# Facile Fabrication of 3D Hierarchically Porous Carbon Foam as Supercapacitor Electrode Material
## 2 Experimental  
Starch was utilized as the carbon source through a facile solvothermal process. Typically, Starch and Na\({}_{2}\)CO\({}_{3}\) were mixed with a mass ratio of 1:1 in 75 mL ethyl alcohol. Afterward, the mixture wastransferred into a 100 mL Teflon-lined stainless steel autoclave, solvothermally treated at 180 \({}^{\circ}\)C for 16 h, and then naturally cooled down to ambient temperature. The product was filtered and dried in a vacuum at 80 \({}^{\circ}\)C for 24 h. The sample was heated from an ambient temperature to 850 \({}^{\circ}\)C at the rate of 5 \({}^{\circ}\)C/min in a nitrogen atmosphere and held at 850 \({}^{\circ}\)C for 1.5 h. Finally, the resulting product was washed with a dilute HCl solution to get rid of the residual Na\({}_{2}\)CO\({}_{3}\) and deionized the water to a neutral pH, and dried at 80 \({}^{\circ}\)C for 24 h in a vacuum oven. The obtained sample was denoted as SCF. For comparison, the pure starch without Na\({}_{2}\)CO\({}_{3}\) was dealt with otherwise similar conditions, the product was denoted as SC.  
The morphologies of the samples were characterized using a scanning electron microscope (SEM, Hitachi S4800, Tokyo, Japan). The X-ray diffraction (XRD) patterns were recorded with an X-ray diffractometer (PANalytical, Almelo, The Netherlands) with Cu K\(\alpha\) radiation (\(\lambda\) = 0.1542 nm). The Raman spectra were measured on a Micro Raman Spectrometer (JOBIN YVON, Paris, France) with an excitation wavelength of 632.8 nm. The specific surface area and analysis of porosity for materials were characterized by N\({}_{2}\) adsorption/desorption isotherms at 77 K with an ASAP 2010 instrument (Micromerities, Norcross, GA, USA). The specific surface area and pore size distribution were determined according to the Brunauer-Emmett-Teller (BET) equation and the non-local density functional theory (NLDFT), respectively. The microspore volume (Vmic) was analyzed by the t-plot method. Microporosity was the ratio of micropore volume to total volume.  
All electrochemical measurements were performed in a three-electrode setup: a titanium plate coated with slurry as the working electrode, a platinum foil as the counter electrode, and a saturated mercurous sulfate electrode (MSE) as the reference electrode. A solution containing 5 M H\({}_{2}\)SO\({}_{4}\) served as the electrolyte at room temperature. Cyclic voltammograms (CV) and galvanostatic charge/discharge (GCD) were measured by an electrochemical workstation (CHI 660D). The working electrodes were prepared with the as-prepared materials, acetylene black, and PVDF (Polyvinylidene Fluoride) in a mass ratio of 8:1:1. The resulting slurry was dropped evenly onto the titanium sheet substrate (1 cm \(\times\) 1 cm) and dried at 70 \({}^{\circ}\)C in a vacuum oven overnight. The loading weight was controlled to be 1 \(\pm\) 0.1 mg. Then the dried finished electrode was immersed in an H\({}_{2}\)SO\({}_{4}\) (5 M) solution for infiltrating the active compositions completely. Electrochemical impedance spectroscopy (EIS, Nyquist plots) was carried out in the three-electrode system at an open circuit potential over a frequency range from 0.01 Hz to 100 kHz with a 10 mV amplitude.  
The capacitance values were calculated from cyclic voltammetry curves according to the following formula:  
\[C=\frac{\int_{V_{a}}^{V_{c}}I(V)dV}{2\times m\times v\times(V_{c}-V_{a})}, \tag{1}\]  
where \(C\) is the specific capacitance, \(I\) is the current value of the CV curve, \(v\) is the scanning speed of the CV curve, \(m\) is the mass of the active material, and (_Vc-Va_) is the potential window.  
The capacitance values were also calculated from galvanostatic charge-discharge curves according to the following formula:  
\[C=\frac{I\times dt}{m\times(V_{c}-V_{a})}, \tag{2}\]  
where \(C\) is the specific capacitance, \(I\) is the current value of the GCD curves, \(dt\) is the time of the galvanostatic discharging, \(m\) is the mass of active material, and (_Vc-Va_) is the potential window.