Supporting Information
Thermoelectric Properties of Nanoporous ThreeDimensional Graphene Networks
Pradheep Thiyagarajan1, Min-Wook Oh2, Jong-Chul Yoon1,
and Ji-Hyun Jang1,*
1. Interdisciplinary School of Green Energy and Low Dimensional
Carbon Materials Center, UNIST, Ulsan 689-798, Korea.
2. Creative Electrotechnology Research Center, Korea
Electrotechnology Research Institute, Changwon, Korea
Corresponding author: clau@unist.ac.kr
Experimental Procedure
Colloidal Silica (CS) particles (20-30 nm), Poly vinyl alcohol (PVA, Mw = 31,000–50,000) and
iron chloride were obtained from Sigma-Aldrich and used without any further purification. PVA
(10 wt. %) was dissolved in DI-water at 90°C and then 350 (phr: part per hundred parts of resin)
by weight of FeCl3 was added to PVA solution. The PVA/FeCl3 solution was made into CS/PVA
/FeCl3 disks, through vacuum filtration technique reported earlier. The disks were vacuum
annealed in chemical vapor deposition system (CVD) at room temperature for overnight to
remove moisture. The disks were carbonized at 1000°C for 30 min under Ar flow rate of 3L/min
and H2 flow rate of 100 sccm at pressure of ~4.0 torr. The samples were cooled rapidly to room
temperature. To remove the SiO2 particles and iron from the 3D graphene networks (3D-GN);
3D-GN@SiO2/Fe powders were immersed in HF for 3 hrs and HCl for 12 hrs. Nanoporous 3DGN powders were washed and dried at 90°C for 3 hrs.
Characterization techniques
The morphology of the samples was visualized using Field Emission scanning electron
microscope (Hitachi-S 4800) and Transmission electron microscope (JEM-2100, 200 kV).
Surface analysis of 3D-graphene was performed using micro-Raman spectroscopy to determine
the quality of graphene. Raman spectra were recorded using a micro-Raman spectrometer
(WITec, alpha300R) with an incident wavelength of 532 nm. The laser power was set at 2 mW to
avoid damage by laser irradiation. Chemical composition of the 3D-GN was measured using an
X-ray Photoelectron spectroscopy system (XPS, Thermo Fischer UK) with an Al Kα source.
Thermoelectric Characterization
3D-GN pellets used for the measurements were made using spark plasma sintering system (Dr.
Sinter, SPS-systex, Japan). The 3D-GN powders were consolidated at 1273 K under a pressure of
50 MPa for a holding time of 5 min. The Hall Effect measurements were made to determine the
carrier concentration using ECOPIA HMS-3000 system by means of the Van der Pauw method.
Thermal conductivity measurements were performed on the disc shaped pellet by means of Laser
flash apparatus (LFA 457 model) from 298 K-773 K. The thermal conductivity was calculated
using the following equation κ = adc , where a is the thermal diffusivity value measured using
LFA instrument, d is the density of the 3D-GN (0.63 g/cm3) and c is the specific heat of 3D-GN
(0.70 J/gK at 300K). The electrical resistivity values by varying the temperature were also
obtained using the ULVAC ZEM-3 (M10) system. The bar-type pellet used for the measurement
of the electrical resistivity as shown in fig S5 has dimensions of 10 x 2.5 x 1.5 mm3. The
resistivity of the samples was measured by passing current (I) through the sample and measuring
the voltage (∆V) between two points in a sample with known dimensions. From the measured
results, the resistivity is calculated using ρ =
∆𝑉
𝐼
𝐴
∗ 𝐿 , where A is the cross sectional area of the
sample and L is the distance between the points of measurement. The electrical conductivity
values were obtained from the measured electrical resistivity values using the relation σ =1/ρ.
Fig S1: Digital photograph image of 3D-GN pellet used for thermoelectric measurements.
Fig S2: Schematic diagram illustrating growth conditions for synthesizing 3D-GN.
Fig S3: Digital photograph image of the synthesized gram-scale 3D-GN.
Fig S4: (a) Low magnification SEM image of 3D-GN (scale bar: 10µm). (b) TEM image
exhibiting 3D-GN (scale bar: 0.2µm).
Fig S5: X-ray diffraction data of 3D-GN.
Fig S6: XPS spectrum of 3D-GN.