Interconnected Copper Cobaltite Nanochains as Efficient. Electrocatalysts for Water Oxidation in Alkaline Medium

Transcription

1 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 , India. * sunil111954@yahoo.co.uk S-1

2 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

3 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

4 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

5 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

6 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

7 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

8 Figure S11. Cyclic voltammograms at different scan rates ( 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 CCO CCO CO S-8

9 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

10 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 (0.2) work CuCo 2 O 4 /NrGO (0.14) GC-RDE 1M KOH NiCuO x GC-RDE 1M NaOH >400-6 Cu 0.7 Co 2.3 O 4 (0.1) GCE 1M KOH 7 ma cm -2 7 Co 3 O 4 NPs (1.0) Ni foam 1M KOH Cu 0.5 CuCo 1.5 O 4 (3.0) Ti 1M KOH 5 ma cm -2-9 NiCo 2 O 4 (0.07) GC-RDE 1M NaOH NiCo 2 O 4 (2.7) Ti substrate 1M NaOH > Ni x Co 3-x O 4 (7.4) Ni substrate 1M NaOH ZnCo 2 O 4 Pt substrate 1 M KOH Au/NiCo 2 O 4 Ti foil 1 M KOH Co 3 O 4 /SWNT (0.05) ITO 1 M KOH 580 ph~7 15 NiCo 2 O 4 NWs ( 1.0) FTO 1 M KOH Crumpled graphene- CoO (0.7) - 1 M KOH NiCo LDH/carbon paper (0.08) - 1 M KOH Reduced Co 3 O 4 (0.136) - 1 M KOH ~ Mesoporous Co 3 O 4-1 M KOH RuO 2 (0.8) GC-RDE 1 M KOH Cu 2 O Cu foams Cu foams 1 M KOH 350* Co 3 O 4 thin film FTO 1M NaOH *ir-compensated S-10

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