Transition metal alloy integrated tubular carbon hybrid nanostructure for bifunctional oxygen electrocatalysis

Synthesis of cost-effective, robust, and efficient bifunctional electrocatalyst for the development of rechargeable Zn-air batteries (ZAB) is of considerable interest. Herein, we demonstrate the synthesis of NiCo alloy integrated nitrogen-doped tubular carbon (TC) nanostructure (NiCo–N-TC) using metal-organic self-assembly of M(II)-melamine-dipicolinic acid (DPA) (M: Ni(II), Co(II)). The NiCo alloy particles of as-synthesized NiCo–N-TC catalyst are confined at the tip like a cork. The as-synthesized catalyst was structurally engineered by acid treatment. The engineered catalyst (NiCo–N-TC-H) has an open-head hollow nanoarchitecture with uniform distribution of ultrafine NiCo alloy particles on the TC framework. The NiCo–N-TC-H catalyst follows desired 4-electron pathway for the electroreduction of oxygen in both alkaline and acidic pH. It has outstanding bifunctional electrocatalytic activity towards oxygen reduction and oxygen evolution reaction in alkaline electrolyte with a very low potential gap (ΔE) of 0.74 V. Acid-treatment-induced increase in surface area, and graphitic-N and carbon content facilitates the overall bifunctional activity. The bifunctional activity of NiCo–N-TC-H is successfully utilized for the development of rechargeable ZAB. It has long cycling stability and delivers high open circuit voltage (1.54 V), power density of 148.8 mW cm⁻², and high voltaic efficiency.