Electrochemical quartz crystal microbalance (EQCM) studies of ions and solvents insertion into highly porous activated carbons

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1 Supporting Information Electrochemical quartz crystal microbalance (EQCM) studies of ions and solvents insertion into highly porous activated carbons Mikhael D. Levi a, Naomi Levy a, Sergey Sigalov a,gregory Salitra a, Doron Aurbach a1, J. Maier b a Department of Chemistry, Bar-Ilan University, Ramat-Gan 529, Israel.. a1 Fax: , aurbach@mail.biu.ac.il b Max Planck Institute for Solid State Research, Heisenbergstr. 1, 7569 Stuttgart, Germany S1

2 1. Microscopic and porous structure characterization of the Kuraray YP- 17 activated carbon used in this study A Volume of N 2 / cc STP/g) Relative pressure p/p o B Cumulative pores volume /cm 3 g TOA + TEA + C Pores width / Å Figure S1. SEM image (Inspect S, FEI company, USA) of pristine Kuraray YP-17 carbon powder (A), N 2 adsorption and desorption isotherms at 77 K (Autosorb-1M, Quantachrome Instruments, USA) of the same carbon powder (B), and a plot of the cumulative pores volume versus pores width, calculated from the adsorption isotherm using DFT method (C). The red arrows show the pores widths corresponding to the (unsolvated) diameters of TOA + and TEA + cations, respectively. S2

3 2. Preparation of coatings from a slurry composed of a carbon powder, 9%, and PVdF binder, 1% in N-methyl pyrrolidone on a quartz crystal surface Figure S2. A sketch showing schematically the process of coating of the AT cut 5MHz Maxtek's 1 inch diameter quartz crystal with a slurry containing 9 % carbon particles and 1 % PVdF binder in N- methylpyrrolidone. The crystal is placed into a stainless steel mask (frame), so that only Pt or Au electrodes of the crystal are exposed to spray of the slurry from a home-made spray gun (pulverizer). The crystal is put onto a hot plate at a temperature of 12 C. Pure Ar or N2 gasses enter a home-made spray head under the elevated pressure. The slurry is continuously mixed in a beaker using a magnetic stirrer. Crystals coated with composite carbon deposits are dried in an oven for 3 min at 12 C. After cooling to room temperature, the crystal is placed into a Maxtek crystal holder linked through a rubber o-ring to a glass electrochemical cell. Prior to contact with the crystal the solution was deairated by pure argon whereas during the measurements the argon flux was directed above the solution to protect it from contamination by oxygen (from air). S3

4 3. Supplementary Figures and Table related to EQCM and in-situ conductivity characterization of carbon coated electrodes Table S1. The series of quaternary ammonium and lithium tetrafluoroborates: the ionic radii (literature data), pzc (potential of zero charge), pzmc (potential of zero mass change, which separates adsorption of anions and cations) obtained from the in situ conductivity and the EQCM measurements, respectively. Cation Unsolvated pzc / V [c] pzmc / V [c,d] radius / nm [a] Li TEA TBA TOA +.56 [b] [a] Kubota, S.; Ozaki, S.; Onishi, J.; Kano, K.; Shirai, O. Analyt. Sci. (The Japan Society for Analytical Chemistry) 29, 25, 189. [b] Estimated using the data from: Mysik, R.; Pinero, E.R.; Pernak, J.; Beguin, F. J. Phys. Chem. C, 29, 113, [c] Li/.1 M LiBF 4 in PC reference electrode was separated from the working electrode compartment by a glass frit. [d] Polarization at high negative charge densities results in trapping of cations and their slow release during the subsequent anodic scan, which may shift the value of pzmc towards pore positive potentials (insertion of anions helps to keep electroneutrality inside the pore). For this reason, we list the values of pzmc for the cathodic scan, from 4.1 to 1.75 V (anions are not trapped at high anodic polarizations, and as a result, the cation-anion mixing is less apparent compared to the reverse anodic scan). S4

5 2 15 m / µg cm -2 1 C + Q < pzc Q > 5 pzmc A E / V (vs. Li/Li + ) Figure S3. The mass change of the cations and anions, m, adsorbed at the negatively and positively charged carbon surface, respectively, as a function of the electrode potential, E, obtained by EQCM in parallel to the CVs for the same carbon coating in.25 and.1 M TEABF 4 in PC (the blue and black solid lines, respectively). The related CV are shown in Figure 2A in the main text. The locations of the potential of zero charge (pzc) and the potential of zero mass change (pzmc), separating the adsorption of cations and anions are indicated. S5

6 I / µα A TEA + TOA + TBA + Li B E / V (vs. Li/Li + ) Conductance / ms E / V (vs. Li/Li + ) Figure S4. Simultaneously measured CV curves (A) and in situ conductance (B) of the AC electrode in.1 M solutions of different quaternary ammonium and lithium tetrafluoroborates in PC: Li + (red), TEA (blue), TBA (green), TOA (rose). Scan rate 1 mvs -1. The minima on the conductance curves were identified with the potential of zero charges, (pzc). Measurements of in-situ electronic conductivity of microporous AC electrodes for evaluation of their pzc in case of the absence of specific adsorption of ions was first introduced by B. Kastening (B. Kastening, M. Hahn, J. Kremeskiitter, J. Electroanal. Chem. 1994, 374,159). The experimental set-up that we used differed from that used by Kastening et al. who characterized a single carbon particle. We used interdigitated Au microelectrodes (see Z. Pomerantz, M.D. Levi, G. Salitra, R. Demadrille, A. Fisyuk, A. Zaban, D. Aurbach and A. Pron, Phys. Chem. Chem. Phys., 28, 1, 132 and E. Pollak, G. Salitra, V. Baranchugov and D. Aurbach, J. Phys. Chem. C, 27, 111, 11437) covered with composite carbon slurry in a similar way as we cover the quartz crystals for the EQCM measurements. The second method for evaluation of pzc was the potential of immersion of AC electrode into deairiated electrolyte solution, in which the electrode is further characterized by CV and EQCM. The third method is identification of minima on the CV curves related to semiconducting behavior of highly porous disordered carbons (for most detailed information see: R. Kotz, M. Hahn, O. Barbieri, J.-C. Sauter, R. Gallay, Proceedings of the 13 th International Seminar on DLC and Similar Energy Storage Devices, Dec. 8-1, 23, Deerfield Beach, USA). S6

7 A I/ν / mc V m / µg B E / V (vs. Li/Li + ) E / V (vs. Li/Li + ) Time / min 1.7 Figure S5. A family of the CVs measured at different scan rates (presented in the form of the differential capacitance: the current is divided by the scan rate, (A) and the accompanying mass peaks changes (B), for the carbon-coated quartz crystal electrodes in.1 M LiBF 4 / PC. The black, red and blue curves correspond to 1, 2 and 5 mvs -1, respectively. Note a considerable overlapping of the cation's flux-out and the anion's flux-in when coming from the negatively to positively charged electrode surface. The reason is the Li-ions trapping at high negative charge densities. S7

8 Γ / nmol cm I / µa E / V (vs.li/li + ) Q / mc cm -2 Figure S6. The amount of cations and anions, Γ, adsorbed at negatively and positively charged carbon surface, respectively, as a function of the charge density, Q, for two different concentrations of LiBF 4 dissolved in PC (.5 and.1 M relate to the solid blue and black lines, respectively). The related CVs are shown as inset (scan rate 2 mvs -1 ). The theoretical Γ versus Q plots (the broken red straight lines) were calculated on the basis of the Faraday law. S8