Cathodic Corrosion at the Bismuth-Ionic Liquid Electrolyte Interface under Conditions for CO2 Reduction

Transcription

1 Supporting Information Cathodic Corrosion at the Bismuth-Ionic Liquid Electrolyte Interface under Conditions for CO2 Reduction Jonnathan Medina-Ramos a ; Weiwei Zhang b ; Kichul Yoon b ; Peng Bai c ; Ashwin Chemburkar c ; Wenjie Tang c ; Abderrahman Atifi d ; Sang Soo Lee a ; Timothy T. Fister a ; Brian J. Ingram a ; Joel Rosenthal d,* ; Matthew Neurock c, *; Adri C. T. van Duin b, *; Paul Fenter a, * a Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, IL b Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA c Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN d Department of Chemistry and Biochemistry, University of Delaware, Newark, DE Index Page Figure S1 Scheme of X-ray transmission cell used in X-ray reflectivity and 2 electrochemical measurements. Figure S2 Electron density profiles of Bi/Graphene/SiC electrodes in solution. 3 Figure S3 Reflectivity of a Bi thin film in Ar-saturated MeCN containing 100 mm 4 [BMIM]OTf in its pristine state and after cyclic voltammetry. Figure S4 Bi (001) Bragg peak image on a Pilatus X-ray detector and its 5 integrated intensity along the X-axis used to determine the lateral size of Bi (001) crystalline domains. Figure S5 Change in lateral size of Bi (001) domains, and reflectivity as a function 6 of potential applied for Bi thin film cathodes in MeCN containing 100 mm [BMIM]OTf saturated with Ar, or 100 mm TBAPF 6 saturated with CO 2. Figure S6 Extended results from ReaxFF calculations on the binding of cations 7 [EMIM] +, [BMIM] + and TBA + onto Bi (001). Figure S7 Cation-to Bi (001) surface binding configurations obtained via ReaxFF. 8 Figure S8 Binding energies for cations [EMIM] +, [BMIM] + and TBA + onto a Bi 9 (001) surface, obtained via ReaxFF and DFT calculations. Figure S9 The density of states for a pristine Bi slab determined via DFT. 10 Table S1 Fitting parameters for low-angle reflectivity data 11 Table S2 Fitting parameters for CTR data 12 1

2 (a) (b) K in θ Q 2θ K out 2D X-ray detector CCD Figure S1. Scheme of the X-ray transmission cell used for in situ reflectivity and electrochemical measurements. Front view (A) and vertical cross section of the transmission cell (B) depicting vectors representing the incident (K in), scattered (K out), transmitted (black arrow), momentum transfer (Q, blue arrow), incident (θ) and scattering angle (2θ). 2

3 Figure S2. Electron density profiles showing all the layers that comprise the Bi thin film used as a working electrode (SiC substrate, graphene, Bi (001) and the amorphous bismuth component) immersed in a CO 2-saturated acetonitrile containing 100 mm [BMIM]OTf (fluid layer), after two and three CVs were between 0.3 V and 1.9 V, at 10 mv/s. Overlaid to each profile is the electron density profile of the working electrode/electrolyte system obtained through fitting of the low-angle reflectivity signal (solid black line). 3

4 Figure S3. Crystal truncation rod (CTR) signals from a Bi thin film immersed in an Ar-saturated acetonitrile solution containing 100 mm [BMIM]OTf, before (blue) and after running one (cyan squares), two (yellow diamonds) and three (white squares) cyclic voltammograms between 0.3 V and 1.90 V vs. Ag/AgCl, at 10 mv/s (the CTRs after one, two and three CV have been scaled by multiplying the original reflectivity by factors of 10 2, 10 4 and 10 6, respectively, in order to improve data visualization). The solid red lines represent the best fitting of the corresponding CTR curve, while the dashed red lines correspond to the bets fitting of the CTR recorded for the pristine film, which is overlaid to the rest of CTRs collected after one, two and three CVs for comparison purposes. 4

5 Figure S4. Two-dimensional image of the Bi (001) Bragg peak collected by the Pilatus detector (a) and its integrated intensity projected along the X-axis (b). The color scale bar to the right of (a) indicates the order of magnitude of the Bragg peak intensity reported in a logarithmic scale. A leastsquares fitting of the projection of the Bragg peak intensity with respect to the X-axis (b) shows that it is comprised of a Gaussian (FWHM I = 1.95) and a Lorentzian (FWHM II = 15.7) function element. The Gaussian component describes the X-ray beam s coherence while the Lorentzian function (FWHM) defines the average lateral size of the Bi (001) crystalline domains. 5

