Pumping Electrons from Oxygen-Bridged Cobalt for Low-Charging-Voltage Zn-Air Batteries

Reducing the charging voltage is a prerequisite for improving the chargeability and energy efficiency of Zn-air batteries (ZABs). Herein, Fe³⁺ pumps electrons from oxygen-bridged cobalt (Fe-O-Co) and induces the accelerated charging kinetics. For the liquid ZABs, a charging voltage of around 1.94 V at 10 mA cm^-2 was displayed, which slightly increased 2% after continuous cycles for 180 h. A steady charging voltage of around 1.87 V at 10 mA cm^-2 was also exhibited for quasi-solid-state ZABs. Control experiments and characterization show that the interactions between the O^2- and Fe³⁺ sites are relatively weaker than those between the O^2- and Co³⁺ sites. Compared with Mn³⁺, Zn²⁺, and Cu²⁺, Fe³⁺ effectively pumps electrons from Co sites to generate the active species for the oxygen evolution reaction. Thus, the deprotonation behavior and *OH conversion were improved. This work demonstrates the oxygen electron bridge modulated electron transfer between dual metal sites, contributing to the improvement of low-charging-voltage ZABs.