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Single-atom catalysts (SACs) are attractive candidates for oxygen reduction reaction (ORR). The catalytic performances of SACs are mainly determined by the surrounding microenvironment of single metal sites. Microenvironment engineering of SACs and understanding of the structure-activity relationship is critical, which remains challenging. Herein, a self-sacrificing strategy is developed to synthesize asymmetric N,S-coordinated single-atom Fe with axial fifth hydroxy (OH) coordination (Fe-N3 S1 OH) embedded in N,S codoped porous carbon nanospheres (FeN/SC). Such unique penta-coordination microenvironment is determined by cutting-edge techonologies aiding of systematic simulations. The as-obtained FeN/SC exhibits superior catalytic ORR activity, and showcases a half-wave potential of 0.882 V surpassing the benchmark Pt/C. Moreover, theoretical calculations confirmed the axial OH in FeN3 S1 OH can optimize 3d orbitals of Fe center to strengthen O2 adsorption and enhance O2 activation on Fe site, thus reducing the ORR barrier and accelerating ORR dynamics. Furthermore, FeN/SC containing H2 O2 fuel cell performs a high peak power density of 512 mW cm-2 , and FeN/SC based Znair batteries show the peak power density of 203 and 49 mW cm-2 in liquid and flexible all-solid-state configurations, respectively. This study offers a new platform for fundamentally understand the axial fifth coordination in asymmetrical planar single-atom metal sites for electrocatalysis.
Li et al. (Sat,) studied this question.