Supporting Information for Iridium-tungsten Alloy Nanodendrites as ph-universal Water Splitting Electrocatalysts Fan Lv, Jianrui Feng, Kai Wang, Zhipeng Dou, Weiyu Zhang, Jinhui Zhou, Chao Yang, Mingchuan Luo, Yong Yang, Yingjie Li, Peng Gao, and Shaojun Guo* & ѳ Department of Material Science and Engineering, College of Engineering, Peking University, Beijing 100871, China. & BIC-ESAT, College of Engineering, Peking University, Beijing 100871, China. Electron Microscopy Laboratory, and International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China Department of Energy and Resources Engineering, College of Engineering, Peking University, Beijing 100871, P. R. China. ѳ Beijing Key Laboratory for Magnetoeletric Materials and Devices (BKL-MEMD), Peking University, Beijing 100871, China. Email: guosj@pku.edu.cn 1 / 30
Figures Figure S1. (a, b) Low-magnification TEM image and size distribution of IrW NDs. 2 / 30
Figure S2. HRTEM image and corresponding FFT patterns of the IrW NDs. 3 / 30
Figure S3. HAADF-STEM image of IrW NDs. 4 / 30
Figure S4. TEM images of IrW NDs with different diameters by changing the amount of glucose and keep other parameters consistent. (a) 10 mg glucose, (b) 80 mg glucose. 5 / 30
Figure S5. (a, b) TEM images of Ir nanoflowers synthesized without adding W(CO) 6. 6 / 30
a 0.1 b 0.1 c ECSA = 78.2 m 2 g -1 Pt ECSA = 58.2 m 2 g -1 Ir 0.1 ECSA = 38.7 m 2 g -1 Ir j(ma ) 0.0-0.1 j(ma ) 0.0-0.1 j(ma ) 0.0-0.1-0.2 Pt/C IrW/C -0.2-0.2 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 Ir/C 0.0 0.1 0.2 0.3 0.4 0.5 0.6 E(V) vsrhe E(V) vsrhe E(V) vsrhe Figure S6. CVs of the (a) Pt/C, (b) IrW/C and (c) Ir/C in 0.1M HClO 4. The potential ranges are 0.05 V-1.05 V vs RHE for Pt/C, and 0.05 V-0.55V vs RHE for IrW/C and Ir/C. 7 / 30
Figure S7. The relationship between TOF and the measured potentials for Ir/C, Pt/C and IrW/C catalysts in 0.1 M HClO 4 (a) and 0.1 M KOH (b). 8 / 30
a j(ma cm -2 geo) 0-5 -10 IrW/C Intial IrW/C after 1000 cycles 0.1 M HClO 4 b j(ma cm -2 geo) 0-10 -20-30 IrW Intial IrW after 1000 cycles 0.1 M KOH -15-0.02-0.01 0.00 0.01 0.02 E(V) vsrhe -40-0.15-0.10-0.05 0.00 0.05 E(V) vsrhe Figure S8. HER polarization curves of IrW/C before and after durability test of 1000 cycles at the scan rate of 20 mv s -1 in 0.1 M HClO 4 (a) and 0.1 M KOH (b). 9 / 30
Figure S9. TEM images of IrW/C after HER durability test in 0.1 M HClO 4 (a, b) and 0.1 M KOH (c, d). 10 / 30
Figure S10. The Tafel slopes of Ir/C, Pt/C and IrW/C corresponds to the HER process in 0.1 M HClO 4 (a) and 0.1 M KOH (b). 11 / 30
Figure S11. Three different adsorption sites of H over IrW including top site of Ir, top site of W and the hollow site surrounded by two Ir atoms and one W atom. 12 / 30
Figure S12. The optimized adsorption structure of H atom over Pt and Ir for calculating free energy diagram in acid media. 13 / 30
Figure S13. The initial state, transition state and final state of the most advantageous path of water dissociation over Pt, Ir and IrW. 14 / 30
Figure S14. The initial state, transition state and final state of the disadvantageous path of water dissociation over IrW. 15 / 30
Figure S15. The initial state, transition state and final state of the Heyrovsky step over Pt, Ir and IrW. 16 / 30
