Supporting Information

Transcription

1 Supporting Information Activity and Selectivity Control in CO2 Electroreduction to Multicarbon Products over CuOx Catalysts via Electrolyte Design Dunfeng Gao,, Ian T. McCrum, Shyam Deo, Yong-Wook Choi,, Fabian Scholten,, Weiming Wan, Jingguang G. Chen,, Michael J. Janik,*, and Beatriz Roldan Cuenya*,, *Corresponding author: Department of Interface Science, Fritz-Haber Institute of the Max Planck Society, Berlin, Germany Department of Physics, Ruhr-University Bochum, Bochum, Germany Department of Chemical Engineering, The Pennsylvania State University, 51 Greenberg, University Park, Pennsylvania, 16802, USA Department of Chemical Engineering, Columbia University, New York, New York 10027, USA Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973, USA 1

2 Calculation of the Faradaic efficiency of gas products: f gas = f flow c gas V m n F 100 I 60 Calculation of the Faradaic efficiency of liquid products: f liquid = c liquid V n F Q total 100 Calculation of the partial current density: j gas/liquid = I S f gas/liquid 1000 fgas: Faradaic efficiency of gas product, %; fliquid: Faradaic efficiency of liquid product, %; rgas: production rate of gas product, nmol s 1 cm 2 ; rliquid: production rate of liquid product, nmol s 1 cm 2 ; fflow: flow rate of CO2, ml min 1 ; I: electrolysis current at 60 min, A; cgas: volume ratio of gas product, determined by online GC; Vm: the molar volume of an ideal gas at 1 atmosphere of pressure, ml mol 1 ; cliquid: the concentration of liquid product after 1 hour of electrolysis, determined by HPLC or liquid GC, mol L 1 ; V: the volume of the electrolyte in the working cell, L; Qtotal: total charge consumed in 1 h of bulk electrolysis, C; n: number of transferred electrons for certain product; F: Faradaic constant, C mol 1. S: the effective geometric surface area of the electrode. 2

3 Table S1. Sample preparation details and electrolyte description. Sample Sample pre-treatment Electrolyte used for CO2 electroreduction Purpose in this work EP Electropolished Cu foil - CO-TPD O2P2 O2P10 O2P2-Li O2P2-Na O2P2-K O2P2-Cs O2P2-KI O2P2- CsI O2 20W 2min plasma treated Cu foils O2 100W 10min plasma treated Cu foils O2P2 after 30 min immersion in 0.1 M LiHCO3 O2P2 after 30 min immersion in 0.1 M LiHCO3 O2P2 after 30 min immersion in 0.1 M KHCO3 O2P2 after 30 min immersion in 0.1 M CsHCO3 O2P2 after 30 min immersion in 0.1 M KHCO M KI O2P2 after 30 min immersion in 0.1 M CsHCO M CsI - SEM, CO-TPD, XPS - CO-TPD 0.1 M LiHCO3 SEM, XPS, EC* 0.1 M NaHCO3 SEM, XPS, EC* 0.1 M KHCO3 SEM, XPS, EC* 0.1 M CsHCO3 0.1 M KHCO M KI 0.1 M CsHCO M CsI SEM, CO-TPD, XPS, EC* SEM, CO-TPD, XPS, EC* SEM, CO-TPD, XPS, EC* EC*: CO2 electroreduction measurements. 3

4 Table S2. Elemental composition (atomic percentage, at%) as determined by EDX of O2-plasma treated Cu foils (O2P2) shown in Figure 1 in the as-prepared state, after sample immersion in the different electrolytes for 30 min before and after 1 h of CO2 electroreduction (EC) at 1.0 V vs RHE. Error bars were obtained by averaging data from at least six different positions of two identical samples. Samples Concentration (at%) Cu O I O2P2 58 ± 2 42 ± 2 0 O2P2-Li O2P2-Na O2P2-K O2P2-Cs Before EC 55 ± 2 45 ± 2 0 After EC 95.3 ± ± Before EC 54 ± 2 46 ± 2 0 After EC 94.6 ± ± Before EC 52 ± 3 48 ± 3 0 After EC 95.5 ± ± Before EC 54 ± 2 46 ± 2 0 After EC 95.4 ± ± Before EC 46 ± 1 12 ± 3 42 ± 3 O2P2-CsI After EC_particle 67 ± 1 6 ± 1 27 ± 2 After EC_foil 94 ± ± ± 1 O2P2-KI Before EC 48 ± 1 17 ± 1 35 ± 2 After EC 94 ± 2 6 ± 2 0 4

