Unravelling the Tip Effect of Oxygen Catalysis in Integrated Cathode for High-Performance Flexible/Wearable Zn–Air Batteries

Abstract

The exploration of high-efficiency transition metal–nitrogen–carbon (M–N–C) catalysts is crucial for accelerating the kinetics of oxygen reduction/oxygen evolution reactions (ORR/OER). Fine-tuning the distribution of accessible metal sites and the correlated triphase interfaces within the M–N–C catalysts holds significant promise. In this study, we present an integrated electrocatalyst comprised of tip-enriched NiFe nanoalloys encapsulated within N-doped carbon nanotubes (NiFe@CNTs), synthesized using an in-situ wet-electrochemistry mediated approach. The well-defined NiFe@CNTs catalyst possesses a porous heterostructure, synergistic M–N_x–C active sites, and intimate micro interfaces, facilitating accelerated redox kinetics. This leads to exceptional OER/ORR activities with a low overall ΔE of 630 mV. Experimental results and density functional theory calculations unveil the predominant electronic interplay between the apical bimetallic sites and neighboring N-doped CNTs, thereby enhancing the binding of intermediates on NiFe@CNTs. Molecular dynamics simulations reveal that the local gas–liquid environment surrounding NiFe@CNTs favors the diffusion/adsorption of the OH⁻/O₂ reactants. Consequently, NiFe@CNTs contribute to high-performance aqueous Zn–Air batteries (ZABs), exhibiting a high gravimetric energy density (936 Wh kg_Zn^–1) and superb cycling stability (> 425 h) at 20 mA cm^–2. Furthermore, solid-state ZABs based on NiFe@CNTs demonstrate impressive electrochemical performance (e.g., peak power density of 108 mW cm⁻², specific energy of 1003 Wh kg_Zn^–1) and prominent flexibility. This work illuminates a viable strategy for constructing metal site-specific, cobalt-free, and integrated M–N–C electrocatalysts for multifunctional catalysis and advanced/flexible energy storage applications.

Graphical Abstract