Supporting Information Interconnected Copper Cobaltite Nanochains as Efficient Electrocatalysts for Water Oxidation in Alkaline Medium Ayon Karmakar and Suneel Kumar Srivastava * Inorganic Materials and Nanocomposite Laboratory, Department of Chemistry, Indian Institute of Technology, Kharagpur 721302, India. *E-mail: sunil111954@yahoo.co.uk S-1
Supplementary Figures Figure S1. Calibration of SCE with respect to RHE. Figure S2. FTIR spectra of the solvothermal products obtained at (a) 150, (b) 180 and (c) 210 C temperatures. S-2
Figure S3. FESEM images (a, b, c) and corresponding EDX spectra (d, e, f) of the solvothermal products obtained at (a) 150, (b) 180 and (c) 210 C temperatures respectively. Figure S4. TGA curve of the solvothermal products obtained at 150, 180 and 210 C. S-3
Formation mechanism. The possible formation pathway of copper cobaltites is established on the basis of the observations from XRD and FTIR of the precursors obtained at three different preparative temperatures. It is hypothesized that metal glycolates were formed after dissolving desired proportions of the cobalt and copper nitrates in ethylene glycol. 1 Further, metal glycolates were transformed to the cyclic metal carbonates in presence of urea at reaction temperatures of 150 C and above. 2-4 This transformation proceeds through metal co-ordinated 2- hydroxyethyl carbamate intermediate by releasing ammonia. Additionally, further deammonization of the intermediate led to the formation of cyclic metal carbonates. 2 The formation of metal carbonates also evidenced by the presence of CO 2-3 ions in the precursors from FTIR and also from XRD. Finally, calcination of the precursors at 400 C in air led to the desired copper cobaltites. In view of this, the plausible step wise formation mechanism is shown in Scheme S1. Scheme S1. Probable mechanistic pathway of the formation of Cu x Co 3-x O 4. S-4
Figure S5. EDX spectrum of octahedral CuO, present in CCO-210. Figure S6. FESEM images (a) low magnification, (b) high magnification, (c) TEM image, (d) HRTEM image and the inset shows SAED pattern of CCO-180. S-5
Figure S7. EDX spectra and elemental compositions of (a) CCO-150, (b) CCO-180 and (c) CCO-210 respectively. Figure S8. (a) FESEM image of CCO-180 and elemental mapping of (b) Cu, (c) Co and (d) O in CCO-180. S-6
Figure S9. (a) N 2 adsorption desorption isotherms and (b) pore size distributions of CCO- 150, CCO-180, CCO-210 and CO-180 respectively. Figure S10. Overpotential (η 10 ) of CCO-150, CCO-180, CCO-210 and CO-180. S-7
Figure S11. Cyclic voltammograms at different scan rates (10 100 mv s -1 ) in the nonfaradaic region of (a) CCO-150, (b) CCO-180, (c) CCO-210 and (d) CO-180. Table S1. ECSA and RF values of CCO-150, CCO-180, CCO-210 and CO-180 respectively. Sample in (mf) ECSA in (cm 2 ) RF Codes CCO-150 0.266 6.65 95 CCO-180 0.331 8.27 118 CCO-210 0.043 1.07 15 CO-180 0.042 1.05 15 S-8
