Dual Active Sites Engineering on Sea Urchin‐Like CoNiS Hollow Nanosphere for Stabilizing Oxygen Electrocatalysis via a Template‐Free Vulcanization Strategy

Abstract

AbstractManipulating electronic structure and defects is crucial to achieve on‐demand functionalities of bimetallic sulfide catalysts for oxygen reduction/evolution reactions (ORR/OER). Here, via a vulcanization strategy, defects‐abundant NiCo2S4 needles obtained from sea urchin‐like NiCo2O4 are anchored on surface of hollow carbon‐sphere (NiCo2S4/HCS). NiCo2S4 nanoneedles (≈7.5 nm) are radially grown on shell of HCS with a cavity (254.5 m2 g−1), and their surface becomes rougher after vulcanization due to anion exchange reaction. As‐marked NiCo2S4/HCS‐3 exhibits better ORR activity (half‐wave potential of 0.89 V) and methanol tolerance than Pt/C (0.86 V). NiCo2S4/HCS‐3 shows a lower OER overpotential (310 mV) than RuO2 and retains 90.9% of initial activity after 9 h. Notably, zinc–air battery with NiCo2S4/HCS‐3 reveals highly‐stable charging/discharging voltages of 2.11/1.16 V with a negligible fading for 200 h. NiCo2S4 grown on outer/inner surfaces of HCS expands spatial distribution of active sites to enhance reactants‐electrode contact and charge transfer. Theoretical calculation shows that Co‐site with an electronic state near Fermi energy level is chiefly‐responsible for ORR, while Ni‐site mainly affords high OER activity. Bader charge analyses reveal that S doping increases the charge density and redox active sites in NiCo2S4. It sheds light on the understanding of electrocatalytic mechanisms on bimetallic sulfides for electronic device.