# Macroporous Activated Carbon Derived from Rapeseed Shell for Lithium-Sulfur Batteries
## 3 Results and Discussion  
SEM characterization was used to investigate sample morphology. During the comparison of four samples, macropores could not be observed in AC-0-800-1 (Figure 1a). However, three-dimensional interconnecting macropores were observed in AC-2.5-800-1, AC-5-800-1, and AC-10-800-1 samples (Figure 1b-d). Thus, macropores were formed from activation reaction of KOH. As the concentration of KOH increased, the macropore walls of AC became thinner until they collapsed. The macroporous structure of AC is conducive to the infiltration of sulfur into nanopores of AC during the preparation of sulfur/AC composite. TEM image of AC-5-800-1 also proved the macroporous structure of AC (Figure 1e). Furthermore, high-magnification TEM image exhibited that the macropore wall contained significant amounts of small-sized nanopores (Figure 1f). Abundant nanopores are beneficial for a homogenous distribution of sulfur. The pore structure of the AC samples was analyzed by the N\({}_{2}\) isotherm adsorption-desorption method. As presented in Figure 2a,c, all samples showed combined isotherms between type I and type IV behavior. According to the classification of the International Union of Pure and Applied Chemistry, type I corresponds to adsorption on microporous solids, whereas type IV corresponds to adsorption on mesoporous solids, indicating the presence of both of micro- and mesoporous structures in the AC  
Figure 1: SEM images of (**a**) Activated carbon (AC)-0-800-1, (**b**) AC-2.5-800-1, (**c**) AC-5-800-1, (**d**) AC-10-800-1; (**e,f**) TEM images of AC-5-800-1. samples. The high nitrogen uptake at low relative pressure of less than 0.1 in the adsorption branch of AC samples corresponded to a large amount of micropores. During this process, monolayer adsorption occurred, owing to the strong interaction between the nitrogen molecules and the pore wall. After the relative pressure reached 0.1, the adsorbing amount continually increased with increasing relative pressure, indicating the occurrence of multi-layer adsorption in mesopores. A slight hysteresis loop can be observed at relative pressures from 0.4 to 0.55 for AC-5-800-1, AC-10-800-1, and AC-5-800-3; such loop is commonly related to capillary condensation in mesopores. When the relative pressure approached 0.9, a further increase in volume was detected, indicating the existence of macropores in the samples. Figure 2b,d illustrate the pore size distribution curves based on the Barrett-Joyner-Halenda (BJH) equation. AC samples exhibited a pore distribution at about 2 nm, corresponding to high amounts of micropores and small mesopores. Table 1 summarizes the pore structure parameters of the AC samples. The Brunauer-Emmett-Teller (BET) specific surface area and pore volume of the samples depended mainly on the amount of KOH and the activated temperature. In all samples, AC-5-800-1 exhibited the largest BET surface area and the highest pore volume. AC-5-800-1 was further studied as a loading framework for sulfur due to its optimal pore structure parameters. For conciseness, AC-5-800-1 and the obtained sulfur/carbon composites are referred to as AC and AC/S composite in subsequent sections. Figure 3a presents the XRD patterns of pure \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Samples**} & **Brunauer–Emmett–Teller (BET)** & **Pore Volume** & \multirow{2}{*}{**BJH Average Pore Size (nm)**} \\  & **Surface Area (m\({}^{2}\) g\({}^{-1}\))** & **(cm\({}^{3}\) g\({}^{-1}\))** & \\ \hline AC-2-5-800-1 & 1211 & 0.66 & 2.8 \\ AC-5-800-1 & 2090 & 1.28 & 2.7 \\ AC-10-800-1 & 2082 & 1.24 & 2.6 \\ AC-5-700-1 & 1157 & 0.63 & 2.7 \\ AC-5-800-3 & 2035 & 1.22 & 2.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Pore structure parameters of AC samples. Figure 2: (**a,c**) N\({}_{2}\) adsorption–desorption isotherms of activated carbon (AC) samples; (**b,d**) Barrett–Joyner–Halenda (BJH) pore size distribution curves from adsorption branch of AC samples. sulfur, AC, and AC/S composite.