Customizing the anisotropic electronic states of janus-distributive FeN4 and NiN4 dual-atom sites for reversible oxygen electrocatalysis

Non-bonding-type dual-metal atom sites have emerged as a frontier for bifunctional electrocatalysis, however, respectively customizing the local electronic states of two metal sites remains elusive. Herein, by fabricating FeN4 and NiN4 single atoms that Janus-distributed on the inner and outer of sulfur-doped carbon hollow spheres, namely FeN4-SC-NiN4, we demonstrate the sulfur-induced anisotropic electronic regulation for Fe/Ni dual-atom sites and build “one stone two birds” bidirectional facilitation mechanism for reversible oxygen electrocatalysis. For the separated FeN4 and NiN4 sites, the ambient sulfur reduces the charges of FeN4 sites while downshifts the d-band center of NiN4 sites. Such enlarged difference in electronic structure respectively promotes OH* desorption at FeN4 sites but accelerates O2 * stripping at NiN4 sites, enabling the FeN4-SC-NiN4 dual-atom sites to feature simultaneously enhanced oxygen reduction (E1/2 =0.844 V) and oxygen evolution (η10 =246 mViR-free) activity, together with a small potential gap (0.632 V) and superior long-term cycling stability for Zn-air battery.