FIGURE 3 Synthesis and characterizations of control samples: (a) Scheme of the formation of Ni@C. (b) SEM images. (c, d) TEM images of Ni@C. (e) Scheme of the formation of Ni@NC. (f) SEM images. (g, h) TEM images of Ni@NC.
It is well known that lignin and chitosan are two of the most abundant biomass resources, which have rich hydroxyl groups or/and amine groups in their structures (Figure S5), suggesting the possibility that they can be used as chelating agents instead of D-glucosamine hydrochloride to synthesize Ni@N-C SAC. The aberration-corrected HAADF-STEM images of the two prepared catalysts using lignin and chitosan as chelating agents shown in Figure 4 reveal the atomically dispersed Ni sites supported on both carriers. Other characterizations of the catalysts, including SEM images (Figure S6), EDS analysis (Figure S7), together with XRD and XPS analysis (Figure S8) further reveal that Ni is atomically dispersed on the carrier of catalysts, regardless of the chelating agent is lignin or chitosan. ICP analysis indicates that Ni loading of the catalysts obtained from lignin and chitosan are 8.1 wt% and 7.5 wt%, respectively. The above results indicate that two readily available waste biomass resources are successfully used as chelating agents to synthesize Ni@N-C SAC, demonstrating that the chelation-anchored strategy is a universal method.