Rod-shaped α-MnO2 electrocatalysts with high Mn3+ content for oxygen reduction reaction and Zn-Air Battery

Abstract Manganese dioxide (MnO2) is a potential efficient candidate for the catalysis of oxygen reduction reactions (ORR) in alkaline electrolyte. In this work, potassium permanganate (KMnO4) was reduced by silicon nanowires (SiNWs) and hydrofluoric acid (HF) to prepare α-MnO2 with a rod-like structure. The α-MnO2 prepared at 120 °C (α-MnO2-120) demonstrated excellent activity for ORR and had an oxygen reduction pathway of four-electron. In 0.1 M KOH electrolyte, it showed a large half-wave potential of 0.85 V vs. RHE and a high initial potential of 1.01 V vs. RHE. The diffusion-limiting current of α-MnO2-120 catalyst (7.0 mA cm−2) is also quite stable. The excellent ORR activity of α-MnO2-120 is attributed to the high Mn3+ content and sufficient oxygen vacancies. In addition, the zinc-air battery using the α-MnO2-120 catalyst displays an open circuit potential of 1.27 V, a maximum power density of 240 mW cm−2 at a current density of 0.33 A cm−2 and superior stability.