Copper Nanoparticles Installed in Metal Organic Framework Thin Films. are Electrocatalytically Competent for CO 2 Reduction

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1 Supporting Information Copper Nanoparticles Installed in Metal Organic Framework Thin Films are Electrocatalytically Competent for CO 2 Reduction Chung-Wei Kung 1, Cornelius O. Audu 1, Aaron W. Peters 1, Hyunho Noh 1, Omar K. Farha 1,2 *, and Joseph T. Hupp 1,3 * 1 Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States 2 Department of Chemistry, Faculty of Science, King Abdulaziz University, Jeddah, Saudi 3 Argonne National Laboratory, 9700 South Cass Ave., Argonne, Illinois, 60439, United States Experimental Section Chemicals. All chemicals [benzoic acid (Sigma-Aldrich, 99.5%), zirconyl chloride octahydrate (Sigma-Aldrich, 98%), N,N-dimethylformamide (DMF) (Fisher Chemical, 99.8 %), hydrochloric acid (HCl) ( %, Avantor), acetone (Fisher Chemical, 99.5%), Bis(dimethylamino-2-propoxy)copper(II) (Cu(dmap) 2 ) (Strem Chemicals Inc., 97%), heptane (Sigma-Aldrich, anhydrous, 99%), sodium perchlorate (Aldrich, 98%), sodium hydroxide (Sigma-Aldrich, 98%), dimethylsulfoxide (DMSO) (Alfa Aesar, 99.9%), and deuterium oxide (Cambridge, 99.9%)] were used as received without further purification. Deionized water was used for preparing aqueous solutions. The chemicals used for synthesizing the 1,3,6,8-tetrakis(p-benzoic acid)pyrene (H 4 TBAPy) linkers were the same as those reported in our previous work. S1 S1

2 Preparation of NU-1000 and NU-1000 thin film. The synthetic procedure for the H 4 TBAPy linker and NU-1000 are the same as those reported in our previous study. S1 The NU-1000 thin films were grown on fluorine-doped tin oxide (FTO) conducting glass substrates by a solvothermal approach slightly modified from the one reported previously. S2 Briefly, the FTO glass substrate (8 Ω/sq, Hartford Glass), with a size of cm, was washed and pretreated with 0.5 mm H 4 TBAPy in DMF at room temperature for 12 h. Then, 2.7 g of benzoic acid and 105 mg of zirconyl chloride octahydrate were dissolved in 8 ml of DMF in a 20 ml screw-thread scintillation vial (28 mm 61 mm, with foil-lined urea cap) and heated at 80 C for 2 h. The solution was cooled and 40 mg of H 4 TBAPy was then added into this solution and the mixture was sonicated for 20 min. The pretreated FTO substrate was then immersed into the solution, with the conducting side facing downward. Thereafter, the vial was placed on the bottom of a gravity convection oven (VWR symphony ) with the temperature set at 90 C for 18 h. After the thin-film growth, benzoates coordinated to the Zr 6 node were removed via an acid wash and the obtained thin film was activated following the procedure reported previously. S2 The NU-1000 thin film was then obtained (Figure S4). Installation of Cu(II) via SIM in NU-1000 and NU-1000 thin film. In an argon-filled glove box, 80 mg of Cu(dmap) 2 was dissolved in 20 ml of anhydrous heptane. Then, 80 mg of NU-1000 was added into the solution and the mixture was kept for 24 h at room temperature, resulting in NU-1000 turning green in color. The mixture was decanted and the powder was washed with 20 ml of heptane three times, waiting 3 h in between each S2

