A macroporous titanium oxynitride-supported bifunctional oxygen electrocatalyst for zinc–air batteries

Abstract

Efficient and durable catalysts for the oxygen reduction reaction and oxygen evolution reaction (ORR/OER) are in high demand for the development of rechargeable zinc–air batteries. Herein, we report a three-dimensional ordered macroporous titanium oxynitride (3DOM TiO_xN_y)-supported bifunctional catalyst, in which active N- and S-codoped carbon and ultrafine cobalt (Co-NSC) were embedded. The 3DOM structured TiO_xN_y support not only enhances the surface area and electrical conductivity of the catalyst, but it also ensures satisfactory structural stability and efficient mass transportation at the solid–gas–liquid three-phase interface during the oxygen electrocatalysis process. Experimental and density functional theory calculations revealed that the ORR performance was promoted by the Co-NSC sites in this 3DOM Co-NSC@TiO_xN_y electrocatalyst. In situ Raman spectroscopy revealed that during the OER reaction, there was a transition of Co metal into cobalt oxyhydroxide (CoOOH), which is responsible for catalyzing the OER reaction. The 3DOM Co-NSC@TiO_xN_y catalyst exhibited impressive ORR activity, comparable with that of Pt/C, and satisfactory OER activity. The zinc–air battery delivered excellent performance with a power density of 123 mW cm⁻² and satisfactory cycling stability over 300 h at a current density of 10 mA cm⁻². This work highlights the importance of designing metal oxide-supported bifunctional catalysts for the development of efficient and stable electrochemical energy conversion devices.