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.