Band engineering of α-Fe2O3/SnO2 heterojunction photocathode enables highly efficient and stable Li−O2 batteries

Introducing light energy into the charging/discharging process is an effective strategy to reduce the overpotential of Li−O2 battery, which leads that the battery has higher energy conversion efficiency and better battery performance. However, the development has been hampered by the lack of suitable photocatalysts and cathode structure to accommodate the insoluble Li2O2. In order to overcome the aforementioned difficulties, a bifunctional photocatalyst α-Fe2O3/SnO2 (FS) heterojunction was designed as the cathode to improve the charging/discharging overpotentials simultaneously. The photogenerated electrons and holes from FS participated in the oxygen reduction reaction (ORR) and oxygen revolution reaction (OER) under illumination, giving rise to an ultra-low charging/discharging overpotential of 0.01 V (energy efficiency up to 99.7%), which improved the electrochemical reaction kinetics of the Li−O2 battery strikingly. In addition, the FS cathode exhibited excellent cycle stability under light (the battery energy efficiency can still maintain 80% after 252 cycles). The bifunctional catalyst designed in this paper has profoundly proved that the band engineering strategy can effectively utilize solar energy and provide important insights for understanding the mechanism of photo-assisted Li−O2 battery.