Supporting Information Enhanced Activity and Stability of Carbon-Decorated Cuprous Oxide Mesoporous Nanorods for CO 2 Reduction in Artificial Photosynthesis Luo Yu a, Guojian Li a, Xiaoshu Zhang a, Xin Ba a, Guodong Shi a, Yong Li a, Po Keung Wong b, Jimmy C. Yu c and Ying Yu a * a College of Physical Science and Technology, Central China Normal University, Wuhan 430079, China b School of Life Science, The Chinese University of Hong Kong, Shatin, NT, Hong Kong SAR, China c Department of Chemistry, The Chinese University of Hong Kong, Shatin, NT, Hong Kong SAR, China * Corresponding author. Tel: 86-27-67867037; email: yuying01@mail.ccnu.edu.cn S1
S1. Supplementary Figures and Table Figure S1. XRD pattern of Cu(OH) 2 NTs. S2
Figure S2. XPS survey spectrum of C-2/Cu 2 O. S3
Figure S3. SEM (a1~d1) and HRTEM (a2~d2) images of C-x/Cu 2 O samples prepared with different glucose concentrations: (a1 and a2) 1 mg ml -1 ; (b1 and b2) 3 mg ml -1 ; (c1and c2) 4 mg ml -1 and (d1 and d2) 5 mg ml -1. S4
Figure S4. DF-STEM image of another C-2/Cu 2 O nanorod and its corresponding elemental mapping images of C, Cu and C+Cu. S5
Figure S5. UV-vis diffuse reflectance spectra of pure Cu 2 O and C-x/Cu 2 O. S6
Figure S6. Photocurrent density plots of (a) C-1/Cu 2 O, (b) C-3/Cu 2 O, (c) C-4/Cu 2 O and (d) C-5/Cu 2 O with light on/off cycles under visible light irradiation. S7
Figure S7. Photocurrent density (at the end of the last light cycle from the photocurrent density plots) and photostability of the C-x/Cu 2 O samples as a function of glucose concentration. The insert shows the relationship of glucose concentration and the average carbon layer thickness of the C-x/Cu 2 O samples. S8
Figure S8. (a) Total yield (CH 4 and C 2 H 4 ) over C-2/Cu 2 O under prolonged irradiation. (b) Time-dependent hydrocarbon evolution yield over C-x/Cu 2 O. S9
Figure S9. Gas chromatograms of O 2 evolved from the photocatalytic reaction over C-2/Cu 2 O under different irradiation time. S10
Figure S10. Photoluminescence (PL) spectra of pure Cu 2 O and C-2/Cu 2 O. S11
Figure S11. Photocatalytic activity of C-2/Cu 2 O for apparent quantum efficiency determination. S12
Table S1. AQE comparison of C-2/Cu 2 O with that of Cu 2 O-based and other representative photocatalysts during photoreduction of CO 2. Catalyst Light source Co-catalyst Hole scavenger Products AQE Reference Carbon-decorated Cu 2 O mesoporous 350W Xe lamp No No CH 4, C 2 H 4 2.07% This work nanorods λ > 420 nm (400 nm) Cu 2 O/reduced ChemSusChem graphene oxide 150 W Xe lamp rgo Na 2 SO 3 CO 0.34% 2014, 7, (rgo) full spectrum (400 nm) 1086-1093 Phys. Chem. Cu 2 O/RuO x 150 W Xe lamp RuO x Na 2 SO 3 CO 1.6% Chem. Phys. full spectrum (400 nm) 2014, 16, 5922-5926 450 W Xe lamp ACS Catal. Oxygen-deficient 400 nm < λ No No CO 0.134% 2016, 6, TiO 2 < 700nm (400-554 nm) 1097-1108 Small CdS-WO 3 300 W Xe lamp No No CH 4 0.4% 2015, 11, heterostructures λ > 420 nm CH 3 OH (420 nm) 5262-5271 g-c 3 N 4 /reduced 15 W energy- Nano Energy grapheme oxide saving daylight rgo No CH 4 0.56% 2015, 13, (rgo) lamp (250-388 nm) 757-770 Catal. Sci. Technol. Mesoporous 300 W Xe lamp No No CH 3 OH 0.18% 2013, 3, g-c 3 N 4 flakes λ > 420 nm C 2 H 5 OH (λ > 420 nm) 1253-1260 Ultrathin 300 W Xe lamp ACS Appl. ZnGa 2 O 4 with an IR No No CH 4 0.035% Mater. Interfaces nanosheets cut filter (280 nm) 2014, 6, 2356-2361 S13
Chem. Commun. Mesoporous 300 W Xe lamp 1 wt% Pt No CO, CH 4 0.2% 2011, 47, Zn 2 GeO 4 full spectrum (251 nm) 2041-2043 Self-doped Energy Environ. SrTiO 3-x with 300 W Xe lamp 0.3 wt% Pt No CH 4 0.2% Sci. 2011, 4, oxygen vacancies λ > 420 nm (600 nm) 4211-4219 Cobalt-containing Angew. Chem. zeolitic imidazolate 500 W Xe lamp Co-ZIF-9 Triethanol- CO 1.48% Int. Ed. framework (Co-ZIF-9) λ > 420 nm amine (TEOA) (420 nm) 2014, 53, /[Ru(bpy) 3 ]Cl 2 6H 2 O 1034-1038 S14
S2. Apparent Quantum Efficiency Calculation Apparent quantum efficiency (AQE) is an important parameter to evaluate the performance of phtocatalysts, which is defined as the following equation: 1-3 AQE = Number of reacted electrons Number of incident photons 100% (1) Eight and twelve electrons are required to convert CO 2 to CH 4 and C 2 H 4, respectively, so AQE for CH 4 and C 2 H 4 can be calculated using the following equations: 4 AQE -CH 4 = 8 thenumber of evolved CH 4 molecules the number of incident photons 100% (2) AQE - C 2 H 4 = 12 thenumber of evolved C2H 4molecules the number of incident photons 100% (3) In the following, we describe the AQE determination at λ 0 = 400 nm for C-2/Cu 2 O. 1) The CH 4 and C 2 H 4 production was measured using a similar experimental setup applying a λ = 400 nm band-pass filter for 8 hours. The results are shown in Figure S11, and the amount of CH 4 and C 2 H 4 molecules evolved in 8 hours were 0.064 and 0.082 µmol, respectively. 2) The average intensity of irradiation after the 400 nm band pass filter was determined to be 749 µw cm -2 by a light meter (LI-COR Biosciences, LI-250A) at room temperature and at the distance of 24 cm away from the light source, which was the exact distance that the catalyst was placed. 3) The irradiation area was controlled to be 1 cm 2 (0.11 mg). 4) The number of incident photons (N) is 4.34 10 19 as calculated by equation (4). S15
