## 3 Results
### XRD Analysis  
Figure 10 shows the XRD patterns of the three biocarbons. The biocarbon samples exhibit similar X-ray diffraction patterns.  
The three samples display a structure that lacks a definite pattern, known as an amorphous structure. They also exhibit broad reflection peaks at approximately 8, 26, and 45 degrees. Specifically, the peaks observed at 20 values of 24 and 44/45 degrees match the (002) and (100) planes, respectively. These findings have been supported by previous research [45; 46]. The broad diffraction pattern observed for the (002) plane indicates the presence of graphene sheets stacked parallel to each other in the carbon materials [47].  
Additionally, the presence of the (100) plane suggests the existence of sp\({}^{2}\) hybridized carbon arranged in a honeycomb structure. This arrangement enhances the material's conductivity [48; 49]. These characteristics are expected to impact the electrochemical properties and the morphology of the composite electrodes made from the biocarbon material and the interface with the electrolyte.  
Table S2 reviews the peaks obtained from the diffraction pattern of the three biocarbons, all carbonized for 1 h at 1000 \({}^{\circ}\)C. Notably, the blue shark chondroitin sulfate sample exhibits a significantly higher intensity in the (100) plane, indicating a higher density of pores within the solid-state graphitic carbon [30; 50]. The interlayer spacing, calculated from  
Figure 10: X-ray diffraction (XRD) patterns for gelatine and chondroitin sulfate-based carbons (1 h at 1000 \({}^{\circ}\)C).  
the (002) plane, is 2.8 A for chondro sulfate derived from blue shark and 3.5 A for the commercial source. For blue shark gelatine, the value is 3.5 A. The interlayer spacing for pure graphene is 3.35 A [51], with the blue shark chondro sulfate-based carbon displaying a lower value.  
Determining the interlayer spacing of a material, such as carbon, through X-ray diffraction (XRD) can provide valuable information about its structure. However, the interlayer spacing calculation accuracy depends on several factors, including the broadness of the XRD peak. XRD is based on the principle of Bragg's Law, which relates the X-ray diffraction angles to the crystal lattice's interplanar spacing. In the case of layered materials like graphite or graphene, the interlayer spacing can be determined by measuring the angle at which the diffraction peak occurs [52].  
When the XRD peak is broad, it suggests that the material has a high degree of disorder or a relatively large distribution of interlayer spacing. In such cases, accurately determining the interlayer spacing becomes more challenging due to the overlapping diffraction patterns. The broadening can result from various factors, including stacking faults, lattice strain, or the disordered stacking of layers [53].  
The XRD peak should ideally be sharp and well-defined to obtain accurate interlayer spacing calculations. A broad peak indicates that the interlayer spacing may not be accurately determined from the diffraction pattern alone. The interplanar distance values determined by XRD agree with those obtained from the UHR-STEM analysis. For blue shark-based samples, the d spacing is nearly identical; for the commercial sample, the interplanar spacing obtained via UHR-STEM is significantly lower. Considering the broad character of the peaks, determining the interplanar distance may not be as accurate using the X-ray diffraction technique as it is with UHR-STEM. A comparison between the two methods can be observed in Table 3.