α-MnO₂ as an advanced bifunctional ORR/IOR electrocatalyst for Zn-air battery

Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are important reactions for rechargeable Zinc-air batteries (RZABs). Unfortunatly, OER holds a high thermodynamic equilibrium potential and complex reaction path, which require an large votage to derive this reaction and greatly hinder its commercial application. Herein, α-MnO₂ was successfully achieved and as the bifunctional ORR/iodide oxidation reaction (IOR) electrocatalyst. In alkline media, α-MnO₂ exhibits fast kinetics and low oxidation potential for IOR. Expectedly, α-MnO₂ exhibits remarkable IOR activity in 1.0 mol/L KOH with 0.5 mol/L KI. Compared with potential at 10 mA/cm² for OER (1.709 V vs. RHE), the potential at 10 mA/cm² reduce 398 mV (1.311 V vs. RHE) for α-MnO₂ during IOR process. α-MnO₂ also provides small Tafel slope of 57.5 mV/dec. Additionly, α-MnO₂ represents outsanding ORR performances with respect to Pt/C. As an air electrode for RZAB, the fabricated RZAB delivers excellent performances. To be specific, at 5 mA/cm², the voltage gap between charging and discharging reduces from 0.97 V to 0.61 V, energy efficiency increses from 54.9% to 66.2%. This work provide an unique strategy to construct bifunction ORR/IOR electrocatalysts and promote the commercialization of RZABs.