Hollow nanocage with skeleton Ni-Fe sulfides modified by N-doped carbon quantum dots for enhancing mass transfer for oxygen electrocatalysis in zinc-air battery.

Constructing nonprecious-metal catalysts for oxygen reduction/evolution reactions (ORR/OER) in Zinc-air battery (ZAB) by structural regulation is crucial, but balance between stable structure and efficient mass transfer is still ambiguous. Here, hollow bimetallic sulfide nanocages with anchored N-doped carbon-quantum-dots are synthesized using a selective-etching method (Ni-Fe-S/NCQDs). The marked Ni-Fe-S/3NCQDs exhibits a promising half-wave potential of 0.85 V (E 1/2 , ORR) and an excellent overpotential of 0.295 V at 10 mA cm−2 (OER). Ni-Fe-S/3NCQDs has a negative E 1/2 shift of only 12.8 mV after 5000 cycles (ORR) and a current-density decline of only 7.05 % after 20 h tests (OER). Ni-Fe-S/3NCQDs with porous-hollow structure (478.35 m2 g−1) facilitates mass transfer and exposure of active-sites. Ni/Fe oxyhydroxides (in-situ X-ray diffraction) contributes to excellent OER activity/stability. ZAB with Ni-Fe-S/3NCQDs can be repeatedly charged and discharged for 240 h at 10 mA cm−2. It provides a new strategy for constructing open-hollow structure to improve ORR/OER performances. [Display omitted] • NCQDs-anchored bimetallic sulfide nanocages with hollow structure are prepared. • Synergies between Ni-Fe-S and N-species boosts electron transfer to promote 4e- ORR. • Interaction between NiOOH and γ-FeOOH (in situ formed) promotes O 2 generation (OER). • Porous hollow interior creates numerous active interfaces and mass transfer pathways. • NCQDs on the nanocage surface protect active species to stabilize ORR/OER activity [ABSTRACT FROM AUTHOR]