0.2 IrW/C oxidation 0.2 Ir/C oxidation 0.1 H upd Oxidation 0.1 H upd Oxidation j(ma ) 0.0 j(ma ) 0.0-0.1 Ir(III)/Ir(IV) -0.1 Ir(III)/Ir(IV) -0.2 0.0 0.4 0.8 1.2 1.6 \ E(V) vsrhe -0.2 0.0 0.4 0.8 1.2 1.6 E(V) vsrhe Figure S16. The oxidation process of IrW/C and Ir/C through potential cycles between 0.05 V and 1.5 V vs RHE before electrochemical activity test. 17 / 30
a 10 IrW/C Ir/C Pt/C 0.1 M HClO 4 b IrW/C Ir/C Pt/C 0.1 M KOH TOF (s -1 ) 1 TOF (s -1 ) 1 0.1 1.4 1.5 1.6 1.7 1.8 E(V) vsrhe 0.1 1.4 1.5 1.6 1.7 1.8 E(V) vsrhe Figure S17. The relationship between the TOF and the measured potentials for Ir/C, Pt/C and IrW/C catalysts in 0.1 M HClO 4 (a) and 0.1 M KOH (b). 18 / 30
a j(ma cm -2 geo) cj(ma cm-2 geo) 40 30 20 10 IrW/C Ir/C Pt/C 0.1M KOH Overpotenial (mv) b 600 450 300 271.8 mv dec -1 83.1 mv dec -1 58.0 mv dec -1 0 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 E(V) vsrhe 150-0.4 0.0 0.4 0.8 1.2 LogCurrent (ma cm -2 ) 5 4 3 2 1 @1.53V vs RHE 0.1 M KOH 1.0 0.8 0.6 0.4 0.2 TOF (s -1 ) d j(ma cm -2 geo) 40 30 20 10 IrW/C Initial IrW/C after 1000 cycles Ir/C Initial Ir/C after 1000 cycles 0.1 M KOH 0 0.0 0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 E(V) vsrhe Figure S18. OER activity and durability of IrW NDs in KOH. (a) OER polarization curves of IrW/C, Ir/C and Pt/C with 95% ir-compensation in 0.1 M KOH at the scan rate of 5 mv s -1 and (b) the corresponding Tafel slopes, (c) Current density (left) and TOFs normalized by the ECSA (right) at 1.53 V vs RHE of IrW/C, Ir/C and Pt/C in 0.1 M KOH, (d) OER polarization curves of IrW/C, and Ir/C before and after durability test of 1,000 cycles between 1.25 V and 1.7 V. 19 / 30
Figure S19. TEM images of Ir/C before (a) and after (b) OER durability test. 20 / 30
Figure S20. EDS mapping images of IrW/C after OER durability test. 21 / 30
Figure S21. XPS spectra of and IrW/C (a) and Ir/C (b) before and after OER durability test in HClO 4. 22 / 30
Figure S22. Optimized clean surface of the model of IrO 2 (110) and W-IrO 2 (110). 23 / 30
Figure S23. Optimized adsorption structure of OH, O and OOH on IrO 2 and W-IrO 2. 24 / 30
Tables Table S1. Summary and comparisons of some recently reported representative HER electrocatalysts in acidic electrolytes Sample IrW/C Mass Loading electrolyte Current Density/mA cm -2 Overpotential (mv) 10.2 µg Ir /cm -2 0.1 M HClO 4 10 12 TOF 3.35 s -1 @ 10 mv References This work Ru@C 2 N 0.285 mg cm 2 0.5 M H 2 SO 4 10 22 0.67 s -1 @ 25 mv Nature Nano. 12, 441 446 (2017) SV-MoS 2-0.5 M H 2 SO 4 10 170 0.31 s -1 @ 0 mv Nature Mater. 15, 48 53 (2016) CoPS nanoplates - 0.5 M H 2 SO 4 10 48 - Nature Mater. 14, 1245 1251 (2015) CoMoS x 50 µg cm 2 0.1 M HClO 4 5 207 - Nature Mater. 15, 197 203 (2016) [Mo 3 S 13 ] -2 clusters 0.1 mg cm -2 0.5 M H 2 SO 4 10 180 - Nature Chem. 6, 248 253 (2014) M-MoS 2 43 µg cm -2 0.5 M H 2 SO 4 10 175 - A-Ni C 0.283 mg cm -2 0.5 M H 2SO 4 10 34 - Nature Comm. 7, 10672 (2016) Nature Comm. 7, 10667 (2016) MoS 2 /CoSe 2 0.28 mg cm -2 0.5 M H 2SO 4 10 70 - Nature Comm. 6, 5982 (2015) Rh/Si 0.193 mg cm -2 0.5 M H 2 SO 4 50 110 - Nature Comm. 7, 12272 (2016) 25 / 30