5 Table S3. Total Faradaic efficiencies (FE) and partial current densities for C2+ products of Cu catalysts from this work compared to the literature. Catalyst Plasma-oxidized Cu foil Plasma-oxidized Cu foil Plasma-oxidized Cu foil Plasma-oxidized Cu foil Plasma-activated Cu nanocube Plasma-oxidized Cu foil Electrolyte Potential / Current density C 2+ FE (%) Partial current density for C 2+ (ma cm 2 ) 0.1 M KHCO V vs RHE M CsHCO V vs RHE M CsHCO M CsI 0.1 M CsHCO M CsI 1.0 V vs RHE V vs RHE Ref. this work this work this work this work 0.1 M KHCO V vs RHE M KHCO M KI 1.0 V vs RHE Cu 2O film 0.1 M KHCO V vs RHE Cu mesocrystals 0.1 M KHCO V vs RHE Cu 2O-derived Cu films 0.1 M KHCO ma cm electrodeposited Cu 2O 0.1 M KHCO V vs RHE electrodeposited Cu 2O 0.5 M KHCO V vs Ag/AgCl Bi-Phasic Cu 2O-Cu 0.1 M KCl 1.6 V vs RHE Oxide-derived Cu Foam 0.5 M NaHCO V vs RHE Oxide-derived Cu 0.1 M KHCO V vs RHE Cu-halide confined mesh Nano Dendritic Cu Cu nanoparticle ensembles 3 M KX (X = Br, I, or Cl) 0.1 M KBr 2.4 V vs Ag/AgCl 2 V vs Ag/AgCl M CsHCO V vs RHE Oxide-derived Cu 0.1 M CsHCO V vs RHE Oxide-Derived Cu 4Zn 0.1 M KHCO V vs RHE

6 Figure S1. SEM images acquired on the O2P2 samples in the as-prepared state (a), after 30 min immersion in 0.1 M LiHCO3 (O2P2-Li, b), 0.1 M NaHCO3 (O2P2-Na, d), 0.1 M KHCO3 (O2P2- K, f) and 0.1 M KHCO M KI (O2P2-KI, h), and after 1 h of CO2 electroreduction at 1.0 V vs RHE (c,e,g) in the corresponding electrolytes. The scale bars in the main images and inserts are 5 µm and 500 nm, respectively. The images in (f,g) were reproduced from the reference. 2 6

7 Figure S2. (a) Quasi in situ Cu 2p XPS spectra of O2P2 after 1 h of CO2 electroreduction at 1.0 V vs RHE in different electrolytes containing CsI, Cs, K, and Li, as well as the as-prepared O2P2 sample. Quasi in situ I 3d (b) and O 1s (c) XPS spectra of O2P2 after 1 h of CO2 electroreduction at 1.0 V vs RHE in 0.1 M CsHCO M CsI solution. 7

8 Figure S3. Roughness factor determination. Double-layer capacitance measurements by cyclic voltammetry between 0 and 0.25 V vs RHE, after 1 h of CO2 electroreduction in different electrolytes at 1.0 V vs RHE. In the case of 0.1 M CsHCO M CsI and 0.1 M KHCO M KI, the samples were transferred to 0.1 M CsHCO3 and 0.1 M KHCO3 for capacitance measurement, respectively, after 1 h of CO2 electroreduction at 1.0 V vs RHE and thorough washing with water. The roughness factor of an electropolished Cu foil (EP) measured in 0.1 M KHCO3 solution is used as reference and defined as 1. 8

9 Figure S4. Electrochemical surafce area (ECSA) normalzied current densities as a function of applied potential for O2-plasma-treated Cu foils in different electrolytes after 1 h of CO2 electroreduction. Solid lines are guides for the eye. The ECSA of each sample was calculated by multiplying the geometric surafce area with the roughness factor in Figure S3. 9

10 Figure S5. Faradaic efficiencies of C2H4 (a), C2H5OH (b), n-c3h7oh (c), CH4 (d), CO (e), HCOO (f), C2H6 (g), CH3COO (h) and H2 (i) as a function of applied potential for O2-plasmatreated Cu foils in different electrolytes after 1 h of CO2 electroreduction. Solid lines are guides for the eye. 10

11 Figure S6. Potential-dependent Faradaic efficiencies of ethylene, ethanol, n-propanol and total C2+ products over plasma-oxidized Cu foils in CO2-saturated 0.1 M KHCO3 solution. 11

