Ball mill-assisted synthesis of NiFeCo-NC as bifunctional oxygen electrocatalysts for rechargeable zinc-air batteries

Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are the core of clean energy technology. Oxygen electrocatalysts based on earth-abundant metals are of prime importance. Trimetallic catalysts have demonstrated reliable activities but their average performance, difficult synthesis techni-ques, and high synthesis costs limit their widespread use. Herein, the facile ball milling technique is introduced as an efficient and low-cost method for the synthesis of catalysts based on trimetallic NiFeCo nanometer-scale particles distributed over a CNT-graphene-like (NiFeCo-NC) structure. NiFeCo-NC is synthesized instantaneously from ball milling of melamine with industrial carbon nanotubes (CNTs) along with trimetallic particles. Results demonstrate that the NiFeCo-NC2 catalyst, synthesized from 2 g of melamine per 1 g of each metal salt, performed well in both ORR and OER. The potential difference between the half-wave reduction potential of the ORR (E-1/2) and the oxidation potential at 10 mA cm(-2) (E-10) in OER reveals a better performance of the NiFeCo-NC2 as a bifunctional catalyst than other syn-thesized materials and reference catalysts. A zinc-air battery (ZAB) having the NiFeCo-NC2 catalyst per-forms better than the batteries using other catalysts. The NiFeCo-NC2 catalyst also exhibits excellent methanol tolerance, revealing its applicability for direct methanol fuel cell (DMFC) applications. Ball milling offers a simple, effective, versatile, and cost-effective mechano-chemical procedure for the con-comitant one-pot mixing-synthesis of materials. (C) 2022 Elsevier B.V. All rights reserved.