Supporting Information

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1 Supporting Information Cellulose Fiber-based Hierarchical Porous Bismuth Telluride for High-Performance Flexible and Tailorable Thermoelectrics Qun Jin a,b, Wenbo Shi c,d, Yang Zhao a,c, Jixiang Qiao a,c, Jianhang Qiu a, Chao Sun d, Kaiping Tai a, *, Hao Lei d, *, Xin Jiang a,e, * a Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang , China. b University of Chinese Academy of Sciences, Shenyang , China. c School of Materials Science and Engineering, University of Science and Technology of China, Shenyang , China. d Surface Engineering of Materials Division, Institute of Metal Research, Chinese Academy of Sciences, Shenyang , China. e Institute of Materials Engineering, University of Siegen, Paul-Bonatz-Str. 9-11, Siegen 57076, Germany. * kptai@imr.ac.cn S 1

2 Figure S1. (a) Dynamic thermogravimetric analysis (TGA) of the cellulose-fibers (CFs) paper in the inert gas environment. The inset shows the optical image of the CFs-paper. (b) Calibration for sputtering power dependent deposition rate of Bi 2 film. S 2

3 Figure S2. A home-built laser micro-cutting system with beam resolution better than ~2 μm. S 3

4 Figure S3. Experimental setup for the bending test and the schematic of resistances measurement by 4-point configuration, where R is the convex/concave bending radius. The samples were attached to the surface of glass tubes with different radii. The relative resistance changes of the samples with various bending radii were used to evaluate the mechanical flexibility. S 4

5 Figure S4. X-ray diffraction patterns of the Bi 2 /CF (green), the Bi 2 /SiO 2 /Si (red), the Bi 2 /polyimide (blue), the sputtering target (black) and the standard reference of rhombohedral Bi 2 phase (JCPDS # , pink). S 5

6 Figure S5. Top-view and cross-section SEM images of the Bi 2 /SiO 2 /Si sample (a), (b) and Bi 2 /polyimide sample (c), (d). S 6

7 Figure S6. SEM images of the cut edges of the Bi 2 /CF (a) and the Bi 2 /polyimide (b) samples tailored by paper scissors across the thickness. S 7

8 Figure S7. For the pores with sizes smaller than ~200nm, the adsorption isotherms (a) were used to calculate the specific surface area (SSA) with the BET equation. P/P 0 values between 0.05 and 0.2 were used to calculate the SSA via multi-point BET method. The calculated SSA is 0.95 m 2 /g. For the pores with sizes larger than ~200nm, the nano-xrt analysis (b) was employed to determine the SSA of ~0.77 m 2 /g. The total SSA is estimated from the sum of these two values. S 8

9 Figure S8. False-colored 3D-XRT image of the Bi 2 /CF sample (a) and the 2D projections of the 3D-XRT image (b). The Bi 2 films were deposited by low and high deposition power, respectively (See the context). S 9

10 Figure S9. Schematic illustration of the sample preparation for the in-plane thermal conductivity measurement using laser micro-cutting system. Inset shows the optical image of the prepared samples for laser-flash test. S 10

11 ( 10 2 μw m -1 K -2 ) Bi 2 /SiO 2 /Si Bi 2 /polyimide Bi 2 /CF Optimized Bi 2 /CF T (K) Figure S10. The power factor of the Bi 2 /SiO 2 /Si sample, Bi 2 /polyimide sample, Bi 2 /CF sample and Bi 2 /CF sample with optimized carrier concentration. For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article. S 11

12 a C (J g -1 K -1 ) b D (mm 2 s -1 ) c (W m -1 K -1 ) C CF C 0 C BT D CF D 0 ML 0 CF Figure S11. Temperature dependent specific heat capacity (a) thermal diffusivity (b) and thermal conductivity (c) of the Bi 2 ( C BT T (K) ), Bi 2 /CF mixture layer ( ML ), pure CFs-paper ( C CF, D, CF CF ) and Bi 2 /CF sample ( C, 0 D, 0 0 ). The heat capacity of CFs-paper ( C CF ) was measured, which is comparable with the reference. 1 The heat capacity of Bi 2 ( C BT ) was from literature. 2 S 12

13 R/R Bending times Figure S12. The results of cyclic bending test for the Bi 2 /CF sample at concave-bending radius of 10 mm. R 0 is the original flat state resistance and R is the flat state resistance of the sample after bending cycles. S 13

14 S (μv K -1 ) Original flat state Concave-bending radius of 10 mm Concave-bending radius of 7 mm Holder ΔT Sample -120 I ΔU I T (K) Figure S13. Seebeck coefficients of Bi 2 /CF sample in concave-bending state. The bending state ZT value (radius of ~7 mm) is estimated to be ~0.32 at 330 K, if the flat state κ l (presuming the lattice thermal conductivity κ l is not sensitive to bending state) and concave-bending state κ e were used in the calculation. Insets are the photograph and schematic illustration of the bending state Seebeck coefficient measurement. S 14

