Customizing oxygen electrocatalytic microenvironment with S, N codoped carbon nanofibers confining carbon nanocapsules and Co9S8 nanoparticles for rechargeable Zn-air batteries

Rational design and modulation of oxygen electrocatalytic microenvironment are crucial for achieving high performance in rechargeable Zn-air batteries (RZABs). We report a high-efficiency bifunctional electrocatalyst based on S, N codoped carbon fibers confining carbon nanocapsules attached with Co9S8 nanoparticles to customize the oxygen electrocatalytic microenvironment. The inner carbon nanocapsules function as a “gas buffer”, while the outer fiber skeleton acts as a self-supporting structure, which jointly refine the oxygen electrocatalytic microenvironment and improve accessibility of the active sites. Such a unique nanostructure proves advantageous for O2 adsorption/diffusion and mitigation of local pH changes during oxygen reduction reaction, and favors the release of generated O2 and the transfer of interfacial electron during the oxygen evolution reaction as well. The constructed liquid RZABs deliver a large peak power density (280 mW cm−2) and robust cyclability (1200 h at 10 mA cm−2), and the assembled quasi-solid state flexible RZABs further indicate long-term durability. [Display omitted] •S, N codoped carbon fibers confining carbon nanocapsules attached with Co9S8 NPs are constructed.•DFT confirms the curved structures can optimize the free energy of Co9S8 for intermediates.•CNC/Co9S8@SNCF exhibits outstanding pH-universal ORR performance and OER activity.•The Zn-air battery shows a large peak power density (280 mW cm−2) and robust cyclability (1200 h at 10 mA cm−2).