3 washing step. Fresh heptane (20 ml) was then added and the mixture was kept overnight. Thereafter, the mixture was decanted and the obtained greenish solid was removed from the glove box. The solid was then placed in a drying oven at 100 C in air overnight to completely remove the heptane. The greenish powder was designated as Cu-SIM NU To install Cu(II) into the NU-1000 thin film, 1.0 mg of Cu(dmap) 2 was dissolved in 10 ml of heptane in an argon-filled glove box. Thereafter, a NU-1000 thin film grown on FTO was immersed in the solution and kept for 24 h at room temperature. The thin film was washed with heptane three times and immersed in 10 ml of fresh heptane overnight. The thin film was then removed from the glove box and placed in a drying oven at 100 C in air overnight. The resulting greenish thin film grown on FTO was designated as Cu-SIM NU-1000 thin film (Figure S4). Furthermore, Cu-FTO was prepared by simply replacing the NU-1000 thin film with a bare FTO substrate in the procedure mentioned above. Electrochemical measurements. All electrochemical experiments were performed on a CHI 660 electrochemical workstation (CH Instruments, Inc., USA). A three-electrode electrochemical setup in a sealed two-compartment cell (35.64 ml for each compartment) was used, with a platinum coil and Ag/AgCl/KCl (3 M) electrode (BASi) as the counter electrode and reference electrode, respectively. The Cu-SIM NU-1000 thin film, NU-1000 thin film, Cu-FTO or bare FTO substrate, all with an exposed geometric area of 0.66 cm 2 controlled by scraping residual film and pasting the polyimide insulating tape, served as the working electrode. The electrolyte consisted of 18 ml of 0.1 M NaClO 4 aqueous solution S3

4 in each compartment of the cell for all electrochemical experiments. Nitrogen or CO 2 was purged into the electrolyte for 20 min before electrochemical experiments if needed. Electrochemical data were converted to reversible hydrogen electrode (RHE) by adding ( ph) V to the measured potential. The pretreatment of the Cu-SIM NU-1000 thin film, which electrochemically reduced Cu(II) to metallic Cu, was conducted by applying a constant potential of V vs. RHE for 20 min to a fresh Cu-SIM NU-1000 thin film in nitrogen-purged electrolyte (ph = 7.20). Before all chronoamperometric experiments with Cu-SIM NU-1000 thin films, the above pretreatment was conducted. The electrolyte in both compartments was then purged with CO 2 for 20 min. Instrumentation. Thin-film and powder X-ray diffraction (XRD) patterns were collected on a Rigaku ATX-G workstation. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) measurements were conducted on a Hitachi SU8030, and the transmission electron microscopy (TEM) images were obtained on a Hitachi HT7700 TEM. EDS elemental mapping of the scraped thin film was conducted on a Hitachi SU8030 with a scanning transmission electron microscopy (STEM) sample holder. X-ray photoelectron spectroscopy (XPS) was measured on ESCALAB 250Xi, Thermo Scientific. UV-visible (UV-vis) absorption spectra were collected on a Shimadzu 1601 UV-vis spectrometer. Spectroelectrochemical experiments were conducted on the same UV-Vis spectrometer coupled with a CHI 1200 potentiostat (CH Instruments, Inc., USA). Nitrogen adsorption isotherms were collected on an ASAP 2020 (Micromeritics). S4

5 Inductively coupled plasma optical emission spectroscopy (ICP OES) measurements were conducted on a Thermo icap The ph values of the electrolytes were measured by an Oakton ph meter. After each chronoamperometric experiment, 200 µl of the headspace in the compartment of the working electrode was injected into a gas chromatograph (GC) equipped with a Restek ShinCarbon ST packed column and thermal conductivity detector (TCD) to analyze the gas-phase products. The electrolyte after each chronoamperometric experiment was analyzed by 1 H nuclear magnetic resonance spectroscopy (NMR, Agilent DD2 600 MHz). The NMR sample was prepared by mixing the electrolyte with deuterium oxide containing DMSO as the internal standard at a ratio of 9:1 and the sample was analyzed on the 1 H NMR instrument in water-suppression mode. Intensity (a.u.) (iii) (ii) (i) Cu-SIM NU-1000 NU-1000 Simulated NU-1000 (iii) (ii) (i) Theta (degree) Figure S1. Powder XRD patterns of NU-1000, Cu-SIM NU-1000, and the simulated pattern of NU S3 S5

