Synergistic Effect of Co 9 S 8 and FeS 2 Inlaid on N-Doped Carbon Nanofibers toward a Bifunctional Catalyst for Zn-Air Batteries.

The development of economical and energy-efficient electrocatalysts is essential for the wide-scale application of secondary zinc-air batteries (ZABs). Herein, we prepared Co 9 S 8 and FeS 2 nanoparticles inlaid on N-doped carbon nanofibers (Co 9 S 8 -FeS 2 @N-CNFs), which were derived from the in situ growth of Fe-doped ZIF-67 nanosheet arrays on electrospun nanofibers and a subsequent sulfidation process. The Co 9 S 8 -FeS 2 @N-CNFs display excellent electrocatalytic performances for OER ( E j =10 , 330 mV) and ORR ( E 1/2 , 0.80 V) as well as a smaller charge and discharge gap (Δ E , 0.76 V) in KOH electrolyte, allowing it to be employed as an attractive air cathode bifunctional catalyst for secondary ZABs. The electrocatalytic performance of the composite materials (Co 9 S 8 -FeS 2 @N-CNFs) is obviously better than that of the single-component materials (FeS 2 @N-CNFs and Co 9 S 8 @N-CNFs). The improved catalytic performance is mainly attributed to the synergistic effect of the two transition-metal sulfides and the optimization of the structure. Furthermore, the peak power density of the assembled aqueous/solid-state ZABs based on Co 9 S 8 -FeS 2 @N-CNFs can reach 214 and 91 mW cm -2 with excellent stability, respectively, which outperforms the ones based on commercial precious-metal-based catalysts. We anticipate that our work will provide new inspiration for the design of MOF-derived sulfides as multifunctional catalysts.