12 Figure S7. FE ratio of C2+ / C1 as a function of applied potential for O2-plasma-activated Cu foils in different electrolytes after 1 h of CO2 electroreduction. Solid lines are guides for the eye. 12

13 Figure S8. Partial current densities of n-c3h7oh (a), HCOO (b), H2 (c), C2H6 (d) and CH3COO (e) as a function of applied potential for O2-plasma-treated Cu foils in different electrolytes after 1 h of CO2 electroreduction. Solid lines are guides for the eye. 13

14 Figure S9. Correlation between C2H4 partial current density and CO binding energy of electropolished (EP) Cu measured in 0.1 M KHCO3, plasma activated Cu (O2P2) measured in 0.1 M KHCO3 and 0.1 M CsHCO3, KI-pretreated O2P2 measured in 0.1 M KHCO M KI, and CsI-pretreated O2P2 measured in 0.1 M CsHCO M CsI. The highest CO desorption peak temperature of each sample in Figure 3 was used to calculate the binding energy following a firstorder Redhead model. 14

15 Figure S10. Partial current densities of H 2, C 1, and C 2+ products as a function of applied potential for O2-plasma-activated Cu foils in 0.1 M CsHCO M CsI solution after 1 h of CO2 electroreduction. Solid lines are guides for the eye. 15

16 Figure S11. Images of surface and adsorbate structures Images are rendered with VESTA. 16,17 16

17 Figure S12. Equilibrium adsorption potential calculated for adsorption of Li, Na, K, and Cs at 1/9 ML on Cu(100) in the absence and presence of near-surface solvent (6H2O*). 17

18 Figure S13. Surface normal dipole moment generated on the adsorption of Li, Na, K, and Cs at 1/9 ML on Cu(100) in the absence and presence of near-surface solvent (6H2O*). 18

19 Figure S14. Equilibrium adsorption potential for: K* at 1/9 ML on Cu(100), 1/9 ML with 2/9 ML of sub-surface oxygen on Cu(100), 1/4 ML on Cu(100), 1/4 ML on the missing row reconstruction ( DV ) of Cu(100), and 1/4 ML on the missing row reconstruction of Cu(100) with 1/2 ML O*. DV reconstruction from Duan et al

20 Figure S15: Equilibrium potential for adsorption of Li, Na, K, and Cs at 1/9 ML on Cu(100) with 6H2O* in the absence and presence of co-adsorbed I*. Calculated equilibrium adsorption potential for 1/9 ML I* in the absence of cations (Cu(100) with 6H2O*) is 1 VNHE. The effect of I* on K* and Cs* adsorption is due to the disruption of the water structure near the adsorbed cation in the presence of adsorbed iodine. Figure S15 shows the adsorption potentials of the alkali metal cations (at 1/9 ML) on Cu(100) in the presence of co-adsorbed iodide (at 1/9 ML) and 6H2O*. The effect of co-adsorbed iodide on alkali metal cation adsorption is small, showing a slight weakening effect on adsorption of the larger (K, Cs) cations. As iodide adsorbs with significant electron transfer (retaining only a small charge), we believe this effect is due to co-adsorbed iodide physically blocking some of the nearsurface solvent from approaching the adsorbed cations. A similar effect was seen in our prior work where the weakening effect of iodide on the CO2 electroreduction intermediates was accentuated in the presence of solvent. 2 While these results, in both our prior work, 2,18 and Fig. S14, support that co-adsorbed iodide directly affects the adsorption strength of many reaction intermediates as well as the alkali metal cations, we leave elucidation of the exact mechanism for the effect of iodide on reaction rate and mechanism (particularly in the presence of Cs*) for future work. As CuI nanocrystals were observed to remain stable in the Cs containing electrolyte, but not in the K containing electrolyte, the effect of iodide and of the alkali metal cations on the restructuring and stability of the electrode surface must also be examined. 20

