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 techniques, 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 (E1/2) and the oxidation potential at 10 mA cm−2 (E10) in OER reveals a better performance of the NiFeCo-NC2 as a bifunctional catalyst than other synthesized materials and reference catalysts. A zinc-air battery (ZAB) having the NiFeCo-NC2 catalyst performs 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 concomitant one-pot mixing-synthesis of materials.