter. The light/dark short circuit photocurrent response under zero bias was recorded with an Agilent digital multimeter. All experiments were carried out under ambient conditions. Photocatalytic reaction. Reactions were carried out in a Pyrex top-irradiation reaction vessel connected to a glass closed gas circulation system. H 2 production was performed by dispersing.1 g of catalyst powder in an aqueous solution (1 ml) containing triethanolamine (1 vol.%) as sacrificial electron donor. In the case of deposition of Pt, an appropriate amount of H 2 PtCl 6 was dissolved in the reactant solution S1. The reactant solution was evacuated several times to remove air completely prior to irradiation under a HBO mercury short-arc lamp (5W) and a water filter. The wavelength of the incident light was controlled by using an appropriate long pass cut-off filter. The temperature of the reactant solution was maintained at room temperature by a flow of cooling water during the reaction. The evolved gases were analyzed by gas chromatography equipped with a thermal conductive detector. Figure S1. Enlarged TEM images of S2

3 1.35 / V ads (cm 3 /g) /1. /1.5 bulk g-c 3 Volume dv/dr (cm 3 /g) /1. /1.5 bulk g-c P/P Pore Size (nm) Figure S2. N 2 adsorption-desorption isothermal and corresponding BJH pore-size distribution curve of mesoporous g-c 3 sample. The pore-size distribution was determined from the desorption branch of the isothermal. V ads (cm 3 /g) P/P Volume dv/dr (cm 3 /g) Pore Size (nm) Figure S3. N 2 adsorption-desorption isothermal and corresponding BJH pore-size distribution curve of g-c 3 samples synthesized at different temperatures. The pore-size distribution was determined from the desorption branch of the isothermal. S3

4 Amount of evolved H 2 gas (μmol) Reaction Time (h) Figure S4. Time courses of H 2 production from water containing 1 vol.% triethonalminde as an electron donor by bare under visible light irradiation (of wavelength larger than 42 nm). The system produces hydrogen gas from water without using any metals. Intensity (a.u.) Used Fresh θ (degree) Figure S5. XRD patterns of /.2 before and after the photocatalytic reaction. S4

5 Intensity (a.u) 6 C 55 C 5 C 45 C θ (degree) Figure S6. XRD patterns of synthesized at different temperatures. F(R) 4 o C 45 o C 5 o C 55 o C 6 o C λ (nm) Figure S7. Diffuse reflectance absorption spectrum of synthesized at different temperatures. S5

6 1 8 6 T % 4 2 fresh used Wavenumber (cm -1 ) Figure S8. FTIR spectra of before and after the photocatalytic reaction. Table S1. Textural and photocatalytic properties of prepared at different temperatures a. catalyst a For reaction conditions, see Experimental Section. b BET Surface area. c Pore volume. d Average pore size determined by BJH method. e H 2 evolution rate. SA b (m 2 /g) PV c (cm 3 /g) PD d (nm) HER e (μmol/h) f Turnover frequency: n (H 2 ) per n (melem units) per hour TOF f 1 (h -1 ) S1 Kraeutler, B & Bard, A. J. Heterogeneous photocatalytic preparation of supported catalysts photodeposition of platinum on TiO 2 powder and other substrates. J. Am. Chem. Soc., 1, 4317 (1978). S6