N = E 749 10 6 1 3600 8 400 10 9 = hc 6. 626 10 34 3 10 8 = 4.34 10 19 (4) 5) The AQE for CH 4 and C 2 H 4 was calculated based on the equations (2) and (3), respectively. AQE -CH 4 = 8 thenumber of evolved CH 4 molecules the number of incident photons 100% = 8 N A C [ H4] N 100% = 8 6.02 10 23 0.064 10 6 4.34 10 19 100% = 0.71% (5) AQE - C 2 H 4 = 12 thenumber of evolved C2H 4molecules the number of incident photons 100% = 12 N A [ CH 2 4] N 100% = 12 6.02 10 23 0.08 2 10 6 4.34 10 19 100% = 1.36% (6) Therefore, the total AQE of C-2/Cu 2 O at λ 0 = 400 nm was 2.07%. Where: N is the number of incident photons E is the total incident energy on photocatalyst (J) λ is light wavelength (m) h is Planck s constant (J s) c is speed of light (m s -1 ) N A is Avogadro s number (mol -1 ) [CH 4 ] and [C 2 H 4 ] are CH 4 and C 2 H 4 amount (mol) respectively after 8 hours S16
S3. Where Are the Electrons and Holes Going? Scheme S1. Schematic illustration of the reaction pathways of the electrons and holes generated from pure Cu 2 O and C-2/Cu 2 O under visible light. The thickness of the solid curves with arrows in the figure represents the possibility of the different pathways through which electrons and holes to go, and the thicker solid curve indicates larger possibility, while the thinner means smaller possibility. Semiconductor photocatalysis mainly involves two steps. The first is the photo-absorption, in which semiconductor photocatalysts convert light into energetic electrons and holes. 5 Then, these photoinduced electrons (or holes) subsequently migrate across both the bulk and the surface of photocatalysts to arrive at the catalytically reactive sites if they are not recombined, where the surviving electrons S17
and holes catalyze water splitting, CO 2 reduction, and contaminant degradation. 6 During these processes, e-h pairs are formed within several femtoseconds, their journeys from bulk to reactive sites require hundreds of picoseconds, and catalytic reactions between e/h and adsorbed reactants occur on a time scale ranging from several nanoseconds to several microseconds. 7 So, it is inevitable that e/h will react with the semiconductor not only during their journeys from bulk to surface but also at the surface waiting for photocatalytical reaction if the material is not too stable. Therefore, it is imperative to develop strategies like metal or metal oxide modification, surface defect engineering, heterojunction construction, and photoelectrochemical catalysis as the reviewer recommended, to ameliorate this situation. In fact, the study of photoelectrocatalysis is undergoing in this system, and some appealing results are being collected in our lab. Based on the above discussion, a schematic illustration of the reaction pathways for the electrons and holes generated from pure Cu 2 O and C-2/Cu 2 O is proposed in Scheme S1. For both pure Cu 2 O and C-2/Cu 2 O, there are mainly four pathways for photoinduced electrons and holes. Specifically, it includes 1 oxidization of H 2 O to O 2 and 2 oxidization of Cu 2 O to CuO for holes, 3 reduction of CO 2 and 4 reduction of Cu 2 O to Cu for electrons, and 5 bulk recombination and 6 surface recombination both for holes and electrons. However, compared to pure Cu 2 O, the processes of 2456 have been greatly reduced, while those of 13 dramatically improved for C-2/Cu 2 O. Thus, C-2/Cu 2 O is much robuster than pure Cu 2 O. S18
S4. Supplementary References (1) Morris, A. J.; Meyer, G. J.; Fujita, E. Accounts Chem. Res. 2009, 42, 1983-1994. (2) Sun, J.; Zhang, J.; Zhang, M.; Antonietti,M.; Fu, X.; Wang, X. Nature commun. 2012, 3, 1139. (3) Li, Y.; Wang, W. N.; Zhan, Z. L.; Woo, M. H.; Wu, C. Y.; Biswas, P. Appl. Catal. B. 2010, 100, 386-392. (4) Liu, L.; Jiang, Y.; Zhao, H.; Chen, J.; Cheng, J.; Yang, K.; Li, Y. ACS Catal. 2016, 6, 1097-1108. (5) Bai, S.; Jiang, J.; Zhang, Q.; Xiong,Y. J. Chem. Soc. Rev. 2015, 44, 2893-2939. (6) Kamat, P. V. Chem. Rev. 1993, 93, 267-300. (7) Zhang, J. Z. J. Phys. Chem. B 2000, 104, 7239-7253. S19