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 TiOxNy)-supported bifunctional catalyst, in which active N- and S-codoped carbon and ultrafine cobalt (Co-NSC) were embedded. The 3DOM structured TiOxNy 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@TiOxNy 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@TiOxNy 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.