Figure S12. (a) Electrochemical double layer capacitance ( ) and (b) ECSA (blue) and RF (green) of CCO-150, CCO-180, CCO-210 and CO-180 respectively. Figure S13. XRD patten of CO-180. S-9
Table S2. Comparison of electrocatalytic oxygen evolution activity in alkaline medium of some electrocatalysts available in literature. Catalyst (mg cm -2 ) Substrate Electrolyte η 10 (mv) Tafel slope (mv dec -1 ) Reference Cu 0.3 Co 2.7 O 4 nanochains This GC-RDE 1 M KOH 351 63.3 (0.2) work CuCo 2 O 4 /NrGO (0.14) GC-RDE 1M KOH 360 64 5 NiCuO x GC-RDE 1M NaOH >400-6 Cu 0.7 Co 2.3 O 4 (0.1) GCE 1M KOH 480 @ 7 ma cm -2 7 Co 3 O 4 NPs (1.0) Ni foam 1M KOH 497-8 Cu 0.5 CuCo 1.5 O 4 (3.0) Ti 1M KOH 420 @ 5 ma cm -2-9 NiCo 2 O 4 (0.07) GC-RDE 1M NaOH 419.3 51.3 10 NiCo 2 O 4 (2.7) Ti substrate 1M NaOH >400 59 11 Ni x Co 3-x O 4 (7.4) Ni substrate 1M NaOH 361.6 66 12 ZnCo 2 O 4 Pt substrate 1 M KOH 390 46 13 Au/NiCo 2 O 4 Ti foil 1 M KOH 370 63 14 Co 3 O 4 /SWNT (0.05) ITO 1 M KOH 580 104 @ ph~7 15 NiCo 2 O 4 NWs ( 1.0) FTO 1 M KOH 460 90 16 Crumpled graphene- CoO (0.7) - 1 M KOH 340 71 17 NiCo LDH/carbon paper (0.08) - 1 M KOH 367 40 18 Reduced Co 3 O 4 (0.136) - 1 M KOH ~410 72 19 Mesoporous Co 3 O 4-1 M KOH 476 20 RuO 2 (0.8) GC-RDE 1 M KOH 387 64.6 21 Cu 2 O Cu foams Cu foams 1 M KOH 350* 67.5 22 Co 3 O 4 thin film FTO 1M NaOH 377 58.1 23 *ir-compensated S-10
References (1) Xie, X.; Shang, P.; Liu, Z.; Lv, Y.; Li, Y.; Shen, W. Synthesis of Nanorod-Shaped Cobalt Hydroxycarbonate and Oxide with the Mediation of Ethylene Glycol. J. Phys. Chem. C 2010, 114, 2116 2123. (2) Bhanage, B. M.; Fujita, S.; Ikushima, Y.; Arai, M. Transesterification of Urea and Ethylene Glycol to Ethylene Carbonate as an Important Step for Urea Based Dimethyl Carbonate Synthesis. Green Chem. 2003, 5, 429 432. (3) Li, Q.; Zhang, W.; Zhao, N.; Wei, W.; Sun, Y. Synthesis of Cyclic Carbonates from Urea and Diols over Metal Oxides. Catal. Today 2006, 115, 111 116. (4) Wang, P.; Liu, S.; Zhou, F.; Yang, B.; Alshammari, A. S.; Lu, L.; Deng, Y. Two-Step Synthesis of Dimethyl Carbonate from Urea, Ethylene Glycol and Methanol Using Acid Base Bifunctional Zinc-Yttrium Oxides. Fuel Process. Technol. 2014, 126, 359 365. (5) Bikkarolla, S. K.; Papakonstantinou, P. CuCo 2 O 4 Nanoparticles on Nitrogenated Graphene as Highly Efficient Oxygen Evolution Catalyst. J. Power Sources 2015, 281, 243 251. (6) McCrory, C. C. L.; Jung, S.; Peters, J. C.; Jaramillo, T. F. Benchmarking Heterogeneous Electrocatalysts for the Oxygen Evolution Reaction. J. Am. Chem. Soc. 2013, 135, 16977 16987. (7) Wu, X.; Scott, K. Cu x Co 3 x O 4 (0 x < 1) Nanoparticles for Oxygen Evolution in High Performance Alkaline Exchange Membrane Water Electrolysers. J. Mater. Chem. 2011, 21, 12344 12351. (8) Chou, N. H.; Ross, P. N.; Bell, A. T.; Tilley, T. D. Comparison of Cobalt-Based Nanoparticles as Electrocatalysts for Water Oxidation. ChemSusChem 2011, 4, 1566 1569. S-11
