Supplemental Information for: Orientation-Dependent Oxygen Evolution Activities of Rutile IrO 2 and RuO 2

Transcription

1 Supplemental Information for: Orientation-Dependent Oxygen Evolution Activities of Rutile IrO 2 and RuO 2 Kelsey A. Stoerzinger, a,b Liang Qiao, c Michael D. Biegalski, c Yang Shao-Horn a,b,d, * a Department of Materials Science & Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA, 02139, USA b Electrochemical Energy Laboratory, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA, 02139, USA c Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, TN, 37831, USA d Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA, 02139, USA Contents: Table S1...2 Figure S1..2 Figure S2..3 Table S2...3 Figure S3..4 Table S3...4 Figure S4..4 Figure S5..5 Table S4...5 Figure S6..5 References

2 Table S1. Conditions for pulsed laser deposition Film Substrate # Pulses Temp ( C) IrO 2 (100) SrTiO IrO 2 (110) BaTiO 3 /MgO RuO 2 (100) SrTiO RuO 2 (110) MgO Figure S1. (A) Normal 2θ ω scans of (110)-oriented IrO 2 (light orange) and RuO 2 (light blue) grown on (001) MgO; (100)-oriented IrO 2 (dark orange) and RuO 2 (dark blue) grown on (001) SrTiO 3. Peaks marked with * are from the substrate. The peak marked with ^ arises from <0.3% (100)-orientation. (B) Phi scans in-plane, aligned to the noted reflections for films grown on MgO. Films orient 45 to the substrate; scans were shifted to plot on a common axis for easy viewing. (C) Phi scans in-plane, aligned to the noted reflections for films grown on SrTiO 3 (STO). Films orient 45 to the substrate; scans were shifted to plot on a common axis for easy viewing. 2

3 Figure S2. Atomic force microscopy (AFM) of film surfaces before electrochemistry; the 500 nm scale bar is the same for all images. (A) (100)-oriented IrO 2, (B) (110)-oriented IrO 2, (C) (100)-oriented RuO 2, and (D) (110)-oriented RuO 2. Corresponding roughness factors can be found in Table S2. Table S2. Root mean square (RMS) roughness from AFM before any electrochemistry measurements and after all electrochemistry (see Figure S4) Film RMS roughness (nm) Before RMS roughness (nm) After IrO 2 (100) IrO 2 (110) RuO 2 (100) RuO 2 (110)

4 Figure S3. Schematic of the determination of q Fe(CN)6+KOH, the cathodic charge of the oxidation peak of the outer sphere redox couple [Fe(CN) 6 ] 3-/4-. Cyclic voltammetry (CV) at a scan rate of 10 mv/s in 0.1 M KOH, Ar-saturated with 10 mm each [Fe(CN) 6 ] 3-/4- in (B) showing the current per surface area (i) for the noted cycle vs. the ohmic-corrected applied voltage (E-iR). Table S3. Integrated cathodic charge q Fe(CN)6+KOH, determined as illustrated in Fig. S3 q Fe(CN)6+KOH [mc/cm 2 ] IrO 2 (100) 5.44 IrO 2 (110) 4.33 RuO 2 (100) 6.22 RuO 2 (110) 5.91 Figure S4. Atomic force microscopy (AFM) of film surfaces after all electrochemistry measurements; the 500 nm scale bar is the same for all images. (A) (100)-oriented IrO 2, (B) (110)-oriented IrO 2, (C) (100)-oriented RuO 2, and (D) (110)-oriented RuO 2. Corresponding roughness factors can be found in Table S2. 4

5 Figure S5. Tafel plot showing E-iR vs. i on a logarithmic scale. Colored lines correspond to CVs of the 10 th OER cycle, averaging forward and reverse sweeps to correct for capacitance. Data for particles of RuO 2 (dark gray, filled) and IrO 2 (light gray, open) were extracted from 1. The fit lines to determine the Tafel slopes in Table S3 are shown in shades of gray. Table S4. Comparison of Tafel slopes low [mv/decade] high [mv/decade] IrO 2 (100)* IrO 2 (110)* RuO 2 (100)** RuO 2 (110)** * Tafel slope fitting for IrO 2 films was between V vs. RHE (low) and V (high). ** Tafel slope fitting for RuO 2 films was between V vs. RHE (low) and V (high). Figure S6. Schematic projection of (A) (100)-oriented surface and (B) (110)-oriented surface, with unit cell dimensions given for RuO 2 2 (IrO 2 a = 4.51 Å, c = 3.16 Å) 3. Species unique to the surface are annotated, including coordinatively undersaturated sites (M cus, M = Ir, Ru, blue), bridging oxygen (O br, orange), and 3-fold coordinated oxygen (O 3f, 5

6 orange), in addition to fully coordinated metal sites (M, blue). References (1) Lee, Y.; Suntivich, J.; May, K. J.; Perry, E. E.; Shao-Horn, Y. Synthesis and Activities of Rutile IrO 2 and RuO 2 Nanoparticles for Oxygen Evolution in Acid and Alkaline Solutions. J. Phys. Chem. Lett. 2012, 3, (2) Hepel, T.; Pollak, F. H.; O'Grady, W. E. Effect of Crystallographic Orientation of Single Crystal RuO 2 Electrodes on the Hydrogen Adsorption Reactions. J. Electrochem. Soc. 1984, 131, (3) Bolzan, A. A.; Fong, C.; Kennedy, B. J.; Howard, C. J. Structural Studies of Rutile-Type Metal Dioxides. Acta Crystallographica Section B 1997, 53,