Decoupling Electrolytic\nWater Splitting by an Oxygen-Mediating\nProcess

Decoupled water electrolysis systems, incorporating a\nreversible\nredox mediator that allows for the construction of membrane-free electrolyzers,\nhave emerged as a promising approach to produce high-purity hydrogen\nwith remarkable flexibility. The key factor crucial for practical\napplications lies in the development of mediator electrodes that possess\nsuitable redox potential, high redox capacity, excellent cycling reversibility\nand stability. Herein, we introduce a novel concept of oxygen-mediating\nredox mediators (ORMs) employing Bi<sub>2</sub>O<sub>3</sub> as an\nexample material, which are capable of sequestering oxygen during\nthe hydrogen evolution reaction and subsequently releasing it to generate\noxygen gas under alkaline conditions. Thanks to its remarkable reversible\nredox activity and specific capacity, the Bi<sub>2</sub>O<sub>3</sub> electrode boasts an impressive reversible specific capacity of 300.8\nmA h g<sup>–1</sup> and delivers outstanding cycling performance\nfor >1000 cycles at a current density of 2.0 A g<sup>–1</sup>. Furthermore, the implementation of such a decoupled alkaline water\nelectrolysis system can be integrated with a Bi<sub>2</sub>O<sub>3</sub>–Zn battery, enabling both power-to-fuel (hydrogen production)\nand chemical-to-power (rechargeable Bi<sub>2</sub>O<sub>3</sub>–Zn\nbattery) conversion. With many oxygen-carrier materials readily available\nand the potential integration with rechargeable alkaline batteries,\nthis study provides an alternative competitive route for membrane-free\ndecoupled water splitting through the oxygen-mediating mechanism with\ncombined energy transformation and storage.