(9) Rosa-Toro, A. L.; Berenguer, R.; Quijada, C.; Montilla, F.; Morallo, E.; Va, J. L. Preparation and Characterization of Copper-Doped Cobalt Oxide Electrodes. J. Phys. Chem. B 2006, 110, 24021 24029. (10) Wang, J.; Qiu, T.; Chen, X.; Lu, Y.; Yang, W. Hierarchical Hollow Urchin-like NiCo 2 O 4 Nanomaterial as Electrocatalyst for Oxygen Evolution Reaction in Alkaline Medium. J. Power Sources 2014, 268, 341 348. (11) Li, Y.; Hasin, P.; Wu, Y. Ni x Co 3-x O 4 Nanowire Arrays for Electrocatalytic Oxygen Evolution. Adv. Mater. 2010, 22, 1926 1929. (12) Lu, B.; Cao, D.; Wang, P.; Wang, G.; Gao, Y. Oxygen Evolution Reaction on Ni- Substituted Co 3 O 4 Nanowire Array Electrodes. Int. J. Hydrogen Energy 2011, 36, 72 78. (13) Kim, T. W.; Woo, M. A.; Regis, M.; Choi, K. S. Electrochemical Synthesis of Spinel Type ZnCo 2 O 4 Electrodes for Use as Oxygen Evolution Reaction Catalysts. J. Phys. Chem. Lett. 2014, 5, 2370 2374. (14) Liu, X.; Liu, J.; Li, Y.; Li, Y.; Sun, X. Au/NiCo 2 O 4 Arrays with High Activity for Water Oxidation. ChemCatChem 2014, 6, 2501 2506. (15) Wu, J.; Xue, Y.; Yan, X.; Yan, W.; Cheng, Q.; Xie, Y. Co 3 O 4 Nanocrystals on Single- Walled Carbon Nanotubes as a Highly Efficient Oxygen-Evolving Catalyst. Nano Res. 2012, 5, 521 530. (16) Yu, X.; Sun, Z.; Yan, Z.; Xiang, B.; Liu, X.; Du, P. Direct Growth of Porous Crystalline NiCo 2 O 4 Nanowire Arrays on a Conductive Electrode for High-Performance Electrocatalytic Water Oxidation. J. Mater. Chem. A 2014, 2, 20823 20831. (17) Mao, S.; Wen, Z.; Huang, T.; Hou, Y.; Chen, J. High-Performance Bi-Functional Electrocatalysts of 3D Crumpled Graphene-Cobalt Oxide Nanohybrids for Oxygen Reduction and Evolution Reactions. Energy Environ. Sci. 2014, 7, 609 616. S-12
(18) Liang, H.; Meng, F.; Caban-Acevedo, M.; Li, L.; Forticaux, A.; Xiu, L.; Wang, Z.; Jin, S. Hydrothermal Continuous Flow Synthesis and Exfoliation of NiCo Layered Double Hydroxide Nanosheets for Enhanced Oxygen Evolution Catalysis. Nano Lett. 2015, 15, 1421 1427. (19) Wang, Y.; Zhou, T.; Jiang, K.; Da, P.; Peng, Z.; Tang, J.; Kong, B.; Cai, W. B.; Yang, Z.; Zheng, G. Reduced Mesoporous Co 3 O 4 Nanowires as Efficient Water Oxidation Electrocatalysts and Supercapacitor Electrodes. Adv. Energy Mater. 2014, 4, 1400696, DOI: 10.1002/aenm.201400696. (20) Tüysüz, H.; Hwang, Y. J.; Khan, S. B.; Asiri, A. M.; Yang, P. Mesoporous Co 3 O 4 as an Electrocatalyst for Water Oxidation. Nano Res. 2013, 6, 47 54. (21) Jung, S.; McCrory, C. C. L.; Ferrer, I. M.; Peters, J. C.; Jaramillo, T. F. Benchmarking Nanoparticulate Metal Oxide Electrocatalysts for the Alkaline Water Oxidation Reaction. J. Mater. Chem. A 2016, 4, 3068 3076. (22) Xu, H.; Feng, J.; Tong, Y.; Li, G. Cu 2 O-Cu Hybrid Foams as High-Performance Electrocatalysts for Oxygen Evolution Reaction in Alkaline Media. ACS Catal. 2017, 7, 986 991. (23) Jeon, H. S.; Jee, M. S.; Kim, H.; Ahn, S. J.; Hwang, Y. J.; Min, B. K. Simple Chemical Solution Deposition of Co 3 O 4 Thin Film Electrocatalyst for Oxygen Evolution Reaction. ACS Appl. Mater. Interfaces 2015, 7, 24550 24555. S-13