fig2
![Heterogeneous single-atom catalysts for energy process: recent progress, applications and challenges](https://image.oaes.cc/412b5842-a04b-4be1-8dae-44815d7d6412/5490.fig.2.jpg)
Figure 2. (A) Illustration of the preparation process of single iron atomic sites supported on nitrogen, phosphorus, and sulfur co-doped hollow carbon polyhedron (Fe-SAs/NPS-HC) by pyrolysis combined with a heteroatom doping strategy; Reproduced from Ref.[33] with permission from Springer Nature. Electrochemical and physical characterization of different catalysts. (B) Pt L3-edge XANES for Pt