Photo‐Assisted Zn‐Iodine Battery via Bifunctional Cathode with Iodine Host and Solar Response Boost

Abstract The aqueous photo‐assisted battery is considered an efficient means of converting and storing solar energy in one device. However, identifying a suitable photocathode with excellent iodine capture capabilities for photo‐assisted Zn‐iodine batteries still remains challenging. In this work, bifunctional BiOI is prepared as sole cathode material for a photo‐assisted Zn‐iodine battery while simultaneously realizing an iodine host and solar responsiveness. The as‐presented BiOI with abundant vacancies offers highly reversible photo‐assisted iodine redox reactions. Meanwhile, the dual reaction routes involving vacancy iodine storage and reversible two‐steps iodine redox are confirmed by in / ex situ characterization techniques during the energy storage process. Consequently, the assembled battery exhibits areal capacity of 0.24 mAh cm −2 at 1 mA cm −2 with coulombic efficiency exceeding 96.5%. More impressively, benefiting from the wide visible light absorption of the BiOI cathode, the battery demonstrates a much enhanced specific areal capacity of 0.4 mAh cm −2 at 1 mA cm −2 under sun illumination, representing a remarkable increment of 60% compared to that in the dark environment. This work expands the utility of cathode materials for a photo‐assisted Zn‐iodine battery.