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, FeCl3, NiCl2 and melamine at 900 ℃ in N2. 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 RuO2 catalyst, and the overpotential (Ej=10 mAcm-2 - E1/2) 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/RuO2-based ZABs, highlighting a sustainable biowaste upcycling of shrimp shell valorization on energy storage. • A sustainable strategy is developed to upcycle shrimp-shell extraction waste into FeNi nanoalloy-encapsulated N-doped carbon nanotube catalysts. • FeNi nanoalloys confined within NCNTs create abundant Fe/Ni-Nx active sites and accelerate charge transfer for bifunctional ORR/OER catalysis. • The optimized 3FeNi-NCNTs deliver Pt/RuO2-comparable ORR and OER activity with a low ΔE of 0.76 V in alkaline media. • Zn-air batteries based on 3FeNi-NCNTs achieve high peak power density (173.6 mW cm-2) and large specific capacity (809.9 Wh kg-1). • Flexible solid-state Zn-air batteries exhibit long cycling stability (140 h) and robust performance under mechanical bending.