Activating inverse spinel NiCo2O4 embedded in N-doped carbon nanofibers via Fe substitution for bifunctional oxygen electrocatalysis

To improve the structure-dominant activity, rational design of oxide-based materials remains challengeable in bifunctional oxygen electrocatalysis , especially from the perspective of electronic modulation. Herein, we demonstrate that the electron configuration of inverse spinel NiCo 2 O 4 can be activated by controllable substitution of Fe into the octahedral centers. Fe-substituted NiCo 2 O 4 nanoparticles embedded in porous N-doped carbon nanofibers (NiCo 2- x Fe x O 4 /NCNF), which were synthesized by scalable electrospinning, exhibit a correlated relationship with Fe atomic content and achieve an optimal bifunctional activity (ΔE = 0.74 V) at 0.25 at.%. Theoretical calculation shows that the substitution of Co 3+ by Fe 3+ modulates the electrons filling in e g orbital of octahedral cation via delocalizing the electrons around O anions. The increased density of states around the Fermi level further regulate the adsorption energy of oxygen intermediates and lead to better bifunctional performance than commercial Pt/C + RuO 2 in rechargeable Zn-air battery. This work provides a new pathway to develop cost-effective bifunctional electrocatalysts for electrochemical energy storage and conversion .