6 a b c Normalized signal d Cu Zr Distance (µm) Figure S2. SEM images of a) NU-1000 and b) Cu-SIM NU c) SEM image of a crystal of Cu-SIM NU-1000 selected for EDS elemental line scan. d) Signals of Zr and Cu obtained from the line scan in c). 800 Cu-SIM NU-1000 N 2 uptake (cm 3 /g) Relative pressure (P/P 0 ) Figure S3. Nitrogen adsorption isotherm of the Cu-SIM NU S6

7 Figure S4. Photo of the NU-1000 thin film and Cu-SIM NU-1000 thin film. Cu-SIM NU-1000 thin film Cu 2p 3/2 Intensity (a.u.) Satellite for Cu 2+ Cu 2p 1/2 Satellite for Cu Binding energy (ev) Figure S5. XPS spectrum of the Cu-SIM NU-1000 thin film in the region of Cu 2p. S7

8 Current density (ma/cm 2 ) Cu-SIM NU-1000 thin film Scan rate: 50 mv/s Tested in N 2 -purged 0.1 M NaClO 4 (aq) V pretreated V pretreated V pretreated Before pretreatment E (V) vs. RHE Figure S6. CV curves of the Cu-SIM NU-1000 thin films before and after the electrochemical pretreatments at various potentials. Cu 2p 1/2 Pretreated Fresh Intensity (a.u.) Satellite for Cu 2+ Satellite for Cu 2+ Cu 2p 3/ Binding energy (ev) Figure S7. XPS spectra of the Cu-SIM NU-1000 thin films before and after the electrochemical pretreatment, measured in the region of Cu 2p. S8

9 Figure S8. EDS mappings of the nanoparticles appearing from the bottom edge of the MOF microrod, presented in the scraped Cu-SIM NU-1000 thin film after the pretreatment. S9

10 Absorbance Cu-SIM NU-1000 thin film/fto After pretreatment (Held at V vs. RHE) Before pretreatment Tested in N 2 -purged 0.1 M NaClO 4 (aq) Wavelength (nm) Figure S9. UV-vis spectra of the Cu-SIM NU-1000 thin film/fto electrode before and after the electrochemical pretreatment, measured in the N 2 -purged 0.1 M NaClO 4 aqueous solution. A constant potential of V vs. RHE was continuously applied to the electrode during the UV-vis measurement of the spectrum after pretreatment. Current density (ma/cm 2 ) Cu-SIM NU-1000 thin film V vs. RHE V vs. RHE V vs. RHE V vs. RHE V vs. RHE Time (s) Figure S10. Amperometric curves of Cu-SIM NU-1000 thin films measured in CO 2 -purged 0.1 M NaClO 4 aqueous electrolyte at various applied potentials. S10

11 Intensity (a.u.) a (ii) (i) After the pretreatment and electrolysis Fresh thin film (ii) b (i) Theta (degree) Figure S11. a) XRD patterns of the Cu-SIM NU-1000 thin film before and after pretreatment followed by electrolysis at V vs. RHE in a CO 2 -purged 0.1 M NaClO 4 aqueous electrolyte. b) SEM image of the Cu-SIM NU-1000 thin film after pretreatment and electrolysis at V vs. RHE. Reference (S1) Wang, T. C.; Vermeulen, N. A.; Kim, I. S.; Martinson, A. B. F.; Stoddart, J. F.; Hupp, J. T.; Farha, O. K. Nat. Protoc. 2016, 11, (S2) Kung, C.-W.; Mondloch, J. E.; Wang, T. C.; Bury, W.; Hoffeditz, W.; Klahr, B. M.; Klet, R. C.; Pellin, M. J.; Farha, O. K.; Hupp, J. T. ACS Appl. Mater. Interfaces 2015, 7, (S3) Mondloch, J. E.; Bury, W.; Fairen-Jimenez, D.; Kwon, S.; Demarco, E. J.; Weston, M. H.; Sarjeant, A. A.; Nguyen, S. T.; Stair, P. C.; Snurr, R. Q.; Farha, O. K.; Hupp, J. T. J. Am. Chem. Soc. 2013, 135, S11