15 a ( 10 4 S m -1 ) T (K) b (μv K -1 ) T (K) c ( 10 2 μw m -1 K -2 ) T (K) Figure S14. Temperature dependence of (a) electrical conductivity, (b) Seebeck coefficient and (c) power factor of the p-type (Bi, Sb) 2 /CF sample. S 15

16 1 μm Figure S15. SEM image of the TE device leg tailored by the laser micro-cutting system, where no-crack edge can be detected. S 16

17 Note 1 Determination of the preferential orientations Based on the XRD patterns, the corresponding orientation factors (F X ) can be calculated with the Lotgering s method: 3 F X P P 1 P 0, (S1) 0 with I( X ) P, (S2) I( hkl) and I0( X ) P 0, (S3) I ( hkl) 0 where ΣI(X), ΣI 0 (X), ΣI(hkl), and ΣI 0 (hkl) are the sum of the integrated intensities of the X and (hkl) reflections for the oriented sample and the non-oriented one, respectively; P and P 0 is the ratio of the sums for the oriented sample and the non-oriented one, respectively. The X reflections stand for the (006), (015), (1010), (0015) and (0210) reflections in our work. Based on the obtained experimental XRD patterns compared with standard PDF card (PDF# ), the F values can be determined for the Bi 2 /CF, the Bi 2 /SiO 2 /Si, the Bi 2 /polyimide and the sputtering target, which were listed in Table S1. Table S1. Calculated orientation factors F of the X plane. X Bi 2 /CF Bi 2 /SiO 2 /Si Bi 2 /polyimide Sputtering target S 17

18 Note 2 Thermal conductivity measurements Laser-Flash (NETZSCH LFA-467) method is used to measure the thermal diffusivity (D). To determine the thermal conductivity (κ), the density (ρ) and the specific heat capacity at constant pressure ( C ) are also measured to calculate the p D Cp. One hundred of Bi 2 /CF samples (in Figure S9) were utilized for D measurements from RT to 480 K using multilayer sample holder. The specific heat capacity of CFs-paper was measured by differential scanning calorimetry (DSC, NETZSCH STA-449 F3) with sapphire as reference sample, which is comparable with the reference. 1 The heating rate was 2 K/min. The heat capacity of Bi 2 from literature 2 was adopted. The density ρ was determined by mass (m) and volume (V) of Bi 2 /CF samples, based on the equation: ρ = m/v. The measurement uncertainties for density, C p and thermal diffusivity were ~5%, ~10%, ~3%, respectively. Therefore, the combined uncertainty for thermal conductivity was ~15%. The heat capacity of the Bi 2 /CF sample ( C 0 ) can be derived from the heat capacities of the Bi 2 ( C BT ) and CFs ( C CF ) using the mixture relationship: C 0 v0 CBTvBT CCFvCF (S4) The thermal conductivity of Bi 2 /CF mixture layer ( ML ) can be derived from the thermal conductivities of the CFs ( CF ) (the CFs layer without Bi 2 deposition as shown in Figure S9) and total {(Bi 2 +CFs)* + (CFs) # } whole sample ( 0 ) using the following equation: V ML V ML CF CF (S5) where BT and CF are the mass fractions of the Bi 2 and CFs, respectively, V ML and V CF are the volume fractions of the Bi 2 /CF mixture layer and the CFs layer without Bi 2 deposition, as shown in Table S2. S 18

19 Table S2. Parameters for the thermal conductivity measurements. Parameters Symbol Unit Bi 2 (CFs) total (Bi 2 /CF)* + (CFs) # (Bi 2 /CF)* (CFs) # Volume fraction V Mass fraction v Density of mass ρ g/cm Specific heat C J/g K Thermal diffusivity D mm 2 /s Thermal conductivity κ W/m K C BT C CF C 0 D CF D 0 CF 0 C CF D CF ML CF Note: *Mixture Layer (ML); # CFs Layer without Bi 2 deposition as shown in Figure S9. S 19

20 References: 1. Hatakeyama, T.; Nakamura, K.; Hatakeyama, H., Studies on Heat Capacity Of Cellulose And Lignin by Differential Scanning Calorimetry. Polymer 1982, 23 (12), Mills, K. C., Thermodynamic data for inorganic sulphides, selenides and tellurides. Butterworths: London,, 1974; p 845 p. 3. Lotgering, F. K., Topotactical Reactions with Ferrimagnetic Oxides Having Hexagonal Crystal Structures.2. J Inorg Nucl Chem 1960, 16 (1 2), Zebarjadi, M.; Joshi, G.; Zhu, G. H.; Yu, B.; Minnich, A.; Lan, Y. C.; Wang, X. W.; Dresselhaus, M.; Ren, Z. F.; Chen, G., Power Factor Enhancement by Modulation Doping in Bulk Nanocomposites. Nano Lett 2011, 11 (6), S 20