## 2 Results and Discussion
### Synthesis and Characterization of the Co@g-C\({}_{3}\)N\({}_{4}\)/G Heterostructure Composites
For the Co@g-C\({}_{3}\)N\({}_{4}\)/G composites, most of the characteristic peaks of N-containing heterocycles generated from residual g-C\({}_{3}\)N\({}_{4}\) were overlapped by graphene, while only a peak at \(\sim\)1575 cm\({}^{-1}\) referred to g-C\({}_{3}\)N\({}_{4}\) still reappeared. These results indicate that some g-C\({}_{3}\)N\({}_{4}\) in the Co@g-C\({}_{3}\)N\({}_{4}\)/G precursor under thermal treatment is partially decomposed, which is consistent with the previous result in [37; 38]. To further determine the surface chemical state for the as-prepared samples, X-ray photoelectron spectroscopy (XPS) was performed. It was seen that two samples exhibited three distinct peaks at \(\sim\)285.0, 399.1, and 533.1 eV (Figure 3b), corresponding to C 1s, N 1s, and O 1s, respectively. Furthermore, a Co 2p signal located at 781.5 eV was observed in the spectrum of the Co@g-C\({}_{3}\)N\({}_{4}\)/G sample. The corresponding atom ratios of the three samples (including the pure g-C\({}_{3}\)N\({}_{4}\) originated from our recent work [42]) are listed in Table S1. Especially, the peak intensity of N 1s for the Co@g-C\({}_{3}\)N\({}_{4}\)/G and g-C\({}_{3}\)N\({}_{4}\)/G samples decreased sharply compared with that in the pure g-C\({}_{3}\)N\({}_{4}\) sample (Figure S4). This significant difference is also recognized in Table S1, with the N atom ratios for the Co@g-C\({}_{3}\)N\({}_{4}\)/G (\(\sim\)7.12 at%), g-C\({}_{3}\)N\({}_{4}\)/G (\(\sim\)8.7 at%), and g-C\({}_{3}\)N\({}_{4}\) (\(\sim\)75.02 at%) samples. According to other reported analogous g-C\({}_{3}\)N\({}_{4}\)/graphene composites [37; 49], it can be further speculated that the added limited g-C\({}_{3}\)N\({}_{4}\) in the precursor is decomposed partly under carbonization treatment. The N 1s XPS peak for the g-C\({}_{3}\)N\({}_{4}\)/G sample can be deconvolved into four peaks (Figure 3c), which are indexed to pyridinic N (\(\sim\)398.5 eV), pyrrol N (\(\sim\)399.9 eV), graphitic N (\(\sim\)401.2 eV), and oxidized N (\(\sim\)402.8 eV) [37; 51], respectively. As for the Co@g-C\({}_{3}\)N\({}_{4}\)/G sample, all the fitted peaks for the high-resolution N 1s spectra had a slight shift toward higher binding energies, suggesting that some of the Co atoms in Co@g-C\({}_{3}\)N\({}_{4}\)/G bound with N atoms to form Co-N\({}_{x}\) bonds [52; 53]. It needs to be pointed out that these predominant pyridinic and pyrrolic nitrogen atoms have abundant chemisorption sites for polysulfides [16; 25] and that the Co-N\({}_{x}\) bonds can act as electrocatalytic centers for polysulfide adsorption/conversion [52; 54], thus propelling the redox kinetics of sulfur species. The fitted high-resolution Co 2p spectrum in the Co@g-C\({}_{3}\)N\({}_{4}\)/G sample included four peaks (Figure 3d), which are assigned to the respective Co 2p\({}_{3/2}\) (\(\sim\)781.1 eV), Co 2p\({}_{3/2}\) satellite (\(\sim\)785.9 eV), Co 2p\({}_{1/2}\) (\(\sim\)796.9 eV), and Co 2p\({}_{1/2}\) satellite (\(\sim\)803.2 eV) [55]. Interestingly, the characteristic peaks of Co 2p\({}_{3/2}\) (Co 2p\({}_{1/2}\)) are exactly situated between Co\({}^{0}\) 2p\({}_{3/2}\) (Co\({}^{0}\) 2p\({}_{1/2}\)) and Co\({}^{2+}\) 2p\({}_{3/2}\) (Co\({}^{2+}\) 2p\({}_{1/2}\)), indicating a cationic environment of Co species [54; 55; 56; 57]. These results further reveal that a certain number of Co atoms in yir Co@g-C\({}_{3}\)N\({}_{4}\)/G sample were prone to coordinating with N atoms to construct Co-N\({}_{x}\) structures. Visible Adsorption Experiments of Prepared Materials toward Li\({}_{2}\)S\({}_{6}\) Solutions and Morphologies of g-C\({}_{3}\)N\({}_{4}\)/G- and Co@g-C\({}_{3}\)N\({}_{4}\)/G -PP Separators  
To better verify the capturing ability of Co@g-C\({}_{3}\)N\({}_{4}\)/G toward polysulfides, visible Li\({}_{2}\)S\({}_{6}\) solution entrapment experiments were carried out and are shown in Figure 4a. First, host materials with the same mass (10 mg) were added independently to the prepared Li\({}_{2}\)S\({}_{6}\) solution (2 mL) for static adsorption tests.