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

Abstract

Manipulating 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.