Bioderived FeNi encapsulated N-doped carbon nanotubes for high-performance ORR/OER bifunctional catalysis

The extraction of chitin/chitosan from biowaste shrimp shells involves the heavy use of strong acids and alkaline solutions, resulting in a series of decomposed amino acids in the extraction waste. Herein, we demonstrate a new strategy to grow FeNi nanoalloys encapsulated in nitrogen-doped carbon nanotubes (3FeNi-NCNTs) at a high percentage by sintering the extracted amino acids, FeCl 3 , NiCl 2 and melamine at 900 ℃ in N 2 . The FeNi-NCNT exhibits a competitive limiting current density in oxygen reduction reaction (ORR) to the commercial 20% Pt/C, with the onset potential and half-wave potential at 0.98 V and 0.84 V versus RHE. The oxygen evolution reaction (OER) performance also rivals the RuO 2 catalyst, and the overpotential (E j =10 mAcm -2 - E 1/2 ) of as low as 0.76 V, highlighting a green pathway to yield superior bifunctional catalysts at low cost. When used in zinc-air batteries (ZABs), the aqueous ZAB showed excellent cyclic and rate performance, together with the peak power density and specific capacity of 173.6 mW cm -2 and 809.9 mAh g -1 (corresponding to an energy density of XXX Wh kg -1 based on the mass of consumed zinc); and the flexible ZAB with a polyacryl-amide hydrogel electrolyte also exhibited a high peak power density of 133 mWcm -2 and a long cycle life of 140 h, superior to the reference Pt/RuO 2 -based ZABs, highlighting a sustainable biowaste upcycling of shrimp shell valorization on energy storage. Graphical