Electronic Supplementary Information

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1 Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A. This journal is The Royal Society of Chemistry 2017 Electronic Supplementary Information Large area photoelectrodes based on hybrids of CNT fibres and ALD grown TiO 2 A. Moya a, N. Kemnade b, M. R. Osorio c, A. Cherevan b. D. Granados c, D. Eder b, J.J. Vilatela a a. IMDEA Materials, Madrid, Spain. b. Institut für Materialchemie, Technische Universität Wien, Vienna, Austria c. IMDEA Nanoscience, Madrid, Spain. a) b) S1

2 c) d) Figure S1: ac) Scanning Electron micrograph at different magnifications of TiO 2 /CNT fibre with 20nm of metal oxide thickness showing that the effective coating of the porous structure of the CNT fibre with the metal oxide. d) Crosssection SEM image of a TiO 2 /CNT fibre hybrid S1

3 Figure S2: SEM images of a) pure CNT fibre, bf) CNT fibre with ALD deposition of 10, 20, 40,60 and 80 nm of TiO 2 confirming the controlled deposition of the metal oxide layer on the CNT fibre for all the thickness.. S2

4 Figure S3: Xray diffraction patterns of TiO 2 /CNT fibre sample after ALD process and before annealing at 400 C, which shows that the ALD deposition consisted in an amorphous layer of TiO 2. S3

5 Figure S4: TEM images of TiO 2 /CNT fibre with 20 nm of TiO 2 thickness at different magnification, showing the conformality of the metal oxide coating the CNT fibre surface and confirming no porosity of the inorganic layer. S4

6 Table S1: Summary of XRD and Raman spectroscopy data for different samples Sample XRD ( ) Eg (cm 1 ) D (cm 1 ) G (cm 1 ) 2D (cm 1 ) CNTf (pristine) / (1344.4) (1578.8) (2679.5) CNTf (after O 2 plasma) nm 25.24/26.09 (150.2) (1351.2) (1583.1) (2692.5) 20 nm 25.21/26.11 (148.2) (1352.4) (1584.4) (2695.2) 40 nm 25.22/26.11 (147.9) (1352.7) (1585.0) (2695.4) 60 nm 25.23/26.17 (146.9) (1352.9) (1585.2) (2695.7) 80 nm 25.36/26.32 (147.1) (1352.5) (1585.1) (2695.5) Linewidth (cm 1 ) CNTf (pristine) (32.67) (27.82) (57.36) CNTf (after O 2 plasma) nm (20.42) (35.45) (32.23) (61.75) 20 nm (18.10) (34.84) (31.3) (59.49) 40 nm (16.69) (36.51) (33.92) (61.85) 60 nm (15.22) (35.88) (31.99) (60.33) 80 nm (15.35) (37.10) (31.88) 58.2 (60.86) Data after crystallisation in parenthesis Calculation of TiO 2 strain from Raman measurements. The Raman data in the manuscript give a downshift of 3cm 1 for the E g1 mode going from 10 nm to 80nm thickness films. It is assumed that the 80nmthick sample reflects mainly the unstrained state. The authors could not find reports on the dependence of Raman modes of TiO 2 with stress/strain. In the absence of these data, the case of hydrostatic pressure is used for reference. Swamy et al provide experimental results for the rate of Raman upshift with pressure 1, following a linear trend with a slope of approximately w P = 2.9 cm 1 /GPa Thus, 3cm 1 would correspond to a pressure of 1.03 GPa.

7 The stress components in the hybrid are nontrivial to find. Even treated with continuum mechanics the coating corresponds to a thick layer under a complex stress at its interface with CNTs and released at its outer surface. Furthermore, the dependence of the E g1 mode on the stress tensor components is not known. In view of these difficulties, as a first approximation we consider the hydrostatic stress: P = σ hydr = σ 11 + σ 22 + σ 33 3 It follows that σ hydr = 1.03 GPa. With knowledge of the Young s modulus of ALDgrown anatase (151GPa) 2, the volumetric strain comes out as ε = V = σ 11 + σ 22 + σ 33 V 0 3 E = σ hydr E = 0.7 % This estimate is of a similar order as the XRD data for TiO 2 and Raman data for the CNTs.

8 Figure S5: a) Raman spectra of pure CNT fibre and TiO 2 /CNT fibre with different metal oxide thickness before annealing at 400 C and b) evolution of the peak position of the main Raman bands of the CNT as a function of the ALD thickness. S5

9 Figure S6: Hybrid sample produced by thermal growth at 300 C, which shows a poor contact between the components. Figure S7: Photograph of a flexible freestanding electrode after peeling the sample off the substrate used for ALD and sintering. S6

10 Figure S8: Effect of the anatase thickness on the optical properties of the hybrid material. The absorbance of the samples with different TiO 2 thickness has been calculated using the absorption law for an indirect semiconductor at a wavenumber of 400nm. 1 V. Swamy, A. Kuznetsov, L. S. Dubrovinsky, R. A. Caruso, D. G. Shchukin and B. C. Muddle, Phys. Rev. B,, DOI: /PhysRevB L. Borgese, M. Gelfi, E. Bontempi, P. Goudeau, G. Geandier, D. Thiaudière and L. E. Depero, Surf. Coat. Technol., 2012, 206, S7