6 Calculation of the Average Lateral Size of Bi (001) Domains Present in the Sputtered Bismuth Films. The FWHM of the Lorentzian component from Figure S4-b is used to calculate the magnitude of the parallel momentum transfer, Q //. Then, the average lateral size of Bi (001) domains, D, is given by D = 2π/ Q //. 1 Figure S5. Change in lateral size of Bi (001) domains, and reflectivity as a function of potential applied for bismuth thin film cathodes in acetonitrile solution containing 100 mm [BMIM]OTf saturated with Ar (a-c), or 100 mm TBAPF 6 saturated with CO 2 (d-f). Figures (a) and (d) describe the potential function applied during voltammetry, (b) and (e) show the lateral domain size change (open red diamonds), and (c) and (f) plot the total reflectivity (open blue circles) as a function of time. 6

7 Figure S6. Snapshot of the Bi (001) structure in the presence of low density (a) [EMIM] +, (b) [BMIM] +, and (c) TBA + containing solutions after 100 ps of simulation (bismuth is shown in mauve, hydrogen in gray, nitrogen in blue and carbon in cyan). Atomic density profiles (e) and total Bi migration numbers (f) for the Bi (001) slab along the z-direction in low density [EMIM] + (brown), [BMIM] + (red) and TBA + (blue) containing solutions after 100 ps of simulation. The gray trace shows the initial Bi (001) atomic distribution. 7

8 Figure S7. Cation-to Bi (001) surface binding configurations. Side views (top three panels) and top views (middle three panels) and charge distribution at the Bi surface (bottom three panels) for (a-c) [EMIM] +, (d-f) [BMIM] + and TBA + binding onto Bi (001), respectively (bismuth is shown in mauve, hydrogen in gray, nitrogen in blue and carbon in cyan). 8

9 Figure S8. Binding energies for cations [EMIM] +, [BMIM] + and TBA + onto a Bi (001) surface, as a function of average excess charge per surface atom given in e /Bi atom. Figure (a) plots the binding energies for these cations obtained via ReaxFF calculations, while figure (b) corresponds to binding energies for [BMIM] + and TBA + determined using DFT for a 37-Bi cluster model. 9

10 Figure S9. The density of states for a pristine Bi slab. 10

11 Table S1. Fitting parameters for the low-angle reflectivity signal shown in Figure 1a, obtained using MotoFit. Parameter (units) Pristine film After one CV Number of layers 3 3 Scale 1 1 Background 0 0 Fluid layer thickness (Å) Infinite Infinite Fluid layer SLD (10 6 Å 2 ) Bismuth topmost layer thickness (Å) 27.2 ± ± 3 Bismuth topmost layer SLD (10 6 Å 2 ) 49 ± 1 42 ± 3 Bismuth topmost layer roughness (Å) 6.3 ± ± 0.3 Bismuth bottom layer thickness (Å) 33.6 ± ± 3 Bismuth bottom layer SLD (10 6 Å 2 ) 60.7 ± ± 0.1 Bismuth bottom layer roughness (Å) 3.3 ± ± 1 Graphene layer thickness (Å) 11.4 ± ± 0.06 Graphene layer SLD (10 6 Å 2 ) 13.9 ± ± 0.1 Graphene layer roughness (Å) 1.0 ± ± 0.1 SiC substrate thickness (Å) Infinite Infinite SiC substrate SLD (10 6 Å 2 ) 27 ± 1 27 ± 1 SiC substrate roughness (Å) 1.0 ± ± 0.1 χ

12 Table S2. Fitting parameters for the CTR data shown in Figures 1b and S2, obtained via modeling of the data as described above. Parameter (units) Pristine film After one CV After two CVs After three CVs SiC c-lattice (Å) Graphene c-lattice (Å) Number of graphene layers Graphene layer thickness (Å) Graphene rms width (Å) 0.94 ± ± ± ± 0.06 Height of the first graphene layer from the top of SiC (Å) 3.26 ± ± ± ± 0.06 Graphene coverage (%) 70 ± 4 70 ± 4 70 ± 4 70 ± 4 Bi (001) c-lattice (Å) ± ± ± ± Bi (001) film thickness (Å) 36.4 ± ± ± ± 0.9 Bi (001) rms width (Å) 3.8 ± ± ± ± 0.7 Height of Bi (001) film first layer from the top graphene layer (Å) 4.15 ± ± ± ± 0.05 Bi (001) film coverage (%) 80 ± 8 90 ± 7 82 ± 7 99 ± 8 χ R-factor References 1. Fenter, P. A., X-ray Reflectivity as a Probe of Mineral-Fluid Interfaces: A User Guide. In Reviews in Mineralogy and Geochemistry, GeoScienceWorld: 2002; Vol. 49, pp