## 3 Results and Discussion
Co-GHCP showed a similar decomposition temperature, reaching to 400 \({}^{\circ}\)C. However, the weight loss continued when the temperature was over 450 \({}^{\circ}\)C, and the residual weight was 18.4 wt% at 800 \({}^{\circ}\)C. This phenomenon could be attributed to the decomposition of the Co (II) porphyrin group, where the dissociation of cobalt ion with the generation of radical groups may have induced the decomposition of the porphyrin groups [38]. Overall, the Co-GHCP and GHCP had excellent thermal stability and moderate carbon yields, which were good precursors for the preparation of carbon materials (PCs). As-prepared Co-GHCP and GHCP showed solid powder with the color of atropurpureus. After the heat treatment, the color of the Co-GPC and GPC changed to black (Figure 2a). As a typical example, the morphology and microstructure of the porous carbon Co-GPC was investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In Figure 2b-e, the Co-GPC showed several free-standing nanosheets, with a size ranging from a hundred nanometers to several micrometers, which was similar to other graphene-coupled porous polymers and porous carbon. In addition, the 2D morphology with visible wrinkles could be clearly observed even after high temperature pyrolysis, indicating the flexibility feature of the porous carbon nanosheets, originating from the template of graphene [39]. More importantly, no bare graphene sheets or free porous polymeric nanoparticles were observed in either the SEM or TEM, which was attributed to the efficient RAFT polymerization and nucleophilic substitution reaction for the polymerization of monomers on the surface of the GO. In the enlarged TEM image, alternating light and dark regions could be easily observed, suggesting the creation of a porous structure in the framework of carbon materials during pyrolysis [40]. As indicated by elemental mapping in Figure 2f, homogeneous distributions of C, N, and Co elements in the Co-GPC further confirmed the introduction of the Co (II) porphyrin group into the skeletal framework of the porous carbon. To reveal the porous nature of the as-prepared materials, the nitrogen adsorption/desorption properties of the Co-GPC, Co-GHCP, GPC, and GHCP were tested. As shown in Figure 3a, the  
Figure 2: Morphology characterization of as-prepared nanosheets. (**a**) Co-GHCP, GHCP, Co-GPC and GPC. Scanning electron microscopy (SEM) (**b,c**), transmission electron microscopy (TEM) (**d,e**), and SEM-EDX (Energy Dispersive X-Ray Spectroscopy) elemental mapping (**f**) of Co-GPC. hysteresis loops of the isotherms for all the samples could be classified as type IV, according to the International Union of Pure and Applied Chemistry (IUPAC) classification, indicating the presence of many mesopores in the porous materials [41]. The specific surface areas of the Co-GHCP and GHCP were 130.8 and 143.7 m\({}^{2}\) g\({}^{-1}\), respectively, based on Brunauer-Emmett-Teller (BET) calculations. These small specific surface areas were ascribed to the large number of flexible polymeric chains, as well as the chloride anions in the hypercrosslinked polymeric frameworks. Moreover, the pore size distributions of the Co-GHCP and GHCP analysis using nonlocal density functional theory (NL-DFT) revealed similar mesopores centered around 3.0 nm (Figure 3b). After pyrolysis at 800 \({}^{\circ}\)C, the BET surface areas of the porous carbon nanosheets were increased significantly relative to the pristine hypercrosslinked polymers. In this study, the specific surface areas of the Co-GPC and GPC were found to be 257.8 and 272.5 m\({}^{2}\) g\({}^{-1}\), respectively. Notably, the average pore sizes of the porous carbon materials had also relatively increased, which showed several broad peaks between 3 and 7 nm. This possibly alludes to an increase of the rigid framework through the partial degradation of the polymer chain and recombination of the fragments under the carbonization conditions, as described in reference [31].