Table S2. Summary and comparisons of some recently reported representative HER electrocatalysts in alkaline electrolytes. Sample Mass Loading electrolyte Current Density/mA cm-2 Overpotential (mv) TOF Reference IrW/C 10.2 µg /cm -2 0.1 M KOH 10 29 1.95 s -1 @ 10 mv This work Ru@C 2 N 0.285 mg cm 2 1 M KOH 10 17 0.75 s -1 @ 25 mv Nat. Nano. 12, 441 446 (2017) CoMoS x 50 µg cm 2 0.1 M KOH Ni(OH) 2 / Pt-islands/ Pt(111) surface Co(OH) 2 /Pt( 111) - - 0.1 M KOH 0.1 M KOH 5 ~158-10 ~138-10 ~248 - Nat. Mater. 15, 197 203 (2016) Science 334, 1256 (2011) Nat. Mater. 11, 550 557 (2012) MoNi 4 /MoO 2 43.4 mg cm -2 1 M KOH 10 15 0.4 @ 50 mv Nat. Comm. 8, 15437 (2017). Pt NWs/SL - Ni(OH) 2 16 µg /cm -2 0.1 M KOH 10 48 - Nat. Common. 6, 6430 (2015) np-cuti - 0.1 M KOH 10 47 - Nat. Commun. 6, 6567 (2015) NiO/Ni -CNT 0.28 mg cm -2 1 M KOH 10 80 - Nat. Commun. 5, 4695 (2014) Pt 3 Ni 2 -NWs -S/C 15 µg /cm -2 0.1 M KOH 10 45 - Nat Commun. 8, 14580 (2017) 26 / 30
Table S3. Dissolved amount of Ir from IrW/C and Ir/C catalysts in electrolyte after durability test examined by ICP-AES. Sample Dissolved Ir (µg) Percentage of dissolved Ir from the initial mass IrW/C 0.11 5.5 % Ir/C 0.32 16 % 27 / 30
Table S4. Adsorption energies of OH, O and OOH on IrO 2 (110) and W-IrO 2 (110) with corresponding d-band centers (Integrated from -5 ev to 0 ev vs. Fermi level). Model d-band center (ev vs. Fermi level) Intermediate Adsorption energy (ev) OH -4.65 IrO 2 (110) -1.74 O -3.69 OOH -2.18 OH -4.34 W-IrO 2 (110) -1.82 O -3.57 OOH -2.15 28 / 30
Table S5. Summary and comparison of some recently reported representative overall water-splitting electrocatalysts in acidic or alkaline electrolytes. Sample Mass Loading electrolyte Current density ma cm -2 ) Overpotential (mv) References IrW/C 30 µg cm -2 0.5 M H 2 SO 4 10 50 250 310 This work Ni-Co complexes /1T MoS2 1 mg cm -2 1 M KOH 10 250 Nat. Commun. 8, 15377 (2017) NiFe-MOF - 0.1 M KOH 10 320 Nat. Commun.8, 15341 (2017) IrNi NCs 12.5 µg cm 2 0.5 M H 2 SO 4 10 350 Adv. Funct. Mater. 27, 1700886 (2017) Ir/GF 0.82 mg cm -2 0.5 M H 2 SO 4 10 320 Nano Energy 40, 27 33 (2017) NiFeOx 0.6 mg cm -2 1 M KOH 10 280 Nat. Commun. 6, 7261 (2015) Co 0.85 Se/NiFe- LDH 2.7 mg cm -2 1 M KOH 20 480 Energy Environ. Sci. 9, 478-483 (2016) NiCoP ~1.6 mg cm -2. 1 M KOH 10 350 Nano Lett. 16 7718 7725 (2016) Hierarchical NiCo 2 O 4 hollow microcuboids 1 mg cm -2 1 M KOH 10 20 420 510 Angew. Chem. Int. Ed. 55, 6290 6294 (2016) 29 / 30
Table S6. Frequencies of HER and OER intermediates. IS, TS and FS represent for initial state, transition state and final state. Model Intermediate Frequency (cm -1 ) H 2 O (IS) 5723.37, 421.45, 282.12, 121.46, 103.57, 83.49, 51.74, 12.35, 7.13 *H + OH (TS) 620.37, 469.70, 427.99, 341.17, 219.54, 128.82, 112.39, 85.29, 219.12i IrW (HER) *H + OH (FS) *H + H 2 O (IS) 3727.80, 581.41, 525.08, 103.55, 97.72, 94.21, 93.46, 13.49, 4.11 520.32, 413.65, 405.88, 371.27, 329.08, 251.10, 239.34, 158.53, 125.40, 101.95, 47.58, 14.35 * + H2 + OH (TS) 618.75, 483.12, 435.49, 414.30, 351.14, 203.91, 134.71, 123.47, 74.33, 17.60, 8.51, 104.32i * + H2 + OH (FS) 1285.61, 845.94, 449.78, 310.41, 161.78, 98.27, 56.60, 33.23, 25.76, 11.50, 9.23, 1.47 OH 2764.62, 1911.14, 892.64, 124.31, 88.50, 72.03 W-IrO 2 (OER) O 87.49, 22.83, 12.68 OOH 1347.81, 550.35, 241.92, 201.70, 90.27, 61.25, 38.49, 15.37, 12.11 30 / 30