# Facile Fabrication of 3D Hierarchically Porous Carbon Foam as Supercapacitor Electrode Material
## 3 Results
The I\({}_{\rm D}\)/I\({}_{\rm G}\) of SCF is 1.16 higher than SC (0.98), showing the strengthened intensity of the disorder and defects induced by the Na\({}_{2}\)CO\({}_{3}\) activation [21]. Na\({}_{2}\)CO\({}_{3}\) also plays the role of the template, therefore, the generated macropores further increase the disorder degree of the carbon foam. The appearance of the broad 2D band elucidates that the obtained materials are with great graphitization, which may have a positive effect on maintaining the integrity of the testing structure and efficiently enhance the conductivity of the materials [22]. Figure 4: (**a**) X-ray diffraction XRD patterns; (**b**) Raman spectra of SCF and starch-derived carbon SC. Figure 3: (**a**) The N\({}_{2}\) adsorption/desorption isotherm of SCF and (**b**) the corresponding pore size distribution calculated by the non-local density functional theory NLDFT model with the enlarged image in the inset. Electrochemical performances of as-obtained materials in 5 M H\({}_{2}\)SO\({}_{4}\) are exhibited in Figure 5. The cyclic voltammograms (CVs) of SCF with different scanning rates in Figure 5a show almost rectangular shapes at a potential window ranging from 0 V to \(-\)0.8 V referred to as _MSE_. The CV curves of SC and SCF at 10 mVs\({}^{-1}\) are shown in Figure S2a where SC hardly shows a rectangular shape. The significantly improved current and the quasi-rectangular shapes suggest that more energy can be reserved in the SCF electrode through a fast ion adsorption mechanism [23]. Figure S3 shows CV curves of SC at different scanning rates. In Figure 5b, SCF exhibits a 90.8% capacitance retention with the increasing scan rate from 10 mVs\({}^{-1}\) to 50 mVs\({}^{-1}\), higher than SC. Figure 5c shows the galvanostatic charge-discharge (GCD) curves of SCF at various current densities. Different from the GCD shape of starch-derived carbon (Figure S2b), these profiles are basically linear and symmetric, suggesting the high coulombic efficiency and great reversibility of this material [24]. The specific capacitances of carbon foam calculated from the GCD profiles are 179.6, 168.7, 164, 135, and 113 F\(\cdot\)g\({}^{-1}\) at 0.5, 1, 2, 5, and 10 A\(\cdot\)g\({}^{-1}\), respectively. With the increasing current densities from 0.5 A\(\cdot\)g\({}^{-1}\) to 10 A\(\cdot\)g\({}^{-1}\), SCF exhibits a 61.8% capacitance retention in Figure 5d, higher than SC electrode. To further investigate the cycling stability of carbon foam, galvanostatic charge/discharge tests for 1000 cycles at a current density of 0.5 A\(\cdot\)g\({}^{-1}\) was conducted. After 1000 cycles, there was 98.9% capacitance retention at 0.5 A\(\cdot\)g\({}^{-1}\) (Figure 5e). Figure 5f shows the Nyquist plots of SCF and SC electrodes in the frequency range of0.01 Hz-100 kHz. The value of the EIS curve intersection at the Z' axis shows the internal resistance (\(R_{s}\)). The smaller diameter of the semicircle in the high-frequency region manifests the smaller charge transfer resistance (\(R_{ct}\) = 0.243 \(\Omega\)), which relates to the conductivity and porous texture of SCF [19; 25]. In the set of Figure 5f, the shorter length of the Warburg impedance (\(W\)) area with a 45-degree slope reveals the lower ion transportation resistance and better ion diffusion, which results in the great rate capability of SCF [26]. In the low-frequency region, SCF exhibits a steep line with a higher slope, indicating better capacitive performance [27]. The supercapactive property comparison of SCF and other previously reported carbonaceous materials are summarized in Table 1. The great capacitive performance mainly benefits from its highly developed micropores that guarantee a large surface area for charge accommodation. The excellent rate and cycle capabilities of SCF can be attributed to the massive macropores and mesopores. The former acts as ion-buffering reservoirs to minimize the ion diffusion distances and the latter provides low resistant pathways for ion transportation [28].