## 3 Results
### Preliminary Results: Ball-Milling Effect  
Several methods, such as chemical functionalization, doping with heteroatoms, chemical activation during carbonization, and ball-milling, are used to enhance carbon materials'  
Figure 14: Nyquist plots for blue shark chondro sulfate (**a**), commercial chondro sulfate (**b**), and blue shark gelatine (**c**) -based carbons (+0.5 V vs. Ag). R(RQ) and RQ fitted to experimental data. (**d**) Differential capacitance (F cm\({}^{-2}\)) curves measured at the carbon/DES interface in the accessible potential window (0–1 V). performance by changing the materials' characteristics (e.g., increasing their surface area, porosity, conductivity, etc.). Although the electrochemical performance of the blue shark-based carbon materials presents lower capacitance values when compared to commercial carbons [64; 65], these sustainable carbons can provide a starting point for the application of techniques to enhance their characteristics. In a previous paper [12], the authors successfully used chemical activation of the carbon precursor (prawn and squid chitins) during the carbonization process to improve the surface characteristics and electrochemical performance of the carbon materials. In this work, a different approach was taken by using ball-milling, a greener route to modification of carbon materials [66; 67], thereby avoiding the use of wet chemistry processes. The ball-milling of the bio-carbon samples was performed, fixing the bouncing frequency (25 Hz) and size of the stainless steel balls (1 cm). The ball-milling times applied were up to 5 h. A BET analysis was performed for all the new ball-milled samples, with the results in Tables S3-S5 in the Supplementary Materials. Figure 15 presents the S\({}_{\text{BET}}\) and D\({}_{\text{P}}\) for the different milling times and the galvanostatic charge-discharge curves for the higher surface samples. Figure 15: S\({}_{\text{BET}}\) (**a**), D\({}_{\text{P}}\) (**b**) for different ball-milling times and galvanostatic charge–discharge curves (**c**), in ethaline at 30 \({}^{\circ}\)C (1 st cycle at 1 A g\({}^{-1}\)) (for the best performing materials) and for gelatine and chondro-based sulfate-based carbons. The maximum surface area is reached at different times for the different biocarbons. Figure 15a,b show that the blue shark chondroit sulfate-based carbon reaches the maximum surface area and pore diameter after 3 h of ball-milling. In contrast, commercial chondro-based carbon takes 1 h, and blue shark gelatine-based carbon takes only 15 min. After the maximum values are achieved, they start to decrease, and the particles tend to agglomerate, leading to a decrease in surface area (breakage/rewelding process), as already stated by [PERSON] et al. [68] and [PERSON] et al. [19]. Considering these results, a GCD analysis was performed with the materials presenting a higher surface area and pore size. Figure 15c presents the GCD analysis with the blue shark chondroit sulfate, commercial chondro sulfate, and the blue shark gelatine-based carbons (1000 \({}^{\circ}\)C for 1 h) before milling (continuous line) and after milling (line-dot-line). These studies were performed using the same electrolyte and conditions presented earlier. Figure 16 presents the comparison between the specific capacitance of non-milled and ball-milled materials, showing that the ball-milling applied to these carbons can significantly increase the specific capacitance of these materials, with an increase of \(\times\)3 in the case of the blue shark chondroit sulfate-based carbon, followed by the rise of \(\times\)5 in the blue shark gelatine-based carbon, and \(\times\)2.5 for the commercial chondro sulfate-based carbon. The difference in the optimal ball-milling time and the rate of increase in the specific capacitance can be associated with the distinct characteristics of the three carbon precursors. No changes are observed when comparing the capacitance retention before and after the milling process.