Pumping Electrons\nfrom Oxygen-Bridged Cobalt for Low-Charging-Voltage\nZn-Air Batteries

Reducing the charging voltage is a prerequisite for improving\nthe\nchargeability and energy efficiency of Zn-air batteries (ZABs). Herein,\nFe<sup>3+</sup> pumps electrons from oxygen-bridged cobalt (Fe–O–Co)\nand induces the accelerated charging kinetics. For the liquid ZABs,\na charging voltage of around 1.94 V at 10 mA cm<sup>–2</sup> was displayed, which slightly increased 2% after continuous cycles\nfor 180 h. A steady charging voltage of around 1.87 V at 10 mA cm<sup>–2</sup> was also exhibited for quasi-solid-state ZABs. Control\nexperiments and characterization show that the interactions between\nthe O<sup>2–</sup> and Fe<sup>3+</sup> sites are relatively\nweaker than those between the O<sup>2–</sup> and Co<sup>3+</sup> sites. Compared with Mn<sup>3+</sup>, Zn<sup>2+</sup>, and Cu<sup>2+</sup>, Fe<sup>3+</sup> effectively pumps electrons from Co sites\nto generate the active species for the oxygen evolution reaction.\nThus, the deprotonation behavior and *OH conversion were improved.\nThis work demonstrates the oxygen electron bridge modulated electron\ntransfer between dual metal sites, contributing to the improvement\nof low-charging-voltage ZABs.