Pt/C as a bifunctional ORR/iodide oxidation reaction (IOR) catalyst for Zn-air batteries with unprecedentedly high energy efficiency of 76.5%

Rechargeable Zn-air batteries (ZABs) are promising for energy storage and conversion. However, the low energy efficiency caused by the high charging voltage greatly hinders their commercialization. Herein, potassium iodide (KI) is introduced to ZABs to change the oxidation pathway from the sluggish oxygen evolution reaction (OER) to I- oxidation reaction (IOR) with faster kinetics and lower oxidation potential. Unexpectedly, the commercial carbon-based catalyst Pt/C with poor OER activity exhibits remarkable IOR activity. Benefitting from its high oxygen reduction reaction (ORR) activity, the fabricated ZABs deliver a low charging voltage of 1.68 V, high energy efficiency of 76.5%, and long cycle life of over 80 h at 5 mA cm−2. Density functional theory (DFT) calculation is conducted to reveal the IOR catalytic mechanism of the Pt/C catalyst. This work will reverse the traditional mindset on catalyst selection from ORR/OER to ORR/IOR and boost the commercialization of rechargeable ZABs.