Nanoporous-Structured Fe-NC Single-Atom Electrocatalysts Based on Lotus Seedpods and Industrial Acid Residues for Efficient Oxygen Reduction Reaction

The efficiency of the oxygen reduction reaction (ORR)plays a pivotalrole in determining the performance of electrochemical energy storagedevices, such as rechargeable zinc-air batteries (ZABs). Economicaland active electrocatalytic materials are highly desired to driveefficient ORRs. Carbon-nanostructure-based catalysts derived fromnatural biomass or waste, featuring distinct low cost and sustainability,have been deemed as a promising candidate to substitute expensivenoble-metal-based catalysts for ORR. In this work, we report a greenand cost-effective strategy to produce nanoporous Fe-NC single-atomelectrocatalysts (SACs) for efficient ORRs, using both iron-containingindustrial spent acid (SA) residue and the natural biomass of thelotus seedpod (LS) as the main raw materials. The SA features twounique advantages for the SAC synthesis: the Fe3+ actsas a Lewis acid scissor to generate rich nanopores,and the HCl can remove aggregates to purify the catalyst. The synthesizedFe-NC SAC shows an improved electrocatalytic activity of the ORR witha high half-wave potential up to 0.866 V versus RHE, as compared tothe standard 20% Pt/C one, assigned to its favorable surface area,hierarchically nanoporous structure, and accessible single atomicactive sites. The ZAB assembled using the Fe-NC SAC exhibited high-powerdensity (140.2 mW cm(-2)) and long-term durability.The study demonstrates a sustainable ambition of reusing industrialwastes and converting biomass into low-cost and high-value materialsfor energy conversion technology.

Automated summary

This study reports a green and cost-effective strategy to produce nanoporous Fe-NC single-atom electrocatalysts for efficient oxygen reduction reactions (ORRs), aiming to improve the performance of rechargeable zinc-air batteries (ZABs). The catalysts, derived from industrial spent acid residue and lotus seedpod biomass, possess the advantages of low cost and sustainability. The synthesized Fe-NC SACs exhibit high electrocatalytic activity and long-term durability, attributed to their favorable surface area, hierarchically nanoporous structure, and accessible single atomic active sites.