Photo Self‐Charging Zinc‐Ion Batteries Enabled by a 12‐Electron‐Transfer Organic Photocathode

ABSTRACT

A photocathode is critical for realizing bifunctionality of solar energy harvesting and storage within a single device, but it still faces challenges such as low photoelectric conversion efficiency (PCE) and poor light stability. Herein, a covalent organic framework (COF) named BQQPH was proposed as a photocathode material. It exhibits a reversible Zn ^{2 +} /H ⁺ co‐intercalation accompanied by a 12‐electron transfer process, where C═O groups bond with H ⁺ , and C═N groups bond with Zn ^{2 +} . Photoexcitation induces substantial electron accumulation at the C═O and C═N active sites, which serve as electron traps to enhance the coordination affinity of Zn ^{2 +} and H ⁺ . Thus, the photocathode achieves a high discharge capacity of 411 mA h g ^{− 1} at 1 A g ^{− 1} , with 99% capacity retention (170 mAh g ^{− 1} ) even after 6000 cycles at 30 A g ^{− 1} and the corresponding PCE reaches 8.5%. Additionally, BQQPH exhibits a bandgap of 1.8 eV, the corresponding band structure can achieve photo self‐charging in thermodynamics. Without any external power supply, the battery achieves a high photo self‐charging voltage of 1.2 V and a discharge capacity of 248 mA h g ^{− 1} . This study offers insights into the design of organic photocathodes for photo‐rechargeable batteries.