21 References (1) Gao, D.; Zegkinoglou, I.; Divins, N. J.; Scholten, F.; Sinev, I.; Grosse, P.; Roldan Cuenya, B. Plasma-Activated Copper Nanocube Catalysts for Efficient Carbon Dioxide Electroreduction to Hydrocarbons and Alcohols. ACS Nano 2017, 11, (2) Gao, D.; Scholten, F.; Roldan Cuenya, B. Improved CO2 Electroreduction Performance on Plasma-Activated Cu Catalysts via Electrolyte Design: Halide Effect. ACS Catal. 2017, 7, (3) Ren, D.; Deng, Y.; Handoko, A. D.; Chen, C. S.; Malkhandi, S.; Yeo, B. S. Selective Electrochemical Reduction of Carbon Dioxide to Ethylene and Ethanol on Copper(I) Oxide Catalysts. ACS Catal. 2015, 5, (4) Chen, C. S.; Handoko, A. D.; Wan, J. H.; Ma, L.; Ren, D.; Yeo, B. S. Stable and Selective Electrochemical Reduction of Carbon Dioxide to Ethylene on Copper Mesocrystals. Catal. Sci. Technol. 2015, 5, (5) Handoko, A. D.; Ong, C. W.; Huang, Y.; Lee, Z. G.; Lin, L.; Panetti, G. B.; Yeo, B. S. Mechanistic Insights into the Selective Electroreduction of Carbon Dioxide to Ethylene on Cu2O-Derived Copper Catalysts. J. Phys. Chem. C 2016, 120, (6) Kas, R.; Kortlever, R.; Milbrat, A.; Koper, M. T. M.; Mul, G.; Baltrusaitis, J. Electrochemical CO2 reduction on Cu2O-Derived Copper Nanoparticles: Controlling the Catalytic Selectivity of Hydrocarbons. Phys. Chem. Chem. Phys. 2014, 16, (7) Kim, D.; Lee, S.; Ocon, J. D.; Jeong, B.; Lee, J. K.; Lee, J. Insights into an Autonomously Formed Oxygen-Evacuated Cu2O Electrode for the Selective Production of C2H4from CO2. Phys. Chem. Chem. Phys. 2015, 17, (8) Lee, S.; Kim, D.; Lee, J. Electrocatalytic Production of C3-C4 Compounds by Conversion 21

22 of CO2 on a Chloride-Induced Bi-Phasic Cu2O-Cu Catalyst. Angew. Chem. Int. Ed. 2015, 54, (9) Dutta, A.; Rahaman, M.; Luedi, N. C.; Mohos, M.; Broekmann, P. Morphology Matters: Tuning the Product Distribution of CO2 Electroreduction on Oxide-Derived Cu Foam Catalysts. ACS Catal. 2016, 6, (10) Li, C. W.; Kanan, M. W. CO2 Reduction at Low Overpotential on Cu Electrodes Resulting from the Reduction of Thick Cu2O Films. J. Am. Chem. Soc. 2012, 134, (11) Yano, H.; Tanaka, T.; Nakayama, M.; Ogura, K. Selective Electrochemical Reduction of CO2 to Ethylene at a Three-Phase Interface on copper(i) Halide-Confined Cu-Mesh Electrodes in Acidic Solutions of Potassium Halides. J. Electroanal. Chem. 2004, 565, (12) Reller, C.; Krause, R.; Volkova, E.; Schmid, B.; Neubauer, S.; Rucki, A.; Schuster, M.; Schmid, G. Selective Electroreduction of CO2 toward Ethylene on Nano Dendritic Copper Catalysts at High Current Density. Adv. Energy Mater. 2017, 7, (13) Kim, D.; Kley, C. S.; Li, Y.; Yang, P. Copper Nanoparticle Ensembles for Selective Electroreduction of CO2 to C2 C3 Products. Proc. Natl. Acad. Sci. 2017, 114, (14) Lum, Y.; Yue, B.; Lobaccaro, P.; Bell, A. T.; Ager, J. W. Optimizing C-C Coupling on Oxide-Derived Copper Catalysts for Electrochemical CO2 Reduction. J. Phys. Chem. C 2017, 121, (15) Ren, D.; Ang, B. S. H.; Yeo, B. S. Tuning the Selectivity of Carbon Dioxide Electroreduction toward Ethanol on Oxide-Derived CuxZn Catalysts. ACS Catal. 2016, 6,

23 (16) Duan, X.; Warschkow, O.; Soon, A.; Delley, B.; Stampfl, C. Density Functional Study of Oxygen on Cu(100) and Cu(110) Surfaces. Phys. Rev. B 2010, 81, (17) Momma, K.; Izumi, F. VESTA 3 for Three-Dimensional Visualization of Crystal, Volumetric and Morphology Data. J. Appl. Crystallogr. 2011, 44, (18) Akhade, S. A.; McCrum, I. T.; Janik, M. J. The Impact of Specifically Adsorbed Ions on the Copper-Catalyzed Electroreduction of CO2. J. Electrochem. Soc. 2016, 163, F477 F